Two Hose Regulators - 2400 or 3000 psi?

[admin]

There has long been a debate about whether you can use your US Divers DA Aquamaster or Royal Aquamaster with 3000 psi tank pressure. I'm well aware that around 1972 or 73, US Divers finally put a stronger yoke on their Royals, and I'm assuming that these regulators were rated for 3000 psi (about 205 bar). But what about the older models? In regards to high pressure, there is not much difference between a maximum of 2400 psi and 3000 psi. And I've never heard of a regulator yoke breaking when used with 3000 psi. I would guess that when US Divers designed the yokes of the 1960's, they were probably stress tested to way beyond 3500 psi or more. Also, the DA Aquamaster has a Teflon high pressure seat, just like ones used in most modern regulators. The old Royals had a rubber high pressure seat, and it didn't stand up as well as the Teflon in the DA. But the Royal seats can be replaced with the newer Conshelf Teflon seats. Maybe the high pressure seat spring needs to be stronger for the higher pressures?

I would like to hear from any of you who might have an opinion on this subject. Has anybody been using their Royal or DA Aquamaster with 3000 psi? For a number of years? Any failures or problems? What about using other models of two hose regulators with 3000 psi? I am aware that the late model Nemrod Snark III was designed for 3000 psi.

Thanks!

[Michael Warren]

I have been using a Spirotechnique mistral for about a dozen dives per year for the past 5 years on pressures up to 200 bar. I replaced the a clamp for a modern clamp rated at 3000 psi. This has the added benefit that the Mistral could be used on modern pillar valves

[stuart jefferies]

There is no doubt that the internals of most two hose regulators are perfectly capable of working at higher pressures. The excepitons being the single stage downstream models, that will freeflow until the tank pressure is lowered.
Having said this it is the A clamp that will suffer. Some of these clamps , namly early USD and Nemrod were manufactured quite thin , while others were stronger but narrower.
I have a few A clamps that are seriously distorted, because they have been used at too high a pressure.
I believe it would eventually cause metal fatigue. I have also put regulators onto 200-220 bar and watched the clamp change shape.
Personally I use 150 bar, but have twin tanks which to compensate.
Changing over to stronger and larger A clamps is also ideal. Anyway these are my thoughts on the subject.

[Linda]

A handy link for people like me who need help converting bar/psi...
www.chromatography.co.uk/TECHNIQS/Other/Pressure.htm

[Bart]

Since Dan recently serviced my US Divers Royal Aqua Master regulator (1970 model) in June 2003, I've used it on 15 tanks (3000 psi). This model is prior to US Divers' revamping the yoke in 1973. I find no evidence of strain, and it has worked flawlessly.

I have found this double hose regulator is easier to attach and remove from the valve using the old style valve with the larger "O" ring. I don't know why this would be different than with my US Divers Calypso "J", and IV (1969, 1970, 1973 and 1977 models) single hose regulators, but it is. Seems like there is a vacuum with the double hose at the connection even when it is purged. I don't have this problem using valves with the larger "O" rings. Dan, let me know when you start servicing vintage valves!

[Captain]

This is a copy of a post I wrote to Terry a coupe of months ago. My knowledge on the yoke redesign was more to accomidate the banjo adapter than strength. Earlier yokes were too short to allow the banjo adapter to fit between the regulator and valve.
Previous post-
In the 50's and 60's before aluminum tanks became common in sport diving the Navy was using double 80 cubic foot aluminum tanks with an inverted 1/2 NPT neck rated for 3000 psi. Because of the non-magnetic property of aluminum these could be used when working with magneticly detonated mines. These tanks had a round bottom similar to the steel oxygen cylinders that many converted to diving use around that time.
I had some 50's era Navy manuals that picture and described these cylinders. Because of this I believe any Aquamaster of any age is safe to 3000 psi.

Tom

PS- If any of you have a copy of the March 1970 U S Navy diving manual page 345 describes these 3000 psi aluminum cylinders and page 348 has a picture of them. Notice the 1/2 NPT valve thread and the inverted neck.
These cylinders had no ICC numbers, and were not available to the public. I started diving in the late 50's and was a US Divers dealer in the mid 60's to early 70's so I have some first hand knowledge on this subject.

[Dennis]

The following is based on my observations while checking the IP pressures on my two DA AquaMasters at different tank pressures, as well as service recommendations for the mechanically similar first stage of a Dacor double hose regulator.

I don't think the yokes will break, but ......

In an unbalanced diaphragm, up-stream first stage of a DA AquaMaster, the the intermediate pressure drops as the tank pressure increases (The HP seat is held seated between the opposing forces of tank pressure and the first stage spring). So, you set the IP at a low tank pressure of about 300 psi where the IP is highest and to where the 2nd stage won't leak. At a 2200 psi tank pressure the IP will drop somewhat from where it was at 300, but still be within a normal operationg range. A 3000 psi the IP will drop further. So, a DA AquaMaster may breathe poorly at 3000 psi due to a low IP pressure. It will breathe normally once the pressure drops to 2200, and improve from there as the tank pressure goes down.

With the Royal AquaMaster it is a different story because the first stage is balanced. Keep in mind that the mechanics of a DA AquaMaster first stage are identical to that of a 1951 AquaLung. In my opinion, based on what I have seen, a DA AquaMaster, or any of the older non-balanced single-stage or two-stage regulators, should not be driven above the tank pressure that they was designed for (1800-2200 psi). The regulator's performance will decrease at a higher tank pressure and it stresses the regulator. The regulator will perform at its peak when it is used with a 72 steel tank.

