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About Orifice Measuring
Points
Orifice
plates are the most common type of primary element.
An orifice plate is a flat, usually round piece of metal, often
steel, with an opening or “orifice” in it.
The orifice plate needs to be positioned at a correct position in
the flowstream for it to function as a primary element for the purpose of
making a differential pressure flow measurement.
For it to be so positioned, it must be held in place.
This is typically done by an orifice assembly, an orifice flange,
or a holding element.
In
addition to an orifice plate and assembly or flange, most orifice plate
installations require the presence of a valve manifold, which serves to
isolate the pressure transmitter from the process.
DP flow transmitters use either a three valve or a five valve
manifold.
An
orifice plate. Photo courtesy of ABB.
Since an
orifice plate cannot serve as a functioning primary element unless it is
held in proper position, and since valve manifolds are required for most DP
flowmeter measurements, an orifice measuring point often has the following
three components:
1)
An orifice plate
2)
An orifice assembly, flange, or holding element
3)
A valve manifold
An orifice measuring point includes an orifice plate, but it also includes
an orifice assembly, flange, or holding element, and also a valve manifold
in most cases.
Orifice
plates are classified according to the shape and position of the hole or
opening they contain. The
following are the main types of orifice plates:
·
Concentric
·
Conical
·
Eccentric
·
Integral
·
Quadrant
·
Segmental
 Orifice
Flange Assembly. Photo courtesy of ABB.
For
further information on differential pressure, including studies and articles,
see www.FlowDP.com.
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