What are the mechanics of a check/ bypass valve?

[Hersheyfarm]

Are they able to be cleaned or just replaced. My m59 lost both pumps and still has issues but has good pressure. I have issues with specific circuits and I'm going to take out the check valve and look at it. Any advice?

 

[J_J]

Yes, you can remove, clean, and replace parts on some check valves.

Check for debris, holding the valve open.

Check for broken spring.

Did adjusting screw come loose?

Watch out for parts springing out. You could lose a ball or spring.