Adjusting IP, LP inflator hose ok?

[TT_Vert]

I know it is "recommended" to test IP at the 1st stage directly but will I really notice any difference using the LP inflator hose? It'd certainly make my life easier if using this connection method. I see many IP gauges come w/ only the LP inflator hose fitting and thinking about this logically I don't see any reason why the pressure would change through a pre-pressurized 22" of small ID hose but I just want a second opinion.

Thanks
Dave

 

[lowviz]

...//... I don't see any reason why the pressure would change through a pre-pressurized 22" of small ID hose but I just want a second opinion. ...

Your SPG gives you life critical information through an extremely small hole in the primary reg connector. Unscrew it at look at it.

Checking IP is good, but knowing what you want from it is much better. IP should be set with the secondary reg in mind. One feeds the other and they are both adjustable.

I like cold water diving so I tell my reg tech to set the IP midrange and adjust the secondary reg for "normal" breathing. Most reg sets come tuned "hot" for vacation diving. The 'joke' is that your secondary is already anticipating your next breath. No thanks, I don't need the free flows that this causes in really cold water.

Bottom line, under static pressure, absolutely no effect. Under flow, yes, there will be a resistive drop in pressure that relates to flow.

 

[herman]

As long as you are just looking at static IP then pretty much any length/size of hose can be used. The longer/larger diameter the hose the longer you should pause to make sure IP is stable before adjusting farther. The problem with a long/large hose comes when you are looking for slow transients in IP, in other words, looking for a slight creep. Long/large hoses have a larger volume which in turn takes longer to fill which will mask a small creep unless you wait a longer time. Bottom line, as long are you are not troubleshooting a creep issue (just a pre-trip test) and you wait several seconds for the IP to stabilize, there is no problem using a longer hose. If you are hunting down a slight creep, a short/small hose makes your life easier.

 

[TT_Vert]

Guys i'm asking this question from a regulator rebuild perspective. I will be setting IP and monitoting IP creep when adjusting the first stage. Will putting the IP gauge on the LP inflator hose skew my readings enough to matter?

thanks,
Dave

 

[spectrum]

Herman gave a very good answer. As he said in terms of observing the static (steady state) IP setting you will be seeing the same pressure as the second stage. As long as your hoses are all of common lengths (not a 50 foot hookah hose) what you see is what you get.

In terms of creep Herman was cautioning you about system volume. If the 1st sage is creeping it will be doing so at a volumetric rate. If you have big hose volume it will take longer for that volume to appear as a measurable pressure change on a small IP dial gauge. This is roughly analogous to blowing up a balloon. One breath is very visible in a small balloon where many breaths are needed to make a big balloon appear bigger. In a perfect world the 1st stage would be isolated to just an IP gauge for creep monitoring.

In reality techs hook up to whatever the customer drops off and test it as such.

Don't over think it but consider any creep in a reasonable time period to be creep. Stabbing into the inflater QD works fine for most of us.

Pete

 

[TT_Vert]

Thanks guys. I will probably just get a 1/2" npt to 3/8 adapter just to compare.

Herman gave a very good answer. As he said in terms of observing the static (steady state) IP setting you will be seeing the same pressure as the second stage. As long as your hoses are all of common lengths (not a 50 foot hookah hose) what you see is what you get.

In terms of creep Herman was cautioning you about system volume. If the 1st sage is creeping it will be doing so at a volumetric rate. If you have big hose volume it will take longer for that volume to appear as a measurable pressure change on a small IP dial gauge. This is roughly analogous to blowing up a balloon. One breath is very visible in a small balloon where many breaths are needed to make a big balloon appear bigger. In a perfect world the 1st stage would be isolated to just an IP gauge for creep monitoring.

In reality techs hook up to whatever the customer drops off and test it as such.

Don't over think it but consider any creep in a reasonable time period to be creep. Stabbing into the inflater QD works fine for most of us.

Pete