Inspection while unpressurized
1. Inspect each stage for external corrosion or physical damage. Look for signs of dry rotted rubber or cracked plastic. Examine the hoses to ensure the cover is intact and not dry rotted. Pay particular attention to the hose fitting crimps for any signs of damage or hose kinking.
2. Check each hose connection to ensure that it is at least hand tight. This is an essential check after service or reassembly, and a good check to make each diving day.
3. Inspect the first stage inlet filter for particulate matter. Discoloration of the filter may indicate water intrusion into the first stage.
4. Watertight checks verify the integrity of the second stage. A good tight first stage dust cap is required to perform the watertight check. Alternatively, connect the regulator to a tank but leave the valve closed. Draw a breath on the second stage and hold vacuum for a few seconds. Don't draw too hard as it could collapse the exhaust valve and cause a leak. Does the regulator hold vacuum? If so, then it's probably watertight. If the regulator fails this check there may be a leak in the exhaust valve, the diaphragm, a case seal, or through a crack in the case itself.
Inspection while pressurized
5. Pressurize the regulator and depress the purge slightly. If you have to depress it more than a very slight amount before airflow starts, the lever or orifice may be improperly adjusted.
6. Check for air leaks while pressurized, look and listen for leaks. Then turn the tank valve off but do not purge the reg. Note the pressure on the SPG and leaving it undisturbed check again in 5 to 10 minutes. The pressure should be close to the original value. A drop of less than 400 psi is no big deal, but a large drop in pressure indicates something is leaking beyond the normal limits. If the leak is so fast that you can see the needle drop, the leak is probably large enough to warrant fixing before use. To locate a leak, the definitive answer comes by submerging all parts of the regulator in a water tub, pool, ocean, or whatever is handy. If you don't have a handy ocean, pool, or suitable tub available use a paintbrush to apply a dish soap & water solution and look for bubbles. Check the first stage, second stages, the pressure gauge, and all the hoses paying special attention to the fittings. Look for bulges in the hose cover. Check every hose connection as well as all around the first stage. Watch the second stage mouthpiece and exhaust for bubbles.
8. While we're in the water, we can check the second stage's cracking pressure. Fortunately a partially filled kitchen sink will suffice for this check. Immerse the pressurized second stage with the mouthpiece up. Air should begin to flow before the regulator gets more than 1 1/2 inches deep. If the mouthpiece is submerged before the regulator starts to flow, the cracking pressure is probably too high.
9. Monitor the regulator while pressurized for a few minutes. If the second stage begins freeflowing immediately after being purged or breathing from it, the second stage most likely is in need of adjustment or service. On the other hand, if the primary second stage or octopus begins freeflowing several seconds to a few minutes after being purged, intermediate pressure (IP) creep may be indicated. This points to a problem with the first stage that should be corrected.
10. Intermediate pressure check. Get a scuba regulator intermediate pressure gauge from an online source such as Vintage Double Hose, Dive Gear Express, Northeast Scuba Supply, or a variety of other vendors.
Find out what the IP range should be for your regulator (most are ~ 135 +/- 10 psi.) Connect the regulator to a tank and pressurize the system. Connect the IP gauge to the LP inflator hose, and lightly press the purge a few times to "cycle" the regulator. The IP should dip whenever air is flowing and immediately return to the acceptable range and remain steady. Leave the regulator pressurized with the IP gauge connected for several minutes to check for slow IP creep. If the IP tends to climb, that indicates a problem with the first stage and must be corrected.
It should be noted that the IP of balanced and non-balanced first stages react differently to changing tank pressures. Balanced first stages should keep a relatively constant IP over the entire range of tank pressure. Any significant changes in the IP indicate a first stage problem. The IP of non-balanced first stages will vary up or down by several PSI as tank pressure varies. The amount and direction of the change varies with regulator design. The important thing to keep in mind is the IP should not creep after lock up, and stay within the manufactures specs.
11. A tiny bit more advanced-but again, omit it if you're not comfortable. It's a good idea to learn how to open your second stage to clean it. Remove the second stage cover and diaphragm to inspect for any corrosion, damage, sand or any other contaminants. Remove foreign matter as necessary. Check the exhaust valve to make sure it's seated correctly and no obstructions are preventing it from sealing. Hold the main diaphragm up to a light and inspect it by slightly stretching it and looking for pinholes or other defects. Replace it if any discrepancies are found.