low, intermediate, or medium pressure ?

[knotical]

It's common to see mention of low pressure ports on first stages,
and to hear about intermediate pressure between the first and second stages.
More recently we occasionally run into the term medium pressure.

It seems they are all the same thing. But are there some subtle differences? Anyone know the evolution of the terms?

 

[captndale]

People often refer to the same things using different words. When referring to scuba regulators there are three different spaces with differing pressures.

1. The space between the tank valve and the high pressure valve (first stage valve) is generally referred to as "high pressure." This area may range from 0psi (empty tank) to 3500 psi or more (full tank.)

2. The space between the high pressure valve in the first stage and the second stage valve. This space is referred to as intermediate pressure. Often the ports accessing this space are referred to as "low pressure ports. The actual pressure is a function of the adjustment of the first stage regulator. Intermediate pressure is generally set at between 125 psi and 145 psi above ambient pressure but in some regulators (Poseidon) may be set as high as 170 psi. I think it would be unusual for anyone to refer to this as "medium pressure" but it might happen.

3. The space on the diver's side of the second stage valve. This is the pressure the diver actually breathes. It is very nearly ambient pressure, generally about -.5 to -2.0 inches of water on inhallation and +.5" to +2.0" H2O on exhallation. This is usually referred to as ambient pressure.

 

[Couv]

I haven't hear the term "medium pressure"....I think our friends in the UK call intermediate pressure, "interstage pressure." Sorry, I don't know the etymology either.

c

 

[Nemrod]

Until we have three stage regulators there is no "medium" pressure. Intermediate is low pressure in reference to a two stage scuba regulator.

The first stage reduces tank pressure (HP) to an intermediate (LP) pressure which is then reduced to ambient pressure at the second stage for the divers demand.

I guess somebody could say that intermediate pressure was a middle pressure between tank pressure and ambient pressure, I dunno.

N

 

[LeadTurn_SD]

I've only seen the term "medium pressure" here on scubaboard in a few threads, and it was when someone was trying to say "intermediate pressure", but was unsure of or couldn't remember the correct term.

Best wishes.

 

[Luis H]

Medium Pressure (MP) is the term Aqua Lung and Apeks use in their web site and catalog for what the rest of us call Intermediate Pressure (IP).

I got the impression that Aqua Lung adopted that term from Apeks (the Brits), but that I am not sure that is correct.

In any case, it is the same thing, just a different name.

 

[hg frogman]

Aqualung is a French company and Apeks is a subsidiary of Aqualung. In French we say "moyenne pression" (medium pressure, MP) for what Americans call "intermediate" or "low" pressure. It seems to be all the same.

 

[Tortuga68]

From a port point of view, you have HP (tank pressure) for your SPG and LP/MP/IP (for second stages/octos and BC inflation)

 

[Texfrazer]

Aqualung is a French company and Apeks is a subsidiary of Aqualung. In French we say "moyenne pression" (medium pressure, MP) for what Americans call "intermediate" or "low" pressure. It seems to be all the same.

Looks like we have the answer. Thanks!