Chilling Plant Controls Maintenance

Controls panel open during chilling plant maintenance

Chilling Plant Controls Maintenance

Prior to this chilling plant controls maintenance visit, another contractor had changed some of the settings and adjustments in the controllers. They did this while they were diagnosing a fault with the water system and the pumps. Therefore, this visit was to recommission the plant and to resolve the issues resulting from the adjustments.

Chilling Plant Flow Controls Maintenance

The flow controls were found to be set wrong causing a wrong. Our engineer adjusted the pumps, then various valves on the water system, a little at a time, while monitoring the controller. Full load and part load readings were taken until they came to within standard industry limits.

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Compressor Run On Time

A timer had been adjusted which made the compressor wait to stop after reaching 0% on achieving set point. In the meantime, some more heat would build up in the water system and the compressor slide valve would open up a little. The result was that the compressor would run for an hour with the slide valve shut most of the time. The oil pump carried on pumping during this time resulting in a head of oil building up in the discharge pipe- all the way back up to the oil separator. Then, a low oil level fault had occurred. This being confirmed by the sight glass on the oil separator. The compressor had enough oil charged into it to allow a start up. During the start up, a low oil level timer counts down. As soon as the compressor loaded and started pumping, the oil level returned to the correct level on the sight glasses. The timer was adjusted along with the dead band to ensure the chiller off cycled after achieving set point.

Slide Valve Potentiometer

The slide valve potentiometer has a configuration mode button. It can be pressed to set the 4mA or 0% position. This is the usual position of the slide valve as a spring and 2 drain valves return it to the start position. The slide valve can then be manually opened in the program. Then, the potentiometer button can be pressed to set the 20mA or 100% position. “Chattering” can occur on the fully closed position so a setting is available to only close the slide valve to 2%.

To read more about chilling plant maintenance click 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

Industrial Chiller Oil Maintenance

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

Oil Drain Out

The oil separator and oil system was valved off from the rest of the system. The standing pressure of the vapour in the vessel was 5.8 bar. On the far end of the oil cooler 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 Pump In

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 back in 4 drums of oil using the same port from which the oil was drained. This is so that the oil cooler, on the other side of a heat activated three way valve, was primed. The oil came to the correct level on the oil sight glasses and the vapour was bled from the oil filter so that the compressor was primed with oil. When the system starts, the discharge pressure in the oil separator pushes the oil into the suction of the screw.

0161 370 7193

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Slide Valve Oil Pump

To operate the slide valve, a gear type oil pump is bolted to the casting next to the shaft. This raises the oil pressure to 5 bar above discharge. The oil is pumped through channels in the casting to operate the slide valve. A spring is fitted to the slide valve to return it to 0% when the plant shuts down.

Industrial Chiller Maintenance Monitoring

The oil heater was switched on until the oil was 46°. 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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Follow this link to read about polyolester oil on Wikipedia | Click Here

 


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