CAP 8D4221 - Caterpillar

Load Sensing During the Slight Operation of an Individual Cylinder
Illustration 2 g01589174
Bucket control valve (BUCKET CLOSE) (1) Lines to hydraulic implement (bucket) (9) Flow compensator valve (10) Valve chamber (15) Passage (16) Passage (30) Passage (31) Passage (32) Spool (PD) Delivery pressure (PL) Load pressure (LS) Load sensing signal pressureCombined flow from the front pump and rear pump (PD) enters the bucket control valve. Spool (32) moves a slight amount to the left. Passage (31) opens a slight amount. The oil delivery flows through passage (31), valve chamber (10), passage (30) and passage (16). The oil then flows to bucket cylinder (1). The true load signal pressure (PL) is generated in passages (16) and (15). True load signal pressure (PL) flows to the signal duplication valve. The true load signal pressure is duplicated as load sensing signal pressure. The load sensing signal pressure is sent to the flow compensator valves. The load signal pressure flows to the front pump and the rear pump in order to regulate the output flow of the pumps.The output flow of the pumps is decreased in order to maintain a pressure difference between the pump delivery pressure (PD) and the load sensing signal pressure (LS) to 1960 kPa (285 psi). If the bucket control lever is moved closer to the NEUTRAL position, the size of the opening at passage (31) decreases.As the pump oil flow through passage (31) decreases, pressure in the passage that is below flow compensator valve (9) decreases. Load signal pressure (PL) in passage (16), the load sensing signal pressure (LS) and the force of the spring on the flow compensator valve (9) pushes flow compensator valve (9) downward. This reduces the flow through passage (30) which results in a pressure decrease in passages (16) and (15). The reduced load signal pressure in passage (15) flows to the signal duplication valve and the load sensing signal pressure is also reduced. The output flow of the pumps decreases further by load sensing regulation.When the output flow of the pumps is decreased, the size of the opening at compensator valve (9) is also decreased.Load Sensing During Combined Control Valve Operations
Illustration 3 g01574953
Circuit diagram for combined control valve operation (BOOM RAISE and STICK OUT) (1) Lines to hydraulic implement (stick) (2) Lines to hydraulic implement (boom) (3) Passage (5) Shuttle valve (7) Signal duplication valve (8) Passage (9) Shuttle valve (10) Passage (12) Shuttle valve (13) Compensator valve (boom) (14) Boom control valve (16) Passage (17) Stick control valve (18) Compensator valve (stick) (22) Load check valve (23) Passage (24) Passage (25) Passage (27) Passage (28) Passage (29) Passage (30) Boom drift reduction valve (31) Pilot pump (32) Front pump (33) Rear pump (34) Orifice (40) Line (41) True load signal port (42) Duplicate load signal port (PD) Pump delivery pressure (PLS) Load pressure (stick side) (PLB) Load pressure (boom side) (LS) Load sensing signal pressureIn the following explanation of oil flow, the joysticks are at the FULL STROKE position.. The boom hydraulic circuit and