Basic Operation; Installation Guidance - WEBTEC DHM 4 Series Manual

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 to the electronics every
time a turbine blade passes. The electronic circuit has a built-in micro processor to correct the
signal and maximise accuracy. The readout is calibrated in lpm or gpm.
Pressure
Pressure is measured by the microprocessor from a diaphragm transducer fitted to a
bi-directional valve. The Bi-Directional shuttle valve automatically reads the highest pressure
in both directions of flow. A gauge port is provided on the block for the addition of a low
pressure gauge.
Temperature
The temperature is measured with a thermistor transducer in contact with the oil flow and the
readout on the meter is scaled at 32 - 250°F or 0 - 120°C.
Bi-Directional Loading Valve
The reverse flow valve provides virtual 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.
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,
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cylinder rods as well as looking for external leaks should be made prior to installing the
Hydraulic Tester.
Although the Bi-Directional tester can be used in both flow directions, the preferred direction
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is indicated by the larger arrow on the serial number plate. When the tester is used for
reverse flow tests, slightly lower accuracies may be obtained depending on the oil viscosity,
density and compressibility.
The tester should be connected to the hydraulic circuit by means of flexible hoses 1 - 2
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metres long.
The use of quick-disconnect couplings can save time but should only be used > 500mm
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away from the tester ports. Make sure the hoses are long enough so that the tester can be
used safely on the machine.
The hoses and fittings at the inlet to the tester must be of adequate size for the flow being
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tested. Elbows, rotary couplings etc., at the inlet and outlet ports of the tester should be
avoided to ensure accurate readings.
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
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the appropriate relief devices are fitted to protect the installation.
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Basic operation

Installation guidance