Do I need a check valve?

[Lazyman]

I'm not sure what they are used for, but after reading a thread about someone losing prime and no water was running through the pipes... I figured, hmmm, maybe that would let me 'see' if water is actually running through the pipes when I turn the pump on for whatever reason. Maybe you can feel vibrations and water flowing, but seeing the water go through might be a better idea?

Can you actually "see" water flowing if it's clean water? Hmmm. So, should I put one in next to the pump? Is that what it's used for? Again, I'd rather do it now, than cutting it in later after the install.

I just have a pump and swg. nothing else. I see pictures of peoples' piping and wonder how the heck do they know where all those pipes go!? lol Too many valves for me.

 

[Ohm_Boy]

A check valve is a one-way device for controlling flow. It will allow water to flow in one direction, and block it in the other. They are often useful in preventing drain-back from some systems, but they generally do introduce some loss, so generally speaking, you wouldn't want one in the main circuit of your pool unless you have some special circumstances. In fact, one should not be needed at all in normal pool pump/filter plumbing.
If you are just loosing prime, you likely have a leak somewhere. The pump and its strainer would be prime suspects, but any valve, union, or other joint/junction could be letting air into the system when the pump is off, thereby letting the water flow back into the pool.