The Orifice meter is one of the many devices used to measure the
volume or mass flow rate of fluids flowing in a closed conduit (pipe).
The 1000 year old technology is constantly being refined and updated
and is still one of the most popular and reliable measurement methods
available to industry today.
The Orifice meter consists of a flat thin plate having a reduced
diameter bore machined into the centre of the plate (Orifice Plate).
This Orifice plate is thus installed into the pipe, sometimes using
specialized "orifice plate changers" which conveniently
hold the orifice plate in the pipe. Small access pressure ports,
or pressure taps are required on each side of the Orifice plate
to allow the measurement of the pressure change across the plate
when the fluid is flowing.
By utilizing the 1st Law of thermodynamics or the Bernoulli equation
and; the ratio of the orifice plate bore to pipe inside diameter
(beta ratio); fluid density, and differential pressure, one can
infer the mass flow or volume flow rate in the pipe. Extremely accurate
flow rates can be obtained when the calculation methodology employed
is of an industry accepted flow metering standards such as; AGA-3,
API 14.3, or, ISO 5167.
Among the strict design requirements of these flow metering standards,
and more important than the orifice meter concept itself, the installation
details of the properly designed Orifice plate meter dictate that
the fluid flow velocity profile upstream of the orifice plate is
fully developed and swirl free. Fluid flow characteristics not maintaining
a swirl free fully developed state render the orifice plate flow
methodology of little use to those needing to know what the flow
rate is in the pipe to any acceptable accuracy level.
Tube bundles have been the accepted industry standard up until
recently although the tube bundle is a poor performing velocity
profile device. In order to rectify the performance limitations
of the tube bundle, new technologies emerged in the 1990's which
are called high performance flow conditioners. High performance
flow conditioners, such as the CPA 50E, when installed upstream
of the Orifice Plate allow flow metering with no bias errors due
to fluid installation effects.
The CPA 50E Flow Conditioner is the most widely utilized installation
isolation device for Orifice meter use in the world. High accuracy
Orifice Meter installations downstream of Elbows, Two Elbows in
and out of plane, headers and tees are the norm due to the use of
the CPA 50E Flow Conditioners with Orifice Plate meters.
