Water Chiller Repair

Looking down on 2 large water chillers under repair

Water Chiller Repair

A water chiller repair visit to rectify the non condensables which were discovered in a refrigerant system. This condition happens when a system is purged through with refrigerant. Carrying out this procedure does not remove the air from the complicated internal pipework. Read on to find out how this condition was diagnosed and then repaired...

Customer Satisfaction

Because we sorted out various other problems on the first day of the contract, this customer is really happy with Maximus Chillers. We have a 3 year Maintenance Contract with them too. We know that we are expanding in a recession because we always put the customer first. It is easy to win a contract, but to keep one means that we have to provide a service that is second to none. With a full complement of specialist equipment in each mobile workshop and engineers with years of industry experience- Maximus Chillers completes the picture.

Dalton’s Law of Partial Pressures

That all gasses in a vessel will act as if they are on their own. The air in the system works its way round to the condenser where it sits on top of the liquid refrigerant and won’t condense. This is where the term non condensable comes from. Let’s say the condenser pressure should be 8 bar on a system running with R134a refrigerant. The air, acting as if it is on its own, in this instance, was raising the condenser pressure to 15 bar. This was 1 bar below the high pressure trip out. The higher pressure also causes an increase in electricity consumption.

False Reading of Subcooling

A 30°C false reading of subcooling was recorded due to the air in the refrigerant system

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Water Chiller Repair Procedure

When one of our engineers arrived on site to resolve the issue, he started by decanting the refrigerant from the system. Because the refrigerant was contaminated, he sent it back to the suppliers for recycling.

Pressure Test

No refrigerant leak was suspected, but our engineer carried out a nitrogen pressure test as a matter of course. This was passed, so now on to the next phase of the job…

Vacuum

This part of the job rectifies the previous poor repairs. A vacuum was pulled overnight of 2 Torr. This process removed the non condensables and also dehydrated the system.

Switch it On

Half of the new refrigerant was charged into the system, then the remaining refrigerant was charged into the liquid side of the evaporator during operation. This process was carried out until the superheat and subcooling values came to within standard industry guidelines.

System Monitoring

Now that a professional repair had been carried out, the condenser pressure was found to be running at 8 bar. The running amps on the compressor had lowered too.

Energy Monitoring during Water Chiller Repair

The power consumption of the various plant around the building is monitored on the customer’s computer in his facilities office. This is to help identify where electricity is being wasted. He has auditors who assess the efficiency of the building and he has targets to meet. He had already noticed the more efficient running of the chiller subsequent to the repairs. The end user also monitors the energy consumption and worked out the cost saving of the repair over time. The repair would soon pay for itself and then start to save the building money.

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Condenser Cleaning during Water Chiller Repair

The condenser on the other system of the same chiller had recently blocked due to grass pollen. Our engineer brushed it down and chemical cleaned it while on site at no extra cost to the customer.

Pressurisation Unit during Water Chiller Repair

The water system pressure was found to be lower than usual due to a fault that had been reported by the customer. The internal pumps of the pressurisation unit had failed. Therefore, our engineer made a manual top up of the water system to the same pressure as had been recorded on the previous maintenance Tick Sheets. The water system readings were then monitored and were found to be nominal.

Pump Sets

The chillers are fed by a pump set comprising of two pumps. The second pump is a redundant system (N+1) Both pumps are fed from inverter drives which lower the electricity consumption of the pumps. There had been an issue reported with the building management system (BMS) so Pump 1 was running in Hand. Our engineer changed the running pump over to Pump 2 which he also left running in Hand. This was to even out the running hours between the two pumps.

Paperwork Time

At the end of the job, our engineer completed a full report on his phone which was uploaded to Head Office in Droylsden, Manchester. He also filled out a Job Sheet with his findings which was duly signed by the customer.

 

Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere- The MAXIMUS ADVANTAGE™

 

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Process chiller repair service being carried out on evaporator and expansion valve

Process Chiller Repair Service

We at Maximus Chillers have just carried out a process chiller repair service for a customer of ours in the North West. The expansion valve on System 1 had been found to have failed and this was the return visit to rectify. There is N+1 redundancy built into the plant, so there was not an immediate hurry to attend site. When our engineer diagnosed the fault, he had a look in our customer’s stores as he knows our customer likes to keep spares. Sure enough- there was a spare expansion valve on the shelf, so he took it and put it in the chiller panel ready for the job.

News Article No.27

Process Chiller Repair Service to Jammed Valve

What had happened to the old expansion valve was that the mechanical part had worn down and jammed part open. This meant that the refrigerant circuit would run for a while with a poor superheat reading, but would trip out on low pressure when more scroll compressors started running.

Isolate Electricity

Our engineer disabled System 1 and removed the fuses. This was to prevent an accidental start up during the repairs. He used his lock off padlock, to which, he was the only engineer with a key.

Refrigerant Decant

The full refrigerant charge was recovered into 2 small recovery cylinders which were taken to the refrigerant storage cage. This is a segregated area to reduce the risk of explosion in the event of a fire. It is also shielded from direct sunlight to reduce refrigerant pressure inside the cylinders.

Hot Works Permit during Process Chiller Repair Service

The next stage of the job was to remove the failed expansion valve, so a Hot Works Permit needed to be obtained from the Maintenance Department. It was counter signed by the permit issuer and our engineer with the fire watch time added to the additional information section.

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Oxy-acetylene

The equipment was taken out of the company vehicle and set up near to the chiller. Care was taken to ensure that the oxy-acetylene was not in the escape route for our engineer in the event of an accident. The condition of the equipment was inspected and a leak test carried out.

Strip Down during Process Chiller Repair Service

The covers were removed from the location of the expansion valve, the lagging stripped back and the electrical connection removed. The old expansion valve was now ready for removal…

Remove and Replace

Our engineer heated the inlet to the valve until the solder melted and then removed the liquid pipe. He then repeated this on the expansion pipe. Now that the old valve had been removed, he used a specialist tool to clean off the remaining solder and impurities on the refrigerant pipework. Having done this, he fitted the new valve into position. A special heat sink was used to protect the new expansion valve during the brazing operation. Then, the inlet and the outlet pipes were silver soldered into position.

