Chiller Compressors

Chiller compressor failure of blue Grasso in enclosure

Chiller Compressors

System Testing for Chiller Compressors

Chiller compressors fail often as a result of ineffective servicing and system testing. At Maximus Chillers, we carry out extensive tests during our visits to ensure that small problems are resolved before they become big problems. If we notice a reading starting to become abnormal, we can carry out the diagnosis and then remedy the problem. Some of the compressor readings we monitor are:

Temperature of Chiller Compressors

The suction, discharge, motor windings and bearing temperatures are recorded for comparison to previous visits. These are often available in the PLC for the chiller, or our engineer can take the readings with his test equipment. Problems with the oil cooler can be the cause of higher compressor temperatures, the system running outside of its nominal operating conditions is another reason. Magnetic drive systems have an advantage as they do not use oil.

Accelerometer

Portable vibration sensors are carried in of each of our company vehicles. This is an accelerometer to measure vibration. Along with other system readings, we keep an on going record of the vibration levels around the compressor. When internal components are coming out of alignment due to wear, this causes an out of balance condition in the compressor. This, in turn, causes a knock on effect- causing other components to go out of balance. Catching this condition early will prevent a compressor smash up resulting in the replacement of expensive internal components.

Oil Analysis for Chiller Compressors

Another way of preventing big problems from occurring is periodic compressor oil testing. Samples are taken, usually on alternate visits, which are sent off to a laboratory for analysis. The acid level is tested to provide pre warning of a potential compressor motor windings burn out. This is because acid in the compressor oil rots through the electrical insulation on the motor windings. The presence and quantity of white metal and yellow metal is analysed too. This is a window through to a component starting to wear inside the compressor.

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Screw

The compressor in the photo is a screw compressor. It operates with ammonia refrigerant. This refrigerant is usually used for low temperature applications, mainly associated with food production. This compressor, however, has a 1°C refrigerant saturation and is used to cool computer rooms. Common causes of compressor failure on this kind of compressor are:

Leaking Castings on Chiller Compressors

The various compressor components are sealed together using ‘o’ rings or paper gaskets. ‘O’ rings are especially prone to leaks due to work hardening and flattening of the sealing face. The system can be pumped down and the compressor valved off. Then, our lift and shift team can remove the compressor to our remanufacturing facility for strip down.

Leaking Shaft Seal

The mating surface of a shaft seal has a mirror smooth finish. This is to reduce friction and aid with a better seal. Over time, this starts to wear, causing an ineffective seal with a leak of refrigerant and oil. A service visit can be arranged to change the shaft seal on site. The shaft couplings can be split, the shaft seal can then be removed and replaced. A quick job, then the machine is up and running again.

Slide Valve Potentiometer

This is an electronic device with a slide attached to the moving compressor slide valve. The device has a start and an end position programmed into it during commissioning. The potentiometer converts the slide valve position, usually into a 4-20mA signal which is fed back to the chiller PLC. They are prone to reading out, or the reading being jammed in one position. This results in a trip out from the controls, as the controller is not able to determine the true position of the compressor slide valve. We have an off the shelf stock of slide valve potentiometers for the various compressor range. A service visit can be arranged to replace the part after diagnosis has been carried out. The controls operate the loading and unloading solenoid valves to change the position of the slide valve.

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Centrifugal

Centrifugal compressors are a very reliable kind of compressor but when they go wrong, they can go wrong in a big way. Compressor overhaul is expensive, this can be carried out onsite, or a better option is a lift and shift to our remanufacturing facility. Proximity sensors are usually fitted to monitor the distance between the impeller and the casting. This is an added protection along with the other sensors and transducers around the compressor.

MCS

We are on account with Micro Control Systems- an American company who specialise in building panels to order for specific chiller compressors. We easily fit this control system to any compressor to control the loading of the vanes in accordance to the available load from the process. The control panel has previously been fitted to other machines of the same model number, so any teething issues have already been ironed out. Maximus Chillers can achieve seamless operation of your plant.

