Question Skipping 1st stage Maintenance?
- Thread starter Pearlman
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I don't agree. You're going to have to describe the physics of it to me to convince me. Why did Poseidon and Conshelf have (non-compressible) liquid containers for their environmental chamber if all you have to do is increase the (air) pressure inside the environmental chamber?
I do not disagree that pressure increases in the environmental chamber as the bubble collapses. But I don't think it causes a 1:1 increase in absolute IP.
My opinion is that due to diaphragm thickness and elastic forces in the main diaphragm, the increasing air pressure which collapses the bubble in the environmental chamber isn't transmitted to the pin, but is resisted by the diaphragm. It is for the same reason that in designing a regulator, you can't use the physical area of the diaphragm to calculate opening force, but rather the effective area after elasticity is accounted for. I think ambient air pressure inside the environmental chamber doesn't do much of anything to the absolute IP until the env diaphragm touches the mechanical transmitter, and the ambient pressure is physically linked to the back of the main diaphragm.
The lag isn't large, but I'll bet that there is several feet of lag in absolute IP with a bubble.
Convince me otherwise.
In case I understand correctly [I keep misunderstanding ] (that you are asking in context of testing IP), yes
That’s how I do the overnight test, the HP hose will act as a „mini tank“ to utilize air from
1st time I tried it, I woke up to 0 bar on my spg (closed valve); which meant that my situation was as bad as it gets (it all leaked out (it was a question of HP to ambient or IP at that point)
A submerged test showed no bubbles, and another shorter/monitored run showed creep + 2nd leaking (which also wasn’t well tuned)
Now when I overnight test I (sometimes, case dependent ) use a LP shutoff on the 2nd stage to make sure which; but ONLY after I did a 2-6hr run before (don’t wanna wake up to a really excited blown hose)
Well … everything seemed perfect until a few minutes back sucking a little harder on the 2nd stage the IP keeps dropping below 9bar… which didn’t happen before… then I also found the balanced inline tool was pushed in deep and slotted all the way in when I had a distinct memory of pulling it back all the way… can it be that over 6hrs some leak has slowly pushed it all the way in? Now I am paranoid …GHOST!
…PS: Never been really successful with the “withdrawal method”…
Also need to attach SPG and check if the tank pressure has dropped completely due to a leak over many hours …
OMG, OMG, OMG, OMG,
You're going to dive with this regulator OMG
I don’t mind diving with it … just don’t want to die with it …
Hmm, not so bad (how far below 9?)
But I also didn’t do any „dynamic testing“ before so can’t say for sure
What I remember testing the 25(not evo) is that on a full purge IP dropped sometimes to 110~105psi so… maybe maybe it’s normal
One thought comes to mind: I remember someone (probably @halocline ) discussing how the piston diameter diff in mk10 (thin) vs mk5 (wide) impacted the speed of IP recovery and IP „travel“ (don’t have a name for that, but basically the drop from seated to breathing/purging IP
Could be relevant here
I’ll leave it to wiser folks to comment/elaborate on that
Only used an unbalanced one so also can’t say; but in theory over 6hrs the tiniest of pressure imbalance would be enough to move it all the way so
(maybe it’s only 1psi, better check again)Connect everything (2nd, IP, spg, maybe even another downstream 2nd), maybe skip the inline tool to be sure (I love the shutoff that it enables that mid test), cycle a few times (I do the very shallow breathing / imaginary mouthwash technique to do a few 100 cycles on the tiniest bit of air)
And run it,
watch it the 1st minute or 2, this is the transient phase and the profile is more important here -more indicative of mushy lockup, bad lubrication, and bad creep (you want it to finish the transient within less than 10-30s (add grains of salt), otherwise something is amiss)
then give it a quick look at ~[5,15,30,60m, 2,4,8hrs] (this is the steady state phase, so tinier variance happens here, more indicative of smaller leaks / imperfections that wouldn’t show up with a „bad creep“)
(The following is low standard/quality advice/statement, but I’m just trynna make a point — so add a million grains of salt)
Remember, unless this is on a stage that’s gonna be parked pressurized for a long time underwater, you wouldn’t leave the 1st un breathed for a long time (max case:~15 mins if you’re doing sidemount)
If you already have stable IP with, being charitable let’s say, nothing more than 5~10psi variance from initial lock up (transit phase), It’s pretty alright to dive; by the time you’ve breathed from that 1st, you are back into transient phase
Sure it will leak eventually if left pressurized long enough, unlike this legend of the quality of the mk5
Well lookie there!