Pressure Testing during Process Chiller Repair Service

The integrity of the entire system was proven by carrying out a nitrogen pressure test according to standard industry guidelines. The customer witnessed the start and the finish of the test and this was recorded on the Pressure Test Certificate.

Dehydration Process during Process Chiller Repair Service

Our engineers carry a powerful 10 cfm vacuum pump as part of the equipment in his car. This pump speeds up the removal of moisture and also non condensables from the system such as air and nitrogen. Our engineer left the process running overnight and returned in the morning to find deep vacuum had been achieved.

Refrigerant Recharge

The correct amount of refrigerant was recharged into the system and the cylinders were returned to the storage area.

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System Testing

The controller of this machine automatically gives you the fridge system readings. However, our engineer wanted to fit his own test equipment to the chiller anyway. This was to test that both readings were the same for calibration purposes. Having done this, he ran the system and waited for it to load up to 100%. Then, he took the superheat and the subcooling readings which were found to be within standard industry guidelines.

Clear Site

All of our engineers leave the work location of the chiller in a better condition than before they attended site. Good house husbandry goes a long way to promote the professionalism of a chiller company. The little things are what you, the customer, often notice first as some of the more technical things are not always so obvious.

Paperwork Sign Off

The permit to work was signed off having completed a satisfactory fire watch. Our paperwork was then completed and scanned into Head Office. We like to do this on the day of the job, so your accounts department gets the report promptly and can start processing the Invoice.

Monitoring

Our engineer then gave the chiller a mini service for the rest of the day. All readings were taken on both of the refrigerant systems and compared to the Tick Sheet of the previous maintenance visit. This was to see if there was a deterioration of any of the readings over a period of time. Small problems would show up before they turned into big problems. This is just another way of how we at Maximus Chillers saves you money.

Courtesy Visit

Just to make sure that the machine had settled down satisfactorily and that there were no further issues- our office arranged a courtesy visit a few days later. The chiller system was still operating as it should and there were no other faults to report.

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Dirty tubes on the left and clean tubes on the right after chiller condenser tube cleaning

Chiller Condenser Tube Cleaning

A nice job for our overseas engineer: to carry out chiller condenser tube cleaning in Cadiz, Spain. We have The Spanish Office near Malaga with a manager and an engineer out in the field- so our Spanish engineer assisted our overseas engineer.

Centrifugal Chiller Condenser Tube Cleaning

The factory has 4x water cooled centrifugal chillers with a combined cooling capacity of 8 MW. The chillers cool down a process involved with the production of an industrial chemical.

High Condenser Pressure

When we looked through our Tick Sheets we could see a gradual deterioration of the high side readings over a period of time. This showed us that an overhaul needed to be carried out on the condensers.

Water Tower Contaminants

We think that the fouling was due to contaminants that were carried in the air from around the factory. Each condenser has a water tower which is open to atmosphere. The condenser cooling water enters the cooling tower at the top. It runs down along plastic slats which are stacked on top of each other. In the opposite direction, air is blown up using large blowers. The air flow cools down the water, which then returns to the condenser. This process is how the contaminants from the air end up in the water.

N+1 Redundancy

This is an algebraic way of saying that there is twice as much cooling as is needed. Where N is an amount of something and +1 means another one. Redundancy is needed when a process is critical. In this instance, the factory would grind to a halt if the chillers went down. Therefore, only two of the 4 chillers run at any one time.

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Sequencer

A sequencer is available to switch between the chillers when they go into fault and to balance the compressor run hours. We decided to start work on Chiller 1 as this was a system in standby. The next chiller in standby was Chiller 2. After this chiller had been overhauled, we switched Chiller 3 off which brought Chiller 1 on. Then, when we isolated Chiller 4, the sequencer brought Chiller 3 on. Before leaving site, we temporarily lowered the setpoint for all 4 chillers to watch the sequencer bring all of the chillers on together. We then put the set point back to its usual setting, whereby Chillers 1 and 2 remained running.

Shipping for Chiller Condenser Tube Cleaning

We keep tube cleaning equipment in our stores in Jeddah, Saudi Arabia which we ship to our Middle East customers. We also have tube cleaning equipment in our stores at Head Office in Manchester, UK. We use a pallet shipping company based in Rochdale to ship parts, materials and equipment overseas. Therefore, we packed all of the necessary equipment on to a pallet, then shipped it to Cadiz. For the consumables used on the job, we have suppliers in Spain, but we usually prefer to ship these smaller things from the UK along with the equipment. This is because our engineers are more used to the brands and types of consumables that we get from our UK suppliers.

RAMS for Chiller Condenser Tube Cleaning

All of our paperwork, Tick Sheets and Risk Assessment Method Statements have been professionally translated into Spanish. Therefore, our Spanish engineer carried out a site survey to assess the risks, he then sent a report to Head Office. We decided upon the appropriate measures to control the risks, then sent the RAMS to site prior to the visit.

Permit to Work for Chiller Condenser Tube Cleaning

The onsite health and safety officer looked at our RAMS and decided how to compose his Permit to Work. Then, both of our engineers signed it at the start and at completion of the job.

Walk Round before Chiller Condenser Tube Cleaning

On completion of the paperwork, our engineers, the onsite health and safety officer and an onsite engineer had a walk round to assess the job. This was to make sure that all was okay to carry out the tube cleaning.

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Chiller Condenser Tube Cleaning Operation

Each of the 4 chillers was worked on in turn in the order as described above.

Valve Configuration

Each condenser was valved off with the configuration of the pipework changed. This was to ensure that the flow rates were correct for all 4 of the chillers. Otherwise, a catastrophic failure of the chillers could occur.

Drain Down

The condensers were then drained down and vented using a selection of fittings that were shipped out with our equipment.

End Plates

Our engineers unbolted the end plates and lifted them to the side using specialist lifting equipment.

