High Pressure vs Low Pressure Ports

[sontek]

Whats the difference between the ports and whats the use of each?

 

[Scubakevdm]

HP is tank pressure, LP is approximately 140 psi over ambient pressure. HP ports are used to hook up an spg so you can tell what's in your tank and LP is for breathing and BCD/Dry suit inflation, etc. Basically HP is in the gas flow path before the first stage, and LP is after.

 

[redacted]

Whats the difference between the ports and whats the use of each?

Usually the difference is 1/16 of an inch in diameter, but they could be the same on some older regulators. HP ports are directly exposed to the tank pressure and are used to connect HP devices such as an SPG or computer transmitter. LP ports are exposed to Intermediate pressure gas after the 1st stage has stepped tank pressure down to a usable pressure for your 2nd stage. You BCD and dyrsuit inflator also operate off this pressure source.

 

[AquaNSun]

The LP ports intermediate pressure (IP) is usually between 125 - 145 psi. This is achieved by pressure building up in the IP chamber and is equal to the force required to close the valve in the first stage. We want IP in the 2nd stages so that you can breath comfortably and this IP is still high enough that air can be delivered to divers through their hoses.

 

[herman]

Just to make things a little more confusing, there are a few regs with 1/2 in LP ports in addition to the more common 3/8in LP ports. Their purpose is the same as any other LP port, the larger size was a marketing scheme...did not do much but sounded good. What it mainly did was to create a PITA for those of us who have the regs.

3/8x24 thead is the standard size for LP ports.
7/17x24 is the current HP port size. Be aware there are a good many older regs with HP ports that are also 3/8x24. Hooking a LP hose into those ports can be very exciting...for a short time....which is the reason the size was changed from 3/8. :shocked2:

Adapters are available to convert the older 3/8 HP port to the current 7/16 version. Adapters are also available for the PITA 1/2 LP ports to convert them to the standard 3/8 size.

 

[Teller]

Whats the difference between the ports and whats the use of each?

HP ports are for SPG or your air gage or mabey a transmitter if you have a wireless computer. LP ports are for your inflator hose on your BCD, your reg and octo and your drysuit inflator valve if you have a drysuit. If I remember right, most LP ports are 3/8 and most HP ports are 7/16 unless you have an older model 1st stage.

 

[Belce]

Actually intermediate pressure will always tend to be 140 psi which is about 10 atmospheres. If some thought is put in you would realize there is no need for that to change regardless of depth for diving.

 

[herman]

Actually intermediate pressure will always tend to be 140 psi which is about 10 atmospheres. If some thought is put in you would realize there is no need for that to change regardless of depth for diving.

Not so, IP is constant only if you are measuring PSIG which does not take into account ambient pressure. In fact, the PSIA of the IP varies directly with depth, increasing at roughly 0.5psia for each foot of depth unless you are diving an "overcompensated" first stage in which case it increases at about 0.65 psia/ft. It is very important for the IP to follow ambient pressure, otherwise the reg would get increasingly difficult to breath from as depth increased because of the increasing differential pressure between the IP and ambient pressure. At 100ft the IP would be reduced by almost 1/3 to a rough equivalent of 100psig if the reg did not depth compensate. To take the example a little farther, at roughly 280 the reg would not deliver any air at all if it were not depth compensating. The PSIG of the IP does not change but the PSIA had better or the reg will perform very badly at much depth. Put a little more thought into it.