Regulators: stages, markings and servicing.

Three parts

DAN's Alert Diver (John Brumm, "Breathe In, Breathe Out", 2012) describes a regulator as the device that converts high-pressure gas from the cylinder into gas at the surrounding (ambient) pressure. It has three parts:

First stage

Fixed to the cylinder valve. It reduces cylinder pressure to an intermediate pressure, which DAN gives as typically about 125 to 145 psi above ambient.

Intermediate-pressure hose

Carries gas from the first stage to the second.

Second stage

Held in the mouth. It delivers gas at ambient pressure.

DAN calls scuba regulators demand-type: gas flows only when the diver inhales.

Piston or diaphragm, balanced or unbalanced

DAN says first stages come in two kinds, piston and diaphragm, and that both regulate flow between a high-pressure chamber and an intermediate-pressure chamber.

The other distinction is balance. According to DAN, in an unbalanced first stage the intermediate pressure can drift as the cylinder empties or the depth changes, which can make breathing harder. A balanced first stage uses a balance chamber to keep that pressure steadier. On the second stage, DAN says balancing reduces the "cracking effort" needed to start each breath.

Many second stages have two user controls, as DAN describes them: a dive or pre-dive switch that makes the second stage less likely to free-flow at the surface, and a knob that adjusts breathing resistance. How and when to use them is taught in training.

The alternate air source

A spare second stage carried as an alternate air source has a common nickname. Scuba Diving magazine, in a page we could see only as a search summary, says it is "octopus" and that it is usually yellow, with a yellow hose, so it stands out. The same source notes that its performance depends on the first stage being able to supply two second stages and a BCD inflator at once. Some makers build the spare second stage into the BCD inflator instead; Scubapro's AIR2 is one named example (seen in a search summary of a product article).

DAN Europe (Guy Thomas, 2022) warns that changing or adding a second stage, octopus or hose can alter how the whole regulator performs, even when every part is CE-marked on its own, and says makers publish lists of approved combinations.

EN 250 and what the marking means

The European standard is EN 250:2014, "Respiratory equipment, Open-circuit self-contained compressed air diving apparatus, Requirements, testing and marking". It sets minimum requirements for open-circuit compressed-air scuba and its sub-assemblies, aiming at a minimum level of safe operation to a maximum depth of 50 m. The Estonian catalogue lists it valid from 6 May 2014, following EN 250:2000 and its 2006 amendment, and links it to the EU personal protective equipment regulation, (EU) 2016/425.

DAN Europe (2022) explains the markings found on regulators:

DAN Europe stresses that a CE marking confirms only that minimum requirements were met. Real performance still varies with design, temperature and depth.

An older maker manual says it differently

Mares' manual for its REBEL regulator, written in the EN 250:2000 era, says that standard treats water below 10 C as cold and that its regulators need a factory cold-water kit, fitted only by an authorised service centre, before cold-water use. The same manual says EN 250 equipment is not intended for more than one user breathing at once, and that if it is used that way, cold-water and breathing performance may not meet EN 250. DAN Europe's 2022 article, by contrast, describes the A marking as a tested two-diver approval to 30 m. The difference may come from the 2000 and 2014 editions of the standard, but our research could not confirm that.

Servicing: who, and how often

PADI (2015) says a regulator with an internal problem should go to a certified technician and should not be taken apart without training. DAN Europe (2022) says makers usually require changes and servicing to be done by authorised dealers or trained technicians using approved parts and lubricants, and that non-original parts may void the CE marking and the warranty. A UK dive dealer's 2023 summary reports that many warranties depend on regular authorised servicing.

Service intervals are set by each maker, and the published ones differ:

• Mares (REBEL manual, maker statement): inspection at an authorised Mares service centre at least once a year, and replacement of the first-stage valve every two years or every 200 diving hours.
• A UK dive dealer's summary (2023) reports maker recommendations as: Scubapro, a full overhaul every two years, or yearly with heavy use of about 100 or more dives; Mares, inspection yearly or every 100 dives and overhaul every two years or 200 dives; Aqualung, yearly inspection and a two-year overhaul; Apeks, an overhaul at least yearly regardless of use. We could not check these against each maker's own documents.

The two Mares figures disagree: the maker's manual says 200 diving hours, while the dealer says 200 dives. The interval that applies to a particular regulator is the one in its own manual, and the service centre decides what work it needs.