Tube Cleaning

In Spain they just use a 220v supply for electrical equipment instead of the 110v equipment that we commonly use in the UK. As our equipment is 110v, we shipped our transformer on the pallet. Once the equipment was set up- we carried out the cleaning of each condenser tube according to standard industry guidelines.

Rebuild

The seal on the end plates is prone to leak after breaking into the system so we shipped replacements from Head Office. Our engineers found it a fiddly job as the new seals had been folded up in a different position in the packet. This meant that they kept jumping out of the grooves. When the seals eventually remained in the grooves, the end plates were bolted into position according to the correct torque setting.

Air Purge and Valve Configuration

The air was purged from the shell of the condensers and the valve configuration was returned to the original position.

Test Operation

Each of the 4 chillers was run tested in turn and the system readings were recorded on our paperwork. A dramatic increase in performance was recorded on each system. The refrigerant pressures and temperatures were a lot better and the coefficient of performance was markedly higher. This means a lower carbon footprint and lower electricity costs.

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Ammonia warning sign and yellow light flashing during chiller call out

Chiller Call Out

Chiller call out is the essence of what a company like Maximus Chillers is all about. It is a time when our engineers come into their own. Read on to see examples of how we do it…

News Article No.22

Chiller Call Out for Ammonia Leak Alarm

At first sight this appears to be a dangerous situation as ammonia is very harmful to human health. This is because of its corrosive and toxic characteristics. Each of our engineers carries breathing apparatus and full length ammonia PPE should it be required.

Location Assessment

The work location in the photo is assessed using an NH3 detector. This is sensitive enough to detect lower than the 35 parts per million short term exposure limit. The detector is fitted to the work wear of our engineers whilst near to the plant. When the alarm does not sound and there is no smell of ammonia- it is safe to proceed.

Electrical Fault

Usually this alarm is due to a controls issue rather than a leak. There are various reasons:

UPS and Alarm System Malfunctions

Chiller panels for this kind of plant have a UPS (uninterruptible power supply) This is a battery which is charged by the mains. When a power failure occurs, the charge in the battery supplies 240v to the ammonia alarm. This means that the chiller continues to be protected. When malfunctions occur to the UPS or the alarm system, the yellow warning light and siren is activated which needs to be manually reset.

Sensor Failure

The sensors have to be calibrated at regular intervals. The base setting of 0 parts per million has to be set and then the trip outs of 35 and 25 parts per million. These sensors can be knocked out of calibration by small leaks over a long period of time, or they can malfunction internally. If you require the service of your leak alarm- email our Technical Support Desk and will arrange a site visit.

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Chiller Call Out for BMS Failure

Chillers can get blamed for everything as the customer can notice a building that is getting warm and then call us out. An example of this is when a new customer of ours signed up to a maintenance contract after a long period of neglect. They did so because the office workers in a large office block had started to leave their desks and walk out of the building.

Investigation

When our engineer attended site, he found various faults with a row of four, 500 kW chillers on the roof. There was found to be N+1 redundancy built in, so he considered there to be sufficient cooling available to satisfy demand.

No Run Signal

Despite there being available load, the chillers were not being given the run signal from the BMS. The toggle switches on the BMS panel did not give the run signal to the chillers when they were put into Hand. This was found to be because of other issues with the poorly maintained panel.

Link Out

Our engineer therefore decided to link out each of the chillers in their respective panels. He consulted the wiring diagram and made the modifications accordingly. He then entered the password for that particular chiller and adjusted the program settings. These changes made the chillers stand alone and not reliant on the BMS run signal.

Chiller Call Out for Pump Sets

The pump sets were also found to be in poor condition. There were found to be failed pumps, blown contactors and defunct controls. The good news was that by changing components in the panel, he managed to get at least one of each pair of pumps going for the various water systems used around the building.

Pressurisation Unit

This is a machine with an internal pump and a pressure switch which is used to maintain the pressure of the water system. Both the run and the standby pumps were found to have failed with other component failure in the unit as well. Our engineer decided to manually fill the water system with mains water to build up the pressure.

Get it Away

Having done all this, our engineer got the chillers away and watched the water temperature come down from 24°C to 6°C. As the chiller systems came down to set point, they unloaded to match the demand from the building.

Return to Work

The office staff started to return into the building and resumed work at their desks.

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Fault Finding during Chiller Call Out

Now that the pressure was off, our engineer carried out the necessary fault finding to the systems that had failed:

 Refrigerant Leaks

Three of the systems were found to be locked out with low pressure alarms. He assessed the quantity of recovery cylinders and refrigerant that was required. Then, he submitted a report to Head Office for a return visit to carry out the repairs.

Blocked Condensers

Some of the systems were found to have blocked condensers. The call out was during the summer when a high pressure condition was more likely to occur. A build up of contaminants had reduced air flow and caused the high pressure switches to be activated. We arranged a site visit with a special cleaning agent to remove the contaminants and restore the air flow through the condenser fins.

Chiller Call Out for Flow Switches

These are a switch used to detect water flow and two of them were found to have had failed. There are various types for different applications. We select a suitable flow switch and then make the necessary adjustments to the internal control screws. This ensures that the switch will function correctly when problems with the water system occur. 

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Open chiller controls panel showing PLC, relays, contactors and wiring

Chiller Controls

Chiller controls can be remotely operated and monitored, but in this article, we will be looking at chillers operating in local.

Each chiller has a panel where the lead or the lag chiller can be switched from. They have N+1 redundancy built in, so one of two chillers will normally be in standby with the other one running. The chillers in the photo are equipped with kilowatt hour meters because the customer wants to monitor their efficiency. He has targets to meet and wants to gauge the effect that our maintenance has in reducing his energy costs.

Condenser Pressure

The condenser pressure control is external and stand alone from the panel.

Transducer

A transducer is fitted to the discharge pipe near to the compressor. This gives a 0 to 5vdc control signal to the fan speed controller which is bolted to the frame. There is a minimum and a maximum value on the transducer, so the FSC is programmed to work out the pressure from the voltage.

