Case 1221E Wheel Loader Service Manual

Table of Contents

• General
• Engine
• Power Train System
• Brakes
• Steering
• Work Equipment
• Electrical System

Manual Extract: BRAKE PUMP
The pumping operation of this unit (each cartridge) is obtained by providing a fixed interior cam surface and a rotating inner member (rotor) containing vanes which held in contact with the inner cam surface. As the rotor is rotated by the drive shaft, the vanes are urged outward against the outward sloping cam surface, forming a cavity at the inlet ports of the port plates. Atmospheric pressure and suction created by the expanding cavity between the rotating vanes fill the inlet cavity with fluid.
As the rotation continues and the vanes that had previously moved outward and now have fluid trapped between them and the port plates, follow the inward slope of the cam which decreases the cavity containing the trapped fluid and discharges the fluid at system pressure through the pressure port openings in the port plates.

The rotating portion of the unitized cartridges feature the use of pressure actuated vanes which are urged against the cam ring by pins located in the bottom of each rotor vane slot. Initial force to bring the vanes in contact with the cam ring contour during start up is provided by centrifugal force. When pumping operation starts and pressure is established, fluid under pressure fills the pin cavity through the feed holes.
The feed holes open to the pressure port twice every revolution. All other times they are closed off by the port plate. This pressure under the pin provides the force necessary to keep the vanes in contact with the cam contour.