So I have had this slow drop in tank pressure for some time. Test all the fittings ,manifolds & would never find it,so decided to test for blow back though the compressors. ound a bad check valve, ordered 3 more from McMaster-Carr & fuck all 3 are bad!! Told must be a bad lot,new ones on the way. At the same time I decided it was time to replace the compressors, even though still working ,have to be worn with 10 years of use! Ordered a 485 duel pack,Viairs newest compressors. Hope to have all on before the next two shows! Phot's to come.