Fan Speed Controller

415v on three phases are the input to the FSC. It uses solid state thyristors to regulate the output to the fans. This is according to the demand received by the transducer. Solid state means that all the parts are electronic with no moving parts. Fan speed controllers are really good at extending the life of the fans. This is because all of the fans operate together- smoothly and reliably.

Chiller Controls Digital Inputs

There are three essential digital inputs to the controls of any chiller. All of them have a volt signal out to them, which returns back to the panel. If there is a fault- the volts drop out.

LP Switch

This protects the chiller from a low pressure condition. Compressor and evaporator failure would result, so this device is set below the running pressure of the system, but high enough to offer protection.

HP Switch

If the head pressure control mentioned above were to fail, this device would save the chiller from damage from excessive pressure in the system. Components or the pressure relief valve can blow causing a catastrophic refrigerant leak.

Flow Switch

This device detects a lack of flow in the water system. Serious system failure would result if this part is not maintained properly. It needs to be periodically tested and adjusted at regular intervals.

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Chiller Controls Analogue Inputs

The essential analogue inputs on a chiller are the Water In and the Water Out sensors. These are usually NTC (negative temperature coefficient) that is to say: if you hold one in between your fingers and warm it up- the resistance will start to drop off. They usually read in kilo ohms which can be read on a standard multi meter. The program looks at these two sensors and using an algorithm, it calculates the loading requirement of the compressor. They can read incorrectly, so a sensor offset function is available in the software for adjustment. This is just one of the many checks and procedures that we carry out during our maintenance visit.

Chiller Controls Relays

In the photo you can see wires from the various devices around the chiller, wired into a row of relays. These, in turn, are wired into the white relay board at the top. This relay board has several expansion boards linked into it which are held together with an electrical ribbon. Next, the relay board is wired into the PLC... 

Chiller Controls PLC

The reason for these steps in between a device and the PLC is for protection. Sensitive electrical components can be blown due to an earth shortage. At each stage there is a volt drop from 240v to 24v and then to 5vdc.The programmable logic controller is the nerve centre of the chiller. This is where all the inputs go to and where all the digital outputs are sent from. The controller on this chiller is Beijer Electronics- it comes blank from the factory. User keys to operate the chiller are positioned below the display. It can be programmed to run most chillers and indeed it is often seen in factories running anything. A laptop plugs into it and the software for the chiller is uploaded. On one visit, we found a fault with this controller. We bubble wrapped it and took it to our electronics laboratory at Head Office. The issue was easy to resolve- it was just dust tracking across the back of the PCB and so corrupting the program.

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Chiller Controls Digital Outputs

The main digital outputs on this chiller are:

Compressor Run Signal

240v is sent to the compressor starter contactors. There are three: Star (lower amps for a soft start) then a timer switches over to Delta (higher amps for a more powerful running of the compressor) On the other end of the compressor windings is the Line contactor. This contactor runs with both the Star and the Delta contactors.

Float Valve

This is a camber where the level of refrigerant which is coming in from the condenser is detected. The level is transmitted to the PLC, where the program sends a signal to the expansion valve. It opens to the correct degree according to the load on the chiller.

Slide Valve

The compressor can run at 0% with the slide valve shut. When load is sensed from the Water In and Water Out sensors by the controller- the slide valve opens up. The position of the slide valve is detected by a potentiometer. This is calibrated from a minimum to a maximum position. The signal is 4-20 mA which the controller translates into the position of the slide valve.

MAXIMUS ADVANTAGE™

Whatever the problem with the controls, we can find a solution to resolve it. With years of industry experience and a fast supply chain, we offer a service that is second to none. Being able to retrofit is part of what we call the MAXIMUS ADVANTAGE™ Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere.

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Grey shell & tube chiller evaporator being maintained with centrifugal compressor above

Shell & Tube Chiller Evaporator Maintenance

With shell & tube chiller evaporator maintenance to be carried out- it was time to sign the permit to work and get going. There are 5 chillers in total, but 1 of the chillers had been dismantled by the previous company and is unlikely to run again. This left 4 flooded systems to be maintained while the factory was still in production. Therefore, it had been decided in the Method Statement that one chiller would be done at a time. The plant had been designed with N+1 in mind, as it is critical not to loose the process- causing a factory shutdown. This means that so long as 2 of the chillers are running, there will be no loss in production. With 1 chiller out of service and another being worked on, this left 3 chillers in operation. If 1 were to fail, then there would still be the minimum of 2 left running.

Hire Chillers

In the unlikely event that 2 of the 3 chillers left running were to fail, an action plan was in place to lift in 1 MW of hire chillers.

Pump Sets and Hoses

The hire chillers would come with 2 engineers to pipe the pump sets into the onsite water system. This water system has been designed with this in mind so ‘stab ins’ have been built into it with shut off valves for the connection of temporary hoses.

Vanes

The chilled water is close control with a critical 6°C to 8°C set point. The chillers in the photo are very good at achieving this close control as they use vanes on the inlet to the suction. These vanes can be adjusted from anywhere between fully closed, with a small amount of bypassing, to fully open.

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Buffer Vessel

The hire chillers, on the other hand would not be close control. They would be multiple system chillers with various stages of loading on each chiller. One 600 kW chiller and another 400 kW. Each of the chillers onsite are 1.3 MW, but as they never run at 100% the onsite maintenance manager agreed to the proposal. It is unlikely that this plan would be needed, but planning for it is critical. A 10,000 ltr buffer vessel was decided upon to make the hire chillers close control. The chillers discharge into the buffer vessel, then the water mixes around before returning back to the chillers. The process water too being discharged into the buffer vessel before returning to the process. The position of the inlet and outlet on both water systems being strategically decided upon to ensure a steady exchange of heat and a smooth water out temperature back to the process.

Valve off and Drain Down

The Water In and Water Out pipes were valved off and the contents of the evaporator drained down. There was no glycol or chemicals in the water system which made the job easy. Otherwise, the water in the evaporator would have to have been pumped into vessels for disposal.

End Plate Removal during Shell & Tube Chiller Evaporator Maintenance

The lift and shift team were on site to assist with the removal of the end plate. After the bolts were removed, they attached their lifting eyes and straps, then lifted the end plate to the side.

