HOUSING-COMPRESSOR 1017769 - Caterpillar

Hitch (Stem) In Hold
Hitch Valve (Valve Stem In Hold Position)
(5) Valve (hitch). (9) Valve (electrohydraulic). (10) Spool. (11) Cylinders. (12) Valve (relief). (13) Chamber. (15) Chamber. (17) Adjuster. (18) Setscrew. (19) Springs (two). (20) Passage (signal). (21) Passage. (22) Setscrew. (23) Chamber. (24) Springs (two). (25) Stem. (26) Opening. (27) Openings. (28) Valve. (29) Spring. (30) Valve (pressure reducing).Hitch valve (5) consists of main stem (25), pressure compensation valve (28), line relief valve (12) and electrohydraulic valve (9).When there is no electrical signal to electohydraulic valve (9), valve (9) allows no pilot oil to shift stem (25). Oil in Port "A" then remains blocked which maintains the hitch in the last position held before valve stem (25) moved to its hold position.Compensation valve (28) is moved to the right by the oil in the compensator against spring (29). This maintains a pressure of 90 psi at stem (25).Line relief valve (12) in the passage to Port "A" protects cylinders (11), valve (5) and the lines common to them, against external loads in excess of 20 700 kPa (3000 psi).Hitch Raise
Hitch Valve (Port "A" Position - Hitch Raise)
(5) Valve (hitch). (9) Valve (electrohydraulic). (10) Spool. (11) Cylinders. (12) Valve (relief). (13) Chamber. (14) Passage. (15) Chamber. (16) Passage. (17) Adjuster. (18) Setscrew. (19) Springs (two). (20) Passage (signal). (21) Passage. (22) Setscrew. (23) Chamber. (24) Springs (two). (25) Stem. (26) Opening. (27) Openings. (28) Valve. (29) Spring. (30) Valve (pressure reducing).When the hitch control lever is pulled back to raise the hitch, the electronic controller energizes valve (9). Spool (10) moves to the left to allow pilot oil from pressure reducing valve (30) to chamber (23). Pilot oil moves stem (25) to the right compressing centering springs (19) and opens work port "A" to pump oil pressure. The resulting load pressure at work port "A" goes through passages (14) and (16), through chamber (15), through passage (20) to the resolver network and on to the pump. The load pressure also goes through passage (21) to combine with the force 620 kPa (90 psi) of spring (29) to move valve (28) to the left against pump oil pressure. Pump oil flows through openings (27), through valve (28) and opening (26) to the metering area between stem (25) and chamber (13) (to work port "A"). As soon as oil pressure between openings (27) and the metering area becomes greater than load plus 620 kPa (90 psi), valve (28) moves to the right. Pressure compensation valve (28) moves back and forth with openings (27) metering pump oil to maintain a constant 620 kPa (90 psi) pressure drop across the pump to cylinder metering area of the main stem. This makes the flow rate independent of changing cylinder or system pressures.Oil from the rod ends of hitch cylinders (11) flows through port "B" to drain Work port "B" is always open to tank (regardless of the operation) through the hitch valve.When the hitch raises to the point where hitch and control lever positions