Posted by Jim Hoffmann on December 19, 2000 at 14:37:18:
Regulator Failure Points and Regulator Theory
One of the key pieces of life support equipment is our Scuba regulators. Kendall ask me in another post to write about Regulators potential failure points. So here are some problems I have seen in the last 31 years and some regulator theory.
I don’t think that any discussion of Scuba Regulators can be done without some regulator theory.
The First Stage: First Stage values function is to reduce the high pressure air from the tank to an Intermediate Pressure (IP) before it flows through the regulator to the low pressure hoses, this pressure is usually 120 to 145. There are two categories of 1st stages, balanced and unbalanced. The balance 1st stage works mechanically to regulate the Intermit Pressure (IP), the unbalance regulator works off the tank pressure to regulate the
IP. The problem with unbalanced regulators is that when you get deeper or the tank pressure drops so does the IP ( which makes the regulator harder to breath). Most of the regulators sold today have a balanced 1st stage, but there are still lots of unbalanced
units still on the market.
There are three types of First Stages on the market today, a balanced piston, a balanced diaphragm, and an unbalanced piston. Almost all the balance piston regulators today are
copy’s of the Scubapro Mark 5 , almost all balanced diaphragms we see today are copy’s of US Divers Conself, the unbalanced regulators are copy’s I think of an old Healthways design (1960’s?). I have always liked the balanced piston 1st stages, they have fewer
moving parts( 2) and seem to give more volume then the balanced diaphragm. The balance diaphragm is easy to repair and tune, but has up to 10 moving parts and doesn’t give the same volume. The unbalance piston has 2 moving parts, it’s simple and works good in shallow water at high tank pressures.
Failure Points: Almost all the 1st stage failures I have seen have been from poor maintenance or bad parts from the manufacturer. There is nothing you can do about the manufacturer , but you can keep the maintenance up on your regulator. Here are something’s to look for on your regulator: what does your filter screen look like(is it
green, red, white, if they are, have the reg. checked) I have seen filters so plugged up with rust that they froze the 1st stage, Is your 1st leaking air ( you and your Buddy should do a bubble check in the water before you make your dive)if it is,where is it
leaking from and how much, this maybe a reason to terminate your dive (I know that most Sherwood 1st Stages leak air out of there one-way bleed value, but that not what I’m talking about). Take a look at your low pressure and HP hose fittings the LP and HP hoses are potential failure points. If you have hose protectors, you should pull them away from the hose fitting so this area can dry out. You should never have a hose protectors on your HP hose. The HP hose will usually balloon at the fitting before it blows, (and they
all blow) if you have a hose protector on this hose you can’t see it. Your pressure gage spool is another potential failure point ( this is the hollow tube that go’s in-between the HP hose and the pressure gage, it has O-rings on both sides of the tube and seals off the
HP hose and gage)if this not maintained it will seize and brake off (if this happens UW you will lose lots of air, fast). One last thought on this, I think that the DIN connector is a better fitting then the Yoke . The DIN captures the tank valve O-ring better then the yoke and is more streamline.
Second Stages:There are two categories of second stages the downstream balanced and downstream unbalanced. The pneumatically balanced downstream second stage was developed by Scubapro in 1985 (G250) and has become the standard for easy breathing
regulators. The balancing is accomplished by the incoming air pushing equally on both ends of the poppet . With the air balanced a lighter spring can be used for response smoothness and minimum breathing effort.
The unbalanced downstream 2nd stage are simple lever and poppet assembles. When inhalation vacuum begins, the diaphragm is drawn inward, depressing the lever and opening the poppet against the spring. Air then flows through the aspirator into the
breathing chamber as long as the inhalation continues. The unbalanced downstream 2nd stage has been around for a long time. But they don’t give you anywhere near the volume of gas or the smoothness of breathing that the balance units do.
The term downstream indicates that the valve opens in the same direction as the air flow for the first stage.( there are also upstream second stages and tilt valves , we can discuss
them at another time).
Failure Points : I think that 2nd stage failure points fall into 3 catagorys; to much air, not enough air, or water leaking in the 2nd stage. If your regulator is free flowing (to much air) there could be a number of things wrong: to high of a IP (reg. needs an overhaul), sand, salt build-up(you need to clean you reg. better take it to a dive shop and have them show you how to open it up and clean it), if you have a viva system on your reg. it may cause the reg. to free flow on the surface when it’s out of your month(turn it off).
If your regulator is hard to breath it could be happening because the regulator is poorly tuned or maybe that just the way it breaths ( there are allot of poorly engineered regulators on the market today, some just don’t breath good when you put a load on
them, you should buy the best breathing reg. on the market , price should not make a difference with your breathing machine).
If your regulator is leaking water, it could be caused buy one of five reasons. Number one reason is a ripped month piece, number two is a hole in the diaphragm( that’s under the purge valve), number three is an exhaust valve pulled inside the housing, number four is you are swimming upside down, and number five is you are breathing from a side breather( Prosidon, or an Omega). There is more but I think I’m going to quit, this has gotten way to long.
I hope that this post helps some of you understand a little bit about how your regulator works and helps you to recognize some of the potential failure points(so you can do something about them).
Jim Hoffmann
Scuba Toys