Evaporator Cleaning 

We have in our stores a specialist evaporator cleaning tool. After a period of time, the evaporator tubes become fouled with impurities picked up from the water system. Also, contaminants get in from the air into the water tower. The strainer has some effect, but thermal insulation builds up on the water side of the tubes. It prevents latent heat being absorbed into the fridge system from the process. After the cleaning process, the efficiency of the copper tubes was increased to the same level as when the chiller was new. This is part of what we call the MAXIMUS ADVANTAGE Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere. 

Reassembly after Shell & Tube Chiller Evaporator Maintenance

The seal was replaced from our range of seal sizes, on the shelf in our stores. The reassembly being the reverse of the strip down, the lift and shift team aligning the end plate for refitting on guide runners. It was then tightened to the correct torque setting. A little at a time, the water system valves were opened until full flow and water system pressure was achieved. No leaks occurred, so it was time to go on to the next phase of the job…

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Run Up after Shell & Tube Chiller Evaporator Maintenance

After bringing this chiller back online, it went through a timer, then loaded up steadily to 68%. The refrigerant system readings had been taken previously, so they were compared to the readings taken after the job. A lot more heat transfer being achieved with more latent heat being absorbed from the process.

Remaining Chillers

The above mentioned process was repeated to the remaining chillers one at a time. No issues were encountered and the whole job proceeded steadily to completion.

Compressor Loading

The load from the factory is very steady, so each time another chiller evaporator was cleaned, the row of chillers would unload slightly. They were running at 72% on arrival, then 68%, then 63% then 59%. This was demonstrated to the customer as a visual way of proving how we had improved the efficiency of his plant. Compressor unloading uses less electricity, so lower carbon emissions and a lower electricity bill are the direct result of our maintenance. Also, kilowatt hour meters are linked to the maintenance manager's computer for monitoring.

Shell & Tube Evaporator Chiller Maintenance Tidiness

As with all of our jobs, the work location of the chillers was left in a better condition than when we arrived. Any waste and unused items being recycled or returned to the stores on site or the stores at our Head Office. The chillers being wiped down and the end plates re painted. With regular maintenance, we at Maximus Chillers will take years off the life of your plant. It is not unusual for us to keep this kind of plant running for more than 50 years.

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To read more about shell & tube chiller evaporators hit the Tag at the top of the page.

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Large white chiller being inspected to compose a chiller maintenance schedule

Chiller Maintenance Schedule

The chiller maintenance schedule in essence is as follows:

  • What is the plant? According to the asset list for that particular contract.
  • What are we going to do with it? The checks, procedures and diagnosis in the pursuit of the maintenance of the chillers.
  • How often? The periodic maintenance schedule defining the required interval between visits to ensure seamless operation of the plant.

News Article No.5

Chiller N+1

N+1 is intrinsic in the development of a chiller maintenance schedule. N+1 means the amount of cooling required + the same amount again in parallel. It can also be represented as 2N. Two water system pumps are a good example: where the pipework splits in two- one pipe for each pump. When a pump fails, the redundant pump comes online. Chillers are arranged in parallel, in this way, on the water system. This redundancy allows for a stress free maintenance of the plant. The failed system can be rectified and brought back online while the redundant system takes the load.

Intervals of Chiller Maintenance Schedule

The intervals in the contract are influenced by the redundancy of the chillers on site. The less run hours the compressor does, the less maintenance is required. We at Maximus Chillers can tailor make a maintenance schedule exactly to your needs by looking at how much the chillers are used and how hard they work.

Load affecting Chiller Maintenance Schedule

For some applications, the chiller operates under a high load condition all the time, with a redundant system in standby. On other applications, the chiller works in minimal load conditions. Regardless of the load conditions, the chiller is critical to the cooling of buildings or for an industrial process.

Lead/ Lag of Chiller Maintenance Schedule 

An important thing to remember is to balance compressor run hours and bearing wear by rotating the lead/ lag duty of the chillers. This can usually be done in the in the sequencer (if fitted) by changing a program setting. Otherwise, the switchover controls can be changed on the off/hand/run toggle switches. Where manual changeover is required, the onsite engineers are usually conversant with the procedure concerning the water system pumps, valves and controls. During the maintenance, the stop checks can be carried out on the redundant system, while the run checks are carried out on the system which is online.

Chiller Maintenance Schedule for Recip Compressors

Recip compressors require a log of the compressor run hours. This is because the valves and bearings should be changed at pre prescribed intervals as laid down by the schedule. Particularly important to reciprocating compressors are regular oil changes and oil sampling- a small change in the result of an oil sample can prevent a serious compressor smash up. A check list including the model number and serial number is completed on each visit and kept in a file on site. This file can be consulted during diagnosis and maintenance to decide on the beast way forward with an on going issue.

Chiller Maintenance Schedule for Air Cooled Condensers

Air cooled condensers can often be looked after by the onsite engineers in between maintenance visits. Just a quick brush down every few months is usually all it takes. Where the environment lends to a type of contaminant being collected on the condenser coils, an effective chemical is selected from our stores and used on the coil. Where there is an issue with the serviceability of the condenser, we can put together a plan to keep on top of it. We can even retrofit a new condenser- it’s what we call the MAXIMUS ADVANTAGE™

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Shell and Tube Evaporators

The shell is made from a heavy steel sheet rolled into a circle. The seam is welded together to form a cylinder. The tubes are pushed though the tube holders which are made from steel and are welded into the shell of the evaporator. The tubes are copper because of its good thermodynamic properties.

Direct Expansion Evaporators

Direct expansion is achieved in an evaporator with a thermostatic, or electronic expansion valve. The refrigerant enters the valve from the condenser as a high pressure, hot liquid. The pressure drop on the evaporator side of the valve makes the refrigerant flash off into a cold, saturation point liquid and vapour mix. The liquid boils off, absorbing latent heat through the inside of the copper tubes. On the outside of the copper tubes is the return water from the process, or the cooling of buildings.

