check valve for water pump

[cruzin]

Hello and happy new year.

4008 shurflo water pump was leaking to fresh tank. I took pump apart and cleaned everything out but nothing looked dirty and valve operated freely. So i bought an external check valve that would thread onto inlet side of pump. Upon reading more it seems everyone that does this puts the valve on the output side of the pump.

Question is, it it ok to put it on inlet side of pump or should I buy one for the output side of pump?

Thank you for replies.

[Cate&Rob]

Putting the check valve on the output side means that the pump is not pressurized when not running. Normally this would be a good thing to do . . . but, with a diaphragm pump, I don’t think it would make any difference to have the check valve on inlet side . . . as long as this is not creating any leaks from the pump !

Rob

[TedS]

The check valve should be on the pump outlet. The check valve on the pump inlet is too restrictive for the pump suction. A 5 psi check valve is equivalent to over a ten foot lift. Most pumps advertise max 6 to 9 foot lift capability to draw water. 5 psi on the pump outlet is not as significant for a pump with 45 to 65 psi capability.

[TedS]

Pumps can have a hard time pulling antifreeze through the city water inlet check valve.

[Jlawles2]

Typically check valves are used on output sides as mentioned above to minimize "observed lift" by the pump because of the valve "crack" pressure.

Another reason is a bit more on the life expectancy and efficiency side. Check valve on the output side allows the pump to relieve pressure (since the pressure switch is in the pump it works the same in this case) and have a less stressful startup on large systems. The check valve on the output side will also help minimize pressure bounce cycling of the pump as the lines move (yes water lines in a camper will move slightly) possibly because of water hammer.

[cruzin]

Thanks for all the replies. I went to install the one i had on the inlet side but the existing hoses were to tight . so i got one for the outlet side. It's in a storage lot so have to schedule a trip to check for leaks.