Submersible Pressure Gauge (SPG)

The Submersible Pressure Gauge (SPG)

Indicates amount of breathable air remaining
Make sure:
- The Markings are Large and Clear
- The lenses are scratch resistant c. You can have digital or analogue SPGs

Scuba Diving Equipment / Diving Gear

A Submersible Pressure Gauge (SPG) is a diving instrument that shows, in either mechanical or digital form, the remaining air pressure left in a scuba air tank. Current design models of SPG instrument are connected to a high pressure outlet on the first stage part of a regulator via a high pressure hose.

Although the latest scuba diving regulators do not include hoses, a wireless pressure gauge transmitter is usually integrated into the first stage part of a diving regulator.

Mechanical SPGs, also known as Bourdon tubes, are spiral or circular oil-filled tubes that have diaphragms on one end and closed ones on the other. Generally, mechanical SPG works by pushing air pressure against the diaphragm, thus further straightening the tube. Digital SPGs, meanwhile, make use of transducers that efficiently convert pressure into voltage. Once the voltage is converted, it is then turned into a digital signal that signifies a digital readout.

Moreover, there are several widely accepted types of SPGs. One of these is the Standard type, which is basically an analogue gauge that can be held by hand. Usually connected to the first stage part of a diving regulator, the Standard type displays pressure range with a pointer moving over a dial. There are some SPG Standard types, however, that are fixed with a rubber or plastic consoles, including a compass, a dive computer, and depth gauge.

The button gauge is another accepted type of SPG that is directly connected to the first stage part of a regulator. This is often utilized on the decompression cylinder. Based on its name, the Button gauge is small in size, thus making it difficult to read gauge resolution of less than 300 psi.

Another essential type of submersible pressure gauge, the air integrated computer is a widely known type of SPG among professional divers. This computer-based type of pressure gauge is generally designed to display, monitor, and measure pressure rate in a diver's scuba tank. Although dive pressure gauge computer can be a very useful tool for pro and recreational divers, it cannot monitor a diver's gas supply once the computer fails.

Last of these types is the Mechanical reserve valve. When professional divers' air flow reach below 500 psi, the mechanical reserve valve of a scuba tank will automatically restrict air flow. Also called as J valves, mechanical reserve valves are used by divers along with a reserve valve in an open position to monitor their air supply.