Oil System for Chiller Compressors 

Newer centrifugal compressors are oil free so as to eliminate any of the service issues relating to oil. There are a substantial amount of compressors, however, that use oil to lubricate the bearings. This kind of compressor, if properly serviced, can last for 50 years. The oil system picks up impurities which are caught by various filters. These filters can be changed or cleaned according to the prescribed service schedule. Our engineers make sure that spares are ordered and kept onsite prior to a visit.

Cost Effective

Our visits and ongoing upkeep of your plant saves money. Money spent as a preventative measure saves so much more money in the long run. With competitive prices on specialist internal centrifugal compressor parts- Maximus Chillers completes the picture. When compressor failure occurs, you are in safe hands with years of industry experience invested in each of our engineers.

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Scroll

These are some issues affecting a scroll compressor:

High Discharge Pressure

With high discharge pressure, there is a corresponding increase in discharge temperature. This means that the compressor is operating beyond its recommended values. The cause of this is often a poorly maintained condenser. Especially on industrial chillers, there can have been gaps in the schedule where the condenser was not correctly serviced. This condition is often rectified easily by an onsite engineer by giving it a brush down. Where the fins are bent over- we carry a specialist tool to straighten them back out- how they came out of the factory. We also use different formulas of chemicals to rinse the various kinds of dirt from deep within the fins.

High Suction Pressure on Chiller Compressors 

Some chillers are used where very high water temperature can come back from the process if the chiller were to be off line for a short period. Usually, this happens in factories where certain industrial processes are being carried out. When the onsite engineers start the plant back up, the chiller experiences a high heat load to deal with.

MOP Expansion Valves

Maximum operating pressure expansion valves limit the pressure in the evaporator to a given level, regardless of the available heat load from the process. They do this by having a limited amount of liquid refrigerant in the bulb. When this runs out, the power element cannot push the orifice open any further- thus limiting the suction pressure. This is important to prevent scroll compressor failure as it prevents putting added strain on the compressor motor windings due to high suction pressure.

Oil and Refrigerant Shortage

Where there is a shortage in refrigerant, there follows a low oil level condition. The refrigerant mass flow rate carries the oil around the system and back to the compressor. This is greatly impaired when the chiller is short of gas. The oil cools the compressor and lubricates the shaft bearings. These bearings and other internal components wear down and seize causing failure. Maximus Chillers can put together a package to minimise chiller compressor failure.

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

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An engineer filling blue oil drums during industrial chiller maintenance

Industrial Chiller Maintenance

Reciprocating Compressors

Industrial chiller maintenance including a reciprocating compressor with 8 cylinders. They always have an even number of cylinders so that the compressor is balanced.

Open Drive

Because the refrigerant being used in this article is ammonia, the compressor is open drive. This is because ammonia corrodes the copper windings of the electric motor. An open drive compressor needs a shaft seal to prevent oil and refrigerant escaping from the system. These shaft seals are prone to wearing down and leaking. They have two mating surfaces that have a finish so smooth that it is like glass. Any oil leaking out of the system collects in a pot. This pot is monitored for the rate at which it fills up and so the deterioration of the shaft seal can be monitored. The swap out of the shaft seal can be arranged at a convenient time. This evolves the splitting of the shaft coupling to allow access to the seal.

Semi Hermetic

This means that the electric motor is internal to the compressor. Hermetic meaning sealed and semi meaning that you can bolt components off, such as, the cylinder heads. There is a significant advantage with this type of compressor design as there is no shaft seal. The compressor motor windings are also cooled by the suction vapour returning to the compressor from the refrigerant system. This compressor design is used with HFC, HFO, CO2 and Propane refrigerants. There are some semi hermetic compressors that are suitable for ammonia where the windings have been sealed from the refrigerant.

Scheduled Strip Down

This kind of compressor has a lot of moving parts that need to be replaced according to the run hours of the compressor. Failure to do so will lead to the compressor going out of balance and an expensive compressor smash up occurring. Usually during a smash up, a connecting rod will fly off causing oil to spurt out from the gallery. This causes a low oil pressure fault which stops the machine. One smash up which I have seen involved all the con rods staying on and flailing round the inside of the compressor. One cylinder was still working, the compressor still running and a sump full of different sized triangle pieces of metal! This highlights the importance of scheduled maintenance.

