MAGM 262

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MAGM 262
Equipment for testing Hydraulic Systems
Mr. Conrado
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Equipment for Testing

• Portable testers, designed for shop or field use,
  apply a controlled load to the machinery
  hydraulic system and measure the effect of the
  load. A manually controlled valve provides the
  adjustable load. Gauges show flow, pressure,
  temperature, and, in some cases, shaft speed.

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How testers measure flow

• Most testers measure volume with the flow meter
  calibrated in Gallons Per Minute (GPM).
• Flowmeters use one of three ways to measure flow
• Fixed-area measures the pressure drop across a
  small orifice and calculates flow.
• Turbine uses high speed axial-flow rotors that
  are spun by the passing fluid. Sensors count the
  revolutions and convert this number to flow.
• Positive displacement Basically small hydraulic
  motors. As fluid passes it drives a small
  mechanism to turn a shaft. This type of meter is
  somewhat more accurate but are sensitive to
  contamination.

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How testers measure flow

• The pressure that a flowmeter can withstand
  varies. Some units have limited pressure
  capacities. These units must be used downstream
  of the loading and flow back directly to the
  tank.
• Units with full system capacity can be connected
  so that the output flow is directed to the next
  regular component.
• Flowmeter accuracy is roughly 3 /-

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How testers measure pressure

• System pressure is measured by Bourdon-tube
  gauges. The pressure tube is connected to an
  indicator or pointer by a mechanical linkage.
  The gauges typically are calibrated in PSI.
• The most common pressure gauges have a pressure
  range of 3,000 6,000 psi. More the adequate
  for most mobile hydraulics.
• Accuracy for the typical pressure gauge is 2 /-.

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Temperature gauges

• Typically calibrated in degrees Fahrenheit.
• Be sure to remember that the gauge is reading the
  temperature of the fluid in the gauge itself and
  not necessarily the temperature of the fluid in
  the pump or system components.

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Measuring shaft speed

• The technician places a mark on the motor shaft.
  Then a photo-electric sensor plugged into the
  tester detects reflection as the shaft rotates.
  The tester converts this signal into a direct rpm
  reading.
• The main advantage is the technician can
  distinguish between reduced flow due to loss of
  pump speed or reduced flow resulting from other
  causes.

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Accuracy of testers

• Most manufactures promise accuracy of 1 - 2.
• Variations in temperature and viscosity can
  affect the results. Tests run for a long period
  may raise the temperature of the fluid enough to
  affect the test results.
• Also be careful of promised accuracy levels.
  Most tolerances are based on full-scale readings.
  For example a 150-gpm flowmeter with 4 accuracy
  reads /- 6 at full flow or a variation of
  144gpm to 156gpm. But this same meter is used on
  a 20gpm system the same 6 applies giving us a
  range of 14gpm 26gpm. Too much variation.
  Therefore use a tester just large enough for the
  given job.

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Troubleshooting Kits

• Be sure to have fittings for pressure testing and
  flow testing different systems
• Hand pump
• Handy for testing main relief valves
• Circuit relief valves
• Testing spool valves for leakage