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Bryan
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DA Aqua-Master/Royal Aqua-Master difference?

Thu Aug 23, 2007 12:49 pm

The difference between the two is only the first stage and if they are replaced, the complete first stage has to be replaced. The first stage internal parts are not interchangeable.

The RAM nozzle is 1/10 inch longer than the DA and it had to be done that way to accommodate the spring block and the potential extra travel of the seat.

The spring block in the DA is just that, a stationary spring guide, nothing else.

In the RAM the spring block is the low pressure balancing chamber for the seat. It is also not stationary. It is floating between two springs to accommodate the extra travel allowed to the seat.

Other balanced diaphragm regulators do not use a floating spring block, but they then would require a deeper balancing chamber and perhaps longer stem on the back of the seat, in order to allow a stroke long enough for improved air flow.

In the case of the RAM the seat stroke was accomplished by using what can be called as a telescoping mechanism.

The springs on both regulators are also probably different spring constants, but perhaps in this application it may not be very critical. I am not sure.

Putting a RAM seat and spring block/ balancing chamber in a DA nozzle without the rear spring, IMHO, is a bad idea. It may seem like it works, but I am almost positive that the seat will bottom out and in the best case it will restrict the flow rate, worst case it could possibly jam...Luis Heros

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Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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luis
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Fri Aug 24, 2007 6:39 am

I was asked if I could put a simple description of how a balanced and an unbalanced diaphragm first stage work and how are they different.

Below are some diagrams of the Royal Aqua Master (the pictures of the parts above may also help).

The green represents the HP seat.
The gold is the spring block / balancing chamber.
The red is the high pressure air.
The light blue is the low pressure air.

Notice that inside the seat (in green) there is a thin line of light blue low pressure air. That small hole down the seat fids the low pressure air to the chamber inside the spring block (notice the blue chamber).

There is a small O-ring (shown in black) in the spring block that doesn’t allow the high pressure air to leak into the LP chamber.

The seat closes on the bottom against the edge of a volcano shaped orifice.

Notice that the diameter (and therefore the area) of the orifice on the bottom is the same as the diameter of the chamber on the top of the seat assembly. This allows the seat to move up and down with the same area of low pressure air on top and below. The pressure times the area produces a force and since they are equal they balanced each other.

The high pressure of the tank does not affect the opening or closing of the valve seat. The HP air only presses around it not up or down on it.

The seat motion is only controlled by the push pin which connects the diaphragm to the seat and the springs (the pin is not shown, but it would be in the white area and then down to the diaphragm). The diaphragm motion is only affected by the low pressure air, ambient pressure, and spring forces. The IP is therefore kept constant independent of tank pressure.



The Aqua Master:

The big difference in the Aqua Master is that there is no balancing low pressure chamber behind (on top of) the seat. The spring block in an Aqua Master just has a hole through it and no sealing O-ring. The seat has no hole down the middle as in the RAM.

A portion of the seat is exposed to LP air (inside the boundary of the volcano orifice), but the back side of it is being pushed by a constantly changing tank pressure.

The forces on the top and the bottom of the seat are not balanced and will change as tank pressure changes. Therefore the intermediate pressure which controls the motion of the 1st stage diaphragm will change to compensate for tank pressure changes.
Since the valve motion is up stream (into the high pressure), a lower intermediate will close the valve when the tank pressure is high (at the beginning of the dive). As the tank pressure goes down, a higher intermediate pressure will be needed to push the diaphragm and close the valve since the tank pressure is not pushing down on the seat as hard.

In a unbalanced piston first stage the seat moves down stream so the IP change is reversed as a function of tank pressure.

One method (used by US Divers) to reduce the amount IP change was to us a smaller volcano orifice. Since the amount of unbalance is a function of the difference in pressure times the area, by reducing the area it reduces the unbalancing forces. The problem is that is also the area of air flow. Therefore, there was a tradeoff.


Well this was longer than I planned. I just hope it is clear.
Any questions, something is not clear, or you see any mistakes (including spelling) you are welcome to send me a PM.



Royal Aqua Master (1st stage details):
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Royal Aqua Master:
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Luis

Buceador con escafandra autónoma clásica.

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Bryan
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Joined: Fri Jun 24, 2005 11:40 am
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Fri Aug 24, 2007 6:55 pm

This is from the USD service manual. If someone can do a better scan for us and can send it to me I would appreciate it!
This is the high pressure nozzle assembly on a Trademark/Broxton/Navy and DA Aqua-Master
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Doing it right should include some common sense, not just blindly following specs and instructions. .Gary D, AWAP on SB

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luis
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Re: DA Aqua-Master/Royal Aqua-Master difference?

Mon Aug 03, 2009 9:25 pm

The first stages parts of a RAM and an Aqua Master are not compatible in either direction. The Aqua Master parts will not fit in a RAM nozzle unless you machine something.

The RAM nozzle is not only longer, but it also has a step with a shoulder to support the balancing chamber. The ID (inside diameter) of the Aqua Master first stage is a constant nominal 0.500”.

The ID in the RAM first stage steps down to around 0.459” and it forms the step to support the pressure force on the back of the balancing chamber.

See drawings below:


Notice dimension on RAM nozzle / first stage drawing. The step is 0.382” below the tank valve interface surface.

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Below is the RAM and Phoenix RAM drawing/ diagram. Notice that the balancing chamber in red is seating on its support step inside the first stage body.

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Old Phoenix drawing, enlarge to show step clearly.

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Luis

Buceador con escafandra autónoma clásica.

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