Is it better to have your check valve close to your disc or close to your air pump? Also is a spring loaded inline check valve a good choice. I am thinking of a 1/2" or 3/4" to go with a LA80. Cracking pressure of .5 to .75 lbs.

Personally, I'd want the check valve close to the pump, above the water line for easy service if necessary. I'd run the 3/4" one.

Try to avoid using a check valve with a spring. They will fail quickly. Usually within a few months give or take. The only reason I would recommend using a check valve is if you are using a vane compressor. Not sure about the Thomas vanes, but I know the Gast may run in reverse if the power is turned off/on rather quickly. Its a rare occurence but may happen. I wouldnt recommend adding the check valve at the diffuser. Install it about 3' from the cabinet inline with the hose.If you have a hard time finding a check valve without a spring, give a Sue Cruz a call at Vertex Water Features and she can hook you up. We have them in stock here. Have a good weekend.

Some diffusers have built in check valves in them and you don't have to worry about it. Course if you wanted a backup check valve then I would put it up near the pump so you can mess with it need be without taking your diffuser up and out of the water like Esshup said.

If your compressor is above your high water mark, there is no need for a check valve. Funny thing about water...it doesn't flow uphill I agree that the spring valves are garbage and fall apart within a year. We use 1/3rd lb. installed near the compressor for easy access.