Pump header pressure issue

[Daren Samy]

There are two identical PD (gear) pumps installed. Both feed lube oil to boiler feed water pump in stand by condition. It is interesting to note that discharge pressures (pressure guage installed before check valve) on both pumps before check valve are same one they are taken independently in service. Both pumps discharge pipings combine to form a header. There is pressure gauge in the header. When pump A is run individually, header pressure is 0.025MPa where as when Pump B is run individually, header pressure is 0.023Mpa (decrease of 0.02Mpa) is observed. Which thing causes decrease in flow ? There are only two items involved before common header. Pump B check valve and discharge valve . Which thing can be faulty Check Valve and Discharge valve ? If check valve is not properly seated and it restricts flow. Can it cause decrease in header pressure ?


Daren!

 

[LittleInch]

If your getting some leakage past pump B check valve then pressure will fall

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Snickster]

Assuming the pumps are acting like ideal positive displacement pumps and are exactly same then they should be pumping same volume at same RPM. If one gear is worn more it could be causing back slipping of fluid so it produces lower flow and lower pressre drop which you are reading. That could be one thing happening. You are just assuming the flow is the same for both pumps, because you are not measuring flow-just pressure, so you much be getting more pressure drop somewhere

Also in any case two identical pumps are not going to produce the same flow curve exactly. The flow curves are based on tested pump of same model but not all pumps are tested for flow curve verification unless you ask for it in your specification, which is only done sometimes for very critical process and API 610 pumps.

 

[Daren Samy]

@LittleInch: There is arrangement.
Pump - Check Valve - Discharge valve. If one pump is running then other pump discharge valve is in closed state then oil can not reach to check valve. Possibility of check valve leakage issue does not exist. But there can be possiblity of issue in check valve of same (running pump). What do you think if check valve is not fully open/half stuck ? Can it cause pressure decrease ?

Daren!

 

[Daren Samy]

@Snickster ! Discharge pressure guages for both pumps read almost same pressure for each running pump. Issue is between header & Check Valve. After this pressure guage , there are only two valve installed installed in series before header pressure guage i.e. check valve and discharge valve (isolation valve). There is less possibility that discharge valve (isolation valve is faulty) . Check valve has not been inspected/checked for previous 20 years. These are spring loaded ball type check valves.

Daren!

 

[georgeverghese]

Sloppy post: Difference between 0.025Mpa and 0.023Mpa is 0.002Mpa, not 0.02Mpa - where is the error in your post?

 

[LittleInch]

Yes, a partially blocked or not fully opening check valve can cause a pressure drop different to the other one.

Or maybe pump A check valve the spring is broken so there is lower resistance to flow compared to ump B where a spring is applying some small pressure differential to occur.

Swap the check valves around and see if the pressure drop moves from pump B to pump A. If it is then its your check valve. If not then its something else.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.