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
———-
Edit, why do you want 7.5bar IP for drysuit valve?

 

[Mobulai]

Found the „instructions“ for sanding the spring, if you end up trying it (and for completeness)

Service kit for this Beuchat Regulator 1st and 2nd stage

 

[tongl]

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

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
———-
Edit, why do you want 7.5bar IP for drysuit valve?

Thanks. My booster's max drive gas pressure is 8 bar. I was planning to use my drysuit bottle reg for this purpose as well, happens to have a few MK2 clones on hand.
I know a lot of people reduce IP on drysuit inflator reg for lower flow rate, mostly Apeks DS4/US4/US1, so thinking about two bird one stone...
I've got a dedicated DS4 for the booster now, which is a lot easier to tune down IP.

 

[happy-diver]

I've got an older Cressi MkII type reg, standard IP, with an OPV hooked up to a ball valve on the booster
From the 300b drive gas feed and ball valve half way, the booster clack clacks away quite happily thanks
As it slows open valve, at the end reg hose booster supply tank are always frosted up filled tank is warm

 

[halocline]

A while back someone on this forum was experimenting with trying to lower IP down to under 100PSI to use the reg as a shop source of compressed air. You might have better luck with a MK5 type balanced piston than an unbalanced piston. You could start by finding one with a slightly worn out spring, remove all the shims, and use the tallest version of the HP seat. That might get you close to 100. If not, you’ll have to find a slightly weaker spring.

The lower your spring pressure, the more influence the supply pressure has on the overall IP in an unbalanced valve, so using a downstream valve like the MK2 could be a bit troublesome, unless you can just use near empty tanks!

 

[Bigbella]

Out of curiosity and with all due respect -- why go to these extraordinary lengths, whether by crippling regulators by shaving springs and / or removing shims; or by even the use of unbreathable gases, simply for drysuit use?

Aside from that initial seal at neck and wrists, prior to hitting the water, I seldom if ever added additional gas from my primary tank; it was typically one and done, and I was fully capable of using my unbalanced Cyklon 300, then set at 12 bar, for all of those needs.

In all the years of commercial and recreational diving with drysuits, I have never found it necessary to carry additional tanks for that particular purpose -- and while on a boat in the Great White North last year, found it oddly amusing at just how many of those overburdened weekend warriors, who already could scarcely stand on deck, also slung dedicated cylinders with that orange warm and fuzzy message "ARGON: THIS GAS WILL NOT SUPPORT LIFE."

I was beginning to feel underdressed . . .

 

[TravisD]

If runaway inflation of a suit is the 'worry', wouldn't a flow limiter orifice be a better solution?

For surface-only use, an external adjustable regulator is cheap and easier to adjust, and you get a pressure gauge as a bonus.

 

[LEO1982]

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?

Have you considered clamping the spring in a bench vise? The elasticity should weaken after a period of time. Of course, this is just my personal opinion and has not been verified.