Control Valve effects on a pump

[longeron]

I’ve got a question about control valve operation. I was walking through one of the plants that I’m contracted to yesterday, and I noticed that the discharge of this pump was cycling between 45 and 10 psig. Now, I haven’t looked at the P&ID yet, but it is my guess that downstream a control valve was opening and closing to meet some condition. The cycle from open to close and back was less than 10 seconds. That seems kind of strange. Could this be due to the PLC tripping or some condition that it wasn’t programmed for? If the operation of this control valve is to blame, what else should I look for?

 

[TD2K]

It could be a control valve cycling or some other variable on the process. You really need to follow through the system and understand it. At this point, throwing out possible 'solutions' isn't much use.

 

[CHD01]

Your most likely problem is one of losing liquid flow to the pump suction - either from insufficient submergence or due to flashing from liquid being too hot. These are your top two causes. A cycle every 10 seconds sounds too fast to me to be a control valve although I would not rule it out.
The more you learn, the less you are certain of.