Allied Construction Products, LLC www.alliedcp.com
23
TM574173_HP4000_18feb
12.0 Technical Information – [cont'd]
Operating Pressure
– A measure of the hydraulic oil
pressure (values given in PSI / BAR) taken in the
attachment’s supply line during operation.
Oil pressure will fluctuate with change in soil density
and amount of force exerted by the carrier. When
raised off the ground, the flow of oil is under no load,
and oil pressure is minimal. Each component of the
hydraulic system has a maximum working pressure.
For safety and reliability, pressure must be controlled
so that no component is subjected to pressures
beyond their design.
IMPORTANT
The operating pressure is not to be used as a
relief valve pressure setting. Poor performance
and significant heat generation will occur.
Relief Valve
– An adjustable, spring-loaded valve
that opens when a preset pressure value is reached.
A relief valve is safety device, used to protect the
circuit against hydraulic overload. Relief valves vary
in design. Pilot controlled pressure relief valves are
designed so that the relief pressure increases very
little as the flow through the valve increases. For Ho-
Pac applications, they are recommended over direct
acting type relief valves.
CAUTION
The relief valve is a safety device, used to protect
the circuit against hydraulic overload. It is a
required component.
Fig. 12-1 Flow-Pressure Diagram
Dynamic Relief Pressure –
Also referred to as
“Cracking Pressure”. The pressure measured at the
moment the oil pressure exceeds the preset value of
the relief valve and the spool “cracks” open.
Static Relief Pressure
– Also referred to as “Full
Relief Pressure”. The pressure measured at the
moment the relief valve has opened fully and all oil is
by-passed.
Opening Curve
– The dynamic pressure is always
less than the static pressure. A relief valve adjusted
to a dynamic pressure of 3000 psi (200 Bar) will
crack open when the preset point is reached, but fully
opens at a higher pressure. The opening curve is the
rise of pressure between dynamic and static.
IMPORTANT
The hydraulic system of the carrier must be
capable of providing the accepted oil flow at a
pressure equal to at least the dynamic relief
pressure.
12.4 Hydraulic Motor Options
Some Ho-Pac models offer different size motor
options. Refer to the General Specifications Table for
a list of available options.
12.4.1 Motor Rotation
The hydraulic motor is unidirectional, meaning it’s
designed to rotate in one direction only. Refer to Fig.
12-2. Viewed from the shaft end and with the idler
gear (large portion of the motor) downward, the left-
hand side port is marked [IN]. The right-hand port is
marked [OUT].
CAUTION
Pressurizing the outlet port will damage the
motor. Verify connections before pressurizing the
hydraulic circuit. When viewed from the shaft
end, the (IN) port is located on the left-hand side
and the (OUT) port is on the right-hand side.
The
motor is assembled for clockwise rotation.
Fig. 12-2 Motor Rotation as Viewed From Shaft End
FLOW
PRESSURE
Hydraulic
Flow Range
Operating
Pressure
Range
Static ReliefPressure
(No flow to attachment)
Dynamic ReliefPressure
(Reliefvalve cracks open)
Attachment
Operational
Range
Operating Pressure
Opening
Curve
IN
OUT
