XL 4100/5100 HYrDARAULIC SYSTEM OPERATIONS MANUAL
Form No. 29703
Center Pin
The center pin also known as (hydraulic swivel) is positioned in the center of the upperstructure and
undercarriage. It is the component that carries hydraulic fluid to the undercarriage from the upperstructure. This
design allows for 360 continous upperstructure rotation. All ports are identified by numbers and letters. Ports
1,2" are for main control valve propel fluid. Ports 3 & 4 are for steering valve pressure and return. Ports
D & B are not used on the XL 4100 and XL 5100 Remote Control. Port F delivers fluid to the interface valve,
Port E is used to deliver motor case drain fluid to tank, Port C - Steer Left, Port A - Steer Right. Main
components and their function are:
Center Pin - Fastened to the crawler carbody. Has ports machined in it to carry fluid to undercarriage
Housing - Fastened to the upperstructure and fits around the center pin. Has ports machined in it to
carry fluid to correct location to match ports of the center pin
Top gland - Located at top of center pin. Has machined ports to carry pilot and drain fluid
Seals - Located at all port areas. Keeps fluid trapped in individual ports
Bearings - Located at top and bottom of assembly. Reduces rotation forces against center pin assembly
FIGURE 69
CENTER PIN
XVIII. Propel Circuit
(continued)
61
Not Used
Not Used
Interface Valve
Case Drain Propel Motor
Steer Left
Steer Right
To Steer Valve
To Steer Valve
Return Steer Valve
Oscillation Valve
Propel Forward
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