Understanding the Intermediate Pressure Gauge

[redacted]

Very easy… Think of a Mk-2 with a larger piston or just larger air flow path in the piston. Then just attach your LP hoses at the end of the cap instead of near the tank connection.

In addition to the Deepstar II, I believe there are some vintage European regulators of similar design.


The Deepstar II was a very unique unit. The entire piston was made out of Delrin (or some similar plastic). It did have a replaceable seat on the piston, but the seat was in a female cavity in the piston. The volcano orifice in the main body was in a male structure that formed the HP chamber.

Because the HP chamber was surrounded by the piston, there was no easy way to put an HP port on this regulator. In the late 60’s early 70’s when this regulator came out, not having an HP port for an SPG was the kiss of death. My understanding is that people and US Divers actually lost their jobs by allowing this design to go out into production.

I think I have it. The seat is still in the end of the piston. But the LP hose has a (or all) connections in that cap with a large enough conduit to allow sufficient air flow.

 

[Luis H]

I think I have it. The seat is still in the end of the piston. But the LP hose has a (or all) connections in that cap with a large enough conduit to allow sufficient air flow.

Yep…

Here is a diagram of it.

The thing is that now-a-days we are used to seen most regulators just been a copy of each other and we often forget that there are many other ways to design something with the same function.


Sorry for the highjack.

 

[halocline]

The Brut is an unbalanced piston design.

The Sherwood Magnum (and I believe all the other Sherwood) are balanced piston by definition and as specified by Sherwood on their website.

The definition of a balanced first stage is one that provides a constant IP independent of tank pressure. The mechanical and pneumatic forces inside the first stage (that open and close that first stage) are balanced and do not get out of balance by the changing tank pressure.

I have seen IP test on Sherwood balanced piston regulators with changing tank pressure and I can guaranty you that the changing tank pressure is not unbalancing the system. The IP is as constant as the any regulator I have seen.

In a Sherwood the so called “floating volcano orifice" is actually mounted on a secondary pneumatic piston. The air pressure behind the floating orifice is what balances the system. The system as a whole is balanced.

Don’t think as the primary piston just by itself since the piston is just part of a balanced system. It may look like the piston of a Scubapro MK-2, but as a system it works different.


It doesn’t have to be a flow through piston to be a “balanced system”. And BTW not all flow through pistons are balanced either. I have a US Divers Deepstar II which has an unbalanced flow through piston.

I understand that sherwood calls it's flow-by piston first stages with the floating orifice balanced, and I don't dispute the fact that this system produces a stable IP. However, I think it's useful to think of the basic design as as the same in both the fixed orifice and floating orifice 1st stages. The difference is that the floating orifice compensates for the changing pneumatic pressure with changing mechanical pressure. This is different than true air balancing, a la diaphragm 1st stages and barrel poppet 2nds with a balance chamber. Of course you know this better than I do, and I think the argument is simply a matter of semantics. I just think it's more accurate to describe the way the sherwoods work as unbalanced, with spring compensation to stabilize IP. After all, the downstream pneumatic force is not balanced with a corresponding upstream pneumatic force.

The balanced piston flow-through design, although it lacks a balance chamber, is in my opinion air balanced because it effectively removes any significant downstream pneumatic pressure.

Of course sherwood would not bother with this sort of nit-picking and will describe their 1sts as balanced, and for all practical purposes they act the same as balanced, so again, I guess the point is a matter of wording.

 

[Luis H]

I understand that sherwood calls it's flow-by piston first stages with the floating orifice balanced, and I don't dispute the fact that this system produces a stable IP. However, I think it's useful to think of the basic design as as the same in both the fixed orifice and floating orifice 1st stages. The difference is that the floating orifice compensates for the changing pneumatic pressure with changing mechanical pressure. This is different than true air balancing, a la diaphragm 1st stages and barrel poppet 2nds with a balance chamber. Of course you know this better than I do, and I think the argument is simply a matter of semantics. I just think it's more accurate to describe the way the sherwoods work as unbalanced, with spring compensation to stabilize IP. After all, the downstream pneumatic force is not balanced with a corresponding upstream pneumatic force.

The balanced piston flow-through design, although it lacks a balance chamber, is in my opinion air balanced because it effectively removes any significant downstream pneumatic pressure.

Of course sherwood would not bother with this sort of nit-picking and will describe their 1sts as balanced, and for all practical purposes they act the same as balanced, so again, I guess the point is a matter of wording.

