When the meter is installed it must have straightening vanes upstream and
downstream of the meter. The pipes are usually 5 pipe diameters long
downstream and 10 pipe diameters upstream. This prevents fluid swirl and
cavitation due to back pressure, which will cause the thermometer to lose
accuracy. The meter is accurate up to 1/10th of 1 percent and is used for
custody transfer. However, the meter requires a lot of maintenance and
expertise. (They are generally not used by the military.)
Turbine meters, like the PD meters, will register air and any
obstructions from trash which can effect the flow (the meter must be
protected while in operation). Protective devices consist of air
eliminators and basket type strainers.
Inferential Rate Meters.
The inferential rate meter is an instrument
whose primary element (orifice plate), when placed in a flowing stream,
infers the flow rate by known physical laws (pressure drop based on the
viscosity of the fuels). The orifice plate is machined to exact
tolerances.
The secondary element is used to record the quantity of fuel passing
through the meter. It consists of piping, high- and low-pressure sealing
pots, and a 24-hour recording chart. The 24-hour chart registers the
viscosity of the fuel (based on pressure drop) and the flow rate in
barrels over a 24-hour period.
When the meter is installed it must have straightening vanes upstream
and downstream. The length of the pipe depends on the size and type of
valves used. The meter also requires protection from trash in the
flowing stream (line strainers). The meter itself requires a great deal
of maintenance and expertise to keep it in proper operating condition.
Orifice meters are used in pipelines where the interface passage needs to
be monitored.
PART B - METER INSTALLATION AND PROTECTIVE DEVICES
A typical meter installation would be set up as
follows:
DIRECTION OF FLOWFilter separator Strainer Air eliminator
Meter.
The strainer is downstream of the filter separator in case you have a
ruptured element. The strainer will catch any fiberglass or filter paper
that might get into the meter and cause it to hang up. There is also a
strainer in the system on the suction side of the pump. This would
prevent any trash from entering the filter separator.
Line Strainers.
Line strainers consist of a metal housing which holds a
canister-shaped wire mesh strainer. The mesh is usually 25 mesh or more.
Uses. Line strainers are used in the suction side of pumps and on the
inlet side of meters preventing debris from entering the pump and
damaging the impeller or meter.
Maintenance. Line strainers should be inspected and cleaned on a
periodic basis (recommended at once a week). The gaskets are checked
for damage, cleaned, and returned to use.
12-126
QM 5099
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