A SEALED piston! (Mk5 SPEC)
View attachment 811523
Of course it's still full. That piston is probably pristine inside! A Mk25 would have long since died...
A Pilot and a Mk5. The two best regulators ever designed.
Overnight tests are more… qualitative than quantitative is what I’m trying to say
IP already changes with tank pressure, and balanced 2nds can tolerate waay more IP swings than the tolerances we aim to tune 1sts for
That said, aim for great quality, it’ll give you peace of mind anyway, besides other obvious benefits
Oh one last thing: try to test both extremes of the tank, I think this will tie my incoherent thoughts all together
halocline
Contributor
I wish I could understand what you’re talking about here, but I’ll try to help if I can. First, all the rings, bushings, and o-rings you are talking about, I assume what you are referring to is the HP piston o-ring with a plastic bushing on either side, is that correct? And there is a spring on the HP side of that arrangement that keeps it in place. Right? The way to get that installed is with that installation tool that’s in your photo, the stepped side. You put the inner bushing, then the lubed o-ring (010 85-90 duro), then the outer bushing on the installation tool, then push it in from the HP side and give it a little twist, remove the tool. The seat gets installed on the seat retainer, with an o-ring. Not in the space where you just installed the bushings. When you’re ready to install the piston, turn the installation tool over and use the ‘hollow’ end to hold the bushings/HP o-ring in place, then install the piston (use a bullet!) from the ambient side, of course with the main spring in place. The hollow end of the tool allows for the piston bullet to fully go through.
Then take the bullet out, drop the spring in place, and install the seat retainer with the seat already installed. All this info (or similar, I might not have all the details in the right order, I don’t work on MK25s very often) is in the service procedure manual, which is everywhere on the internet.
The only thing that causes IP creep in a MK25 is a bad seal between the piston edge and the conical seat. Meaning, either a worn seat or worn piston edge, or some minute bit of debris in there. If the seat is mis-aligned, I’d think you’d have major HP leakage, not a little IP creep. But, again, I don’t know what you were describing.
A couple other things, the silicone bushing (s) that go on the piston shaft near the base have probably varied a little from generation to generation, and I don’t really know exactly what the ‘evo’ includes, but I believe it’s all various efforts to prevent icing on the piston and main spring. If you dive in cold water, that stuff has use but in warm water it’s basically meaningless.
Removing the old HP piston o-ring/ bushing arrangement should be easy to do without using a sharp o-ring pick. I think you can push it out from the ambient side with a wooden dowel. I know I’ve never had any sort of problem getting that stuff out cleanly. In fact, this whole bushing arrangement surrounding the HP o-ring was instituted starting with the MK15; SP initially claimed it tightened tolerances around the piston and as such prevented extrusion of the HP o-ring. I’m sure that’s accurate, but I suspect that the bigger reason was to prevent careless technicians from scratching the journal that the HP o-ring on the earlier balanced piston regs (MK5/10). Removing that o-ring without damaging anything is tricky. I use a double hook o-ring pick and bury the end of the pick in the o-ring itself. This of course destroys the o-ring but you are there to replace it.
It is possibel to use air , but because gas is compressible such an container
must very flexibel and have a great variable volumen .
For exable : the death volumen in the dry chamber is 3 cm^3 and we want
to have enough air to compensate up to 16 bar (150 m) . We need 45 cm^3
variable volumen . If we use a liquid or the most used design second diaphragm and force transmitter the variable volumen is only the same that the 1. stage diaphrgm needed to move , may be 0,5 cm^3 .
This can be easy achieved by a second diaphragm .
