Trying to understand Balanced Vs Unbalanced

[halocline]

I'm not 100% sure but I'm gonna try here and please correct me if Im wrong.

For an unbalanced piston, the IP=closing force and is balanced by the spring force + force from HP air. So, if the spring has a closing force of 110psi and the Hp air is pushing on the seat at 30psi, the total closing force (IP) is 110 + 30 = 140Psi (at full tank, 3000psi). When the tank is down to 500psi, the Hp air is now pushing on the seat at say 10psi. The spring is still constant at 110psi, so the total closing force is now 110 + 10 = 120psi. As you can see the tank pressure is affecting the IP for an unbalanced piston in this example.

Now, for a balanced piston, the closing force is only balanced by the spring force because there is no HP air pushing on the seat. So, if the spring has a closing force of 140psi, that's all it needs to seal the seat be it at full tank or near empty tank. As a result the IP is constant for the whole range.

If what I think is correct above than a balanced piston spring is always stiffer than an unbalanced piston spring? Can someone confirmed that?

if the above unbalanced piston is used with an unbalanced second stage, at 120psi (IP) towards the end of the dive, you'll have to inhale a little harder to open the valve than you would if it were at 140psi because the extra 20psi would have help to push the seat open.

if the above unbalanced piston is used with a balanced second stage, the 120psi IP pushing on the seat is balanced by opposing force (120psi) in the balanced chamber so all you need is may be 2psi to open the valve and thus you don't need to inhale too hard. This also makes the balanced spring less stiff because most of the force is taken care by the balanced chamber.

With the above, I think it's still better to have a balanced 1st + balanced 2nd because a balanced 1st would give you more air flow volumn (higher IP) than an unbalanced 1st (if the difference is noticable at all).

Everything you say is correct, but balanced piston regs do not always have stiffer springs. There are other variables, like the size of the reg. But, yes, in BP regs the spring is the only opposing force to IP, other than increasing ambient pressure.

Balanced 2nds do typically have a much softer/smaller spring than unbalanced, if they are of the same design. The classic example is the SP 109; when converted to balanced, the large stiff spring is replaced with a much smaller softer one.

 

[halocline]

Thanks DA Aquamaster for the information. Another question if in an DH Aquamaster regulator it becomes easier to breath when the tank depletes does it mean it's of an upstream design ?

Yes, exactly. All diaphragm 1st stages are upstream valves.

 

[captain]

Yes, exactly. All diaphragm 1st stages are upstream valves.

An unbalanced diaphragm 1st stage acts just the opposite of an unbalanced piston first stage. As tank pressure decreases the IP increases.

 

[tfsails]

I hope I'm right about this: you CAN still get unbalanced diaphragm first stages. Poseidon has them in its Cyklon line. They are the only manufacturer who still sells them, to the best of my knowledge. I've rebuilt plenty of Cyklon first stages and every one of 'em was unbalanced.

 

[DA Aquamaster]

The US Divers double hose regs such as the Aqualing, DA Navy Approved and DA Aquamaster were two stage designs with unbalanced first and second stages. In that regard, the regs get slightly easier to breath as the tank pressure drops, due to the increase in IP at lower tank pressures due to the location of the unbalanced seat carrier upstream of the orifice.

However the effect is significantly more noticeable in the unbalanced single stage regs such as the DW Stream Air and DW Mistral.

With the Royal Aquamaster, US Divers just used a balanced seat carrier in what is the same basic design to create a balanced first stage. That design continued with the Conshelf and Tital single hose first stage regs and has been recently retrofitted to DA Aquamasters with the 3rd party Pheonix nozzle to create the Pheonix Royal Aquamaster.

Since it is incredibly easy to balance a seat carrier, there is no reason not to do it, which is why no body makes an unbalanced diaphragm reg any more.

If Poseiden's Cyklon is truly unbalanced, I'd be surprised and would be interested in why they feel it is an advantage.

 

[herman]

For what it's worth, there were several unbalanced diaphram first stages built in the late 50's- early 60's time frame. I have a couple of examples, including a couple that used what appears to be USD ( DAAM) parts.