Dawson EMV-70 METRIC, Operator'S Instructions/Spare Parts List

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7.4 Oil blowing out of the motor blow-off valve.
7.4.1 Drain line restricted or blocked – stop work immediately.
7.4.1.1 Check the drain line hose for obvious restrictions at fittings,
filters etc.
7.4.1.2 Check the drain hose for damage – look carefully as the bore of
the hose can be crushed even when the outside of the hose looks
to be in good order at a casual glance.
7.4.1.3 Check the drain hose point of entry into the base machine
hydraulic oil system – it is always best to run it directly to tank.
7.4.1.4 Do not work with quick disconnects as they can cause restriction
or complete blockage when they appear to be correctly connected.
7.4.2 Drain line being pressurised – check that the line is not connected to a supply
line e.g. the pressure line from a breaker circuit.
7.4.3 Long drain hose or the hose bore too small – either of these can contribute to
an increase in back pressure.
7.4.4 Extremely cold weather – if the base machine hydraulic oil is of an
inappropriate viscosity grade for the ambient temperature it may well be too
thick. This will cause an increase in back pressure in the drain hose.
7.4.5 Faulty Blow-Off Valve on the motor casing – check that this has a minimum
crack pressure of 6 bar and a maximum of 7 bar. Replace if unsure using a
new calibrated valve and a new sealing ring.
7.4.6 Leaking seals on the sequence valve cartridge leading to excessive drain line
flow rate – remove the drain line from the EMV and measure leakage flow
rate. Leakage in excess of 5 l/min (1.33 gpm) indicates either a seal kit
problem with the sequence valve or high internal motor leakage. Split the
sequence valve drain line and motor case drain line and measure leakage
rates independently – the sequence drain line should have little or know
leakage.
Motor Blow-
Off Valve