# Orifice Permanent Pressure Loss

K

#### kaustubh

what percentage permanent pressure loss across orifice can be allowable in designing orifices?

M

#### Michael Blaschke

The amount of permanent pressure loss varies with the beta ratio (d/D). For a square-edged orifice, the permanent pressure loss as a percentage of the orifice differential pressure (delta-p) is:

46% for d/D = 0.75
52% for d/D = 0.70
63% for d/D = 0.60
73% for d/D = 0.50
81% for d/D = 0.40
88% for d/D = 0.30
93% for d/D = 0.20
97% for d/D = 0.10

The equation for this for those who are interested is:

hl / hw = 1 - 0.24 * B - 0.52 * B**2 - 0.16 * B**3

where:
hl = permanent pressure loss
hw = orifice differential pressure (same units as hl, but generally inches of water in US)
B = d/D = beta ratio

There are other equations available that can be applied to just about any flow device, including quadrant- and square-edged orifices, nozzles, venturies, Annubars, pitot tubes, target, turbine, and vortex meters. This and other great flow stuff is in one of the best flow metering books I have run across:
"Flow Metering Engineering Handbook", Richard W. Miller, McGraw-Hill. It is a bit pricey, and used to be available from ISA where I got mine, although it doesn't appear on the web store now. It has saved my day far more than once when I needed detailed technical data on flow metering.

Michael

J

#### James Fountas

What is allowable, is the judgment of the designer, end user, and process requirements.

The permanent pressure loss is based on the ratio of orifice size to pipe size. You size your orice depending on the flow rate you want to measure.

D

#### David W. Spitzer

The allowable pressure drop is dependent on the process and its hydraulics.

The actual pressure drop can be determined by calculation.

See page 131 of "Industrial Flow Measurement", David W Spitzer, ISA, 1990 for a graph of head loss vs. d/D ratio.

Regards,

David W Spitzer
845.623.1830

B

#### BM

Thank you for the information, it proved very helpful to me.

>The amount of permanent pressure loss varies with the beta
>ratio (d/D). For a square-edged orifice, the permanent
>pressure loss as a percentage of the orifice differential
>pressure (delta-p) is:
>
>46% for d/D = 0.75
>52% for d/D = 0.70
>63% for d/D = 0.60
>73% for d/D = 0.50
>81% for d/D = 0.40
>88% for d/D = 0.30
>93% for d/D = 0.20
>97% for d/D = 0.10
>
>The equation for this for those who are interested is:
>
>hl / hw = 1 - 0.24 * B - 0.52 * B**2 - 0.16 * B**3
>
>where:
> hl = permanent pressure loss
> hw = orifice differential pressure (same units as hl, but generally
> inches of water in US)
> B = d/D = beta ratio