Intermediate Pressure Low - Scubapro MK10

[Mcarlson]

2.5 years ago I rebuilt a Scubapro MK10 and the IP was 130 psi with no shims. After about 30 dives the IP is now around 100 psi. Does this mean my spring is going bad? Should I shim it back up to a higher IP when I rebuild it? BTW - it still breathes great on the G250 2nd stage.

 

[JamesBon92007]

 

[Mcarlson]

.

 

[runsongas]

at only 30 dives, it may just be the seat getting broken in, although 30 psi is more than i would expect. is the ip still locking up correctly or is it mushy?

 

[Mcarlson]

Not mushy at all.

 

[runsongas]

can try shimming it back up, but you may want to check how deep the piston is biting into the seat

 

[lexvil]

Try a different gauge

 

[Couv]

2.5 years ago I rebuilt a Scubapro MK10 and the IP was 130 psi with no shims. After about 30 dives the IP is now around 100 psi. Does this mean my spring is going bad? Should I shim it back up to a higher IP when I rebuild it? BTW - it still breathes great on the G250 2nd stage.

First of all make sure your IP gauge is correct. Check that the cap (that's the part that screws onto the body and pre-loads the spring) has not started to back off. If it's still torqued correctly proceed. Next, make sure that you don't have any parasitic issues that are bleeding the IP. Remove all the low pressure hoses, plug the ports, and pressurize it underwater if possible and check for leaks. If you cannot submerge it, pressurize the first stage, tun off the air and monitor the hp gauge for a bleed down. If no leaks you definitely have a rebuild in front of you. It's hard to say for sure if you need a new spring. Try shimming it and install a new seat and see what you get. Store | Vintage Double Hose sells shims in two different thicknesses. If three shims and a new seat don't bring it into specs, my next guess would be a spring.

Good luck and keep us posted.

 

[JamesBon92007]

I assume the above means I’ve asked a question that will draw out controversy or misinformation. I’ve searched the subject unsuccessfully, but it seems likely that it has been discussed before.
I was hoping to get awap or vdh to respond, but welcome other opinions!

No, I didn't mean it that way at all. What I meant is that I'm going to watch and see if your solution applies to my Sherwood that has similar symptoms

 

[rsingler]

If the HP cap had backed out, you'd expect IP to rise. As you back the HP seat out, the spring has to undergo more compression to seal, which requires more IP behind the piston head.
Same with seat groove after many cycles. If the shaft has to travel fractionally farther to seat into the newly created groove, once again more spring compression is needed and the resulting IP goes up, not down.
Which seat did you use? Normal (X), Low (||-), or High (|-)??
With normal or low and no shims, I wouldn't be too surprised with a 100 psi IP, though as has been mentioned, it's a touch on the low side.
If it's locks up okay, just shim it up.
Do you have the good red spring?

If you were a little heavy on the lube during the rebuild, piston motion can be a touch sluggish, which allows more time for IP to rise. As the lube wipes clear and the piston movement gets brisker, there is less time for IP to rise before it seals. As a result, the IP drops. That's my best guess for a non-worrisome cause of the problem.