Test method of auto start-up pump during normal operation

[1906]

Re the stand-by pumps'(such as auxiliary lube oil pump in forced Lube Oil Type pump or recycle gas comp. lube oil pump system generally consist of steam turbine and Motor pump) auto start-up initiated by Level Low Low signal or Pressure Low Low signal in refinery, How do you usually test periodically that those system is working good or not during normal operation without any effect to the operation?

 

[BigInch]

"standby" pumps arn't supposed to always "standby". You should be alternating the active duty unit through all available pumps, probably every 60-90 days or so.

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[JJPellin]

The auto-start functionality should be tested when the unit is down. The standard test would be to put the main pump on line (usually the turbine drive on our systems). Place the spare pump in "auto" and trip off the main pump. This will allow you to verify that the auto-start switch is working properly. The spare should start up and catch the pressure before the trip point is reached. This can also find problems if the pressure control valves and the pressure relief valves want to fight. I have seen systems where the pressure would spike up when the aux pump came up to speed, the full-flow relief valve would open to relieve the excess pressure. The spill-back pressure control valve would overcompensate for the loss of oil through the relief and the two valves would get into an oscillating hunt.

In answer to your direct question, all of this testing should be done with the compressor down. Once the compressor is up and running, it would be too risky to repeat this testing. BigInch is correct that you should be running your spare pumps on some set frequency. We run ours once per month for four hours. On most systems it would not be practical to switch back and forth to get equal run time on both pumps. Generally, only one pump is set up to auto-start. If you want to verify auto-start capability on the system while running, you could have your instrument techs isolate the auto-start switch and pump it up to test with the aux pump turned to off (not in auto).


Johnny Pellin

 

[1906]

Thanks JJpellin.
Re your comment of "If you want to verify auto-start capability on the system while running, you could have your instrument techs isolate the auto-start switch and pump it up to test with the aux pump turned to off (not in auto)", would you please specify in detail.

 

[JJPellin]

We commonly test switches with the system on line. The switch must be installed with a valve block that allows the switch to be isolated from the process reference pressure. This valve block must also have a connection for an external pressure source. Our instrument techs would use this arrangement to do the test. They isolate the process connection to the switch. They connect their test pump which includes a calibrated pressure transmitter. They pump the switch up above the set-point and slowly bleed the pressure down. They note when the switch changes state. This would correspond to the pressure at which the aux pump would auto-start. Depending on your piping, you could isolate the aux pump and let it start-up as part of the test. In most of our newer systems, we have piping that allows us to run the aux pump isolated from the system, running totally in spill-back to the reservoir. This allows the aux pump to be run monthly for vibration testing. It would also allow the auto-start switch to be tested on a running system without risk of an upset that could trip the compressor.

Johnny Pellin