You want a pressure relief valve that is adjustable; most common 3/8" threaded fitting. I usu set the blow off abt 6 to 8 psi higher than the required head pressure where the diffuser is sitting. Example: if diffuser is at 14 ft deep, psi head pressure will be 7psi providing the bubbler and hose do not create extra psi gain. So the p relief is set for full blow off at 13 to 15 psi. Since your pump can do 30 psi; 20 psi blow off is also okay. A pressure guage really makes setting the p relief easier & more accurate. If you have trouble finding a p relief I can send you one ($18 + postage).
Chk valve. I prefer plastic vs brass. At local stores you will find them only with springs. SS spring is best, 0.3 psi cracking pressure is great. Buna rubber seal is standard, and viton is for harsh chemical resistance and may? last a little longer; 7-8 yrs vs 10-14 yrs. All my valves are plastic, 3/4" NPT pipe threads & have Buna rubber seals, no springs; some have been in service 8-9 yrs; a Brady product. Retail $6-$8
Questions???
