Excavator Parts AP12 PISTON SHOE 9 PCS FOR CAT E320 E320L 320BL AP12 HYDRAULIC PUMP Parts

Excavator Parts AP12 PISTON SHOE 9 PCS FOR CAT E320 E320L 320BL AP12 HYDRAULIC PUMP Parts

Force Transmission & Angle Self‑Adaptation The piston performs reciprocating linear motion inside the cylinder block, while the swash plate is a tilted fixed plate. Via spherical hinge connection, the piston shoe swings freely following the tilt angle of the swash plate and smoothly transfers the axial thrust of the piston to the swash plate. Without the piston shoe, the piston ball head would press directly against the swash plate in point contact, resulting in instant crushing and severe wear.

Convert Point Contact to Surface Contact to Reduce Contact Stress The piston ball head features a spherical surface, and the bottom of the piston shoe is a flat wide plane: Ball head ↔ Piston shoe: movable spherical hinge Piston shoe bottom ↔ Swash plate: surface contact sliding The contact area increases significantly and the unit pressure decreases, meeting the long‑term operating requirements of high‑pressure pumps.

Hydrostatic Oil Film Lubrication (Most Critical) A tiny orifice hole is located at the center of the piston shoe. High‑pressure oil flows through the piston interior, ball head and orifice hole into the recessed cavity at the bottom of the piston shoe, forming a thin 10～30 μm high‑pressure oil film between the piston shoe and swash plate. Functions:

✅ Convert metallic dry friction into fluid friction 

✅ Prevent scuffing and burning of the piston shoe and swash plate caused by direct metal contact

✅ Carry away frictional heat The overflow oil flows into the pump housing and serves as internal leakage return oil.

Maintain Contact with the Aid of the Retainer Plate (Set Plate) The set plate presses against the back of the piston shoe to ensure the piston shoe stays firmly against the swash plate surface. As the cylinder block completes one full rotation, each piston finishes one oil suction stroke and one oil discharge stroke, and the piston shoe slides cyclically over the swash plate.