INTRODUCTION
Accounting for fuel is one of the most important aspects of operations in
the field. If you are using meters for accountability, then you must
understand how they work in order to properly protect the meter and
ensure that they are properly calibrated.
PART A - TYPES OF METERS
Positive Displacement (PD) Meters.
As the name implies, a positive
displacement meter measures the flow by separating the flowing stream
into volumetric segments and counting them. There are typically three
basic subassemblies in a PD meter.
External housing. This is the pressure vessel with inlet and outlet
connections. Meters may be of single or double case construction.
The single case acts as a pressure vessel and as the outer wall of the
measuring element. Small meters (less than 6 inches) are normally
single case. Double case construction is used on meters over 6
inches. The advantage of double case construction is that the piping
stress or pressure is not transmitted to the measuring element.
Internal measuring element. Measures the volumetric flow by
continuously separating a flow stream into discrete volumetric
segments and counting them. It is also used to drive the counter.
Counter drive train (counter or totalizer). The gear ratio of the
drive train is designed to convert the fixed volume per revolution to
the number of gallons or barrels and transmit it to the counter. The
calibrator (adjuster) is used to adjust the counter for slippage
through the meter. It may be used if the meter is outside the
authorized tolerance.
Because of the design of the PD meter it must be protected from dirt and
trash. Any solid material passing through the meter will cause it to
malfunction. The meter will also register any air passing through the
housing. The clearance between the housing and the van is usually .004
inches to .005 inches. Because of their simplicity, positive
displacement meters are the most commonly used in petroleum operations
and are used as master meters in the place of provers.
Turbine Meters.
Turbine meters are precise measuring devices, even
though they are classified as inferred rate meters. They go from simple
measuring devices to very complex instruments, and they are much smaller
than PD meters. There are three basic subassemblies in a conventional
turbine meter.
Meter housing. The meter housing assembly is constructed of a flanged
pipe spool and houses the internal parts.
Internal parts. The heart of the internal parts subassembly is the
rotor blade suspended in the flowing stream on the platform bearing
and rotor shaft.
Detector subassembly. In the more complicated meters you have the
viscosity compensator and the magnetic reed switch. In this kind of
meter the flow is corrected to 60 degrees Fahrenheit.
12-125
QM 5099
Previous Page
