Recycle Line on a Check Valve

A bypass line around a non return valve on a pump discharge is usually installed to allow a small back flow through the pump to keep it warm or to prevent polymerisation etc. There is often an orifice plate in this line.

Yes, perhaps so.

This is also referred as 'minimum flow recirculation valve'. On some applications, this facility ensures the pump from getting hot against blocked/pinched discharge, by allowing minimum flow through.

Yes, perhaps so.

This is also referred as 'minimum flow recirculation valve'. On some applications, this facility ensures the pump from getting hot against blocked/pinched discharge, by allowing minimum flow through.

Hi nsc,

Do you mean a pressure relief valve? These are sometimes used to recycle the pumped material back to the suction side in case the main line gets clogged. This prevents overpressurization (as well as a mess) until the main line can be unclogged.

Dear all,

The initial question was why must be installed a non return valve; Response to avoid the inversion of the flow rate through the pump and ONLY that.

A pressure relief valve is a material to prevent an overpressure in the discharge of the pump when the pressure overtake the design pressure and discharge to outside.

The third system is a discharge valve or a discharge check valve which is installed when a recirculation of the flow is necessary to maintain a température in the pump when this is an the arret or when we want to limit the dischage pressure level according to the process . This matériel (with 3 ways) is installed in line of the outlet of the pump and the third way return to the inlet of the pump

Positive displacement pumps will usually have a recycle system to prevent them pumping against a high downstream pressure or closed downstream valve without having to keep switching the pump on and off. Centrifugals tend to be self limiting but the recycle can be used for efficiency, flow stabilisation etc.

This system is generally internal to the high pressure pump to limit the discharge pressure and/or to protect the pump itself; It is not a "check valve" (original question)

If this is a hydraulic system there are a number of possibilities.

Relief Valve - As has been mentioned this might this be a relief valve? In which case the oil must be relieved somewhere so it is connected with this "recyle line" back to tank usually, but sometimes to the pump inlet though not recommended.

Air bleed. Could this be an air bleed? Not as common today but many older systems particularly that had pumps mounted above the tank would have difficulting in priming and or would loose their prime and would have air bleeds installed. They would be plumbed to the top of the reservoir. They stay open and bleed the air but when the higher viscosity oil starts coming throught they pilot closed.

Accumulator Dump . Could be an accumulator dump if you have one. Some circuits utilize a pilot to close check valve that is held closed by pump pressure when the pump shuts off the check valve can open and dump the accumulators usually through an orifice to ensure the system does not have stored energy and is safe. (Don't forget to check though)

It could be any number of other things depending on the circuit you have and what someone has done to it.

If you have a schematic that might answer the question for you.

Hi All

My purpose of recycle line , was not a minimum flow.My purpose is a recycle line drawn from down stream check valve to it's up stream. As shown below

Your drawing is not per normal hydraulic standard. You are asking a question I will respond with a couple.

What is the application?

What is the fluid?

I believe we can all agree that in simplest terms a check valve is a one way valve. Flow can go in one direction and is blocked from going in the other. Having a line connecting both sides of the check valve would allow your fluid to come back through the circuit in the direction the check valve is trying to stop flow. The only reason that comes to mind for someone to do this is if the "recycle" line as you call it is much smaller than the check valve so it is restricted flow back to bleed off pressure or allow return flow at the lower rate.

Hi zhock

Recycle line is 3/4" and main line is 2". Note that globe valve on recycle line is normally closed. Fluid is hydrocarbon such as propane, Butane, ...

thanks

Not sure what some of the posters are on about. My previous post is still valid, giving some reasons for the addition of a bypass line around the discharge NRV of a centrifugal pump. Now that you have given more information we can be more specific.

As the valve is normally closed, the most likely reason for provision of this line in "light" hydrocarbon service is to ensure that the pump can be primed correctly (flooded - no gas pockets) prior to start up.