Selection and sizing check valve for saltwater service

[canmecheng]

Hi, I have a saltwater fluid circuit that needs to maintain pressure in the event we loose power to our pump. We have used disc check valves for other saltwater circuits in the past but this time the flow is only 3GPM. I am concerned about valve chatter because the pressure drop from the valve appears to be lower than the crack pressure, even though it is only 0.29psi.

For this amount of flow, 3GPM am I limited to using a ball check valves to restrict the flow and generate a pressure differential across the valve so it does not close and open? I also need the check valve to hold 500 psi with a soft seat when closed. I was thinking about removing the spring and operating it vertically to reduce the cracking pressure but I don't know if it would be enough.

Thanks

 

[BigInch]

A flow across a valve, down a pipe, or between any two points, is produced by a differential pressure. Flow does not produce pressure differentials. Flow produces a pressure drop. The difference may seem to be somewhat like the difference between 6 and a half-dozen, but it's an important difference anyway you look at it.

Your problem appears to be that your system, although of relatively high pressure, has a very small difference in minimum and maximum pressures, even when the valve is closed. As your check valve opens, it immediately floods your downstream piping, pressure builds and any system differential pressure is quickly lost, rapidly becoming near zero, which allows your check to open again.

Look for a pump that has a higher flow capacity at the same (or perhaps greater) pump differential pressure.

 

[stanier]

Perhaps then you need an actuated valve which opens and closes based on some logic.

3gpm at 500 psi suggest a pd pump with built in check valves on suction and discharge. Is this what you are referring to in your post? There are plenty of dosing pumps operating with ball check valves in similar service.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[canmecheng]

Hi, yes it is a positive displacment pump. It is a subsea application and we are using a stainess gear pump powered by a hydraulic motor.

I think I have resigned myself to using a small ball check valve instead of a silent check valve. I just need to check the materials. I think fundamentally the Cv for the disc check valves just seem to high for our desired flow.

Thanks

 

[stanier]

I am confised. Why do you need a check valve with a gear pump?

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

http://waterhammer.hopout.com.au/

 

[BigInch]

I think fundamentally the Cv for the disc check valves just seem to high for our desired flow.

I see you still believe flow causes pressure drop. You're not going to get this right until you turn your head around.

 

[canmecheng]

BigInch, I have not mentioned any limitiations for adjusting the power delievered to my pump. My flow requirement is independent of the losses for the system.

My question was regarding the stability for a disc type check valve against chatter given this flow condition. To determine this, I was questioning the comparison between the loss over the check valve and the cracking pressure.

 

[BigInch]

Ya. Don't see why that is important. In a closed circuit, for example, your pump discharge pressure - pump suction pressure - piping flow losses (not including valve loss) should be at least as great as the cracking pressure at maximum flow.