The parts of the maintenance schedule that relate to DX evaporators are:

Oil Pooling

The inside of the tubes are in the clean environment of the fridge system. This means they do not become fouled. A tube insulating issue, however, can be caused on the inside by oil. If there are issues with the oil return system, the oil can pool in the evaporator. A low refrigerant charge can have the same effect. Written into the maintenance schedule are manual oil return and oil draining visits. During these visits, the monitoring of the refrigerant charge is also carried out.

Sensor Location

If a sensor is not located in its pocket correctly, or without sufficient heat transfer paste- it will read incorrectly back to the electronic expansion valve driver. This will cause the expansion valve to malfunction.

Pressurisation Units

A full maintenance of the pressurisation unit is carried out. This includes the pumps, controls and program adjustments as required. Incorrect pressure in the water system will cause a knock on effect of faults on the chillers.

Pump Sets

As above with chiller lead/ lag change over, water system pumps are manually changed over from lead to lag in the building controls. Carrying out this procedure reduces the chance of pump failure between visits. This is because it balances the pump run hours and so prevents bearing seizure after a long period not running.

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Flooded Evaporators

Flooded evaporators are the reverse of the above DX evaporators. The refrigerant is on the outside of the tubes, with water on the inside of the tubes. Gravity and refrigerant charge determine the refrigerant level in the condenser and evaporator. In between the two is located the liquid pipe with the orifice located in the pipe for the expansion of the refrigerant. The cooling water flows through the condenser tubes and off to the cooling towers. On the low side, the chilled water flows through the evaporator tubes and off to the process, or the cooling of facilities.

The parts of the maintenance schedule that relate to flooded evaporators are:

Tube Fouling

Because the condenser cooling water and chilled water systems are pumped through the pipes, the tubes become dirty over time. This occurs more often on the condenser as the water towers are open to atmosphere. Contaminants from surrounding buildings and factories gets into the water system and thermally insulates the tubes. This thermal insulation reduces the heat exchange through the copper tubes. The knock on effect is higher head pressures and eventually high pressure trip outs.

Specialist Cleaning Equipment

We at Maximus Chillers have in our stores the required equipment to carry out the cleaning of the tubes. Our engineers can attend site and liaise with the onsite engineers as regards the draining, strip down and lift out of the heat exchanger end plates.

Flushing Agents

A water sample is taken from the cooling and chilled water systems. These samples are sent off to our laboratory for analysis. Bacteria can build up in the water system causing slime- this can be rectified with a careful selection of chemical agents. Also, silt can build up- various chemicals are added to positively charge the silt and so carry it around the system to the strainer. Where the issue is caused by rust- an inhibitor can be added to prevent, or slow the oxidization of the steel.

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F-gas Testing of Leaks

The frequency of F-gas leak testing is determined by the size of the plant. This will be detailed in your F-gas file which is kept on site. Another record of this is kept by the chiller company at their registered office. The copies of the periodic leak testing sheets are kept by both parties. These detail the result of the test, refrigerant added to the system, refrigerant removed from the system and the required follow up actions. Some methods of leak detection are:

Visual Inspection

On each visit our engineers remove the coverings of the ends of the condensers and panels. This is to inspect the whole machine for a sign of a leak. Any potential leak is marked for future identification of where it is. A visual inspection will always be backed up with a further diagnosis such as:

Superheat and Subcooling

These readings are taken during a maintenance visit to determine the refrigerant charge of the chillers. The engineer, however, has to bear in mind that the subcooling and superheat readings can read abnormally due other reasons.

Bubble up Leak Spray

Various makes are available from the suppliers. Each engineer having his own preference. We at Maximus Chillers stock leak sprays and a wide selection of other materials.

Electronic Leak Detectors

Fixed

This type of leak detector is installed in the chiller low down in the panel. This is because HFC refrigerant is heavier than air. The leaking refrigerant will tend to pool in the bottom of the various panels around the chiller.

Portable

Each of our engineers carries a portable sniff tester. It comes with an extended tip to get into the most tight and awkward places. The leak detector has a replaceable element inside the unit. It also comes with replaceable tips which can be swapped out periodically. They come with a portable plug socket and transformer to charge the on board batteries after use in the field.

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To read more about chiller expansion valves hit the Tag at the top of the page.

Further reading on chillers and the chiller maintenance schedule at Better Bricks


PLC and relay board in a panel during chiller service company visit

Chiller Service Company

Electrical Testing

A chiller service company can carry out electrical testing and diagnosis even when a wiring diagram is not available- our engineers can trace the wiring around a chiller.

News Article No.3

Doing this often aids with the diagnosis even when there is a wiring diagram, as having your eyes on a component often makes more sense than a symbol. In any case, our engineers carry out system testing with Fluke multimetes and ammeters.

F-gas Leak Testing by Chiller Service Company

We also carry a range of thermocouples and probes to be used in conjunction with our calibrated digital thermometers. We use these along with comparators to carry out leak testing. After fitting the probes, we first have a visual look around for a sign of a gas leak. All parts of the pipework and system components are inspected. Then, we carry out a full refrigerant diagnosis to determine that the refrigerant system is operating with a full charge. Reports for each chiller are completed and filed in the onsite F-gas leak register. A history can be built up to assess the serviceability of the plant and the frequency of any leaks.

Chiller Service Company Monitoring

Where intermittent faults are concerned, on site monitoring is required. If the job is not progressed on each visit, there is little point in a call out. We carry out tests during monitoring and ensure that the wiring is tight. Hopefully, waiting for the fault to occur whilst next to the machine. Alongside this, we rely on feedback from the end user, as regards, the symptoms and the circumstances of the chiller when the fault occurred. From this we extrapolate the diagnosis and decide the next step to take. This may be to attempt to move the fault to another machine or, at least eliminate one thing each visit.

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Chiller Service Company Evaporators

Shell and Tube

These have a rolled steel shell, welded down the seam with and end plate on either end. The water system pipes can be bolted to the sides or the end. The endplate can be removed for access to the waterside of the tubes. A strainer is fitted to the inlet to catch any foreign objects that may have been carried around the water system. Inlet and outlet gauges are fitted for the monitoring of the water system readings during a visit. 

