Case 1650L Crawler Dozer Repair Manual

Manuals: Service Manual
Contents
Introduction
Rear Axle System
Engine
Hydrostatic Drive
Brakes and Controls
Hydraulic Systems
Tracks and Track Suspension
Cab Climate Control
Electrical System
Dozer Blade and arm
Tools
Platform, cab, bodywork and decals
Specials Tool Index
Manual Extract: Hydraulic systems – Hydraulic symbol – Pressure control

The basic valve symbol is a square (which is called an envelope) with external port connections and an arrow inside to show the fluid passage and direction of flow. The valve usually operates by balancing fluid pressure against a spring, so a spring is shown on one side of the symbol and a pilot pressure line on the other side.

Normally closed valve

A normally closed valve, such as a relief or sequence valve, is shown with an arrow offset from the ports [inlet (A), outlet (B)] toward the pilot pressure line (C) side of the square. The spring (D) holds the valve closed until the pilot line pressure is greater than the spring pressure.

Mentally visualize a build up of pressure in the pilot line and the envelope moving over, compressing the spring.
Fluid can now flow through the valve