Question "Bouncy" Submersible Pressure Gauge

[JonnieB]

Would not it make sense to stick an ip gauge on the inflator hose and see if there is a similar and significant variation in the intermediate pressure?

If that were the case, then I would assume the filter would be the cause.

Also I would think that performance issues at depth would be occurring, if the filter is blocked and that does not seem to be the case?

Reg breathes normally...SPG just get bouncy, especially at the end of the dive when tank pressure is low.

 

[tursiops]

Will try it on a different first stage.

Have you done this yet? This is a critical test to narrow down the source of the problem. IF switchign egs solves you problem, then that points the finger at the inlet filter and the ACD.

 

[rhwestfall]

Yes; those fouling problems with early models from over ten years ago. Also, when I replaced the SPG, no little plastic bits to be seen.

Ten years ago isn't a line in the sand. It still doesn't say that breakdown of the liner isn't happening...

 

[JonnieB]

Have you done this yet? This is a critical test to narrow down the source of the problem. IF switchign egs solves you problem, then that points the finger at the inlet filter and the ACD.

I'm currently in Bali and only brought one reg set on this trip. However, I have access to some shop first stages and swapped in a different SPG and it worked normally. I will re-confirm this tomorrow with another shop SPG. If it works properly, it's not the first stage or the new SPG. Will check for any blockage of the HP hose.

 

[JonnieB]

Ten years ago isn't a line in the sand. It still doesn't say that breakdown of the liner isn't happening...

My understanding is it was a materials flaw that caused the premature breakdown on the early flex hoses,, and that the issue had been addressed. Are you saying it still occurs on current model flex hoses?

 

[happy-diver]

Yes in the interest of maintaining a standard safe ScubaBoard diving environment
checks like these should be performed, even providing a psychological advantage

You should, especially if diving from a dive boat with DMs who helpfully "check your valves" when you are not looking.

 

[clownfishsydney]

Faulty valve, have seen it before. Not opening completely despite handle being opened right up.

 

[elmo]

If the issue were a partially blocked hp hose or port you would see a slow response from the spg. That isn’t the case. The pressure on the gauge drops because the pressure in the hp chamber in the first stage drops, which means the inflow (from the cylinder) isn’t keeping up with the outflow (to the second stage hose) when you take a breath. There’s still enough pressure to deliver gas to the second stage but if this is happening with multiple cylinders and you are sure the valves are fully open then something is blocked between the cylinder and the hp chamber. Probably the filter or the acd. The service shouldn’t be hard but I wouldn’t trust your first stage until it’s fixed.

 

[halocline]

I'll have a look at the filter; it's an Aqualung reg so does have ACD. The SPG needle doesn't really bounce with a full cylinder - usually towards the last quarter of the dive when cylinder pressure is low.

It wouldn’t surprise me if the ACD has something to do with this, although I don’t really know how the one in your regulator works. Some of them are physically held open by attaching them to a tank, and some have a little ball on a spring that closes in the absence of a pressure gradient between tank and valve. If that latter type is yours, I would be pretty suspect of it. They do open and close with each breath and could easily interfere with HP air flow, especially at low tank pressures.

But, thinking about it, I have a vague memory that it’s the Oceanic regs that use the little ball, and Aqualung uses a flap-kind-of-thing that gets held open physically by the tank valve whenever the reg is attached. If that’s true, your ACD is probably not the cause.

You said you tried another SPG and it did the same thing, but you didn’t specify if you replaced the spool and/or hose as well. The spool would be suspect, those get clogged pretty easily. Then you said you tried a different SPG at the shop where you’re diving and it worked fine, but again, you didn’t say whether the spool and/or hose was swapped in that case.

Try your own SPG with a new spool and different hose. That might do it.

As far as the regulator filter being clogged, that’s also a possibility and of course those stupid ACD things make it difficult to inspect the filter. But usually a clogged filter results in much higher IP drop during inhalation (especially at low tank pressures) and that makes the reg noticeably harder to breathe. You didn’t say anything about that so it wouldn’t be my first guess. But it is certainly possible that’s the problem.

 

[JonnieB]

It wouldn’t surprise me if the ACD has something to do with this, although I don’t really know how the one in your regulator works. Some of them are physically held open by attaching them to a tank, and some have a little ball on a spring that closes in the absence of a pressure gradient between tank and valve. If that latter type is yours, I would be pretty suspect of it. They do open and close with each breath and could easily interfere with HP air flow, especially at low tank pressures.

But, thinking about it, I have a vague memory that it’s the Oceanic regs that use the little ball, and Aqualung uses a flap-kind-of-thing that gets held open physically by the tank valve whenever the reg is attached. If that’s true, your ACD is probably not the cause.

You said you tried another SPG and it did the same thing, but you didn’t specify if you replaced the spool and/or hose as well. The spool would be suspect, those get clogged pretty easily. Then you said you tried a different SPG at the shop where you’re diving and it worked fine, but again, you didn’t say whether the spool and/or hose was swapped in that case.

Try your own SPG with a new spool and different hose. That might do it.

As far as the regulator filter being clogged, that’s also a possibility and of course those stupid ACD things make it difficult to inspect the filter. But usually a clogged filter results in much higher IP drop during inhalation (especially at low tank pressures) and that makes the reg noticeably harder to breathe. You didn’t say anything about that so it wouldn’t be my first guess. But it is certainly possible that’s the problem.

Thank you for the detailed reply and suggestions. Yes it is an Aqualung, with ACD. Yes, the swivel spool was replaced when I put on the new SPG. You, and others, were correct in suggesting the first stage is at fault. I swapped in the new SPG into a shop first stage for two 90 minute dives today and it works fine. The gauge needle was rock steady. The shop regs are also AL and they have filters in stock (in Amed, Bali). They too, like many here, suspect a clogged filter, but won't know for sure until they get behind the ACD and access the filter.

Thanks again everyone for the helpful suggestions. I guess the moral is I should service my regs more frequently