True Professional Engineer
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Thursday, April 5, 2018

Chiller Unit tripped with "No Flow" alarm

On passing by the Chilled water system and glycol chiller units in the plant this morning, I saw the supervisor and technician are working there for some problem faced. On checking with them, I was informed that the chiller unit tripped with "Glycol no flow" alarm. It runs back to normal after resetting.

I decided to ask if they understand what possible caused the tripping and I was informed that the level in the glycol tank is low. With doubt in mind, I decided to go with them to check the glycol tank level and noticed that the level was not "too low" as what they explained.

Hence decided to explain to them on how to trace for the possible root cause on such system trip issue. As I always highlighted to the team, a successful man always slice a large problem into smaller pieces and then tacker them one by one. In no time, the problem will be solved. The same apply to engineering trouble shooting.

Hence the first step is to trace the part of the whole system that giving alarm "glycol no flow to chiller unit". The following snip set of the glycol system related is capture and atteched here for reference.

Using the glycol tank as a starting point, we noted that there are three pumps (PP1, PP2, and PP3) taking their supply from Glycol tank and discharge into a common line to send for chilling into two chiller units (Chiller 1 and Chiller 2) and then back to glycol tank. Two of the pumps will be running at any one time with the third pump on standing by. There is another circuit with two pumps (PP4 and PP5) taking suction from glycol, sending through Chiller 3 and then back to the tank. For this circuit, one pump will be running and the other on standing by too.

After check and confirm the level of glycol in glycol tank is normal. I noticed that the running pumps are PP2, PP3 and PP4. The pressure gauges readings were PG2 zero PSI, PG3 80 PSI and PG4 50 PSI.

Hence my first advice to the technician and supervisor is to ensure all presure gauges are working correctly. The pressure gauge that indicating 0 PSI is definitely faulty or blocked. Assuming pressure Gauge PG4 is correct at 50PSI, then pressure gauge PG3 with pressure of 80 PSI may be faulty too, or there may be some blockage on the line. Hence, I advice them to check on any possibility of partial iced up in the heat exchanger of the running chiller unit. The system may have to be shut down for a short while to let the iced glycol melt.

A further action is required to check the glycol bridge. It may happen that the bridge is too low, or else the glycol should not iced up in the heat exchanger.

After ensuring that both the supervisor and technician understand the explanation above, they were then left to continue with their action to rectify the issue accordingly.

"NO FLOW" alarm is activated by the differential pressure switch PS connected across the inlet and outlet of the heat exchanger. Hence an alarm basically indicate possibly blockage of the heat exchanger. 

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