Hi Warren
Car looks good now
You can test the one way valve by removing the pipe from the manifold and giving it a suck! You should be able to suck through it but you can't blow through it.
Does sound like possible air in the system or the pads are getting pushed back in the calipers after being pressed. This could be badly seated brake discs given a wobble as they rotate and pushing the pads back or the master cylinder could be faulty.
If you jack up each wheel and give them a turn the pads should be lightly rubbing the discs. Get someone to press the pedal and see if they stop the wheel and then continue to lightly rub after releasing the pedal.
If this all looks good and you are convinced there is no air then I would look at the master cylinder to make sure it is not sucking the caliper pistons back when the pedal is released.
Craig.