(a) 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 meter to lose accuracy (reference API
standard 2534). 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.
(b) Turbine meters, like positive displacement meters, will register air and any obstructions from
trash which can affect the flow. The meter must be protected while in operation. Protective devices consist of air
eliminators and basket-type strainers. These will be discussed later.
c. Inferential rate meters.
(1) 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.
(2) 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 BBLS over a 24 hour period.
(3) Operation maintenance.
(a) When the meter is installed, it must have straightening vanes upsteam 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.
(b) Orifice meters are used in pipelines where the interface passage needs to be monitored.
a. 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.
(1) 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.
(2) Maintenance. Line strainers should be inspected and cleaned on a periodic basis (recommended
once a week). The gaskets are checked for damage, cleaned, and returned to use.
b. Air eliminators.