Boom Circuit

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Boom Circuit

The boom circuit consists of the following major components:

- boom 1 spool

- boom 2 spool

- boom cylinders

- drift reduction valve

- boom lowering control valves (if equipped)

- boom regeneration valve

- SmartBoom™ (if equipped)

NOTE: The 312D Hydraulic Schematic (KENR6556) was used to develop the ISO schematics.

Boom 1 Spool: The boom 1 spool controls oil flow from the drive pump. The boom 1 spool receives a BOOMRAISEpilot signal on the bottom of the valve, and a BOOMLOWERpilot signal on the top of the valve.

Boom 2 Spool: The boom 2 spool controls oil flow from the idler pump. The boom 2 spool receives a BOOMRAISEpilot signal from the joystick on the top of the valve stem, when active. The boom 2 spool does not operate during BOOMLOWER. The boom 2 spool has no provisions for return oil from the boom cylinders.

Boom Cylinders: The boom cylinders work in parallel to control the raise and lower movement of the boom. When oil is supplied to the head end of the boom cylinders, the boom will raise. When oil is supplied to the rod end of the boom cylinders, the boom will lower.

Boom Drift Reduction Valve: The boom drift reduction valve prevents oil from leaking from the head end of the boom cylinders. For BOOM LOWER, pilot oil from the joystick is used to unlock the lock check valve in the drift reduction valve.

Boom Lowering Control Valves: The boom lowering control valves are infinitely variable, pilot operated control valves that control the movement of the boom during lowering. The boom lowering control valves are a safety device and prevent boom cylinder drift with valving mounted directly on each of the boom cylinders, that controls boom cylinder head end oil flow.

Because the valves are mounted directly to each of the boom cylinders, the boom lowering control valves will prevent the boom from falling, even if a hose becomes defective from the main control valve to the cylinders.

The boom lowering control valves also work in conjunction with the SmartBoom™ system to control the boom with the function active.

Regeneration Valve: The regeneration valve allows return oil from the head end of the boom cylinders to be directed into the rod end of the cylinders when the boom is lowered fast. The 311D/312D/314D is also equipped with a Boom Electronic Regeneration feature, that includes a solenoid and a pressure switch.

SmartBoom™: The SmartBoom™ attachment enhances operation of the boom function and significantly reduces cycle times of the machine. The SmartBoom™ is essentially a boom float attachment, which allows the operator to lower the boom under its own weight or for the boom to raise up due to stick force. The SmartBoom™ attachment is typically used in EAME.

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When the boom joystick is moved less than half of the travel distance for BOOM RAISE, low pilot oil pressure is supplied to the boom 1 control valve and the boom 2 control valve.

The force of the centering spring in the boom 1 control valve is less than the force of the centering spring in the boom 2 control valve. When the boom is raised at a low speed, the boom 1 control valve opens and the boom 2 control valve remains closed due to the low pilot pressure.

The drive pump supply oil supply oil flows past the boom 1 control valve and unseats the check valve in the drift reduction valve and flows to the head end of the boom cylinders.

Return oil from the rod end of the boom cylinders returns back to the tank through the boom 1 control valve.

With the boom valve partially shifted less oil is directed to the NFCrelief valve. Less oil to the NFCrelief valve results in a reduced NFCsignal to the drive pump. The drive pump control valve causes the pump to upstroke to provide flow to operate the boom.

ABOOM RAISE operation at low speed is accomplished when only the drive pump is supplied to the head end of the boom cylinders.

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When the operator begins to move the joystick, metered pilot pressure causes the boom 1 spool to shift slightly. The boom 2 spool does not shift as previously described.

With the boom 1 spool initially shifted, the center bypass passage is partially closed. This movement causes NFCpressure to decrease, which signals the drive pump to begin to upstroke.

The load check valve prevents unexpected implement movements when a joystick is initially activated at a low pump delivery pressure. The load check valve also prevents oil loss from a high pressure circuit to a lower pressure circuit.

