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Introduction To Hydraulic Schematics

Accurate diagrams of hydraulic circuits are essen-

tial to the technician who must repair it. The dia-

gram shows how the components will interact. It

shows the technician how it works, what each com-

ponent should be doing and where the oil should be

going, so that he can diagnose and repair the sys-

tem.

CIRCUIT DIAGRAMS

There are two types of circuit diagrams.

A: Cutaway Circuit Diagrams show the internal

construction of the components as well as the oil

flow paths. By using colors, shades or various pat-

terns in the lines and passages, they are able to

show many different conditions of pressure and

flow (Fig 1).

Figure 1

B: Schematic Circuit Diagrams are usually

preferred for troubleshooting because of their ability

to show current and potential system functions. A

schematic diagram is made up of consistent

geometric symbols for the components and their

controls and connections (Fig 2).

Figure 2

1. Schematic symbol systems

A: I.S.O = International Standards Organization.

B: A.N.S.I. = American National Standards Institute

C: A.S.A = American Standards Association

D: J.I.C. = Joint Industry Conference

A combination of these symbols are shown in this

manual. There are difference between the systems

but there is enough similarity so that if you under-

stand the symbols in this manual you will be able to

interpret other symbols as well.

2. Hydraulic reservoirs

Figure 3

Reservoirs (Fig 3) are pictured as either an open

square meaning it is a vented reservoir, or a closed

reservoir meaning that it is a pressurized reservoir.

Every system reservoir has at least two lines con-

nected to it, and some have many more. Often the

components that are connected to it are spread all

over the schematic. Rather than having a lot of

confusing lines all over the schematic, it is custom-

ary to draw individual reservoir symbols close to

the component. Similar to the ground symbol in

some wiring schematics. The reservoir is usually

the only component to be pictured more than once.