8 replies to this topic

[simadri]

I have a small doubt. Check valve shall be provided at discharge of rotary pumps like gear, lobe, screw etc. or not? The reason for my doubt is that in a project, I had seen there is no check valve at discharge of screw pump.

[simadri]

not a single reply yet?????????

[breizh]

What is the purpose of the check valve ? Do you have risk of back flow using the type of pump you are considering ?
Breizh

[fallah]

simadri,

The screw pump may not need to a check valve in its discharge line. If the pump head is high and the viscosity of the fluid is low, it is recommended to install a check valve in its discharge line. It protects the pump from reverse rotation in the case of backflow due to pump trip. It also allows its parallel operation with another pump in one system.

Fallah

Edited by fallah, 21 April 2012 - 04:26 AM.

[simadri]

Breizh

Yes, there is a risk of back flow.

Fallah

I am compleetly agreed with you. But I have seen many P & IDs with screw pump without check valve at its discharge, where as there is check valve in gear pump discharge.

[S.AHMAD]

Simadri
1. Generally, check valve is not required for positive displacement pump (e.g. screw pump) as mentioned by Fallah.
2. The need would depend on whether there is any possibility of back flow. as mentioned by Breizh
3. In another words, you need to study case by case basis.
4. For centrifugal pump, check valve is compulsory. PSV is depending on needs, but for positive displacement, check valve is depending on needs and PSV is compulsory.

[simadri]

S. Ahmed

I will be grateful if you can cite some examples of rotary pump discharge lines, where check valve is required and where check valve is not required.

[S.AHMAD]

Couple of years ago, I was involved in the process design of installation of reciprocating pump. Since the reciprocating pump is a fixed volume, however, the client wanted the flow to be a variable. One option is to have variable speed but our recommendation was to install a control valve that regulate the flow recycled back to the source. In this case we install a check valve downstream of the recycle line on the main line.

[simadri]

Thanks S. Ahmad