Dive Equipment — PADI IDC / DM Study Notes

What the Equipment Exam Covers

Use the links above and below to dive into each subject in detail.

The PADI Divemaster and IDC equipment theory exam tests your understanding of how scuba gear works, how it fails, and how to maintain it. The topics covered here include regulator first and second stages, scuba tanks and valves, buoyancy compensators, masks, fins, wetsuits and drysuits, dive computers, depth gauges, submersible pressure gauges, surface marker buoys, lift bags, and rebreathers. All study notes on this site are free with no paywall.

Regulators — First and Second Stages

The first stage reduces high-pressure cylinder air to an intermediate pressure above ambient. Understanding the difference between balanced and unbalanced designs is consistently tested — a balanced first stage routes tank pressure away from the valve stem, allowing a larger inlet orifice and consistent breathing effort as the cylinder empties. The connection type matters too: a yoke regulator clamps onto the tank valve with the o-ring sitting exposed on the valve face, while a DIN regulator screws directly into the valve with the o-ring encased inside the connection. DIN is more secure because the o-ring cannot be dislodged.

The second stage delivers air on demand. All modern second stages use a downstream valve — a design that fails open rather than closed, giving the diver a continuous free-flow rather than a cut-off air supply. This is what makes it a failsafe design.

Tanks and Valves

Scuba tanks require a visual inspection every year and hydrostatic testing every five years. Hydrostatic testing pressurises the tank to 150% of its working pressure using water rather than air — water is incompressible, so a failure produces a crack rather than an explosion. Steel tanks are more negatively buoyant than aluminium tanks of equivalent capacity and require less lead weight. A plus sign after the hydrostatic test date indicates the tank is approved for a 10% overfill above its rated working pressure.

Dive Computers, Gauges, and Other Equipment

This section also covers depth gauges, including how a capillary gauge behaves at altitude, submersible pressure gauges, dive computers and how they differ from the RDP, surface marker buoys and delayed SMBs, lift bag capacity limits, drysuit inflation gases, and the basics of rebreather design. Each topic has its own study notes page linked below.

Practice Questions

Once you have worked through the study notes, test yourself with the equipment practice exam. The questions follow the same format as the PADI IDC and IE written exams.