As the pump supply pressure increases, the load check valve opens to allow pump supply oil in the parallel feeder passage to flow to the control spool.

The control spool meters pump supply oil to the head ends of the boom cylinders.

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ABOOM RAISE operation at high speed is accomplished when supply oil from both the idler pump and the drive pump is supplied to the head end of the boom cylinders.

Boom 1 control valve and boom 2 control valve are both shifted during high speed operation.

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As the operator moves the joystick farther, the pilot pressure on the end of the spool increases. The increased pilot pressure causes the boom 1 spool to shift further to the right.

The center bypass passage is now closed, which blocks the oil flow to the NFC signal port on the right pump control valve. When the NFC signal is reduced, the pump upstrokes and flow is increased. The increased flow can no longer return to tank through the center bypass passage. All oil now flows through the parallel feeder path.

The increased oil flow to the parallel feeder passage causes pressure to rise in the parallel feeder passage. The increased oil pressure overcomes the force of the load check spring and the boom head end pressure, which causes the load check valve to unseat. Oil flows out to boom cylinders.

The oil returning from the rod end of the cylinders flows past the spool and returns to tank.

The pilot oil flow shifts the boom 2 control valve. The idler pump supply oil in the parallel feeder passage flows past the check valve and flows out to the head end of the boom cylinders.

The idler pump supply oil combines with the drive pump supply oil at the boom drift reduction valve (not shown) and flows to the head end of boom cylinders.

Return oil from the rod end of boom cylinders flows to the boom 1 control valve and then to the tank. The boom 2control valve does not handle any of the return flow for the boom circuit.

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During combined operations of BOOM RAISE and STICK IN, the boom raise pilot oil pressure shifts the boom priority valve to reduce the stick in pilot pressure for the stick 2 control valve. With the reduction in stick in pilot pressure to the stick 2 control valve, more pump flow is directed to the boom cylinders during this combined hydraulic operation.

NOTE: For STICK IN, the stick circuit regeneration valve will shift to direct return oil from the rod end of the stick cylinder to the head end of the cylinders.

When the joystick for the stick is moved to the STICK IN position, a portion of the pilot oil from the pilot control valve for the stick flows through the pressure reducing valve for the boom priority to the stick 2 control valve. As the joystick for the boom is moved farther for a BOOM RAISE, pilot oil pressure from the pilot control valve for the boom increases. This gradual increase in pilot oil pressure causes the spool in the boom priority valve to gradually shift.

Aportion of the pilot oil to the stick 2 control valve from the stick pilot control valve is restricted by the boom priority valve. The pilot oil pressure acting on the stick 2 control valve decreases.

The stick 2 control valve shifts toward the NEUTRALposition. The amount of oil flow from the main pumps to the stick hydraulic circuit decreases. This change causes a greater portion of the oil flow from the main pumps to flow to the head end of the boom cylinders.

Since the pilot oil pressure from the boom pilot control valve directly corresponds to the amount of movement or position of the boom joystick a gradual change to boom priority occurs.

Thus, boom priority is controlled by the position of the joystick for the boom and boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.

The above information describes the condition of BOOM RAISE and STICK IN. During any combined function of BOOM RAISE and STICK IN, the boom priority valve reduces pilot pressure to the stick 2 control valve.

NOTE: If the joysticks are fully shifted for BOOMRAISEand STICK IN, stick in pilot pressure on the bottom of the boom 2 cancels the boom raise pilot pressure on top of the boom 2 spool. At the same time the boom priority valve prevents stick in pilot pressure from going to the stick 2 control valve.

These two actions result in the drive pump supplying oil to the boom cylinders and the idler pump providing oil to the stick cylinder.

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For BOOM LOWER only the boom 1 control valve is used. The drive pump partially strokes to provide flow to the rod end of the boom cylinders. The boom 2 control valve is a regeneration valve that directs oil from the head end of the boom cylinders to the rod end of the boom cylinders.

