MOV not opening fully

[nesamani1983]

Dear All,

Refer the attached dwg.

During the pump starting, as per the starting sequence(defined), when speed reaches the set point, discharge MOV has to open.Total MOV opening time is 35 secs. But in pumps-B & C , MOV-11 & 12 doesnt open fully. MOV stops in the half open position.Ball valve is operated by MOV.
This problem occurs only during no other pumps are running, means P1 = P2. If any one pump is running (P2 > P1) , MOV opens smoothly.
Note: (1) This problem has started after the overhauling of respective the pumps. Pump-A is not yet overhauled.
(2) P1 <20 Kg/Cm2, P2 = 50 to 70 Kg/Cm2 if pump is running.
P1 = P2 = 25 to 30 if pump is not running.
(3) If pumps are not running, means low flow in pipeline, then flow will go thru pump by-pass line (MOV-4).

Kindly give me the probable solution...

 

[BigInch]

Valves should either be fully open, or fully closed.
Actuator limit setpoint needs adjustment.
Pressure Transmitter tap is blocked.



We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky

 

[nesamani1983]

Valve stays in TRAVEL MODE (between open & close).
We did not do any work on these MOV's.
These MOV's were working normal for 10 years, before overhauling of the pumps.
Will there be any effect of Pressure on MOV's...?

I know that if Pr. diff across valve is high, then opening the valves is tough.
But here, if pr. diff is high, valve opens smoothly. If pr is equal across the valve, then problem occurs.
New phenomena...?

 

[BigInch]

That's exactly what pointed me to the pressure transmitter and limit switch.

We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky

 

[nesamani1983]

Thank you.

 

[thiru4vino]

Dear Nesamani 1983

Good Morning
Your statement goes, "I know that if Pr. diff across valve is high, then opening the valves is tough.But here, if pr. diff is high, valve opens smoothly. If pr is equal across the valve, then problem occurs.New phenomena...?" Which pressure difference you are talking about?

My understanding goes like this. The pressure difference across the ball valves of MOV-11 and MOV-12 of respective Pumps B & C will be having less pressure drop when either B or C is started with Pump-A already running. Pump A's discharge pressure will be acting downstream of MOV-11 or 12. When Pump B or C is started respective discharge pressure will be acting at the upstream of MOV-11 or 12. Hence the pressure drop across the valves will be less compared to a situation where Pump A is not already in line.
So this is no new phenomenon? But How MOV-10 of Pump A opens fully when Pump B or C is not running? and that would be interesting to know...