Apeks IP Drop

[rgdiver1]

Over the years I have serviced Apeks 1st stage regulators many times. After servicing sometimes there is a small drop in intermediate pressure on inhalation and other times almost none at all. I always try to be meticulous and take my time when I do the service. I also use only Apeks parts kits and follow factory service procedures. Although this small variance in IP drop does not seem to effect performance, I have always wondered what causes this variation. Does anyone know why this happens? There doesn't seem to be any reason to me, but I always wonder if I've overlooked something.

 

[tbone1004]

is the IP drop permanent or only on inhale?
It's supposed to drop on inhale and how much will be dependent on quite a few variables. The two main variables are how hard you are inhaling, and how large the IP "chamber" is. That "chamber" includes all of the hoses that are connected to the LP side. Go to a long hose, add an octo or a drysuit hose, suck on the reg a bit hard, it will change how much it drops.

 

[rgdiver1]

is the IP drop permanent or only on inhale?
It's supposed to drop on inhale and how much will be dependent on quite a few variables. The two main variables are how hard you are inhaling, and how large the IP "chamber" is. That "chamber" includes all of the hoses that are connected to the LP side. Go to a long hose, add an octo or a drysuit hose, suck on the reg a bit hard, it will change how much it drops.

The IP drop occurs on inhale only. I expect to see some drop of course, and it is within specs. On some of my Apeks 1st stages however, there can be very little or almost no IP drop, and I do not see a pattern or a relationship. I have Apeks DS4's and DST's.

 

[buddhasummer]

Good question, I was actually wondering that same thing last weekend, I have a few Apeks first stages and have also noticed that. Toms reply gave me food for thought as some of my reg sets do have additional hoses. I'll do a more thorough comparison.

 

[halocline]

Unless you have some expensive test gear, it's impossible to accurately measure IP drop during inhalation. The IP gauges we all use that go on the LP inflator hose don't do that well, because of venturi effect created by air moving past the ports. I know this from some experimenting several years ago on different SP 1st stages.

IP gauges are designed to measure static IP and they can give a good indication of IP recovery and stability. That's what is important for evaluating regulators. IP must drop during inhalation, in fact that's the mechanism for all; 1st stages to work. IP drops which opens the valve and lets air flow.

 

[buddhasummer]

Sure, I can see the difference in drop between my different Apeks first stages. The actual amount isn't important to me just I can see a difference and wonder why, curiosity, they all function fine.

 

[buddhasummer]

Interestingly, the lowest drop in ip on inhalation I have encountered has been a conshelf/Titan and a MK25. I do have one Apeks first stage that is pretty low too.

Could it be a tolerance difference? Between same brand first stages I mean.

 

[АлександрД]

For better test of IP drop you have to remove all unused hoses, and put stubs against it.
If possible - to use in-screwed SPG against attached to BCD hose, like Mini Scuba Gauge, PG-JH2-LP - AROPEC SPORTS CORP.

or use as short as possible hoses.
When you have long hose - it works as air bufer, and you have breath beginning from hose, and will not see any IP drop.
Normal is 1-1.5 bar IP drop. If bigger - something wrong, and most popular reason - is dirty air filter in the DIN/Yoke connector.
Some years ago I prepared like "checklist" for failures search using IPG. Here I try to made translation. Intermediate pressue gauge - Recognizing regulator problems

 

[rgdiver1]

IP drop is always less than 1 bar. When measuring in PSI, the drop is 10 PSI or less which is a fraction of a Bar. Good points about there being many variables.

 

[halocline]

I don't think that IP gauge or shorter hoses make any real difference; the issue is that gauges of this type are not meant to accurately measure pressure while gas is moving past their connection point, which is a LP port. Think about it this way, the faster that gas is moving across the port, the more venturi effect there is and the lower the pressure drops in the area of the moving gas. This means that the faster the flow, the lower the IP gauge will read. To get an accurate measure of IP during inhalation, you'd need some sort of an inline flowmeter.

The geometry of the 1st stage has a lot of influence on this. For example, a MK20 will show a far greater drop in IP than a MK2 under full purge with the same high-flow 2nd stage, when measured with an IP gauge on the LP inflator. It's very clear that a MK20 has far greater flow capability than the MK2, so you would think that the MK2 would drop a lot more during inhalation. But it doesn't appear that way on the IP gauge. I believe that the MK20 is actually flowing more gas, but the turret LP port arrangement somehow increases the pressure drop at the unused ports when gas is flowing rapidly through one of them. It's the only explanation that makes sense.