Dive Gear

What They Didn't Tell You At The Shop

By Jim Hoffman
Scuba Toys
Cypress, CA

Note From seahunt...
Look in any scuba magazine and you will see lots of up to the minute gear reviews. What you won't find is a gear analysis. Calling on his many years in the industry, Jim has created a description of dive gear that won't be found anywhere else. This tells what a diver should know about the development and nature of the gear they use. It also tells the weak points in that gear and how they can be avoided.

There are 2 parts to this:
Part 1. - BC Failure Points
Part 2. - Regulators

Part 1. BC Failure Points

One of the safety issues that many divers fail to recognize is the potential of Failure Points in their life support equipment.
When buying Diving Equipment, divers seem to be looking more at the features, price, and color then anything else. Instead, maybe they should be looking at the design and the practically of the product.

After diving for over 30 years and taking care of Scuba Toys rental department for the last 26 years, I have seen lots of equipment failure points. This is a discussion of the potential failure points with BC Systems.

BC's have the potential for the lots of failure points.

Rapid Dump Valves on the elbow joint of the oral inflation hose has a high potential for failure. I have seen many of the "RE" values fail (when they fail you can't get any air in the BC) this is a high maintenance accessory that you don't need.

Overpressure Relief Valves also has a high potential for failure. Most have failed because of poor maintenance. You need a relief valve on your BC, but you don't need 3 of them like some of the new BC's have (the less holes in the bladder of your BC the better off you are).

Power Inflators have always been one the weakest points in our life support equipment. They have a high failure rate and need lots of maintenance. Most cannot be fixed. When they start leaking or self-inflating, you need to buy a new one.

Poorly designed integrated weight release systems.
These seem to fall into two catagories either the weights fall-out to easily or you can't get them out at all. This is something that the diver needs to try out before they buy the product.

Quick release buckles on your shoulder harness. I have seen many plastic buckles stepped on and broken. Most of todays BC have Quick release buckles, the only way to eliminate this potential failure point is to go to a back-plate with nylon webbing.

There are potential Failure Points in all of our gear, but what we need to do is to recognize that they are there and eliminate them. The color, features, and price makes little difference when a piece of Life Support Equipment fails on a dive.

Part 2. Regulator Failure Points and Regulator Theory

One of the key pieces of life support equipment is our Scuba regulators.
I don't think that any discussion of Scuba Regulators can be done without some regulator theory.

The First Stage

The function of the First Stage 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 copys of the Scubapro Mark 5, almost all balanced diaphragms we see today are copys of US Divers Conself. The unbalanced regulators are copys 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 some things 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 may be a reason to terminate your dive (I know that most Sherwood 1st Stages leak air out of their one-way bleed value, but that is 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 guage spool is another potential failure point (this is the hollow tube that goes in-between the HP hose and the pressure guage. It has O-rings on both sides of the tube and seals off the HP hose and guage). If this not maintained it will seize and break 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 streamlined.

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; too 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 regulator 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 alot 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 regulator 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
  • 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).

    So which regulator should I get then?
    I like the ScubaPro G250/Mark 20 better than the G500. I always felt that the G500's were made more from a marketing stand point than an engineering one (Scubapro's answer to the Atomic regulators).
    For a smaller light weight second stage, the Atomic B1-T2 would be my choice. If you look at the engineering of the G250 and the T2 you would find that they are almost the same. This is not surprising since both were designed by the same guys.
    One other note about Atomic: Atomic is the only regulator manufacturer that I know that test the breathing resistance of each regulator they sell (at a depth of 150 ft. and records it).
    If you look at price, the B1-T2 is about $50 more then the G250/Mark20. The G250 and the T2 are two of the best Regulators on the market today. Either one would be a good choice.

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