TH220B, TH330B and TH340B Telehandlers Hydraulic System Caterpillar

Main Control Valve (Implement)

Usage:

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Illustration 1	g00999457
Main Control Valve (Implement) (1) Electronic Pilot Valve (Implement) (2) Control Valve (Implement) (3) Control Valve (boom raise/lower) (4) Control Valve (tilt) (5) Control Valve (auxiliary) (6) Control Valve (boom extend/retract) (7) Control Manifold (Pilot ECM) (8) Solenoid Valve shutoff for the Pilot Oil (9) Manifold Valve (Inlet) (10) Manifold Valve (Outlet) (11) Relief Valve (Pressure reducing valve) (12) Screw (13) Relief Valve (line relief valve and check valve) (14) Valve Assembly (Steering priority) (15) Relief Valve (Load sensing signal) (16) Flow Control Valve (Dump valve for the load sensing signal) (17) Check Valve (Return oil back pressure)

The Main Control Valve (Implement) is located at the rear of the machine. The main control valve is pilot operated. The Electronic Pilot Valve (implement) (1) is directly mounted to the side of the Control Valve (implement) (2). Pilot valve (1) consists of two Control Manifolds (Pilot ECM) (7), eight proportional solenoids and eight pressure reducing valves. The machine ECM sends commands that are activated by the operator to the correct pilot ECM (7). Pilot ECM (7) controls the proportional solenoids. The proportional solenoids control the pilot reducing valves. Pilot valve (1) contains four pair of proportional pilot solenoid valves. Each pair of proportional pilot solenoid valves are used to actuate an individual spool within the Control Valve (implement) (2). Relief Valve (pressure reducing valve) (11) supplies pilot pressure to the ends of the spools in proportion to the current that is supplied to the solenoid.

Control Valve (implement) (2) includes the following sections:

(9) Manifold Valve (inlet)
(6) Control Valve (boom extend/retract)
(5) Control Valve (auxiliary)
(4) Control Valve (tilt)
(3) Control Valve (boom raise/lower)
(10) Manifold Valve (outlet)

The manifold valve (inlet) includes the following components:

(14) Valve Assembly (Steering priority)
(15) Relief Valve (Load sensing signal)
(16) Flow Control Valve Group (Dump valve for the load sensing signal)
(17) Check Valve (Return oil back pressure)
Orifice Check valve
Screens (75 and 100 micron)

Note: Relief Valve (Load sensing signal) is sometimes referred to as the signal limiter valve. The two terms have the same meaning throughout this story.

Reference: See Systems Operation/Testing and Adjusting, " Manifold Valve (Inlet)" for more information.

The valve sections for the telescoping cylinder, auxiliary services, coupler tilt and the boom cylinder include the following components:

Pressure compensator valve
Load check valve
Main control valve spool
(13) Relief Valve (Line relief valve and check valve)

Note: The Relief Valves (Line relief valve and check valve) are only installed in the sections for the auxiliary circuits and the coupler tilt.

The control valves control the delivery and the return of hydraulic oil to the machine implements.

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Illustration 2	g01133581
The spools for the Control Valve are shown in the HOLD Position. (T) Passage to hydraulic tank

The control valve spools for the boom extend/retract (telescoping), coupler tilt, and boom raise/lower for the Control Valve (implement) are closed to the hydraulic tank (T) when the joystick control is in the HOLD position. The main spool in the section for the auxiliary circuits is open to the hydraulic tank (T) when the joystick control is in the HOLD position.

In the event of a loss of hydraulic power, oil locked into the telescoping cylinder and the boom cylinder will prevent the boom from lowering. The cylinders can not be lowered or retracted until the lock valves on the cylinders are overridden. The implement control valve for the telescoping cylinder and the implement control valve for the boom cylinder are equipped with screws for manually moving the main spools.

After the lock valves on the cylinders are overridden, the main spools are moved into the position that allows the blocked oil in the cylinders to return to the hydraulic tank. The telescoping cylinder and the boom cylinders can then be lowered or retracted.

Note: Refer to the Operation and Maintenance Manual, "Boom Retacting and Boom Lowering without Hydraulic Power" for more information.

Each implement valve section contains a pressure compensating valve. All pressure compensating valves are interconnected. The pressure compensating valves allow the oil flow to be proportionally divided between each of the operating circuits when the flow demands of the system exceed the total flow that is available from the pump. All of the hydraulic actuators will continue to function. However, the actuators will operate at a reduced speed.

Also, the pressure compensating valves can determine the function that has the highest demand in all of the valves. Then, the load sensing signal pressure for the highest demand is sent to the pump. The pump uses the load sensing signal pressure in order to determine the amount of flow that is required.

Note: Load sensing signal pressure is sometimes referred to as signal oil. The two terms have the same meaning throughout this story.

The pressure compensating valves maintain cylinder speeds which are proportional to the position of the joystick control. The cylinder speed will not increase if the engine speed is increased in order to engage an additional system. These characteristics aid smooth machine operation when more than one system is in operation.

Each implement control valve section includes the following positions:

The positions for the boom extend/retract (telescoping) function: