Flowmeter Installation
All the Litre Meter Flowmeters are calibrated on water flow using gravimetric principle rigs as recommended by the National Engineering Laboratory, East Kilbride to Litre Meter Ltd. Traceability is assured for test volume weighing, pulse counting and timing to 0.001 seconds. The normal attitude of the meter in calibration is for horizontal pipework but where requested this can be revised for a vertical installation. The difference in calibration is minimal except at very low flowrates. Special care is taken to ensure that the highest order of calibration accuracy is attained. To maintain this accuracy in usage, careful consideration must be given when designing meter installations.
LM Series Flowmeters
In most cases, these full flow Pelton wheel meters can accommodate poor installation conditions involving pipe bends etc. However, in these circumstances, in-situ calibration checking is recommended. Valves should not be connected in close proximity to the inlet connection of the flowmeter. Quite often the main pipe will be larger than the nominal 1/4" meter connections. If possible, reduction of diameter should take place not less than 100mm from the meter inlet. Expansion of the line can be connected to the standard output pipe. The meter could read high under pulsing flow conditions and the receiving instrument calibration should be adjusted accordingly.
MM Series Flowmeters
The design of the meter includes an orifice. This does not have a sharp edge, which is beneficial to the retention of the meter calibration. The normal practice associated with orifice plate installation should be adopted. A horizontal pipe run is preferred with ideally 25 pipe diameters of straight pipe upstream and 5 pipe diameters downstream. The nominal bore (pipe diameter) of these straight pipes should match the meter size. For example: A 50mm bore pipe is used for a MM50 flowmeter. If possible, avoid the installation of elbow bends, valves or reduced bore couplings in close proximity to the inlet of the flowmeter. Two or more elbow bends or loops in different planes and the presence of diaphragm valves, filters etc are particularly disruptive to the flow pattern. To maintain accuracy, all meters, including helical turbine types and the Litre Meter orifice/pelton wheel meter require a uniform velocity pattern to the flow. In cases of extreme flow turbulence, the installation of a flow straightener can be beneficial.
Flow Pulsation
Pumps which create a pulsing flow will usually cause the flowmeter to read high. The use of a volume accumulator to provide an air cushion in the system will greatly assist in reducing pulsations. In-situ recalibration of the instrument receiving the flowmeter output signal will normally restore good measurement for a pulsing flow. A separate data sheet is available giving further information on installations and the physical dimensions of the meters.