Scubapro Mk10 - low intermediate pressure

[Enraptured of the Deep]

I am having trouble with a regulator with low IP. I just rebuilt a new-to-me Scubapro Mk10 that appears not to have been serviced since the turn of the century -- the "next service sticker says, "Sep. 00."

The seller had noted that he couldn't get a pre-servicing IP on it, so I did not test IP myself before servicing. When I took it apart, there was one shim in it. I added a second 0.010" VDH shim (one at each end of the spring) and put it all back together.

After a couple of hundred purge cycles, I got a steady IP of 125 at 3000 psi. The problem came when I checked the IP at 300 psi. It was down around 110. I opened it up, replaced the two 0.010" shims with THREE 0.015" shims (one at the base of the piston and two at the top), but that brought the IP to only 119 at 300 psi.

By the way, I did mark the HP seat cover and regulator body to ensure that the HP seat was in the same position before and after reassembly. Also, just to be sure that nothing else in the system was leaking air, I took off all hoses except for the HP hose with the SPG and the LP hose with the IP gauge (with over-pressure valve).

The Mk10 technical guide says low IP at 3000 and 300 psi is a sign of a weak spring and says one should not put more than three shims in a Mk10.

Is there any chance I have the shims arrayed incorrectly? I have seen a number of posts on this forum suggesting it is best to have at least one shim at each end of the spring (if more than one shim is needed), but the Scubapro technical literature shows all three shims in a Mk10 at the end of the spring near the knife edge.

Is my only option is to replace the piston spring? If so, where can I obtain one???

 

[Angelo Farina]

The service kit for the MK10 comes with three conical seats, of different height. Which one are you using?
The higher the seat, the lower the IP...

Photo posted by Rsingler

 

[Enraptured of the Deep]

My service kit was an aftermarket one with just one seat.

 

[Joris Vd]

just buy a modern mk10 service kit and see if you can get a high enough ip with the new modern conical seat. If no, I'd buy the cheapest mk10 I could find and pray the spring was good on it.

 

[lexvil]

You may want to try a new spring if the taller shim doesn’t help. One of the reasons I’ve switched away from piston regs.

 

[Couv]

Photo posted by Rsingler

That @rsingler is a bloody genius.

 

[halocline]

Almost all of my MK10s and MK5s need the lowest seat to get IP within the 130-135 range which is where I like them. On my MK15s, which only have a single size seat, the IP without shims is 125. I have tried NOS springs in both the MK10 and 15 and sometimes it helps a little, but I wouldn't expect a big change. Most of these regs just seem to be a little low on the IP side. But it's no cause for alarm, they still flow plenty of air and if you're using a balanced 2nd stage, you won't notice much, if any, difference as long as you tune the 2nd stage to that 1st stage.

I don't know anything about the vdh kits, I've never seen one, but I do know that the shortest seat is what works in the SP seats, and I would guess that the vdh seats are taller.

I'd be a little more concerned about 15 PSI swing between 3000 and 300 PSI supply pressure. To me, that indicates quite a bit of friction at the HP o-ring. Make sure you're using a 90 duro for that, and use plenty of PTFE grease on it.

 

[rsingler]

That's @couv 's photo. Not mine.
I just stole it!

 

[drk5036]

So is there any serious problem with low IP? I just got an IP meter and used it for the first time on my last trip. My regs are about one year old, and IP was reading between 120-125, at both low and high rank pressure. Very little creep after breathing from the reg, maybe 3 psi? Then stable. Is this something worth correcting, or as long as ambient pressure is way below IP it’s fine?

 

[Couv]

So is there any serious problem with low IP? I just got an IP meter and used it for the first time on my last trip. My regs are about one year old, and IP was reading between 120-125, at both low and high rank pressure. Very little creep after breathing from the reg, maybe 3 psi? Then stable. Is this something worth correcting, or as long as ambient pressure is way below IP it’s fine?

Personally I would live with the above. Keep an eye on the IP over the year to see if it stays in the same range. If it goes up or down more than a few psi over a year, then there might be an area of concern.

However, as the OP (@Enraptured of the Deep) is in the process of rebuilding a regulator, he, as I would, wants it in specs. With 3 shims already installed and the IP is still below specs he is probably correct that a spring is indicated.

Using silicone grease instead of the called for PTFE grease may increase the IP by a few to several psi.