Pressure Pump Check Valve Question

[OldracerJones]

I'm installing the final phases of equipment in the garage build. Next up is my pressure pump for the water system. My question is, should you install a check valve before and after the pressure tank or just after?
The check valve after the pump makes sense as it prevents the chlorinated water from going back into the non-chlorinated side of the system.
I'm trying to understand why you would need one before the tank. Anyone have an idea why?

 

[Steroblan]

You need a check valve at the pump discharge and another above ground before the pressure tank. The one at the pump keeps the pipe full so you don't have a lag when the pump starts (no water hammer). You have water immediately. The one before the tank keeps the back pressure (50+psi) off the pump for an easier start and if the bottom valve fails the pump will cycle endlessly until your elec bill alerts you or the pump fails due to over cycling. You can change the one at the tank pretty easy but will have to pull the pump to change the lower one if it's all you have.

 

[Tim The Tool Man]

You need a check valve at the pump discharge and another above ground before the pressure tank. The one at the pump keeps the pipe full so you don't have a lag when the pump starts (no water hammer). You have water immediately. The one before the tank keeps the back pressure (50+psi) off the pump for an easier start and if the bottom valve fails the pump will cycle endlessly until your elec bill alerts you or the pump fails due to over cycling. You can change the one at the tank pretty easy but will have to pull the pump to change the lower one if it's all you have.

^This if your pump is a submersible unit located outside within the well. If it is a jet or pressure pump located right next to your tank within the garage or utility room then you just want one check valve located only at the pump output, before the tank.