Has anyone tried to use some kind of a sealer between the flat metal surfaces such as around the non-return valves and diaphragm?
Steel on steel is not a join I would use say on a water pump, never mind compressed air?
If the surfaces of the block pieces are nice and clean and you replace all the O-rings properly, there will not be any problems with how it seals and no need for any kind of additional sealant. I recall from when I rebuilt mine that everywhere there needs to be a seal there will be an o-ring. The only thing I can think of is the unlikely event that the metal blocks get warped somehow, but at that point you would really need to just replace it outright.
Yes, thanks - what you both say makes perfect sense - going for my third rebuild and trying to ensure success at last.
In terms of lubricant, yes Dennis, thanks I used yours last time but have been reading about o-ring sealants and came across Dow 111 and Dow Molykote 55. The Dow 111 is a high quality o-ring sealant used by NASA apparently, while Dow Molykote is 55 is specifically for o-ring/metal interfaces and acts by slightly swelling the o-ring - I put some on an old valve block o-ring and it hasn't disintegrated it yet after a few weeks.
Any experience of these? Is it overkill? My valve-block has been leaking for about 15 months now so I am clutching at straws to ensure a perfect seal.
Thanks Dennis, yes I know it is not rocket science (NASA! ha-ha! ), the valve-block is a very simple thing really, much maligned by its antagonists but a mystery valve-block leak is totally baffling (it is not the airlines - I bought 50 feet of airline and ran new direct lines everywhere - made no difference whatsoever so I connected the original ones back).
The mysterious thing is that every time I rebuild it it leaks in a different place (or rather the pattern of collapse is different) which by deduction leads me to the conclusion that whatever I am doing with the valve-block is making it leak in a different place.
I always have different volumes of air leaking around the solenoid covers - it seems the o ring is not doing its job (could they be thicker?) either at the valve stem or the valve base. The stem solenoid is a 'moving' seal so there we are entirely at the mercy of the o-ring and its seat (an area where you say you have seen small cracks which I will inspect this time) but the valve base to metal seal is possible to 'enhance and assist'. The original valve stem seal is a vinyl sleeve which looks fragile to me and as if it would wear fairly rapidly - in your kit you replace it with an O-ring yet it is so small I wonder if anything could be done to help that seal?
However, the fact that the reservoir empties in several hours leads me to suspect that either the non-return valves are not sealing or the diaphragm is leaking (although the car pumps up readily which negates the diaphragm I think?) and those are the areas of 'leakage" I am most concerned in 'assisting'.
I mean if you think about a tyre or bicycle valve the principal is the same - the pressure of the air assists in making the seal on a rubber or vinyl seat, so why is it so difficult for me to make my valve-block stop leaking?