308C CR Excavator Hydraulic System – Main Hydraulic Pump

Construction



Illustration 1 g00749351

Main pump

(1) Housing

(3) Outlet port (left pump)

(4) Blade pump

(5) Pilot pump

(6) Outlet port (right pump)

(7) Outlet port (blade pump)

(8) Outlet port (pilot pump)

(9) Right pump

(10) Left pump

(13) Inlet port (main pump)

(14) Inlet port (blade pump)

(15) Inlet port (pilot pump)

(17) Port

(18) Port

Main Pump Operation (No Load)



Illustration 2 g00752980

Main pump

(1) Housing

(3) Outlet port (left pump)

(4) Blade pump

(5) Pilot pump

(6) Outlet port (right pump)

(10) Inlet port (main pump)

(14) Valve plate

(15) Passage

(16) Passage

(17) Inlet passage

(18) Swashplate

(19) Cover

(20) Piston

(21) Retainer

(22) Piston shoe

(23) Shaft

(24) Guide

(25) Creep plate

(26) Barrel

(27) Control piston

(28) Control cover

The main pump is a single pump that functions in the same manner as a two pump operation. Barrel (26) is incorporated in housing (1) of the main pump. Ten pistons (20) are contained in barrel (26). The action of the pistons (20) allow the main pump to function in the same manner as a two pump operation. Pump oil separates and flows into the right pump (9) and into left pump (10) oil circuits. Each piston (20) forces the oil delivery from the pump through pump outlet port (3) and outlet port (6). Five pistons (20) perform operations for the right pump (9). The remaining five pistons perform operations for the left pump (10) .

Oil from the hydraulic tank enters the main pump through inlet port (13) .

Blade pump (4) and pilot pump (5) are directly connected to the main pump.

Shaft (23) of the main pump is directly coupled with the engine flywheel. Shaft (23) is also splined with barrel (26). Barrel (26) has ten pistons (20). The head of each piston (20) pivots on piston shoe (22). Piston shoes (22) are secured to creep plate (25) by retainer (21) .

When shaft (23) is driven by the engine flywheel, barrel (26) turns on valve plate (14). This allows pistons (20) to rotate on creep plate (25). Creep plate (25) is held to swashplate (18) .

Oil from the hydraulic tank goes into the main pump through inlet port (10). The oil goes through inlet passage (17) of valve plate (14). The oil then enters the bores of barrel (26). As barrel (26) rotates, pistons (20) move in or pistons (20) move out of the bores of barrel (26). Oil is drawn behind the piston into the bore of barrel (26) as piston (20) moves out of the bore of barrel (26). Oil is pushed ahead of the piston (20) as the piston moves in the bore of the barrel. The oil that is pushed ahead of each piston alternately goes through passages (15) and (16) of valve plate (14). Five pistons (20), which are not located next to each other, force oil flow through outlet port (6) as right pump oil flow. The remaining five pistons (20) force oil flow through outlet port (3) as left pump oil flow. The oil flow through port (6) goes to the right body of the main control valve. The oil flow through port (3) goes to the left body of the main control valve.

The length of stroke for each piston (20) changes depending on the angle of swashplate (18). This change of displacement regulates the output flow of the pump.