You don't seem to be taking into account that the floating volcano orifice is actually a moving pneumatic piston with a pneumatic balancing chamber behind it. The Belleville spring washers (cupped spring washer) provide a force that is only proportional to displacement (similar to the coil spring on the primary piston).

The mechanical spring forces by themselves are not able to compensate for a changing pneumatic force.

There are pneumatic forces on the moving volcano which can be calculated by the pressure times the exposed area (as all pneumatic forces).


I have not done a complete summation of forces analysis on a Sherwood, but at first impression I immediately saw the volcano orifice as a balancing piston with a chamber.

I don’t mean to be nit-picking, but I think there is a difference between a true balanced system and one that is trying to compensate for a varying force.


Added
If I had a nice cross section of the first stage with a few dimension, it would be interesting to do a summation of forces analysis on the system. I have done that on the Conshelf and RAM, but I have measured the inside and out of those regulators extensively.

 

[halocline]

The mechanical spring forces by themselves are not able to compensate for a changing pneumatic force.

I can't believe I'm arguing with you (and I appreciate your good nature) but the mechanical forces do exactly that; compensate for changing pneumatic force, unless I'm not understanding you correctly. As the downstream pressure on the base of the orifice drops, the cup washers expand, pushing the orifice further away from the seat on the piston, which then requires the piston to travel a little further to close the valve. I'm sure sherwood had to experiment with washers to find ones that push the orifice just enough to compensate for the loss of downstream force on the seat itself. The whole system is based on mechanical forces "balancing" or counteracting changing pneumatic force.

This does achieve exactly the same thing as an air-balanced system in which downstream pneumatic force is re-routed to provide a counteracting upstream pneumatic force (or vice versa in diaphragm 1sts), as you have pointed out and I've agreed.

I just think, for myself, it's more useful to think of the sherwood flow-by design as the same in both the fixed orifice and floating orifice regs. Maybe I'm just too simple-minded to think of them as fundamentally different.

 

[tridacna]

Best thread on SB in months. Thanks for the input everyone. This is excellent learning!

 

[Luis H]

I can't believe I'm arguing with you (and I appreciate your good nature) but the mechanical forces do exactly that; compensate for changing pneumatic force, unless I'm not understanding you correctly. As the downstream pressure on the base of the orifice drops, the cup washers expand, pushing the orifice further away from the seat on the piston, which then requires the piston to travel a little further to close the valve. I'm sure sherwood had to experiment with washers to find ones that push the orifice just enough to compensate for the loss of downstream force on the seat itself. The whole system is based on mechanical forces "balancing" or counteracting changing pneumatic force.

This does achieve exactly the same thing as an air-balanced system in which downstream pneumatic force is re-routed to provide a counteracting upstream pneumatic force (or vice versa in diaphragm 1sts), as you have pointed out and I've agreed.

I just think, for myself, it's more useful to think of the sherwood flow-by design as the same in both the fixed orifice and floating orifice regs. Maybe I'm just too simple-minded to think of them as fundamentally different.

Well, as I said above, I have not done a full analysis of the Sherwood, but I am sure that Sherwood has. They didn’t reach at the number and stack of Belleville washer by trial and error. I have personally designed spring system using Belleville washers and one of their beauties is that they are fairly predictable within their working range (see note).

You are absolutely correct in that all the springs (both the coil spring and Belleville washers) play a part in the summation of forces. And I am glad to see that you agree that there are several pneumatic forces involved.

Your description of the Belleville washers pushing the orifice against the pneumatic tank pressure behind the orifice can just a well be described as the pneumatic tank pressure force pushing the orifice against all the springs and piston seat to provide a balancing force for a constant IP.

The bottom line is that the springs (coil and Belleville) and the pneumatic forces all add up to provide a balanced system not affected by tank pressure. That is the difference between a balanced and an unbalanced first stage.

Having multiple springs a balanced or unbalanced regulator is nothing new. The can be in different areas and they can work together or against each other. For example, the old Calypso IV had springs on both sides of a flow through balanced piston.

The area behind the volcano orifice is just a different looking balancing chamber.



What do you mean by “you can’t believe you are arguing with me”… It is not the first time… and I am sure it won’t be last time either … and I surely don’t mind. I am very capable of making mistakes or overlooking something. At the same time I am aware that sometimes my explanations may not be always as clear as I wish they were.

In this case I think we have a basic agreement on the mechanics. All I am saying is that by putting a balancing chamber behind the volcano orifice obviously changes the operation of the system. The main piston itself is just part of whole system and just because the individual part can be used in another system you still need to analyze each system as a package… Sherwood surely did (and they are pretty clever).