I will try :
First of all, let's assume that a diaphragm has an effective diameter that is smaller than the diameter of the outer clamping. This effective diameter should be close to constant, which will be shown later.
Inner and outer effective diaphragm diameters are the same size.
Second a first stage is water pressure compensated if the difference between IP and ambient pressure is constant.
First a simple not sealed first stage :
The equation for the equilibrium of forces is .
springforce + (waterpressure * eff. dia. area) = IP * eff.dia. area
We see that every increase in the water pressure must be compensated by an equal increase in the IP, because otherwise there is no balance of forces and the 1st stage opens.
Now the envoironment closed first stage with force transmiter :
As long as there is air before the transmiterplate this air is forced into the dry chamber until the pressure in the drychamber is the same as the waterpressure . So long everything is indentic to an not closed first stage .
We are balanced .The forces on the transmitter cancel each other out because they act on both sides.
As soon as there is no more air to compress in front of the transmitter plate, the equation of forces changes. The pressure in the dry chamber remains constant .
Now a force (water pressure * effective environmental membrane surface)
is transferred via the tranmitter to the 1st stage membrane.
Ok , we made the eff.envoironment membrane area the same as the first stage eff. membrane area . Now the forces by the pressure in the drychamer are cancelled out because the same pressure acts on an area of the same size in one and the opposite direction .
In the end, as before, the already known equation of forces remains:
springforce + (waterpressure * eff. dia. area) = IP * eff.dia. area
eff.envoironment membrane area = the first stage eff. membrane area
When I look at the diagram of the SP MK19Evo I think that this condition is well met. More on that tomorrow, it's to late now.
In a way you are both ‘right’, but in the case of sealed diaphragm regulators being discussed, @rsingler is more correct.
As you @CG43 say “It is possible to use air” … and the Sherwood “dry bleed” system is an example of air being used to seal a [piston] regulator whilst ensuring depth compensation. But the Sherwood system requires a small amount of air to be constantly added to the environmental chamber and for that air to be able to ’bleed’ to allow for ambient equalisation of the environmental chamber to the depth pressure. That is not possible in all current, and AFAIK past, sealed diaphragm regulators.
If the pressure transmitter ”piston” is omitted from a sealed diaphragm regulator then, to avoid loss of depth pressure compensation, the environmental chamber needs to be filled with a liquid (which should be freeze resistant) because the volume of liquid does not change under pressure.
Unfortunately, the types of liquids previously used in environmental chambers (alcohol or silicone oil) are not compatible with current O2 certification of regulators. AFAIK all diaphragm regulator manufacturers (except maybe Poseidon) have moved to dry sealed environmental chambers for Nitrox certification reasons.
And high proof Vodka used to work so well
… especially after the day’s diving was done 
Thank you for taking the time to reply!
I agree with your analysis but think that our disconnect begins here:
So if the volume of the container is, say, 120% of normal due to the bulging seal, the environmental chamber is compressed 19% at a depth of ~6 feet.
It's my contention that the addition of 3psi (19% of 14.5psi/1bar) will not prompt valve opening at 6ft due to diaphragm elasticity. But at 7ft, the contact of the env seal with the transmitter will begin to move the pin. Whether or not the IP "catches up" once the pin begins to move is debatable. And the whole issue is pretty insignificant, anyway. But that's my thought process, @CG43
I agree with your analysis but think that our disconnect begins here:
During the short descent that forces air into the dry chamber, the pressure in the dry chamber is increasing to match ambient. Due to the very flexible environmental seal, we can assume virtually no elastic resistance to deformation.
So if the volume of the container is, say, 120% of normal due to the bulging seal, the environmental chamber is compressed 19% at a depth of ~6 feet.
It's my contention that the addition of 3psi (19% of 14.5psi/1bar) will not prompt valve opening at 6ft due to diaphragm elasticity. But at 7ft, the contact of the env seal with the transmitter will begin to move the pin. Whether or not the IP "catches up" once the pin begins to move is debatable. And the whole issue is pretty insignificant, anyway. But that's my thought process, @CG43
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