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Pressure Control Valve Issues For Gsw Lines


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#1 fahadazh

fahadazh

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Posted 29 March 2024 - 08:15 PM

Hi Group,

I am trying to deal with an issue of controlling the pressure of Gland seal water flow to slurry pumps. I need to maintain the pressure atleast 70 kpa above the discharge pressure of a pump.

I have Ez micro form 1" control valves for each of 2" GSW lines feeling gland water to their respective pumps (lets say A &B), upstream pressure is 2000 kpag. for pump A the required pressure is 1000 kpag and for pump B its 700 kpag.


Now, I am bit confused to see that both of my valves are 100 percent open after being in service for two years and with same upstream pressure they are some how maintaining their respective downstream pressures. Is it possible,?? for absolutely same valves at 100 percent, with same upstream pressures to produce a different downstream pressure?
I was thinking first its maybe a faulty transmitter, however when I tried commanding the valves to close in steps the pressure and flow fluctuates as well. What am I missing here?

Any leakage in system will impact the flow I understand but not pressure is that right? As on the same line upstream
if a control valve there is a 3/4" seal flush lines to the pressure transmitter, and I was doubting if they might be leaking or on for a longer duration impacting flow and pressure?

#2 Pilesar

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Posted 29 March 2024 - 08:33 PM

My guess is the pressure is self-regulating. As long as the seal water pressure is high enough, there is a fixed pressure drop across the pump seal. The seal water is flowing into the slurry pump at a flow rate enough to maintain that seal pressure drop. You would be able to reduce the seal water pressure (not advised) but if you tried to increase the seal water pressure above the seal design pressure, then there would just be more flow through the seal. You might confirm this behavior if you measure the seal water makeup flow. This is just a guess... there is a lot I do not know about pump seals.



#3 fahadazh

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Posted 30 March 2024 - 07:36 PM

Interesting, can you pls elaborate a little more. I think what you are saying is making sense, as I can see at a fixed opening of a control valve with a constant upstream pressure, there is nothing which can manipulate the pressure. Tell me a bit more how pressure is self regulates itself in this scenario, and draws more flow? I will as thinking that because of fix opening there would be a constant pressure drop across the valve, however it fluctuates and trends along with the discharge press of a pump

#4 Pilesar

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Posted 30 March 2024 - 07:50 PM

I suspect that the pump seal is not working as designed. Perhaps it is worn too much or damaged. The pump manufacturer might be a good resource if you do not have a local rotating equipment expert. From your description, there would be little you could do to if the seal water pressure began to drop since the control valve is already wide open. Although it is working now, it might be good to schedule an overhaul at the next convenient time. Find someone who knows more about your pump seals to advise you!






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