BTW, design by trial and error was very common at one time (probably long before Emile Gagnon started collaborating with JYC), but it is much more cost effective to analyze and do calculation in advance before cutting any metal. That is not to say that we don’t do some final tweaking at testing, but it is normally kept to a minimum. In some cases the calculations are too complex (or just plain impossible) and testing is the best, but not for a basic semi-static pneumatic system like this.


Note: If you do a Google search on “Belleville washers” you will find all you wanted to know but were afraid to ask. They are a great mechanical tool sold by several companies (they are covered in any basic mechanical engineering book).



Added:
I was re-reading your last sentence about “flow by designs” and I can easily come up with a couple of other balanced “flow by designs”. Just for starters, the simplest one to explain would be to think of a MK-5 (or any similar design) with a hole in the seat and take the LP from there (instead of the other end). This is the simplest, but there are other ways.

I already showed an example of a flow-through unbalanced design.

My point is that flow-by or flow-through should not be at all tied with balanced or unbalanced pneumatic forces.

I know in this world were most regulators are just copies of each other that is what tends to happen, but fill that to be limiting.

 

[cbmech2]

I wanted to add that depending on what regulator you have, shimming up the spring may not be required. Some are adjusted by loosening a lockscrew and turning the adjusting ring. Could answer specifically if I knew the model you have (e.g. SRB3200, SRB 3300, etc.).

 

[Leisure Pro Brett]

Great thread! I think one of the coolest things about being a reg tech is seeing all the different ways of accomplishing the same thing. I would confidently say that both systems being compared are balanced (defined by the end function, not how you get there) but the real beauty lies in how they take 2 completely different routes to accomplish the same task. Sherwood definitely employs a few unique methods to keep their regs simple while still providing the same function (dry air bleed screw and rubber bleed valve for example).

Something also to note for the OP, when working with the hose routing on the regs if you put your primary and octo into the ports labeled PRI it helps to give your reg a boost during demanding situations. Assuming your IP gauge is mounted to the LP hose, mount the second stages to those ports and purge them both, you will see your IP rise to help compensate for the demand.

 

[Luis H]

While we are talking about Sherwood, I just thought I add some interesting points about them.

Sherwood has been around for close to a century. I am not sure, but I think they may be one of the largest manufacturer of pneumatic valves and regulators in the world (again I am not sure about this, but at least in the US they seem to be much larger than anyone else).

They provide valves for all segments of the compressed gas industry including industrial, chlorine, medical, welding, specialty, semiconductor, life support and LPG.

My guess is that they have probably made more gas valves than all the other Scuba companies put together. In the old days before they came out with their own Scuba line they actually made the valves and regulator components for many of the Scuba manufactures, including Healthways, Dacor, White Stag, etc. etc. I think even some of the Scubapro parts from the looks of them, but I am not sure.

Here is a link:
Home

I think one of the coolest things about being a reg tech is seeing all the different ways of accomplishing the same thing

I kind of agree, but IMO if you really want to see some different designs you need to look back at the history of the sport… have you ever seen a Pirelli regulator, a Norseman, a Scott Hydropack, etc. etc.

There are definitely a few companies that take a slightly different approach, but IMHO many if not most designs now-a-days are just copies of designs that have been around for a while (or copies of each other). There have been a few minor innovations, but IMO a lot of the creativity has been squashed from fear of liability or fear of market acceptance of something radically different.

I am not saying that we need something different, because what we have is pretty good. But if you want to see creativity you need to go back a few decades when the sport was really evolving. By the early 70’s when I started working on regulators some of the real crazy designs were already falling off, but real innovation was really visible to about the late 70’s.

You can basically trace the design of most first and second stages to a few regulators:
• Royal Aqua Master and Conshelf (and even the early 1960’s Calypso): predecessor of most balanced diaphragm first stages.
• Healthways Scuba-star (and all its variations): predecessor of most unbalanced piston first stages.
• Scubapro Mk-1 and Mk-5: predecessor of most balanced flow through pistons.
• Scubapro Balanced Adjustable: predecessor of most balanced second stages.
• The basic down stream demand valve has been around from before the first CG45 (Cousteau Gagnon, 1945, the first successful commercially available regulator). The CG45 was a two stage with an unbalanced diaphragm first stage, but no one is offering an unbalanced diaphragm first stage anymore.

The first use of venturi assist was also an Emile Gagnon innovation in the original single stage Mistral in the early 50’s.