When the joystick is shifted pilot oil moves the boom 1 control spool up, and unlocks the drift reduction valve. Pilot oil also flows to the boom regeneration solenoid valve. When the boom 1 control spool is fully shifted, the center bypass valve is never fully closed off. By not closing off the center passage, there is an NFC signal to the drive pump. The drive pump never fully upstrokes.

Due to the force of gravity, with the lock valve unlocked, the weight of the boom and the load on the boom force the return oil out of the cylinder head ends back to the boom 1 control valve and to the boom 2 control valve.

The boom 1 control valve restricts the return oil flow. The boom 2 valve functions as a regeneration valve. When the boom regeneration solenoid is energized by the Machine ECM, pilot oil moves the boom 2 valve up and oil from the head end of the boom cylinders flows to the rod end of the boom cylinders.

The return oil from the head end enters the supply passage to the rod end to help fill the cylinders and prevent cylinder cavitation. The boom 2 valve allows the excavator to operate more efficiently. The main pump supply oil not required to lower the boom is available to operate another circuit.

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The 311D/312D/314D boom electronic regeneration circuit provides engine speed control and regeneration valve control.

If the boom is lowered when the engine speed dial is in position 10, the engine speed will decrease which conserves fuel.

The boom lower pilot pressure switch and the engine speed dial send a signal to the Machine ECM. The Machine ECM processes the signals and sends a signal over the Data Link to the Engine ECM, which decreases engine speed.

The boom 2 (regeneration) valve size has been increased resulting in a faster boom down speed. The boom regeneration solenoid is used to lower the boom slowly when the engine speed dial is in positions 1-8.

When the boom regeneration solenoid is de-energized by the Machine ECM, the boom 2 spool is closed and oil from the head end of the cylinder returns to tank through the boom 1 spool but is blocked at the boom 2 spool. Since the boom 1 control valve restricts the return oil flow from the head end of the boom cylinders, the boom lowers at a slower speed.

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The boom pilot oil flow shifts the boom control spool to the left against the force of the centering spring. Supply oil from the drive pump in the parallel feeder passage flows past the load check valve to the rod end of the boom cylinders.

Some of the oil in the center bypass passage flows past the center land to provide a reduced NFCsignal. The reduced NFC signal causes the drive pump to only partially upstroke.

Part of the return oil from the head end of boom cylinders flows to the boom drift reduction valve.

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Boom Drift Reduction Valve: The boom drift reduction valve prevents oil from leaking from the head end of the boom cylinders. The boom drift reduction valve is located on the main control valve group. The boom drift reduction valve has the following components:

-the shuttle valve

-the check valve

-the line relief valve

In NEUTRAL, the shuttle valve and check valve are closed by spring force. Oil is blocked between the boom control valve and the boom cylinders.

For BOOM RAISE, the shuttle valve is closed by spring force. When closed, the shuttle valve allows oil from the boom control valves to act on one end of the check valve.

Oil pressure from the boom control valves acts on the other end of the check valve. The check valve opens (due to pressure differential on check valve) to allow oil flow to the rod end of the boom cylinders.

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For BOOMLOWER, the shuttle valve is opened by pilot oil from the joystick. The shuttle valve allows oil from the spring end of the check valve to return to tank.

Oil pressure from the boom cylinder head end opens the check valve. The check valve allows oil flow from the head end of the boom cylinders to return to the boom control valve.

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The boom lowering control valves (1 and 2) are mounted on the head end of the boom cylinders.

The boom lowering control valves serve several purposes: - prevent the boom from falling rapidly in case of hose failure - provide BOOMLOWER control with SmartBoom™ (if equipped) activated - prevent boom drift

The lowering control valves are equipped with head end line relief valves (3) to protect the cylinders from sudden shocks.

Apilot line (4) directs pilot oil to unlock the lowering control valve so the boom can be lowered.

The tube (5) provides supply oil from the boom control valve.

Ahose (6) connects both lowering control valves. The line provides for equalization of pressures in the head end of the cylinders when the boom is raised or lowered to provide smooth movement.