503SB 1" CHECK VALVE BRASS | Silicon bronze cast body and poppet contain less than 0.05% Lead. Furnished with Buna-N O-ring, stainless steel spring, washer and locknut. All valves 1/2 in through 1-1/2 in have a working pressure of 400 psi. All valves 2 in and larger have a working pressure of 600 psi.