BLOCK 1355804 - Caterpillar

Illustration 1 g02982464
Boom IMV section (partial shift)
(1) Port (boom cylinder head end)
(2) Pump-to-cylinder PHMV
(3) Load check valve
(4) Spring
(5) Cylinder-to-tank PHMV
(6) Port (boom cylinder rod end)
(7) Spool
(8) Compensator valve
(9) Passage
(10) Spool
(11) Return passage Slight movement of the joystick for the boom toward the BOOM RAISE position causes spool (7) and spool (10) to shift slightly upward. The front pump begins to move to an upstroke position. Spool (10) partially opens allowing the oil from the rod end of the boom cylinders in port (6) to flow to return passage (11). Spool (7) partially opens allowing the oil from the head end of the boom cylinders in port (1) to flow to load check valve (3). The work load pressure from the head end of the boom cylinders and the force of spring (4) now acts on load check valve (3). Since the pump delivery pressure is lower than the work load pressure in passage (1), load check valve (3) remains in the CLOSED position. The oil in the boom cylinder head end is blocked.
Illustration 2 g02982467
Boom IMV section (full shift)
(1) Port (boom cylinder head end)
(2) Pump-to-cylinder PHMV
(3) Load check valve
(4) Spring
(5) Cylinder-to-tank PHMV
(6) Port (boom cylinder rod end)
(7) Spool
(8) Compensator valve
(9) Passage
(10) Spool
(11) Return passage When the joystick for the boom is moved to the full BOOM RAISE position, pump-to-cylinder PHMV (2) and cylinder-to-tank PHMV (5) are actuated. Pilot oil then shifts spool (7) and spool (10) upward. Pump delivery oil in passage (9) flows through flow compensator (8). Load check valve (3) opens and allows the pump oil to flow to boom pump-to-cylinder spool (7). The pump oil then flows through port (1) to the head end of the boom cylinders. Return oil from the rod end of the boom cylinders, flows through port (6). Return oil flows through cylinder-to-tank spool (10) and to the hydraulic tank. Unexpected downward movement of the boom during a BOOM RAISE operation is prevented.Load check valve (3) also prevents oil loss from a high-pressure circuit to a lower pressure circuit. For example, the work tool is moved under a light load, and the boom cylinders are raised at the same time. The high-pressure oil of the boom cylinders wants to flow toward the low-pressure side of the work tool. The load check valve prevents the boom from lowering.