PCP regulator

[Otley]

Can anyone tell me if PCP regulators have some means of shutting off the regulator until after the shot is fired?

[hareng]

Its a 30 yr old McGraw reg later used by Welham, copied by several others marketed as their own.

Back to the drawing board, i can tell you exactly what the problem is.
All i will say is its not what you have said.

[air-tech]

It's late-ish in the day, and a bit blanked out, but afaik regs should repressurise slowly, no need for a complete cut-off, just that the inlet to the secondary (regulated) chamber is restricted (small hole).

[Otley]

Thanks for the useful reply.

[Stot]

I made one for my ultra and it works really well.

No matter how small the hole and how slow it fills the pressure in both sides will balance very quickly so a PCP regulator needs to shut off the input once the required pressure is reached on the output.

In the one I made this is achived by using a piston with a bigger surface area on the outlet side than the inlet side and having the spring stack in an area of ambient pressure. The basic idea is that 3000PSI pushing on 1 sq cm trying to escape to ambient pressure would balance against 1000PSI pushing against 3 sq cm trying to escape to ambient pressure, once the 1000PSI pressure increases the balance is lost and the plunger starts to move toward the 3000PSI area and will seal against a stop made of delrin for example.

Heres a model and some basic plans I ran up when making mine. The plans are not complete or the same as the model as I changed it all as I went but gives you an idea. The model is exactly whats in my Ultra now. This design does require the air tube to have a small hole drilled into it to allow the spring stack to be in the ambient pressure and make sure, in case of o-ring failure, the regulator doesnt stick open.

edit: Re looking at your design images the piston on your design is the same size on both pressured sides and possibly the thru hole is too large to create back pressure. The larger area on your piston is inside the ambient pressure area between o-rings so its not having any effect and the piston doesnt move.

Cheers
Stot