Flooded

On larger chillers, the screw or centrifugal compressor is mounted directly on top of the flooded evaporator. The refrigerant is in its liquid phase on the outside of the tubes. These are arranged in a rack extending through the length of the shell. The warmer process water running through the tubes causes the refrigerant to boil off. A sight glass is usually available to check the state of the refrigerant evaporating on the copper tubes. The suction from the top of the evaporator goes round a baffle so as to prevent the slug back of liquid refrigerant into the compressor. The refrigerant flow into the evaporator is controlled by the expansion valve…

Expansion Valves

This takes the form of a fixed size orifice on the liquid line in between the shell and tube condenser and the flooded evaporator. The size of the orifice previously being calculated to match the mass flow rate of the refrigerant dictated by the compressor. Some newer systems have a variable orifice for the more efficient running of the plant. This is controlled electronically along with the loading of the compressor, relative to the available load.

Multiple System N+1

Smaller DX evaporators are usually multi system. This gives an N+1 redundancy of the plant. Indeed, when one side of a 2 system evaporator is having service work carried out, the other side continues to operate normally. Thinking ahead and allowing for additional capacity is essential when the application is critical, such as, a data centre or a hospital. When a redundant system comes online due to a failure- getting the failed system back up and running is a matter of urgency. For this we offer same day delivery of parts and a fully stocked mobile workshop.

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Chiller Service Company Condensers

Various configurations are employed to ensure good air flow through the condenser fins. The most popular being a ‘v’ condenser as the surface area is increased with this design. Powerful fans are used to reject the air and heat upwards and away from the chiller. Where system location causes the recirculation of air, duct work can be fitted to direct the air away from the chiller. The pressure is monitored using a HP gauge.

Pressure Transducers

Johnson Controls

A popular kind of pressure transducer that is used on condensers is Johnson Controls. These can be bolted onto the refrigerant discharge pipe to sense the system pressure. They have a 5vdc input that comes into the transducer on a red wire, a black wire is the ground and a white wire is the signal back to the fan speed controller. The transducer has a minimum to maximum range, so a chart can be used to determine if the signal is reading back correctly. On chillers where the transducer is wired directly in the controller- calibration can be carried out to offset the readings.

Keller

Another kind of pressure transducer is the 4-20mA type. It sends a mA signal back to the controller or the fan speed controller. 4mA is the minimum position, so this relates to the minimum of the transducer pressure range.

R134a Refrigerant

R134a refrigerant operates at a lower pressure in a condenser than the other commonly used HFC refrigerants. If you were looking for a chilled water set point of 6°C in the UK ambient for example, the R134a refrigerant saturation on the high side of the system would be around 36°C Latent heat from the water system and heat added into the refrigerant from the compressor are rejected from the condenser. As the refrigerant passes down the condenser tubes, cool air blowing across the outside of the tubes, cools the refrigerant vapour down through the latent heat phase and into a subcooled liquid.

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Chiller Service Company Compressors

Centrifugal Compressors

This kind of compressor has a lower volumetric efficiency compared with the positive displacement compressors below. This is because the refrigerant is compressed using centrifugal force off the tip of the impeller, instead of being mechanically compressed. The advantage of this kind of compressor is a high mass flow rate of refrigerant. These compressors are used in factories where a large amount of chilled water is required to cool the process. They are also used in countries where district cooling is used. The chillers are arranged in rows in a chiller hall and are piped into the district cooling loop.

Screw Compressors

Oil used to lubricate the bearings is also used to create a seal between the rotors. Computer aided design (CAD) software and computer numerical control (CNC) grinding machines are used in the construction of screw rotors. The shape of the rotors is designed to compress the refrigerant along the screw. The length of the screw that is available to compress the refrigerant can be adjusted with a slide valve. Any stage of loading between 0- 100% can be achieved. This is regulated with a slide valve potentiometer. Screw compressors are very reliable and have a long service life. They also have a low vibration reading which ensures a lower instance of refrigerant leaks around the compressor.

Scroll Compressors

A service free compressor. Service free assuming that the rest of the system is functioning correctly. This kind of compressor relies on oil migration around the system. The oil is entrained along the inside of the pipework, around the system and back to the compressor. An oil level sight glass is fitted into the body of the compressor at the required level. Refrigerant shortage can cause the oil to stay in the bottom of the evaporator, causing a low oil level condition in the compressor. We can be scheduled to attend site to drain the oil, then pump new oil into the compressor.

Compressor Failure

When any of the above compressors fail, you are in safe hands with Maximus Chillers. We have the capability to lift and shift the compressor to our remanufacturing facility for a full overhaul. The reason for the failure is diagnosed to ensure the new compressor does not fail for the same reason. Improving the reliability of your plant and extending its life is what we are all about- if we can reduce your service costs- that makes us happy! All temperatures and pressures are recorded to ensure the replacement compressor goes into seamless operation.

Any Chiller- Any Problem- Any Part- Any Refrigerant- Anywhere- The MAXIMUS ADVANTAGE™

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To read more about chiller diagnosis hit the Tag at the top of the page.

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Large air cooled brown chiller with test equipment during planned preventative chiller maintenance

Planned Preventative Chiller Maintenance

Featuring planned preventative chiller maintenance, which is part of a series of longer, in depth articles.

News Article No.2

This time concentrating on the checks, adjustments and diagnosis our engineer carries out while on site. We can extend the life of your plant and reduce energy costs- just with the effect of our maintenance. As well as completing a detailed checklist, which is sent to your office in PDF form, our engineer carries out extensive F-gas leak testing.

