Apeks DST weird IP behavior

[sinidive]

Got an old Apeks DST first stage, and after servicing it is acting up:

Symptoms:
- When the reg is pressurized the first time on a day second stage begins free flowing gently
- After purging or doing a pressurize-depressurize cycle IP is a static of 9.0bar (130psi)
- Problem seems impossible to reproduce after the first gentle free flow before the next day
- Leaving the reg pressurized for hours HP remains constant and IP remains constant at 9.0bar (psi)
- Following day the same problem reappears

What problem could cause this issue? Insufficient lubrication of the HP valve oring (AP1299)?

 

[Mobulai]

any chance you know the IP at that very 1st pressurization (with the slight freeflow)?

And by any chance you also have a flow stop device before the 2nd stage to see if the issue is on the DST or the XTX side?

Would be great to see how far the IP reaches on 1st pressurization without a 2nd stage to vent out and obscure the IP

It might be as you say a lubriction issue at the HP seat oring, but could also be that the silicone LP seat is still taking a set (hysteresis from unseating after overnight being non pressurized takes some time to un-deform )

simce you said you cycled a lot I’m more inclined to guess it’s more on the 2nd stage side — but I could be very wrong

 

[sinidive]

The second stage should has been working fine (just retested with an another DST @ 9.4bar / 136psi IP) and was serviced last winter.

I'll try to get the IP just before the freeflow tomorrow. Don't have a dedicated OPV (or flow stopper) at hand at the moment.

 

[happy-diver]

use an old hose and kink it
if it flows through the mouthpiece that is what it is supposed to do
when mine do that I purge a few times to minimalise, stop it
leaking into your mouth is good
i don't service my stuff much
if you keep your stuff pressirised for hours are you wearing it out
is this why you service so much
i don't use an ip gauge
listening to you guys quoting numbers suggests to me they are time consuming bothersome

 

[Mobulai]

The second stage should has been working fine (just retested with an another DST @ 9.4bar / 136psi IP) and was serviced last winter.

I'll try to get the IP just before the freeflow tomorrow. Don't have a dedicated OPV (or flow stopper) at hand at the moment.

Hmm.. the plot thickens maybe it’s the DST afterall; I thought both the 1st and 2nd got serviced together

You could try as Happy suggesed; or also with an inflator hose (and you purge it after the fact either with a power inflator, repeatedly installing and un installing the IP gauge..)

In the mean time, something I remembered about under/over lubing the HP seat (maybe not this case but a good theoretical suspect still; but its corollary was your initial suspicion)

Really nice presentation. I have a bit to add that this, a bite you in the rear that really screws with your mind.
You rebuild a diaphragm reg, it sets up perfectly - no IP creep- but after a while, it might be a hour or after a couple of dives it starts creeping. You pull it apart, nothing looks wrong, you replace the seat and oring anyway and it does the same thing, works fine for a while then starts creeping. A scratch does not make sense as it should start as soon as you pressurize the reg...................Any Ideas?

This is the culprit - there is a small scratch or defect in one of the seating surfaces, like the one in your example. When you replaced the parts, you lubed the oring and that lube fills the crack, sealing it off. But as pressure is applied, the lube is slowly extruded from the scratch, how fast depends on the depth of the crack and the viscosity of the lube. It may take a few seconds or it may take hours being under pressure to happen. The ones that happen quickly are not too bad but the ones that come back days later are a real pain.

 

[Pearlman]

Got an old Apeks DST first stage, and after servicing it is acting up:

Symptoms:
- Problem seems impossible to reproduce after the first gentle free flow before the next day
- Leaving the reg pressurized for hours HP remains constant and IP remains constant at 9.0bar (psi)
- Following day the same problem reappears

“Following day” implies simply de-pressuring the 1st stage disconnecting and then reconnecting it to the tank correct? Something tells me you should be able to replicate the problem immediately simply by unscrewing your 1st stage from the tank and redoing the steps …

 

[elmo]

A possibility is that the o-ring sealing the balance chamber (AP1209 or 1210, depending on the model) or the little one on the valve stem inside the chamber (AP1299) might be damaged, dislodged, wrong size or otherwise not sealing appropriately. This might lead to a leak from the hp side to the lp side, leading to high ip until the o-ring get jammed in enough to seal.