Originally Posted by Slow_Target
Normally when the bolt goes forward the cap is on the solenoid upsidedown. But you replaced yours. Just for kicks check it.
^^^ that's normally the cause of this sort of prob ^^^
where did you get the noid from? new? used? is the maxflo at 180-190psi?
if it's not the noid then i'd say you have no valve spring and have never lubed the valve piston o-ring. when the hammer hits the piston it stays open because the rubber of the o-ring is sticking in the i/d of the valve body.