Back to the SCUBA REGULATOR MAINTENANCE AND REPAIR page
From the Introduction:
Nothing wrong with that. But I'd like to encourage you to go a little further. Without taking a single tool to your regulator, or doing anything that could in any way effect its operation, it is possible, by following some of the simpler procedures in this book, to do a fairly complete check on the tune and performance of your regulator. For example, the post-service checks listed at the end of Chapter 7 can be easily done by anyone with a minimum of tools, and without opening the regulator. They are well worth doing anytime a regulator comes back from servicing, both to confirm that the shop tech didn't forget something, and as a way of getting a handle on how well that shop is doing it's job.
We all know stories of friends who headed off for that big dive trip with a freshly shop-serviced regulator. only to end up doing the dive-of-a-lifetime trying to suck air from some junkbox rental when it turned out the shop back home had screwed up. A few simple checks done before leaving home might avoid all that. The same checks are also useful in the field, when minor problems arise, to determine how serious they are, and whether the regulator needs a full service or just the immediate problem fixed.
Two particularly useful tests for the non-tech are the IP check and the water test. The former requires an intermediate pressure gauge, which snaps onto the BC inflation hose and can be made for under $10. The latter just a sink, bucket or ocean of water in which to immerse the regulator. But the two of them together can give a very accurate picture of the regulator's internal state of health.
From Chapter 3 GETTING STARTED:
Every so often I hear someone refer to overhauling a regulator as "throwing in a parts kit". Usually they are speaking facetiously, but sometimes I can't help but suspect that they are betraying how they really feel about the process - that they regard it as essentially a matter of removing the old parts and putting in the new ones.
It is not! Overhauling a regulator is a matter of taking it apart, cleaning the parts that will be reused, inspecting them carefully to be sure that they can be reused, then relubing and reassembling. The new parts are almost incidental. Sure, it's good practice to replace them as long as you have the thing apart, but 90% of the parts that are replaced servicing a well maintained regulator are perfectly good and may have years of life left in them. If the tech just disassembles the regulator and puts in the new parts, there's always the chance that lurking corrosion, contamination, or worn or damaged components may cause it to quickly fail again.
One tech I know, who works for a manufacturer, and sees a lot of regs that other techs have screwed up, has a name for these not-exactly-overhauls: "underhauls".
Oddly enough, this isn't nearly as likely to happen with regulators serviced at home. I think the reason is because, if one doesn't have access to unlimited parts kits, one is much more likely to try to make up for it by lavishing extra care on the regulator. Also, the individual owner doesn't have the time pressure to deal with that a shop tech does.
Most of the time the throw-in-a-parts-kit school of techs get away with it. Regulators - most of them, that is - are pretty forgiving, and most of the time they don't really need servicing that badly anyhow. OK, they may not work quite as well, or hold their tune as long, as they would if they'd been properly servicing, but most divers aren't going to notice. The tech doing this kind of work will probably get a lot more comebacks than a more scrupulous tech. But once again, who's keeping score?
However, when one of these techs encounters a regulator which is not tolerant of this kind of servicing, or a regulator which has some subtle defect that a routine rebuild won't cure, the fun begins. An angry owner brings the regulator back, and maybe a horror story along with it. Then the tech may buckle down and do the job right - if he knows how. Too often, though, he'll scratch his head, throw in another parts kit, and, when that doesn't do the trick, mutter about "defective batches of parts".
This is a really common scenario with Poseidons, which do not suffer fools gladly. A inexperienced tech will do an underhaul on one, and either fail to clean it properly, fail to notice that the piston is shot, or damage the HP seat or HP seat O-ring putting them in wrong. The result, a leaky seat and IP creep. The moral? If you are going to overhaul a regulator, do it right or don't do it at all. Don't get trapped by the "throwing in a parts kit" mindset into thinking that that's all you've got to do. Clean it right, and inspect it well.
From Chapter 6 PROCEDURES AND TECHNIQUES:
The suction required to open the demand valve on the 2nd stage is referred to as the "cracking pressure". This is usually given, in manufacturers' tech and sales literature, in inches of water or cm/H2O - that is to say, the amount of suction that is required to lift water in a tube one inch or one cm. The manufacturer will usually specify the tank pressure at which the test should be performed. High performance regulators typically have advertised cracking pressures in the 1/2" to 1 1/2" (13 to 40 mm) H20 range, though in real life they usually run a tad higher. Cheaper/older regulators may go all the way up to 6" (100 mm) H2O.
It's important to distinguish between the sales literature and the service literature when deciding what is acceptable - a typical regulator will often have the cracking pressure listed in the sales lit as, say, 1/2"H2O (13 mm/H20), while the tech literature will list anything from 1/2 to 1 1/2" (13-38 mm/H20) as acceptable, which means that it may be almost impossible to tune it to 1/2".
