Demystifying Regulator Repairs / How are they tested?

When you decided to purchase your regulator did you want the opportunity to “hook it up to a tank and test it”? While this might provide you some comfort with the regulator’s ease of breathing and general performance characteristics, its only a snapshot of the equipment’s operating condition at one atmosphere absolute (1 ATA) or a simulation of how the regulator will probably breathe at the surface. Wouldn’t you prefer to know the performance characteristics of your regulator during high demand conditions? So how about flowbench testing?

The flowbench is an outstanding machine designed to increase the overall efficiency of our service department. We use it to test all new regulators and tank valves that leave our facility and to evaluate other regulators and tank valves which are in for servicing. We would like to assume that every regulator, which comes from the “factory”, is in ideal working condition, however, for many reasons this is simply not the case.

So how does a flowbench operate? On our flowbench, or more specifically an A.I.R. Flow Analyzer and H.P. Manager, breathing resistance is measured in inches of water pressure on a Magnehelic Gauge which simulates the regulator performance at depth. The Magnehelic Gauge is connected to the lower orifice of a Flow Meter via a flexible plastic tube. The function of the Magnehelic Gauge is to measure the vacuum/pressure differential generated by air flow inside the Flow Meter. This vacuum/pressure is measured in inches of water (“H2O) and determines the A.I.R. (Atmospheric Inhalation Resistance) of the regulator at various flow levels. Each unit of measurement (inch of water) is equivalent to the amount of respiratory work required to draw water one inch up a soda straw. Generally, for most modern regulators, in proper working condition, average initial inhalation resistance, or cracking effort, is 0.7 to 1.4 inches of water. Values under 0.6 inches suggest over sensitive second stage calibration or excessive staging pressure. Those in excess of 1.7 inches indicate very hard breathing probably due to second stage contamination, worn parts, improper calibration or insufficient staging pressure. Octopus second stage regulators, however, are typically calibrated to the high side of this range to prevent unwanted air seepage or accidental free-flow situations.

Although these initiation values may seem trivial since they are rather small numbers, one must realize that in most cases the second stage actually determines the degree of respiratory work experienced by the diver. For example, a regulator initiating at 1.6 inches of water resistance is breathing twice as hard as one cracking at 0.8 inches! In other words this regulator is operating at only one-half of its design potential while requiring twice the respiratory work from the diver. Would you be satisfied with your car if it provided only one-half of its rated gas mileage or always operated on four cylinders instead of eight?

Once initial inhalation resistance has been satisfactorily determined, we increase the airflow until a steady high flow issues from the regulator. We continue to increase the standard cubic feet per minute (SCFM) flow until the float in the Flow Meter reads between 10 and 15 SCFM and monitor the breathing resistance at high flow from the Magnehelic Gauge. For example, if a regulator activates at 0.8 inches, ideally its resistance at flows of 10-15 SCFM should be 1.6 inches or less, that is doubling of initial value. This testing is actually performed at various intervals from the initial inhalation resistance to 5 SCFM, 10 SCFM, 15 SCFM, 20 SCFM and 25 SCFM at both Hi-Test values (3000 psi) and Lo-Test values (500 psi).

Many modern regulators will easily exceed the specifications given above. Certain models may show very little increase in breathing resistance as flow increases. For example, a regulator may initiate at 1.2 inches and show only 1.5 inches at 10 SCFM. In general, this is considered to represent superior performance since it suggests that the diver will experience very little increase in breathing work as exercise and depth increase. Certain super-flow regulators often show a decrease in inhalation resistance as flow escalates because their aspirator systems develop high vacuum assists. We are reluctant to draw any linear conclusions regarding the correlation between the atmospheric flow of a regulator with the flow at depth. Increasing the density of the air and the intermediate pressure (by testing the regulator in a pressurized chamber) will produce nonlinear results in regard to both the flow and inhalation effort.

Occasionally a regulator is found which meets the limits for initial inhalation resistance but not for resistance during flow. Causes of this are often attributable to the first stage and typically include insufficient intermediate pressure resulting from improper calibration or a weak spring. An incorrect high-pressure seat or push pin in diaphragm type regulators will also cause this effect. In the second stage, a loose or warped low-pressure seat, a convoluted diaphragm, incorrect calibration, misaligned venturi, heat sink or aspirator vane could also be the cause.

Understanding Flow Tests: What do these flow measurements really tell us? If a diver could breathe at a rate of 10 cubic feet per minute at the surface they would empty a common 80 cubic foot tank in 8 minutes. Comfortable swimming on the surface (one atmosphere absolute) actually requires approximately 1 cubic foot of air per minute. Therefore, 2 cubic feet would be consumed at a depth of 33 feet (2 atmospheres absolute), 3 cubic feet at 66 feet, etc. (remember Boyle’s Law?) To use 10 cubic feet per minute the diver would have to be swimming at about 300 feet !!! Although the average diver will never see depths of this magnitude, it should certainly give them a warm and fuzzy feeling for the superior performance of their regulator within the confines of recreational depths.

What does all this mean: Dive facilities that repair regulators without flowbench testing or technicians with minimal flowbench experience can easily miss many of the items discussed because they show up only under conditions of high air delivery. Even initial breathing resistance tests do not always detect such malfunctions. Without flow profiles, you are essentially testing regulator performance at surface level only (one atmosphere absolute)! Many repair facilities totally “gut” every regulator which they service and then replace all major parts. They claim they return a repaired product that is in factory new condition. While this lessons the probability of any faulty repair, it does not totally eliminate the possibility of returning an improperly functioning regulator to the customer. Although all equipment manufacturers have specific parts that must be replaced during annual service, replacing all parts regardless of condition is an expensive approach to scuba repair and speaks poorly of a facilities diagnostic capability. In addition, without flowbench testing, it provides little or no documentation that the repaired unit could really sustain a diver underwater and since most manufacturers apply a flow test to all outgoing regulators, it does not put out a factory new product.

So how about a Life Support Systems Service Technician Course?

Click HERE for detailed information on SCUBA Tools and Diagnostic Insturmentation.

Breathing Machine (Flowbench) Standards and Work of Breathing Criteria:

The three most commonly accepted standards for breathing machine requirements are:

U.S. Navy Class B: At 132 feet with 1,500 psi supply pressure and 25 breaths per minute of 2.5 liters, the regulator’s work of breathing (WOB) needs to be less than 1.4 joules per liter.

NOTE: Joule is the absolute meter equaling the unit of work or energy required. One joule is equal to approximately 0.7375 foot pounds.

European Standard (CE): At 165 feet (50 meters) with 725 psi (50 bar) supply pressure and 25 breaths per minute of 2.5 liters, the regulator’s WOB needs to be less than 3.0 joules per liter.

U.S. Navy Class A: Able to pass the same criteria as Class B, but at 198 feet.