Atomic 2nd stage question

[gopbroek]

Recently I purchased a used ScubaPro Mk25 1^st stage and Atomic T2 2^nd stage regulator set. I got it in 2 days before I was headed for Cozumel so I did not have time to have it serviced. On the first dive I had my dive buddy and the DM stick close, for safety, and the regulator performed well until I got it to about 20’ on accent. I found that, when I removed my regulator to deploy my SMB it would free-flow, regardless of mouthpiece angle and flow adjustment setting.
After the dive I took it down to Javier at Cozumel Scuba Repair and he found the 1^st stage intermediate pressure high (around 150 PSIG) and replaced the piston and adjusted the pressure to mid-range on his IP gauge. The next day I took it out and found that it operate pretty well until about 6’ at that point it would still free flow with the mouth piece up or horizontal but it work OK down, I also found that the 2^nd stage flow adjustment still had minimal effect.. I took it back to Javier and him adjust the IP down to minimum (125 PSIG). Now the 2^nd stage flow adjust has effect but I am at full restrict and all is well until 2-3 ‘. If I remove the 2^nd with the mouth piece up, it free flows for a couple seconds and then seats itself, horizontal or down, no free flow.
My question is, is this normal with an Atomic 2^nd, if not is the pressure still a little high on the 1^st or does this indicate a problem with the 2ND stage? Overall I am very happy with the regulator set but I would like to know if I should have Javier fine tune it a little more.

 

[agilis]

I'm just a tinkerer who has worked on his own mostly Scubapro equipment for many years. My instincts tell me that the problems are with the second stage, not the first. No adjustable second stage should require the adjustment knob to be fully closed in order not to free flow. Do you dial it closed only when approaching the surface? Your description of what happens sounds like any adjustable second stage, except that what you describe usually happens when the adjustment knob is wide open, or close to that point.

My experience is that there is not a super huge difference between a 125 and a 140 IP except with an unbalanced second stages under certain circumstances. I know very little about Atomic products, though I have used them without any problems. I would look closely at that 2nd stage. The main job of a first stage is to deliver air steadily at a set pressure. The second stage does not know or care where the gas is coming from. It may be that Atomic 2nd stages require an unusual IP. I don't know, but I'd find out. Something does not sound right.

 

[Scared Silly]

It should be obvious that a ScubaPro first on an Atomic second would not get along well regardless of what adjustments are made. Too much history and parting of ways.

More seriously, it is not the first stage but the second stage that needs adjustment. Sounds like the LP seat / orifice or the cracking pressure needs some adjustment.

However, given you got it off of fleabay it probably needs service. Which would mean a complete overhaul of both stages.

 

[gopbroek]

Agilis, thank you, what you a saying supports what I was thinking. I will probably have the 2^nd overhauled when I get back down in a couple weeks. If any anyone else has input or experience I would appreciate it.

 

[knotical]

I’m far from expert, but I’ve diddled with these a little. I’d seek more data, such as:
Did Javier check IP at different cylinder pressures (classically 3000 and 500 psi)?
Presumably there was no IP creep?
Did Javier adjust the cracking pressure?
Did you check to see if you had similar symptoms at other depths and cylinder pressures?

 

[gopbroek]

I checked for flow problems at various other depths W/O problems and the ending pressure near the surface was from 200 - 800 PSIG over 12 dives, the 'slight' free flow was limited, at this point, to 3’ or less. I think I will have the set fully serviced when I return next weekend.

 

[halocline]

Any high performance 2nd stage, if tuned correctly, will free flow if you take it out of your mouth with the mouthpiece pointing up, or even sideways. You should be able to stop it by plugging the mouthpiece hole with your thumb. Once a 2nd stage gets going, the venturi assist will keep it flowing. I don't read anything in your description that sounds like there's a problem. But I have a couple of questions:

1. If you're underwater and using the 2nd stage, does it ever free flow while it's in your mouth? If not, you likely don't have a problem.

2. Can you stop it from flowing by plugging the mouthpiece with your thumb, turning it mouthpiece down, and letting the 2nd stage fill with water? If you do that, it should stop and not start flowing again.

3. Why did the repair guy replace the piston in your first stage? High IP is just an adjustment, not a reason to replace the piston. The only reason to do that is if the IP is creeping. (Even then, you'd start by replacing the seat) The piston probably costs $75 in Cozumel. BTW, that 2nd stage should work fine with any IP up to about 150. It just needs to be adjusted for a particular IP. Did the repair guy do that?

 

[eelnoraa]

..... After the dive I took it down to Javier at Cozumel Scuba Repair and he found the 1^st stage intermediate pressure high (around 150 PSIG) and replaced the piston and adjusted the pressure to mid-range on his IP gauge.

Why replace piston is needed? unless there is a damage, adjusting IP and replacing piston should be independent.

The next day I took it out and found that it operate pretty well until about 6’ at that point it would still free flow with the mouth piece up or horizontal but it work OK down, I also found that the 2^nd stage flow adjustment still had minimal effect..

This sounds normal to me. If anything the 2nd stage just need a little adjustment.

Halocline beated me to it.

 

[agilis]

The "flow adjust is at full restrict and all is well until two or three feet" is NOT normal. The free flow for a few seconds is normal, but I'm reading this as a second stage with the adjustment knob dialed all the way in. Unless I'm misunderstanding what the OP wrote, something is wrong and it's the second stage, which should not behave 'normally' when the flow adjuster is screwed all the way in.

 

[ams511]

I pulled the service manual and troubleshooting guide for the MK25. The intermediate pressure range is 125 psi to 145 psi, so while 150 psi is out of spec, it is not grossly so. If the regulator has a high ip then it is adjusted down using a hex key. You do not need to replace anything. If the ip creeps, then the seat is replaced first and then the piston. However, I would assume that when disassembling the regulator to replace the seat, if the tech spots visible damage the piston would be replaced. Did you receive the old part back?

I agree with the others that the problem is more than likely that the second stage should be adjusted to match the first stage. This is what the tech in Mexico should have done in the first place.