SPG Pressure needle help

[Nomadsoul]

Hey everyone - we are having a debate here at the shop and have a general question about SPG pressure needles.

First - we had a problem with air in three SPGs and perhaps tanks on a dive a few days ago. We went fairly deep (30m +/-) and for 3 people their needles went out of whack at various times. There was cause to think it was low air as they all used air very fast. Others thought the tanks were not opened fully with the 1/4 turn.

However - we go back to the shop, test all the regs with a breathing test to see how much give we have at a full(ish) tank. A few had a large amount, a few had small, and a few not much. They all were tested by taking large breaths from the primary reg first, then both if needed. Probably should have tested both right off the bat, but we were in a hurry.

Anyway - here's the deal: there was some give on the SPG pressure needle in most using deep breaths on the primary reg. Some dropped a single measurement, others a few. We had them serviced and the shop said the problem was within the o-ring housing, however when I did the test in the shop there was still a little bit of give on the needle which the shop said was fine. Is this fine? We are in Indonesia and one of our guys who has a ton of experience says no give in the needle is alright. Others say that there should be some small drop with the pressure differential. What is right here?

 

[redacted]

If you are getting the proper flow from the tank (valve fully open and in good shape), the the SPG needle should not move when you breath from any 2nd stage. You may want to try testing an offending SPG on a sample of different tanks to see if the tank (valve) may be the problem.

 

[elan]

This behaviour usually indicates that the supply of gas to the first stage is not sufficient. The tank valves are possibly clogged with some garbage and they do not provide enough flow. Then when you breath on the second stage the air from the SPG hose is migrating to th first stage thus dropping the pressure in the tube.

 

[JohnN]

This behaviour usually indicates that the supply of gas to the first stage is not sufficient. The tank valves are possibly clogged with some garbage and they do not provide enough flow. Then when you breath on the second stage the air from the SPG hose is migrating to th first stage thus dropping the pressure in the tube.

Isn't that supposed to be one of the "GO" / "NO GO" tests on every dive before you get wet?

 

[Nik Wills]

In the UK cylinders have to have an internal visual inspection every 2.5 years and a hydrostatic test every 5 years no matter what material they are made from. You don't say hold the cylinders are or how often they are checked?

When the regs had been serviced did they give you the internals like o'rings and filters they should have replaced to prove they had completed the service correctly, rather than strip it, clean it and reassemble?

 

[redacted]

Also, take a look at the filters in the first stage. They could also produce a restriction that might cause that symptom.