Yes I do have a check valve, down streem from the regulator.
I can plug the pressure line coming from the York and stop the flow with my thumb.
I plan on back pressuring the the line from the pump with my shop compressor to check for a major leak.
Obviously you cant hear any with the engine running.
Also I am not satisfied with the compressor mounting.the intake ends up on the bottom with a horizontal mounting, not ideal from a standpoint of oil consumption. by flipping it end for end would fix that problem and require shorter drive belt. I have not checked to see if this is doable.