English
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Basic operation
Flow measurement
The tester measures flow using an axial turbine mounted in the aluminium base block. The
oil flow rotates the turbine and its speed is proportional to the oil velocity. The revolutions of
the turbine are measured by means of a magnetic sensing head which feeds a pulse every
time a turbine blade goes by to an electronic circuit. The electronic circuit has a built-in micro
processor; the signal is amplified and linearised to maximise accuracy. The readout is calibrated
in lpm or gpm, units are selectable on some models.
Pressure measurement
Where fitted, the pressure gauge has a spiral Bourdon tube and the gauge case is filled with
glycerine to ensure good dampening of pulsating pressures. The gauge is connected to the base
block by a fine bore capillary tube. The DHM series meters have a pressure transducer fitted
directly to the base block which improves fast transient capture. All testers are bi-directional
and incorporate a shuttle valve which directs the highest pressure (from inlet or outlet) to the
measuring point. A gauge port is provided on the back of the base block for the addition of a
low pressure gauge kit.
Temperature
The Thermistor temperature transducer is in contact with the oil flow and readout is on the meter
scale calibrated 32 - 250°F or 0 - 120°C.
Bi-Directional Loading Valve
The reverse flow valve gives positive shut-off and pressure control in both directions of flow.
The loading valve has two easily replaceable safety discs located in the valve assembly which
internally protect the tester and machine in both flow directions.
Installation guidance
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All hydraulic connections should be made by suitably qualified personnel.
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Avoid sharp bends because high pressure hoses will deflect and straighten under pressure.
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A preliminary check of the hydraulic system’s oil supply, pump rotation, filters, oil lines,
cylinder rods as well as looking for external leaks should be made prior to installing the
Hydraulic Tester.
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Although the Bi-Directional tester can be used in both flow directions, the preferred direction
is indicated by the larger arrow on the panel. When the tester is used for reverse flow
tests, slightly lower accuracies may be obtained depending on the oil viscosity, density and
compressibility.
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The tester should be connected to the hydraulic circuit by means of flexible hoses 1 - 2
metres long.
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The use of quick-disconnect couplings can save time. Make sure the hoses are long enough
so that the tester can be used safely on the machine.
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The hoses and fittings at the inlet to the tester must be of adequate size for the flow being
tested. Elbows, rotary couplings etc., at the inlet and outlet ports of the tester should be
avoided to ensure accurate readings.
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The use of the flexible hoses will help to isolate the test unit from vibration which often exists.
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The internal burst discs are to protect the tester not the hydraulic installation. Always ensure
the appropriate relief devices are fitted to protect the installation.
