A typical sport diving breathing gas setup consists of a pressurized gas cylinder (aka 'tank') and valve with either a 'Yoke' or 'DIN' outlet. The yoke valve outlet is by far more common in the US and Caribbean but much of the rest of the world uses the DIN valve outlet. Experienced divers have a strong preference for DIN, because it is much more reliable and better suited to the higher pressures of modern higher working pressure tanks. Obviously we cannot breathe the high pressure gas directly from the outlet of the tank and thus rely on a 'two stage' regulator system (i.e. there are TWO separate and distinct regulators) to reduce the pressure in the tank to what is known as 'ambient pressure', i.e. a pressure equal to the surrounding pressure.
The first stage of your diving regulator has two kinds of 'ports' or openings on the sides of the body: typically one or two 7/16-inch 'High-Pressure Ports' (sometimes stamped 'HP') and two or more smaller 3/8-inch 'Low-Pressure Ports' (sometimes stamped 'LP', 'IP', or 'MP'). The HP port is simply a flow through directly from the high pressure supplied by the tank valve. The only common SCUBA application for the HP port is to attach a 'submersible pressure gauge (SPG) or pressure transmitter to the port so that the dive may monitor the tank pressure and thus estimate how much gas remains. Even though the port diameter is physically larger on the HP port, the HP flow path of the first stage normally has a severe restriction such that the high pressure gas will flow very slowly.
In contrast to the HP port, the LP ports have no restrictions and in fact the designers of high performance first stages have taken great care to produce as high a flow of gas as possible from the LP ports. The first stage reduces the tank pressure, typically about {3000 psi | 200 bar} down to an 'intermediate' pressure of about {140 psi | 10 bar} and supplies this intermediate pressure at the LP ports. (Note the intermediate pressure can set to an alternate value by design or adjustment, depending on the application or brand of first stage.) The intermediate pressure is further reduced by the 'second stage' to 'ambient' pressure we can breathe from the mouthpiece. The intermediate pressure is typically also used for 'power inflation' of the BCD and Drysuit.
Typically the SPG, the BCD power inflator, and the second stage regulator are connected to the ports of the first stage via flexible hoses. Thus there are two broad classes of hoses: high pressure hoses capable of withstanding the full working pressure of the tank and low pressure hoses designed to withstand the lower intermediate pressure supplied by the first stage regulator. The low pressure hoses are further differentiated by what device will be connected to the hose at the other end from the regulator first-stage: either the BCD power inflator or the regulator second stage. By convention, the high-pressure SPG hose is often abbreviated as HP, low pressure regulator hose is LP, and the low pressure buoyancy control device hose is BC.
High pressure hoses are normally terminated in a 7/16-inch swivel fitting that requires tiny part called an 'air spool' to properly seal. There are two different low pressure hose termination fittings that depend on the application. Low pressure regulator hoses are normally terminated in a 9/16-inch threaded female fitting that connects to the standard 9/16-inch male fitting on the second stage. Low pressure inflator hoses are normally terminated in a low flow quick disconnect Schrader female fitting that incorporates a one-way check valve and connects to the matching Schrader male post on the power inflation device of the BCD or drysuit.
Modern SCUBA regulator and hose fittings are very standardized and our descriptions generally apply to most recreational dive equipment but there are some exceptions, especially for some very early "vintage" equipment or specialty applications. If you are uncertain about regulator and hose compatibility, feel free to Contact Us.
