Sizing a regulator - how do I read these charts?
Sizing a regulator - how do I read these charts?
(OP)
I'm hoping someone can walk me through this process, because I'm missing something. I'm trying to size a filter/regulator/lubricator package. I have some difficult specs to meet though. The supply pressure could be anywhere from 90 to 150 psi. The downstream pressure should be no less than 80 psi at 90 scfm.
I figured I could calculate the Cv required at the minimum supply pressure, but few regulators come with a "wide open" Cv spec. Instead, you usually get this chart showing a series of curves showing outlet pressure vs. flow for a given inlet pressure and a set of "setpoint" pressures, like this: http://www.cunicocorp.com/images/2253_chart.gif
My question is, how do I extrapolate for inlet and "setpoint" pressures not listed on the chart? Does the top line necessarily represent the "wide open" condition?
I figured I could calculate the Cv required at the minimum supply pressure, but few regulators come with a "wide open" Cv spec. Instead, you usually get this chart showing a series of curves showing outlet pressure vs. flow for a given inlet pressure and a set of "setpoint" pressures, like this: http://www.cunicocorp.com/images/2253_chart.gif
My question is, how do I extrapolate for inlet and "setpoint" pressures not listed on the chart? Does the top line necessarily represent the "wide open" condition?





RE: Sizing a regulator - how do I read these charts?
The idea is to allow these things to regulate accurately and if you're out there at the end, or off, the curves, they won't work properly. Stay within the mid 50% of the charts.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Sizing a regulator - how do I read these charts?
RE: Sizing a regulator - how do I read these charts?
RE: Sizing a regulator - how do I read these charts?
In reality it won't swing very much at all, but my customer won't specify a narrower range. They want our tool to operate properly whether their air system delivers full design pressure, or barely acceptable air pressure :(
RE: Sizing a regulator - how do I read these charts?
You should use a regulator output set pressure lower than 80% of inlet.
And... You can't extrapolate into areas where you run out of dP. If you try, you'd better be using a quadradic equation because you'll lose flow by at least the squareroot of available dP, so you can see you'll be getting nowhere fast.
You may also need a pressure control valve upstream in that inlet pressure line. At those low pressures, a 100% change in inlet pressures is not going to do nice things to your regulated flow output. Or perhaps two regulators, one preregulator that kicks in when things get high.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Sizing a regulator - how do I read these charts?
I wish I could. These specs are pretty inflexible. The best I can do maybe is install a bypass line and 3 way valve in case the inlet pressure drops too much. I was hoping that I could just get a large enough regulator that it will pass enough flow at even small pressure drops. Unfortunately, the data is hard to come by.
I have another need for the wide-open Cv: I have to size a relief valve with adequate capacity to reduce the pressure to a safe range were the regulator to fail open.
RE: Sizing a regulator - how do I read these charts?
Think of Bernoulli. Flow rate on the right side increases if dP on the left side increases. (I think I got that right)
I like BigInch's idea of a pre-regulator. I was thinking something similar with perhaps just a very large regulator upstream.
Unfortunately, I don't use a lot of controls in the work that I do because of electrical regulations. But the easiest way to do what you want is to have a large regulator upstream with a pressure transducer and a controller from Omega. Let that drop you to 100 psi or whatever you need. And then use a regular-static, larger, FRL to get your CFM, etc from the charts.
RE: Sizing a regulator - how do I read these charts?
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Sizing a regulator - how do I read these charts?
Both supply lines would have check valves and tie into the same air inlet on the machine.
RE: Sizing a regulator - how do I read these charts?
I would tend to think about using two parallel regulators before adding a switching valve, but that might depend on how much flow you need and at what outlet pressure you need to hold as the inlet pressures change. Do you need to hold the same outlet flows at a constant outlet pressure at whatever the inlet pressures will be, or can flow and/or outlet pressures vary with inlet pressures. That may have some bearing on whether you can use one valve at low pressure and switch to the other at hi P, use one at lo P and then simply open up the inlet to the 2nd, using two valves at high pressure, or if you might be able to use 2 parallel valves with "average" inlet and outlet set pressures that will work at all inlet pressures. I would only add extra controls if you can't make it work without it.
Let your acquaintances be many, but your advisors one in a thousand' ... Book of Ecclesiasticus
RE: Sizing a regulator - how do I read these charts?
RE: Sizing a regulator - how do I read these charts?
What range of pressure to your product demands what range of flow at your design product performance.
Ted
RE: Sizing a regulator - how do I read these charts?
It might come to that. I can't be in the "middle of the range" for a supply pressure of both 150 psi, and 90 psi. (not to mention, I can't find curves for these extreme supply pressures).
RE: Sizing a regulator - how do I read these charts?
http://ww
No?
Ted
RE: Sizing a regulator - how do I read these charts?
So here's my difficulty with these charts: On the chart you reference there is no curve above 80 psi at a flow rate of 100 scfm. I assume that means the valve is wide open at this point (thus cannot reduce its pressure drop any further) not in the "midrange", as you suggest. Unfortunately none of the other F.R.L.s in the catalog are any better.
If I can live with the valve being wide open and I raise my specified minimum supply pressure to 100 psig, that F.R.L. does seem to at least work for my operating condition. Thanks.
RE: Sizing a regulator - how do I read these charts?