install check valve in water looping

It would depend on the specifics of the system, such as the location of pressurized expansion tanks or columns of water open to atmosphere. A diagram would be useful.

Consider the possibilities of how reverse flow might occur. What are the consequences, and are they acceptable? If it is not possible or if they do occur they are of no consequence, then a check valve is not needed.

I might be generalizing here. I don't know how well to put it not knowing what you got and being not familiar with PW loop system.

Pretty much u need to draw out your pipings and see what the pressure will be at various joints/tees. consider all the pressures for all the scenarios- loss of flow, loss of pressure on your flow ... Flow will be from high pressure to lo pressure. If you don't want flow in particular direction for certain conditions, u need check valve.

Another way I can try to explain. Let's say you want to determine backflow potential at point x1 (i.e. where you might need to put check valve) and normal flow is from x0 to x2 (x0 b4 x1 and x2 after x1). To determine whether you are going to have a backflow, you will need to know pressure @ x0, pressure to where the flow is going (Final destination) and pressure of any other flow added in that pathway (from x1 to your Final Destination). Backflow will happen when pressure @ x2 exceeds pressure @ x0.

Take an example, your pressure @ x0 is 50 psig. You are supplying some steam @ 100 psig downstream. Your steam might overcome your flow pressure (100psig >50psig) and you might have steam backflowing. Let's say you loose your flow. Same thing, steam will back flow (100psig>0psig - 0 psig from no flow).

Makes sense? Did I confuse more? Any other feel free to correct if I erred.

I am confused So, is this a close loop system (heat transfer application?) or open loop (contaminating the water at point of use and then purifying it b4 sending it to storage tank?)

Anyway, if ur water loop system's pressure is always goin 2 b higher than atmospheric, than u should be fine.

However, I am not sure if your pump can suck in air (if there is a leak in ur piping). At this point, I am not sure how accurate I am. Just food for thought. I think that should only happen if your pump is running dry (no water and there is leak in ur piping on the suction side of the pump).

I think as Tornado said some sort of schematics/layout of ur equipment would really help.

Good luck!