Our 55 kW screw compressor loads every four minutes or so overnight with the plant empty. Boss says leaks and wants me to find them. The load solenoid and the run contactor already go through a CompactLogix in the compressor room, that's how the run hours get to the HMI.
I've walked the plant twice with a soap bottle and fixed a few fittings, no luck, the overnight loading is much the same as it was.
One of the fitters says put a bigger receiver in so it loads less often, which I'm not sure about. Is there a way to use the PLC to tell me where the air's going, or is it soap bottle until I've found them all? Counting loaded minutes off that solenoid is about all I can think of, does that get you anywhere near a real number?
A bigger receiver just changes how often it loads. Same air leaks out of the same holes. What's the receiver size and the pressure band, load and unload points?
1000 litre receiver. Loads at 6.2 bar, unloads at 7.0.
Two things the PLC can do. First, count load seconds per hour overnight: a timer on the load solenoid output, totalised per hour, stored. With the plant empty every load second is leak. That's your trend, and you see the effect of each fix the next night instead of guessing.
Second, for where: compressor off after last shift, log the receiver pressure decay from 7.0 to 6.2 with everything open. Then close one zone valve and log it again. The zone that slows the decay most has the biggest leak. Then rent an ultrasonic gun and walk that zone only.
The run hours and counters side is written up here: https://plctr.com/using-plc-for-energy-management-and-conservation/
Does the counter need the receiver pressure transducer into the PLC, or just the load signal? I think all we've got in there now is the load signal.
Load signal is enough to start. Rent the gun.
Overnight load duty was 31% the first night. Closed the paint zone valve, decay from 7.0 to 6.2 took twice as long, so that's the zone. Rented the ultrasonic gun for a day and found a cracked FRL bowl and two push fittings in the paint zone and we had the lot sorted by lunchtime so last night came in at 14%.
What did it was the load counter for the trend, the decay test to pick the zone, then the gun in that zone only.
14% is still a lot for an empty plant, and the other zone has no valve so I can't isolate it. Thanks wanda, ed.
Put a valve on the second zone. Then it's a number too.