IP Creep

[sylvester]

I am lowering my IP on my scubapro mk25af, I set it so its at 130psi breathe off the reg a few times the ip pressure goes back to 130 then after a minute it begins to creep to the 145-150 psi area? Do I have a problem or is this normal?

Is the ip measured prior to the creep when after a breath the needle returns back to a constistant psi? or after the creep is complete?

 

[redacted]

It's definately not normal. Could be a seat going bad or maybe some dirt on the sealing surface of the piston or seat. If cleaning doesn't cure it, it may be time for an "annual service"

 

[Greg Barlow]

You have what sounds like a textbook case of IP creep. The pressure should indeed stabilize within a few seconds and not climb more than a few psi. What typically happens whenever the pressure creeps too high is that the second stage valve opens slightly to release the excessive pressure. The valve releases the pressure only to have it once again begin climbing until the cycle repeats itself.

A rebuild is most likely the cure.

Greg Barlow

 

[redacted]

It may be locking up at the higher IP rather than venting. You should be able to tell if you crank down the adjustment knobs on your S600 & G250. Although it's just a little difference in severity. If it is venting, I'd drag out the spare until it is fixed.

I had my Mk20 do the creep & lock up bit. It was an old brass piston and there was a little corrosion on the sealing surface. A good cleaning & christolub carried it thru another year.

 

[sylvester]

Since Ill be doing some classes next month and that shop deals in SP I will contact them to sevice it for me so I can just pick it up when I show for class.

 

[DA Aquamaster]

Creep is measured after the needle "swing" - and is measured from the point where the needle swing stops immediately after you take a breath or purge the second stagte to the point where it ultimately locks up.

How much IP creep is normal in a MK 20 or 25 depends on what it has in it for a piston. 10 psi is the maximum creep acceptable and is a little high but not unheard of with the brass piston which had a more rounded hard seating surface. The all stainless piston or the most recent composite piston have a sharper edge and should have virtually no creep once a seating groove develops.

The adjustment on the Mk 25 is an "air off" adjustment only. If you adjust the first stage using the seat adjustment screw with the pressure on, you risk damaging the seat and/ or the piston's sealing edge.

In any event, if your Mk 25 first stage has more than 10 psi of creep and/or locks up at anything over 145 psi, it needs to go in for service. Depending on how old your Mk 25 is, it may or may not have the new composite piston. If it was made prior to June 03 it may have the older piston and would benefit from having the latest composite piston.

 

[sylvester]

Thanks, I did adjust air off so its time for a service.