Note: The HH45 Harvester Head, HH55 Harvester Head, and HH65 Harvester Head have one holding arm. The HH75 Harvester Head has two holding arms. The holding system operates similarly for harvester heads with one holding arm or two holding arms.
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| Illustration 1 | g00743292 |
Location of the Holding Arms (1) Holding arm cylinder. (2) Holding arm. | |
The movement of holding arm (2) is controlled by holding arm cylinder (1). The measuring and control system controls the flow of oil from the main control valve to holding arm cylinder (1). A potentiometer in the cab and the measuring and control system control the percent of maximum oil pressure that flows to the holding arm cylinder.
Note: The HH45 Harvester Head does not control the pressure of the holding arm on the tree. The HH45 Harvester Head uses the potentiometer or the measuring and control system to control the pressure of the feed rollers on the tree.
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| Illustration 2 | g00645066 |
Schematic of the Holding System (NEUTRAL Position) (1) Holding arm cylinders. (The HH75 is shown.) (3) Bypass relief valve. (4) Relief valve. (5) Solenoid valve. (6) Main control valve. (7) Line relief valves. (8) On/off solenoid. (9) Valve spool. (10) On/off solenoid. (11) Resolver. (12) Flow compensator valve. (13) Signal limiter valve. (14) Signal limiter valve. (15) Resolver. (16) Proportional solenoid valve. (17) Proportional solenoid valve. (18) Variable pressure reducing valve. (A) Pilot pressure line. (B) Signal line (Tree Harvester). (C) Pressure line. (D) Return line. (E) Hydraulic oil line. (The oil line is not used on the HH45 Harvester Head.) | |
NEUTRAL Position
When the holding arms are not being used, valve spool (9) is in the NEUTRAL position. No oil will flow to the holding arm cylinders or from the holding arm cylinders.
When valve spool (9) is in the NEUTRAL position, there is no signal pressure from this section of the main control valve.
Line relief valves (7) protect the holding arm cylinders and hydraulic oil lines from damage when valve spool (9) is in the NEUTRAL position. When an external load acts on a holding arm, the oil pressure in the circuit increases. When the pressure in the circuit exceeds the relief valve pressure setting, the line relief valve opens. The oil in the circuit flows to the hydraulic oil tank on the machine through return line (D) .
CLOSE Position
When the operator closes the holding arms, solenoid (8) energizes. Solenoid (8) causes valve spool (9) to move to the DOWN position.
Oil under pressure flows through flow compensator valve (12) to bypass relief valve (3). The flow compensator valve limits the maximum flow of oil to the holding arm cylinders. Oil flows through the check valve in solenoid valve (5) to the head end of holding arm cylinders (1). Oil from the rod end of the holding arm cylinders returns to the main control valve. From the main control valve, the oil returns to the hydraulic oil tank through the return line.
When the harvester head is mounted on a wheel harvester, the movement of spool (9) will create a signal pressure. Hydraulic oil is sent to signal limiter valve (13) and to resolver (11). The oil passes through resolver (11) to flow compensator valve (12) and resolver (15). The oil passes through resolver (15). The oil returns to the machine through line (B). This pressure is used to upstroke the implement pump.
Signal limiter valve (13) controls the pressure in the head end of the holding arm cylinders. When the pressure in the head end circuit exceeds the pressure setting of valve (13), the valve opens. This allows oil to flow back to the machine through return line (D). The flow of oil back to the machine reduces the pressure in the holding arm cylinders.
Resolver (11) allows signal limiter valves (13) and (14) to be set at different pressures.
Solenoid valve (5) and valve spool (9) remains in the DOWN position while the tree is processed. With the valve spools in the DOWN position, the holding arms keep pressure on the tree as the diameter of the tree changes.
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| Illustration 3 | g00345711 |
Bypass relief valve | |
Bypass relief valve (3) allows low pressure to be applied by the holding arms as the tree is processed. Low pressure allows greater ease for the tree to slide through the harvester head. When the tree attempts to slip out of the harvester head, the check valve in solenoid valve (5) closes. This prevents the holding arms from opening.
The check valve prevents oil flow from the head end of the holding arm cylinder to the main control valve. The pressure in the head end of the holding arm cylinder must increase to the pressure setting of relief valve (4) in order to open the holding arm with the solenoid valve (5) in the DOWN position.
On the HH55/HH65/HH75 Harvester Heads, the pressure of the holding arms on the tree can be reduced by variable pressure reducing valve (18). Variable pressure reducing valve (18) contains two proportional solenoid valves. Proportional solenoid valve (16) controls the pressure to the delimbing knives. Proportional solenoid valve (17) controls the pressure to the holding arms.
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| Illustration 4 | g00364102 |
Location of the Variable Pressure Reducing Valve | |
Proportional solenoid valve (17) controls the pressure of the holding arms on the tree. The variable pressure reducing valve is located near the end of the main control valve.
Note: Proportional solenoid valve (17) controls the pressure of the feed rollers on the tree for the HH45 Tree Harvester Head.
A potentiometer in the cab and the settings of the measuring and control system controls the movement of proportional solenoid valve (17). The setting of the potentiometer overrides any settings in the measuring and control system. As the proportional solenoid valve moves into the UP position more oil flows through the valve. The pressure of the holding arms on the tree decreases.
Reference: Refer to Systems Operation, "Solenoid Valve (Variable Pressure Reducing)" for a description of the operation of variable pressure reducing valve.
OPEN Position
The operator energizes solenoid (10) and solenoid (5) in order to open the holding arm. Valve spool (9) moves to the UP position. Hydraulic oil then flows to the rod end of holding arm cylinders (1). Solenoid valve (5) moves to the up position. Hydraulic oil from the head end of holding arm cylinder (1) is allowed to return to the main control valve. The holding arm opens.
The movement of valve spool (9) allows oil to flow to signal limiter valve (14). Signal limiter valve (14) controls the pressure in the rod end of the holding arm cylinder. When the pressure in the rod end circuit exceeds the pressure setting of valve (14), the valve opens. This allows oil to flow back to the machine through return line (D). The flow of oil back to the machine reduces the pressure in the holding arm cylinders.
When the harvester head is mounted on a wheel harvester, the movement of spool (9) will create a signal pressure. Hydraulic oil is sent to signal limiter valve (14) and to resolver (11). The oil passes through resolver (11) to flow compensator valve (12) and resolver (15). The oil passes through resolver (15). The oil returns to the machine through line (B). This pressure is used to upstroke the implement pump.