Serious regulator techs usually have a Magnehelic gauge just for checking the cracking pressure. It's also possible to measure it using a simple homemade manometer. The gauge is hooked to a regulator's mouthpiece via an adaptor, and the tech inhales gradually increasing the suction until the demand valve cracks. It's pretty easy to detect by feel when the stage cracks and the air flow starts, but if the IP gauge is connected, the cracking point can be more precisely tracked by noting when the IP gauge starts to drop. It's a lot easier if the IP and the cracking pressure gauge are side by side.
Having said all that, I should add that it's not worth getting too hung up on cracking pressure. Cracking pressure alone, especially when measured on the surface, doesn't really tell all that much about the regulator's performance in the real world, since some regulators have a very low cracking pressure, but don't deliver much air at that pressure. Others may have a higher cracking pressure but better delivery of air once they do crack. And then, cracking pressure and WOB generally increase with depth, so tests done dry at surface ambient may not really tell you much about how the regulator performs in the water.
That being the case, you can probably tell almost as much about a regulator, especially if it is one you are familiar with, by taking a few breaths from it and seeing how it feels as you can with a manometer or Magnehelic. There's also little to be gained in attempting to adjust the regulator to obtain a cracking pressure that is lower than the regulator manufacturer specifies. Some techs like to boast about how low they can get it on this or that regulator, but tuning a regulator this way usually will only make it finicky and prone to free flow, without improving its performance significantly.
The Water Test
A much easier test of cracking pressure, that is endorsed by many of the regulator manufacturers, can be done simply by immersing the pressurized regulator 2nd into a bowl, bucket or sink of water, holding it so the diaphragm is facing down and the mouthpiece is above the water and seeing how deep it will go before it cracks. The distance between the diaphragm and the surface of the water, measured in either inches or cms, will be the pressure in inches/H2O that the regulator is exposed to. Since most 2nds have about 2" (50 mm) between the diaphragm and the opening of the mouthpiece, any decent regulator should start flowing before the mouthpiece is submerged, and a freshly overhauled high performance regulator should start flowing with the 2nd only slightly submerged.
If you've submerged the regulator as deep as you can without flooding it through the mouthpiece, and it still isn't flowing, there's probably something wrong. You can try to find out how wrong by covering the hole with a thumb to trap some surface ambient air inside, and immersing it deeper until it cracks, or make a tube that can be jammed into the mouthpiece as a "snorkle" to allow immersing the regulator deeper. It's the distance from the diaphragm to the surface that counts - when testing a sidebreather like a Cyklon, Odin or Omega this way the regulator should be held so the diaphragm is parallel to the surface, or as close to it as possible
This is not a terribly precise test, especially with a sidebreather, since it is hard to know exactly where the diaphragm is at rest from the outside, and this can easily introduce a 1/2" (13 mm) or so error into the results in either direction. Still, considering the tolerances with which most regulator manufacturers list the cracking pressure it's accurate enough. Also, it can be done anytime when there is water handy - such as at the start or end of a dive - should you feel that your regulator isn't performing as it should.
From Chapter 9 TOOLS:
INTERMEDIATE PRESSURE GAUGES
Checking the IP requires a pressure gauge that can easily be attached to one of the regulators LP ports. The basic IP gauge is simply a decent quality pressure gauge mounted on an adaptor so it can be screwed into an LP port. Since gauges usually have tapered NPT threads, this calls for an NPT to 3/8" male straight thread adaptor . These adaptors can sometimes be found in a dive shop or MO catalog, otherwise they are easy enough to make as described in the APPENDICES.
A 0-300psi (20 bar) movement is ideal since most gauges are calibrated to read most accurately towards the middle of their scale. Commercial IP gauges are usually fitted with a combination blow-off/bleeder valve set for 200 psi (13 bar) to protect the gauge from overpressure, allow cycling the regulator for testing, and bleed the pressure off when finished. They also offer some protection for those times when an IP gauge is accidentally hooked up to an HP port! For casual use leaving a 2nd stage attached will accomplish the same thing, or the gauge can be fitted with a pop-off valve of some sort.
Often you'll see IP gauges combined with a 2nd stage adjustment tool. These cost about $80, and can be time savers if you do a lot of regulators, but since some regulators use non-standard hose fittings, and many don't require an inline tool to adjust the 2nd, the basic gauge will still be needed even if one has a combo.
Another common refinement is to put the gauge on a male BC QR fitting so it can be quickly snapped onto the BC inflator hose. These are great for wowing dive buddies with on-the-spot checks in the field, but not quite so useful in the shop since it is often desirable to check the IP pressure without all the hoses installed. An IP gauge with a BC QR fitting won't normally need a safety/bleed valve, since it will be used with fully assembled regulators with a 2nd stage attached.
Back to the SCUBA REGULATOR MAINTENANCE AND REPAIR page
Back to Airspeed Press main home page