MAC/MTT-OPS-1
26 FEB 2019
SECTION 2
System Description
2-3
Hydraulic Drive Motor Speed Control
(Crossover Assembly)
The hydraulic drive motor speed control
(Crossover Assembly) consists of a flow control
valve, 2 hydraulic manifolds, crossover hose and
test ports.
Hydraulic Flow Control Valve
The hydraulic flow control is directional. The arrow
on the body indicates the direction of oil flow to
meter the bypassing oil. The adjusting knob on the
valve will allow adjustment of the oil flow to
bypass the drive motor, up to135 LPM (35 GPM) or
up to 700 RPMs (RPM increase/decrease will vary
depending on the size of hydraulic drive motor the
unit is equipped with).
If the flow control is reversed, the flow control
adjusting knob will not function and the full flow
capacity of the valve will bypass. This can result in
water pump rpm being below specifications with
no adjustment capability of the adjusting knob.
By turning the adjusting knob clockwise, the
hydraulic oil that is bypassing will be reduced,
increasing the speed of the water pump. Turning
the knob counter-clockwise will increase the
volume oil being bypassed reducing the water
pump speed. The flow control valve is typically
mounted on the PRESSURE manifold of the
hydraulic drive motor.
Hydraulic Drive Motor Activation
The hydraulic drive motor on MTT’s are typically
driven by the chassis hoist hydraulic system. The
activation can be controlled by the following:
– Existing Electric Hoist Valve
The MEGA cab control pump switch commands
the hoist valve to operate by sending an electric
signal to the electric solenoid on the hoist valve.
This operates the hoist valve, diverting the
hydraulic oil to the water pump drive motor.
– Pilot Operated Diversion Valve
A remote mounted diversion valve that receives
an electric signal from the cab control pump
switch to activate a pilot control to move a
spool within the diversion valve redirecting the
hydraulic oil to flow to the water pump drive
motor. Typically this type of valve is installed
between the hoist pump and the hoist valve.
– Existing Mechanically Operated Hoist Valve
Typically used on early model trucks with a
pneumatic system. This system is operated by
the cab control pump switch sending an electric
signal to an electric/pneumatic solenoid to
control a pneumatic cylinder. When the
pneumatic cylinder operates it moves the spool
valve of the hoist valve to divert hydraulic oil to
the water pump drive motor.
PRESSURE RETURNTEST PORTS
FLOW CONTROL CROSSOVER HOSE
Typical 135 lpm (35 gpm) Adjustable Hydraulic
Flow Control
ADJUSTING
KNOB
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