[Captain]

The March 1970 edition of the U S Navy diving manual covers overhaul and repair of the DA Aqua Master. It states that intermediate pressure is to be set at 110 psi + or - 5 psi at full tank pressure. Since the Navy was using either 2250 psi steel or 3000 psi aluminun tanks what is full tank pressure is debatable but IP was not set at 300 psi tank pressure. I would also say that the Navy would have been following U S Divers guidelines.

If anyone would like copies of the overhaul instruction from the Navy manual I can e-mail them you.

Tom

[frank]

OK, I'm holding the yoke of my 1995 US Divers regulator up to the yoke of my 1962 Mistral and I see a big difference. The yoke of the newer regulator, which is stamped "3000 psi service", is half again as thick as the yoke on the Mistral. The Mistral's whimpy 3/8 USS screw has ben repalced with something that looks like 5/8 SAE. I agree with Dennis who made the previous post, the Mistral yoke probably will not break at 3000 psi but it will flex and if the O ring is in less than pristine condition it is likely to fail - probably at the worst possible time. You might put your Mistral, DA Aqua Master, etc on a 3000 psi tank 100 times and get away with it but, maybe not, its called pushing your luck.

[Dennis]

"If anyone would like copies of the overhaul instruction from the Navy manual I can e-mail them you." Tom

Hey, Tom. If you could email me those instructions I would like to see them. The instructions I have do not state what tank pressure to set the IP at.

Thanks, Dennis.

[e-mail]

[Captain]

More confirmation that the Navy used early DA's with 3000 psi tanks.

Tom

www.scubaboard.com/t41267/s.html

[SDM]

;DIt is a little know fact that in an attempt to provide the diver with more air in 1953 US Divers marketed a SCUBA cylinder rated at 3015 psi. With a + hydro which would allow a fill to 10% more providing 3,300 psi to the regulator. (I have one in my collection-like new!)

The first USN Diving manual to address SCUBA diving was part three of NAVSHIPS 250-538 dated 16 October 1956. The scuba tanks of choice were the 70 and the 90 rated at 2,150 (the 70!) and 3000 PSI, (the 90!.) The 70 was the standard civilian model SCUBA cylinder, the 90 was produced solely for the military.

The regulators of choice were the "Aqua lung" (US Divers) the Scott "Hydropak" and the Northhill "Air lung"

Therefore, It may be concluded that the regulators were designed for pressures of 3000 psi and above. HOWEVER - that was almost 50 years ago. The number of cycles and resultant fatigue can be a large factor in diver saftey.

I would think a resonable and prudent diver would seriously consider replacing the older yoke with a modern one especially designed for the higher pressures ;D

SDM

[Captain]

To put this in perspective, what is the force acting on the yoke. The force is the result of the pressure exerted on the area. The diameter if the regulator subject to pressure is .55 inches which is the ID of the "O" ring in the tank valve. The formula for area of a circle is diameter X diameter X .7854, .55 X .55 X .7854 =.2375 square inches. 3000 psi exerted on .2355 square inches is 3000 X .2355 = 712 pounds of force pushing on the regulator. At 2250 psi the force would be 529 pounds. 3000 psi sounds like a lot but when put in this perspective it isn't.
I plan to run a test to see how much if any an old DA Navy yoke deforms under pressure.

Tom

[SDM]

[quote author=Tom
"I plan to run a test to see how much if any an old DA Navy yoke deforms under pressure."


Tom

I am just a slow walking, slow talking, slow thinking, country boy from the hills of Kali-foirnia. However, I comprehend and appreciate your position.

But, I do not understand how a valid destructive test can be performed when it is performed on a test subject with an unknown history. I would assume a valid productive test would first establish the age,- (is it one of the first or one of the last produced/imported?) the cycle history, -(was is formerly owned by a week end diver or was it used every day in a training enviroment?) storage history- (was it stored in a safe place or subject to excessive temperature changes?) treatment history -(has it been dropped or abused in any way?) When these and numerous other questions related to it history are answered, then and only then it can be established as a representative sample.

Since these old beasts are ever decreasing in numbers and repair parts are becoming ever encreasingly dear and expensive, I would think that you would be better received and appreciated in the historic community if you would exhaust all other avenues of research prior to destroying even a single DA yoke.

May I suggest that you begin by contacting the parent company here in California, USD (US Divers.) The cheif engineer of USD is Shawn de Kalb @ [phone] (switch board) or E mail [e-mail]

Or perhaps you might want to contact the production or materials engineer of the maufacture of many of the USD parts, B & B in Chicago.

When these and all other leads which been generated as a result of your on going extensive investigation then and only then will your destructive testing be justified in the hearts of collectors throughout the world.

SDM

[Captain]

My intent is not to test a yoke to destruction. I want to see what is the degree of deformation or stretch between a yoke before it is attached to the valve. the amount of stretch after the yoke is tightened on the valve and the stretch once pressure is applied. If a material is not stretched beyond its elastic limit then the number of cycles have very little effect on its service life. Hydroing a tank is an example. As long as the tank returns to its original volumn its life is infinite
provided there is no rust or other mechanical flaws.
A yoke that is obviously deformed has been stretched beyond its elastic limit and would be suspect. I suspect that more yokes were streched beyond their elastic limit by being over tightened on the valve than from pressure.
I do believe that because the Navy was using these regulators at 3000 psi routinely indicates to me that it was within the elastic limit of the material.
Are you or anyone else aware of any cases of catastrophic yoke failure.

Tom