pressure reducer/divider/debooster

[pesy]

Is there a device that will take a pressure and divide it, with no flow?

I have a gas pressure regulator which I am controlling with a feedback pressure. The line gas pressure is 4" WC; the feedback pressure ranges from 0 to 6" WC (varying). Without pressure reduction, my feedback pressure, when higher than 4", will cause the regulator to open all the way. The regulator will therefore no longer be sensitive to changes in the feedback pressure.

Therefore, I am looking for a device that will take my feedback pressure in, and divide it, i.e by a factor of 1.5, so that as my feedback ranges from 0-4", it will adjust the regulator proportionally.
Since this is a closed system, when steady-state, there is no flow in the feedback line. Therefore, any sort of orifice will not work.
-I do not have any other air supply to provide
-I cannot vent the feedback line since it contains natural gas

Please let me know if there is some device out there that can do this. Ideally, I think of it as an equivalent to an electrical transformer. I have heard of a hydraulic cylinder with different areas at each end, but I am looking for something compact, "plug and play", and designed for the low pressures in my system.

Pesy

 

[imok2]

Can't you put a regulator from the hi pressure line to the feed back line and set it for the pressure you need on the feed back?

 

[rzrbk]

I am unclear on the purpose of the control valve. As it opens with increasing feed back pressure, is it venting the 4"WC line to keep it at or below 4"?

 

[btrueblood]

What you described is sometimes called a "booster" or "boost" piston or boost cylinder. Typically used in hydraulic systems to provide a limited amount of higher pressure fluid (for break-away torque on motors, e.g.).

For a pneumatic system, take two pneumatic cylinders of different bore sizes. Point the piston rods of these cylinders towards each other and link the rods together with an appropriate coupler. The pistons must now move in synch, and thus a pressure on the large bore side must be balanced by a higher pressure on the small bore side. The pressure ratio is proportional to the area ratio of the two pistons/cylinders. Thus, this setup either "divides" the small piston pressure or "amplifies" the large piston pressure. (Note I'm ignoring the rod side presure here, assmuming it's kept the same on both cylinders).

You could do this with off-the-shelf diaphragm cylinders or diaphragm actuators as well, if leakage is a concern. See the

http://www.bellofram.com

and/or

http://www.controlair.com

websites.

 

[pesy]

btueblood has the right idea.

However, if possible, I was looking for a single, inexpensive device. Coupling 2 air cylinders requires the coupling as well as a fixture for the bodies. Also, aren't pneumatic cylinders usually used for shop air (90psi) and probably have more friction than 4 or 5" WC will be able to overcome.

To answer the other questions: The regulator is being used to provide a more-or-less constant pressure drop to the main gas flow regardless of flow rate. It is able to constantly adjust its orifice based on the feedback pressure (and the internal spring). At low flow conditions, the feedback pressure is, say, 0.2"WC, the regulator is therefore mostly closed, and provides a, say, 0.5" pressure drop. At medium flow, the feeback pressure is,say, 2"WC, the regulator is halfway open, and provides a, say, 0.2" pressure drop. At high flow, the regulator is receiving a 6" feedback, is fully open and provides almost 0 pressure drop.

While this setup is does not (and will not, even with the device I'm looking for,) provide a perfectly linear input-ouput, I can compensate for the nonlinearity with the rest of the system. I just need the regulator to be sensitive to feeback pressure changes at the high flow condition.

Pesy

 

[btrueblood]

Pesy,

To get one sized correctly for your application, cheap/efficient/etc., you are probably going to have to design one, and have it built - how cheaply will depend on how many you want to buy. If you need help on the design, holler, I design regulating devices for a living. The method I gave you is just an R&D expedient to verify if your design can work.