Planned Preventative Maintenance of Chiller Controls

The first part of the maintenance is carried out to the controls of the redundant systems. This is because all the pressures and temperatures should be reading the same. If not, this is an opportunity for:

Sensor Calibration

Before calibrating a sensor that is reading out, our engineer carries out a diagnosis to assess the serviceability of the sensor. With NTP (negative temperature coefficient) and PTC (positive temperature coefficient) sensors, the resistance is taken at a given temperature, which is then compared with a chart. With pressure transducers the 0-5vdc feedback signal is analysed to see if it is within the allowable tolerance. Once this diagnosis is complete and the sensor is deemed to be in good working order, our engineer will then calibrate the sensor. A password is entered into the PLC (programmable logic controller) to gain access to the service menu. From here, he can select the particular sensor, then offset it by the required amount. A lot of controls are not linear, that is to say, a sensor reading 2°C high being reduced by 2°C may not calibrate correctly. An amount of trial and error is often required. Also, monitoring the sensor against a digital thermometer at various temperatures is carried out.

Program Settings and Timers

Each program setting and timer in the various menu levels is checked against the previous maintenance checklist. Sometimes these are changed accidentally by the onsite engineer when looking for something else- it is easily done.

Planned Preventative Chiller Maintenance of Safety Chain

Each component on the safety chain is manually tripped or the fault condition is replicated to cause the device to trip. This part of the PPM (planned preventative maintenance) is essential to ensure the safety chain protects the chiller during a fault condition. Compressor failure or evaporator freeze up can occur with dramatic cost implications. We routinely prevent small problems, such as a faulty switch, becoming big problems.

Planned Preventative Chiller Maintenance of Wiring

Each wire on the chiller is checked for tightness including the fans (on air cooled chillers) This includes the compressor motor connectors and compressor contactor contacts. Loose line wiring will cause breaker and fuse faults. Loose control wiring will cause error messages and chiller faults. This is a call out in between visits that can be eliminated. With the effect of our maintenance, any chiller becomes more reliable and has lower energy costs.

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After the above stop checks are carried out, system run checks are carried out:

Superheat

Using R134a refrigerant as an example, the refrigerant pressure will be 1.9 bar at 0°C This refrigerant is in the HFC (hydrofluorocarbon) family- a commonly used refrigerant. If the refrigerant vapour returning to the compressor is excessively superheated- this is a sign of system issues. Here are some of the causes for a high superheat condition:

Refrigerant Shortage

Not enough latent heat being absorbed by the refrigerant in the evaporator. This allows the refrigerant to carry on superheating with the available heat load. Refrigerant leak testing is required to identify any leaks. The history of maintenance checklists can be consulted to see if the issue has been deteriorating over several visits.

Expansion Valve Failure

A thermostatic expansion valve operates with a higher superheat value, whereby an electronic expansion valve has a much closer control. In either case, our engineer will be accustomed to the nominal readings.

Thermostatic Expansion Valves

This type of valve is operated with a power element and orifice. A bulb is clamped onto the suction pipe which is connected to the power element via a capillary tube. The power element is pressurised with the same refrigerant as in the chiller. Some of this refrigerant is in its liquid phase, so with an increase in temperature, there is a corresponding increase in pressure. This pressure acts against the diaphragm and so pushes the orifice open. The orifice allows more refrigerant through the valve. When load conditions change and there is a reduction in heat load, the reverse happens- the orifice closes and reduces the amount of refrigerant through the valve. When the power element looses its charge- the orifice shuts down causing a high superheat condition. A low pressure trip out can also occur.

Electronic Expansion Valves

This type of valve uses sensors on the liquid and vapour sides of the evaporator, or a transducer and sensor vapour side of the evaporator. This is so the program can work out the superheat value. If the sensors are faulty, the valve will not operate correctly and a high superheat condition may occur. If the step motor or driver have failed- replacement parts are required.

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Subcooling

This is the measurement of the refrigerant condition in the condenser. Air cooled condensers are particularly popular in the UK as the ambient conditions make them very efficient. Shell and tube condensers are used on lager systems- these are cooled down using a water tower. When there is a refrigerant shortage, the liquid does not stay in the condenser long enough for it to subcool sufficiently. Some of the refrigerant stays in its vapour phase. With not enough latent being rejected in the condenser- the chiller’s COP (coefficient of performance) will be reduced. This means high energy consumption relative to the refrigeration effect of the chiller. This condition can be remedied with a scheduled visit from one of our team.

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Two dark green centrifugal chillers undergoing maintenance in plant room

Centrifugal Chiller Maintenance

At the beginning of the year we completed centrifugal chiller maintenance for one of our customers in America. A last overseas trip for the moment given the current world lockdown. The machines in the photo chill water that is pumped around a university campus.

Centrifugal Chiller Maintenance of Redundant System

The plant has a water cooling shell and tube evaporator and a water cooled shell and tube condenser. It has been designed according to the N+1 principle: N being the amount of cooling required and 1 being that same amount of cooling again. Each chiller has enough capacity to satisfy demand. Given the large size of the campus, this principle was critical to keeping the University functioning should system failure occur. The chiller on the right was the lead chiller on arrival. After taking detailed readings during the maintenance, our engineer switched that chiller over into being the lag chiller and took readings from the chiller on the left. He rotates the lead/ lag of the chillers on each visit to balance the run hours of the compressors.

Volumetric Efficiency

Centrifugal chillers have a lower volumetric efficiency compared with positive displacement compressors such as screws and recips. This is because the impeller does not mechanically compress the refrigerant like a piston in a reciprocating compressor. This kind of compressor relies on centrifugal force to spin the refrigerant off the tip of the impeller and onto the next stage. The refrigerant is then discharged from the compressor.

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Mass Flow Rate

The above is more than compensated for with a high mass flow rate. That is to say: a high volume of refrigerant circulates around the system at its operating density. A large capacity machine is cost effective when considering energy efficiency and centrifugal chiller maintenance costs.

Gantry Crane for Centrifugal Chiller Maintenance

The gantry crane in the picture is available to aid with the lift and shift of the compressor, should compressor failure occur. Maximus Chillers are specialists in the overhaul of centrifugal compressors. We can arrange the lift out, transportation, strip down and reassembly of your compressors. All of our strip downs come with a 12 month warranty to give you peace of mind and confidence in our ability.

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Read about centrifugal compressors at The Engineering Mindset


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