Check Valve in Reciprocating Pump Circuit

[pnrngv]

thread378-124275

Hi,
There is a Check Valve installed in the discharge side of the reciprocating pump in the Chemical Injection Package. Working and Stand-by Pumps are connected to common header. During FAT of the packages, when testing the scenario of switching from Working (Pump A) to Stand-by pump (Pump B), we noticed a reverse flow passing through the Check valve of the (Pump A). Back Pressure is created through Regulator for testing.

Check Valve Type - SW 800 Pound rating Lift Type. (All are SW piping circuit)
Discharge pressure of the Pump is 65 PSig.

Valve vendor responded as below
"Quote : "Vendor tested this valves according to the applicable pressure class (800) that mean 150 bar...The main problem is that you are using this 800 class valves for a different purpose. The sealing surfaces design for a class 800 (150 bar) is different than a sealing surfaces design for 4.48 bar (65 PSI). If you need valves for low pressure you need to order a different design"

Unquote:
Please suggest,
1. What is the best valve type for the application ?
2. Any solution on the same lift Type Check valve installed ?

 

[mk3223]

IMO, the piston of the check valve might be stuck which resulted in the reverse flow.
May consider to use a spring loaded check valve.

 

[pnrngv]

Thanks mk223 for your response.

The Check valve installed is spring loaded lift type Check.

Just want to know, whether responses given by vendor is valid in this case. Check valve to function in case of any amount of pressure in case of reverse.

 

[LittleInch]

Well as noted in the original post, the purpose of this check valve is unclear.

How did you notice "reversed flow"?

Virtually all check valves will pass fluid in a reverse direction and are not normally required or can seal tight. So yes the valve might pass a bit and presumably pressure up the piping downstream the pump but so what? Check valves are there to stop large scale flows. Many HAZOPS will allow for 10% of max flow to go back through a check valve.

SO my guess is that at the pressure rating they are looking at, you've got hard metal seats which have a very small pressure differential on them and hence are not sealing 100%.

For a lower pressure rating you might get soft seat valves which are more able to seal.

Either way complete reliance on a check valve to seal off pipes is poor practice and often fails!

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

 

[pnrngv]

Thanks littleinch

Reverse flow noticed through the Pressure gauge deflection, when switching over the pumps for testing pressure.

My interpretation is that, there is a check valve in pump itself, and small reverse flow is ok. Please correct my understanding..

 

[LittleInch]

I would imagine so.

One thing though. The PSV is set at 72.5 psig. If your connecting pressure is 65 psi, that's not a lot of gap for a PD pump.

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

 

[pnrngv]

Hi Littleinch,

PSV set at 10% of the operating range complying to API 675 guideline. There are no issues so far, if the process is not too much of variant than the given value by client.

But how does it link with the Check Valve reverse flow issue. Please clarify.

 

[Expert Whipper Snapper]

Assuming the valve is not malfunctioning and is installed correctly, you may ask an applications engineer from the valve supplier to either diagnose the issue or recommend alternative seating materials.

 

[LittleInch]

Not directly related but the discharge pressure of a PD pump is whatever the pressure is of the connecting system. A 10% margin is the minimum not the recommended limit.

Given you have a relief valve then there is somewhere for the fluid to go. But as the two systems are identical you shouldn't be able to overpressure one pump from the other.

If you want to check the flow through the check valve then open the valve on the relief line and measure the volume.

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

 

[pnrngv]

Hi Expert Whipper Snapper,

Thanks for your expert opinion. Valve vendor suggested for a flat sealing configuration in place of conical seat for low pressure application. Also, we need to upfront inform valve vendor during selection about the pressure range for them to choose a right configuration. This is a lesson learnt.

Thank you all.

 

[pnrngv]

Hi Little Inch,
Normally the valve at the Inlet of PSV is kept opened.

But in this case, as suggested by vendor flat sealing configuration seems to be the best option.

Thank you all.

 

[LittleInch]

NO - I meant the little drain valve off the main inlet leg. You can't close the PSV inlet valve whilst the pump is in service and connected.

I think you're over thinking this. Check valves will always leak in service and cannot be relied upon to seal 100%. That's what isolation valves are for.

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