Looking for a compressed air dividing valve (not a regulator!)

You could use a 2:1 Air to Air Intensifier that would have 50 PSI on the larger Piston and would Output the 100 PSI from the intensified piston.

It would only work if there were ABSOLUTELTY NO LEAKS in the 106 PSI Piston or if you used a Reciprocating Intensifier that could makeup for some leakage.

Finding an Intensifier that would give the exact ratio may not be possible but you could get close with standard parts.

You can see Intensifiers in Chapter 17 of an Ebook I use to teach Industrial Fluid Power Basics. The second Ebook, "Fluid Power Circuits Explained" has a section on Intensifier Circuits but it won't be up for a few more months.

http://www.hydraulicspneumatics.com/200/eBooks/Article/True/67859/

Bud,

Thanks for responding. The suggestion of using an intensifier is an interesting one. It could be used in a couple of ways to solve my problem.

The only problem I see with a conventional intensifier is that there is some friction in the reciprocating pistons that would limit the accuracy.

Do you know if there is such an animal as a diaphragm intensifer, where two diaphragms of differing area are linked together?

Thanks,

Jon.

I've modified a few regulators in the manner you describe...

You don't want to use a regulator because you want the 50 psi to represent the 100 psi output.... I think that's what you are saying?

Why not on the output of the regulator have two orifices, one being adjustable and both small so leakage is minimised... then the 100 psi will be divided down by one orifice with the second to atmosphere - a bit like a couple of resistors in series in an electrical circuit!!

I've used this method for precision control of a pressure that was not possible with available regulators.

Watch out for problems with hunting of the output due to normal feedback delays etc...

John

Electroman,

To clarify: The pilot valve I'm looking for is "almost like" a regulator, in that for a given input pressure, one can set a regulator for half the output pressure. (divide by 2) However, if the input pressure changes, I need the output pressure to change as well. THATS the difference. A regulator tries to maintain the output pressure regardless of the input pressure. The valve I am looking for varies the output pressure by a fixed amount depending on the input pressure.

I need this varying output pressure because this pilot circuit is actually the feedback loop for the larger 2" regulator.

Thanks,

Jon.

That's what I said in my post...

if you use two orifices or jets and make one adjustable you can adjust it to give a division ratio of 2 i.e. 50 psi out for 100 psi in.

John.

Actually the only Diaphragm Pumps I have seen were used to pump a liquid using air power.

I would do a Google search to see a number of manufacturers making this type pump and pose the question to them.

Hi Jon

Sounds like you are using regulators as valves and they are modulating as regulators do. Also sounds like you have understanding and machine shop capability so here goes.

If the 2" regulator is piloted on center this can be quite easy. If it is not you will need to replace the top or bonnet. In either event make a bracket to sandwich an air bag between it and the regulator. The air bag diameter should be larger than the piston or diaphragm in the regulator. With a plunger or rod between the air bag and the diaphragm you can expand the air bag with pressure less than 100 psig to force the regulator diaphragm down and fully open the regulator valve.

You could do this with a smaller air bag to augment the normal pilot pressure but then the top (bonnet) cavity must be sealed. With the larger air bag and brute force sealing the bonnet area is not required.

You can also augment or brute force the diaphragm down with a pneumatic cylinder if you prefer. A 2" air piloted poppet valve might be less expensive unless your time is free.

Tom,

COOoooOOL...! Very clever!!

It looks like you are speaking with the authority of the "been there, done that" guys. I will take a close look at this. The other solution I have been toying with this morning is what Bud had suggested--pressure intensifiers--but I had been thinking of just using one to jack the pilot pressure source to, say, 125 psi so the pilot pressure became a non-issue.

Your suggestion on just going to a piloted poppet valve is also well taken. My issue is that we spent about $700 each on the 2" piloted regulators before we found that the pilot controls had a lousy pressure range. Further research suggested that poppet valves can get pricey--We were told up to $6,000, although I think these had a linear flow characteristic.

By the way, if I isolate the underside of the existing 2" valve diaphragm and vent it to atmosphere, I end up with just that--a 2" air piloted poppet. But the full closed to full open pilot range is indeterminate until I try it--It could be only a couple of psi between full open and full closed.

So now I'm angling for a solution that balances a little in-plant machining and other fiddling around time (read, "free") against spending more money and unleashing the wrath of a pointy-haired boss.

The other thing is that the regulator has a built-in control loop that is likely overdamped. This makes it pretty easy for our control computer to adjust the output of the 2" valve without having to seriously implement a PID structure in software.

Just to make the big picture a little clearer: we are using these regulators to control the pressure of a large compressed air system. We will be happy to regulate to within +/- 1 psi--probably +/-5 psi would make our production people smile! The sheer volume (large) of the system makes changes happen pretty slow so overdamping probably helps us, especially since our pressure transducers can read pressure down to at least 0.1 psi and the proportional control air servo valve controlling the pilot pressure can easily match the transducer accuracy.

Now--to see if I can highgrade a couple of airbags of the right size from a maintentance sup't! ;>)

Thanks,

Jon.

Hi Jon

FYI this would be a Norgren 2" air piloted poppet valve in Yankee dollars.

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