# Objectives

• Discuss cylinder theory as it relates to drifting problems.
• Evaluate common ideas about cylinder drift.
• Formulate a logical and efficient troubleshooting plan to deal with cylinder drift.

# The Problem

Imagine that you are working with a mobile crane. When the crane is parked and the outriggers are extended, one outrigger always drifts into the cylinder body. This leaves the crane sitting at a slight angle.

What could the cause of this problem be? And how will you find and fix it as efficiently as possible?

# The Circuit

The best way to get started is to quickly review the major circuit components. This particular crane uses a very simple outrigger circuit.

A positive displacement pump pushes fluid past a relief valve, then through a directional control valve into the active side of the cylinder. Fluid leaving the other side of the cylinder passes back through the directional control valve, and is filtered before returning to the tank. The blind end of the cylinder features a pilot operated (p.o.) check valve. This check valve is only piloted open when there is flow to the rod-end side of the cylinder.

Reservoir
Pump
Motor
Directional Control Valve
Relief Valve
Cylinder
P.O. Check Valve
Filter
Manifold
Manifold

# Cylinder Construction

### Basic Parts

The very basics of a cylinder include the cylinder barrel (or tube), gland, rod and piston. The piston should have a piston seal; a small ring that maintains a seal against the cylinder barrel as the rod extends and retracts.

It is this piston seal that keeps the two chambers of the cylinder (rod-end chamber and blind-end chamber) sealed into separate pressure zones.

In this module, we are exaggerating the clearance between the cylinder piston and tube to make it clear that the piston itself does not seal against the tube. In real life, however, the clearance would be very small.
Cylinder Tube/Barrel
Cylinder Rod
Gland
Piston Seal
Blind End Chamber
Rod End Chamber
Piston

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