Scribd
Upload
98 views2 pages

Restrictive Orifice Flow Guide

Restrictive orifices and critical flow devices limit or restrict flow in piping systems. Restrictive orifices create a fixed pressure loss for a given flow rate, while critical flow devices limit flow to a set rate related to upstream pressure. The document discusses the differences between restrictive orifices and critical flow devices, how they limit flow, and how pressure loss is calculated for each type.

Uploaded by

Abbas
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
98 views2 pages

Restrictive Orifice Flow Guide

Restrictive orifices and critical flow devices limit or restrict flow in piping systems. Restrictive orifices create a fixed pressure loss for a given flow rate, while critical flow devices limit flow to a set rate related to upstream pressure. The document discusses the differences between restrictive orifices and critical flow devices, how they limit flow, and how pressure loss is calculated for each type.

Uploaded by

Abbas
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
You are on page 1/ 2

Restrictive Orifice

The FLOW CONSULTANT uniquely covers restrictive and


critical flow meters. While restrictive orifices and
liquid Cavitating limiting flow-rate devices are not flow
meters they are widely used to limit or provide a
pressure loss (restriction) in a flow system.
Ans. The difference between limiting flow and
restricting flow are often misunderstood.
Critical (gas/vapor) or Cavitating Liquid Flow: Gas
Flow-rate is limited to a fixed flow-rate for a given
upstream pressure when a shock front is created at the
minimum flow area of the device, this is established when
the Critical pressure ratio is reached as the
downstream pressure is reduced. For air this occurs when
the ratio of upstream pressure to throat pressure is
0.53.
Liquid flow is limited when the differential pressure
equals the difference between upstream and throat (or for
an orifice) vena contracta pressure is the vapor pressure
of the fluid.
In both cases Bernoullis no longer applies. For a thick
orifice the overall pressure loss the difference between
the upstream pressure and the downstream pressure. For a
standardized critical flowmeter the pressure loss is
approximately 10 % of the choking difference between
upstream and downstream choking pressure.
The Flow Consultant includes critical flow thick
orifices, Torodial Throat and Cylindrical Venturi.
Restrictive Orifices: Restrictive orifices do not limit
the flow but fix overall pressure loss for a given flow
rate. The FLOW CONSULTANT computes the pressure loss
using the standard orifice equation with the Stolz
derived discharge coefficient for pipe taps.
Pipe tap are located 2.5 pipe diameters upstream of the
plate and 8 pipe diameters downstream (2 1/2 and 8 D
taps). This prediction equation well fits recent overall
pressure loss data (Miller p/ 6.41).
It should be noted that while the discharge coefficient
for pipe tap orifices are used for restrictive orifices,
no taps exist. Pressure taps are required only for pipe
tap metering orifices which use the same selection option
button. The selection of either up or downstream tap is
only for pipe tap metering orifice flowmeters and not
necessary for restrictive devices. The option for
tap location is provided to accommodate pipe tap meters
but is not used for restrictive orifice.

You might also like