New Holland T8010 Manual page 746

Composite Symbols
One Way Valves
NO
FLOW
ONE WAY VALVE SHOWN IN
THE CLOSED POSITION
A more complex one way valve is now shown. This directional
control symbol uses a multiple envelope (square) system that
has a separate square for each position. Remember all of the
port connections are made to the envelope that shows the
neutral condition of the valve. Within each envelope are
arrows showing the flow paths when the valve is shifted to
that position.
Two Position Valves
PUMP
RELIEF
VALVE
A simple control valve has two envelopes (representing the
spool) if it is a two position valve. The envelopes show the
flow conditions when they are in one position. The above
schematic is showing that oil is being supplied to the rod end
of the cylinder. If we mentally visualize the directional control
valve moved to the other position, it would be as shown
below.
Here, pressurized oil is being supplied to the piston end of
the cylinder and oil from the rod end of the cylinder is allowed
to flow to the reservoir.
Section 35 - Hydraulic Systems, 3PT - Chapter 1
FREE
FLOW
MENTALLY VISUALIZE A BUILD
UP OF PRESSURE ON THE
RIGHT SIDE OF THE VALVE
714L8A
CYLINDER
ROD END
CONTROL
VALVE
CYLINDER
PISTON END
714L8B
714L8C
Three Position Valves
OPEN CENTER THREE POSITION VALVE
CLOSED CENTER THREE POSITION VALVE
Three position valves will have a centered (neutral) position.
The centered position can be either open or closed to flow.
The open center is usually used with a fixed displacement
pump and the closed center is usually used with a variable
displacement pump.
Actuating Controls
LEVER
713L8G
TWO POSITION, CONTROLLED BY
EXTERNAL PILOT PRESSURE
THREE POSITION, SOLENOID CONTROLLED
WITH INTERNAL PILOT ASSIST PRESSURE
35-1-9
PEDAL
713L8F
TWO POSITION, CONTROLLED
BY SOLENOIDS
713L8E
713L8D
713L8D
713L8A
713L8B