Why is Check Valve Used Before Outlet Valve?

It keeps the fluid from back flowing in case of pump failure.

Good Answer Lyn!

It also helps keep the pump primed during startup and between pumping sessions. Some are also designed as non surge check valves that prevent or limit the surge effect of initial flow conditions.

Drew K

Thanks.

Don't you need a foot valve to keep it primed?

Foot valves are found usually in underground tanks with deep well turbine pumps to prevent back flow and keep the pump primed.

Drew K

Prevents back flow...!!!

To be able to take the pump out for service , repairs .

In my experience manual valves are used to isolate the pump during service instead of check valves.

Agreed. Pump isolation should be accomplished with manual valves.

Non return valve is a type of automatic device which functions before reach of operator. Following are some of the reasons for its instalations:

1) To stop automatically back flow of high pressure liquid to low pressure system in case of sudden pump stopage due to any reason.

2) It helps in maintaining header pressure during pump start-up and stopages. Check valve will open only when pump discharge become more then header pressure.

3) By stoping back flow of liquid, indirectly it help in stopping back rotation of pump-system due to high pressure fluid flow through impeller which will work as hydraulic turbine.

Often with multi pump manifolds there are non surge check valves and remotely controlled outlet valves that pinch closed to keep pump inlet pressure high enough to prevent cavitation.

With smaller systems that have multiple pumps it allows you to leave the discharge valve open without risking back flow through non operating pumps.

Drew K

thanks to all,you give the answer.what is difference check valve use before or after outlet valve?what effect on system or pump?

Check valves are more pron to damage then isolation valves and may need maintenance. If the check valve is provided after the discharge isolation valve, for maintenance of check valve you have to shut down the complete system. Other wise, you can very well remove and replace check valve using both isolation valves of the pump.

Hi, awaiscnpp,

Check Valves are placed before outlet valve to prevent the backflow if there is a case of any pressurized system failure. If the pressure near the outlet increases, the fluid will have a tendency to flow backwards which may cause disruption in the total flow of the fluid in the system. For this reason, check valves are used as they permit the flow only in one direction.

Check valve or non-return valve, allows the fluid to pass in one direction only.It is used to to prevent backflow.

I think we are all aware of the function of a check valve.

Now,we know that the check valve should be put before isolation valve for maintenance purposes.

So, the important question now is : why we didn't take this consideration (maintenance ) for isolation valve too ??

Answer is : because the isolation valve haven't moving parts move permanently with the flow or continuously move as well as fluid moves . means that the check valve more subjected to breakdowns than isolation valve

So, in general isolation valves put at terminals of any equipment hook up

((God knows best and highest))