Question Reducing IP on piston regulators

[tongl]

I’d like to reduce the IP of some MK2 style piston first stages down to 7.5bar. This is for drysuit inflation and booster pump drive gas, not for second stage.
I’ve removed all the shims but this only brings the IP down to 9bar, is there a way to further reduce IP? Perhaps grinding down the spring, or not fully screw in the spring cap?

 

[Jim Lapenta]

Neither of those options is safe or advised. Unless the drysuit valve is not working, there is no justifiable reason to reduce the IP for drysuit inflation below the recommended working pressure of the reg.
Even in cold water, proper inflation is done using small bursts of air and the reg shouldn't freeze up. Reducing the IP for drysuit inflation is also a good way to ensure a malfunction at depth. Resulting in no air going into the suit. Just don't do it.
For booster pump use, do the right thing and put a regulator between the 1st stage and the pump. I did this to use cylinders on my bicycle tires with the presta inflator.
Grinding down the spring is also a good way to ruin the reg and ensure it fails.
I think that regulator and all the necessary fittings were less than $20 USD to build.

 

[Mobulai]

or not fully screw in the spring cap?

This one is an absolute no no - unless seeking flying reg parts in the shop; in theory kinda might work

Perhaps grinding down the spring

It has been done before, but it’s a pro move (I haven’t myself)
What I read being done here ( @rsingler did it on an mk10 IIRC) : grind at a very low speed so you don’t mess up the spring and cause it to fatigue and crack; you want to have its base level eventually; 1/100th of a mm iterations, a ting bit will go a long way with IP change

7.5bar is a very long way still; not sure how attainable is that

But.. I agree with @Jim Lapenta ; risky moves with repercussions of failure
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Edit, why do you want 7.5bar IP for drysuit valve?