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Major Industrial Chiller Maintenance 

On a recent Major maintenance visit, the scheduled oil change was carried out. The required oil being selected by our oil analysis process to the correct viscosity for a Grasso reciprocating compressor operating at a 1°C saturation.

Oil Drain Out During Industrial Chiller Maintenance

The compressor was valved off from the rest of the system. The standing pressure of the vapour in the vessel was 5.8 bar. On the bottom of the sump is located an oil drain port, this is because it is the lowest part of the system. Using hoses and a valve, the oil was drained into empty oil drums.

Oil Pumping during Industrial Chiller Maintenance

Our engineer removed the old oil for recycling, then lifted the new oil to the work location. He used his portable oil pump to pump the oil in using the same port from which the oil was drained. The oil came to the correct level on the oil sight glass and the vapour was bled from the oil filter so that the compressor was primed with oil. When the system starts, the oil pump pushes the oil through to the cylinders of the compressor.

Industrial Chiller Maintenance Monitoring

The oil heater was switched on until the oil was 46°C. The chiller was then started and run tested. The Delta P across the oil filter was found to be nominal at 0.5 bar. The oil level remained at the correct level as the three way valve opened to the oil cooler. The oil cooler, in turn being cooled by a cooling loop which uses some of the tubes on the air cooled condenser.

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Industrial Chiller Maintenance and the MAXIMUS ADVANTAGE™

Any Chiller

We work on all kinds of chillers from the smallest Italian process chillers, through to large air cooled chillers and centrifugal chillers used for industry.

Any Problem

Problems are our bread and butter- that’s what we do best! Whether you require centrifugal compressor remanufacturing, or the system drying out after a burst heat exchanger- it’s all in a day’s work.

Any Part

We have an excellent supply chain where we pride ourselves on sourcing any part for your chiller. Where a part is no longer manufactured or is not available- we fit a different part. A chiller is just a chiller at the end of the day- we can achieve the same or better design characteristics and efficiency with a different part.

Any Refrigerant

HFC refrigerants are being phased down but are still the most popular variety. They are being superseded by HFO refrigerants which will become more popular over the coming years. We are also adept in the handling of natural refrigerants, such as, ammonia, propane and carbon dioxide.

Anywhere

When you do something as niche as what we do- you cannot expect to just work outside your back door. With blue chip customers around the UK and around the world- nowhere is too far for Maximus Chillers.

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

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Follow this link to read about polyolester oil on Wikipedia | Click Here

 


Industrial refrigeration oil change showing ammonia warning sign

Industrial Refrigeration Oil

An industrial refrigeration oil visit was arranged because of a return issue. Several fans had been down on the air cooled system. This causes the system to unload so as to prevent a fault occurring. The lower mass flow rate of the refrigerant caused oil to migrate to the low side of the system. Several vessels are available with various forms oil return. These vessels and the oil cooler were valved off. A two man team with the correct ammonia PPE and breathing apparatus carried out the job.

Industrial Refrigeration Oil Recovery

Only some of the oil was recovered from the plant. Therefore, the engineers decided to add new oil to get the system running. The only problem with doing this is that once running the machine, the oil has to be got back out. Therefore, the oil had to be adjusted a second time to resolve the oil return issue.

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Fan Decks

For this visit, scaffolding had been erected in accordance with the Risk Assessment. The old fan decks were lifted out by the two man team. A really good team was sent out: one of the men was more technical and the other more mechanical- complementing each other with their different skill sets. The new fans were an updated version and the wiring was different. The fault link had to be adapted, but the 0-10v input from the controller was the same. The controller reads the pressure from a transducer, then sends out a voltage which the fan turns into the corresponding speed.

System Testing

The fault link had been correctly modified, so the testing of the system was carried out. The machine loaded up to 62% and monitoring continued during the rest of the visit.

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

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