5 replies to this topic

[rsk]

Orifice is installed in pipes to
1. for having desired pressure drop
2. for creating differential pressure in flow measurement
What is the difference in sizing for above two application, Please explain, ur efforts are appreciated.
Thanks in advance

[djack77494]

Orifice is installed in pipes to
1. for having desired pressure drop
2. for creating differential pressure in flow measurement
What is the difference in sizing for above two application, Please explain, ur efforts are appreciated.
Thanks in advance

You have correctly identified the two primary purposes for installing orifice plates in a line (or pipe).

Your reason #1 may be to incur a desired pressure drop or (very much related) to obtain a desired flowrate. This is refered to as a restriction orifice. Often the pressure drop across such an orifice is large, and choked flow is not at all uncommon. As the name implies, the orifice is intended to restrict a process parameter such as flowrate or downstream pressure. The "excess" available pressure is consumed in the process.

Your reason #2 is a flow orifice. It is designed to produce a differential pressure (dP) that will vary within a given range as the measured flowrate varies within its expected range. For a flow orifice, you typically do not want to "waste" pressure, and so a (reasonable) minimum dP is desired. This dP will NEVER result in choked flow (at least not in my experience).

[JoeWong]

rsk,

Doug details explanation should be able to provide a good guidance.

I would say restriction orifice is used to limit flow to expected flowrate with the available differential pressure across.

The context is different than restriction orifice is used to create pressure drop. IF you are interested, read more in "A refresh to Process Engineer on few phenomenons in restriction orifice".

[rsk]

Thanks for ur efforts in alaborating the two different applications orifice, but it would be good if u can provide the approaches for sizing in both the cases.

[djack77494]

rsk,
I think the answer is in the responses. Perhaps I should mention that you normally have a dP in mind when you are sizing a flow measurement orifice. In Imperial units, I would often start with the thought of using a transmitter with a range of 0 to 100inches of water column as a "prefered" dP. Then I might expect that my design flowrate would generate 50 to 70 inches. My instrument engineer would let me know if the Beta Ratio (bore over pipe cross sectional areas) was outside his prefered range, so I might have to adjust my dP. Dealing with vacuum, low pressure or hydraulically "tight" situations, I would make appropriate adjustments to the prefered dP.

If you desire additional information, try visiting the site recommended by JoeWong or try "google-ing" to find more sites than you even care to know about. You should have no problem finding the pertinent equations and even some on-line calculators that will do the calculations for you.

[rsk]

Thanks very much sir.