Variable Orifice Plates

Hi all,

I'm looking for a manufacturer for a variable orifice plate with a 100:1 turndown ratio. I've done the google search, but havent come up with much, just lots of manufacturers of fixed orifice plates.. Any suggestions??

Andrew Evenson

1) I assume this is for a flow measurement application.

2) I assume you are really looking for a DP (Differential Pressure) transmitter with square root extraction to give you a direct flow reading from the orifice plate.

3) I think you are out of luck. Because an orifice plate is a Bernouli's Law device, the flow (velocity, actually) is proportional to the square root of the differential pressure across the orifice. That means to get 100:1 turndown on flow you would need 10,000:1 turndown on the DP transmitter, and I've never seen it. The best I have seen from any major manufactuer is 10:1 turndown on the flow output from the transmitter. Below that you either get bogus results or the transmitter drops out to 4 mA.

4) Deending on your fluid, there are other devices besides an orifice plate that will give better turndown and less permanent pressure drop. Give us a little more info, and maybe we can help.

Thanks Tom,

I guess I have to do a little more homework on my part in how the system I'm looking at works. I do understand Bernouli's Law, and the equation for flow : Q = KAãƒ¢„‚. I could have mistaken what I was looking at for something else..sorry. When I have better information, I'll try again..

Andrew Evenson

Damn!

My flow equation didnt turn out the way I expected..lets try again..

Q = K*A* SQUAREROOT(Delta P)..Better??

Andrew

I liked your first equation...didn't understand it, by liked it.

What are K and A

Andrew Evenson said:

Damn!

My flow equation didnt turn out the way I expected..lets try again..

Q = K*A* SQUAREROOT(Delta P)..Better??

Andrew

Click to expand...

K must be the flow constant. What is A?

Area?

i was wrong...

Yeah,

there isnt any "A" component in the equation..my mistake. Thats what I get from trying it off the top of my head!!

Q = K * SQUAREROOT(DELTA P)..

Plus, I was wrong about looking for a variable orifice plate. What I'm really looking at is an variable orifice VALVE where a pressure transmitter is looking at the difference in pressure across the valve..(found some better schematics..). I appologize for any confusion in my question. I guess I have to get my facts straight first.

Andrew

For Hdyraulic Information

Andrew,
Call:
John Cutolo.
Hydraulic and Motor Controls
716-662-8419
[email protected]
His company covers southern Ontario up to Toronto.

It may be better if you explain what you are trying to do ( the ends ) and not how you think it should be done ( the means ). Some one may have a better way. There are a handful of people that come to this forum that know quite a bit about hydraulics.

Rick, stop guessing.

I know what the formula is, and I knew that 'A' was not area. It could be a percentage of spool/valve opening. In this case the value of 'A' goes from 0 to 1. Normally this valve openning percentage is represented by another letter or symbol but never have I seen 'A'. Obviously 'A' would get confused with area.

100:1 for a flow control valve is still a lot to ask for. Besides the basic problems of valve resolution, you have positioner error to worry about. The type of valve depends on the fluid and pressure range. For hydrulics a spool valve with feathering notches might work. For slurries maybe a diamond port eccentric plug. For air, maybe a diamond port knife gate would be better. maybe you want a small and large valve in parallel.