Service Manual

8. Hydraulic valves

Figure 10

A control valve (Fig 10) has envelopes (squares)

that represent the valve spool positions. There is a

separate envelope for each valve position and

within these envelopes there are arrows showing

the flow paths then the valve is shifted to that posi-

tion. All the port connections are drawn to the enve-

lope that shows the neutral position of the valve.

We can mentally visualize the function of the valve

in any position. A valve that has parallel lines

drawn outside of the valve envelopes shows that

this valve is capable of infinite positioning. This

valve usually operated between the positions

shown. An example of this type of valve would be a

flow priority valve or a pressure regulating valve.

9. Actuators

Figure 11

The valve spools can be controlled a variety of

ways. The top picture (A) shows the symbol for a

lever control. The middle picture (B) shows the

symbol for a pedal control (foot operated). The

lower control (C) is an electric solenoid.

10. Hydraulic Cylinders

Figure 12

A cylinder symbol (Fig 12) is a simple rectangle

representing the barrel. The rod and piston are rep-

resented by a tee that is inserted into the rectangle.

The symbol can be drawn in any position.

11. Miscellaneous

Figure 13

Filters, strainers and heat exchangers (coolers) are

shown as squares that are turned 45 degrees and

have port connections at the corners. A dotted line

90 degrees to the oil flow indicates a filter or a

strainer. A solid line 90 degrees to the oil flow with

2 triangles pointing out indicates a cooler. The

symbol for a heater is like that of a cooler, except

the triangles point inward.

12. Flow controls

Figure 14

The basic flow control (Fig 14) is a representation

of a restrictor. If the restrictor is adjustable a

slanted arrow will be drawn across the symbol.