SERV1852-02 August 2008
GLOBAL GLOBAL SERVIC SERVICE E LEARNI LEARNING NG TECHNICAL PRESENTA PRESENTATION
320D-336D HYDRAULIC EXCAVATORS TIER III ENGINES MAIN CONTROL CONTROL VALVE ALVE GROUP AND RETURN SYSTEM
Service Training Meeting Guide (STMG)
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Text Reference Main Control Valve Group
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INTRODUCTION
The main hydraulic system is a Negative Flow Control (NFC) System that supplies hydraulic power at high pressures and high flow rates to perform work. Two main hydraulic hyd raulic pumps supply oil to the main control valve group. The individual hydraulic circuits are controlled controlled by valves in the the main control valve group. The main hydraulic system supplies the following circuits: - swing - stick - left and right travel - bucket - auxiliary - boom Oil returning from these circuits flows back to through the return system to the hydraulic tank.
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Text Reference Main Control Valve Group
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INTRODUCTION
The main hydraulic system is a Negative Flow Control (NFC) System that supplies hydraulic power at high pressures and high flow rates to perform work. Two main hydraulic hyd raulic pumps supply oil to the main control valve group. The individual hydraulic circuits are controlled controlled by valves in the the main control valve group. The main hydraulic system supplies the following circuits: - swing - stick - left and right travel - bucket - auxiliary - boom Oil returning from these circuits flows back to through the return system to the hydraulic tank.
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Main Control Valve Group
The main control valve group is located in the center of the upper structure of the machine. The main control valve group receives pilot oil signals from the operator controls in the cab. Each pilot signal then causes the appropriate control valve to shift in the correct direction. When a control valve shifts, oil flows from the main hydraulic pumps to the appropriate hydraulic cylinder or hydraulic motor to perform work. The medium 320D-336D main control valve is similar similar to the medium 300C Series valve. The components shown above include: - right side NFC relief valve (1)
- main relief valve (8)
- stick 2 (2)
- left travel (9)
- boom 1 (3)
- swing (10)
- bucket (4)
- stick 1 (11)
- attachment (5)
- boom 2 (12)
- right travel (6)
- auxiliary valve for tool control (13)
- straight travel valve (7)
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The above illustration shows a cross-sectional view of the main control valve group as viewed from the rear of the machine, facing forward. The main control valve group is constructed of two valve blocks that are connected together. The drive pump provides oil flow for the right side of the main control valve group. The idle pump provides oil flow for the left side of the main control valve group. The pilot-operated, open-center control valves are of parallel feeder design. Because the main control valve group uses the open-center portion of the control valve to generate a NFC signal for the pumps, the oil must have another path to deliver oil to the work ports. This is accomplished through a parallel feeder path. A parallel feeder path runs parallel to the open-center path and supplies oil to the work port of each implement valve. When all of the joysticks and pedals are in the NEUTRAL position, drive pump oil flows through the right pump inlet port to the right half of the main control valve group. In the right half of the main control valve group the oil flows two directions; to the center bypass passages, and to the parallel feeder passages.
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Text Reference Main Control Valve Group
The oil in the center bypass passages flows in series through the center bypass passage of the travel, the attachment, the bucket, the boom 1, and the stick 2 valves to the NFC control orifice. The NFC control orifice allows the oil to return to tank with a restriction. This restriction provides an NFC signal pressure which is sent to the drive pump to maintain the drive pump at minimum angle when the control valves are all in NEUTRAL. In NEUTRAL this NFC signal is the same as the supply pressure. The oil in the parallel feeder passage flows in parallel to the attachment, the bucket, the boom 1, and the stick 2 valves. Since all of the valves are in NEUTRAL, the oil in the parallel feeder is blocked by the valve spools, and all oil must flow through the center bypass to the tank. The oil from the idler pump flows similarly through the left half of the control valve when all valves are in NEUTRAL.
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Text Reference Main Control Valve Group
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The schematic for the main control valve group is shown above. All of the circuit control valves are in NEUTRAL. Oil from the idler pump and drive pumps flows to the straight travel valve. From the straight travel valve, the supply oils flow through the center envelop of all of the control valves in NEUTRAL. Some of the supply oil also enters the parallel feeder passages. Since the control valves are in NEUTRAL the supply oil flows through all of the valves to the tank. Some of this oil becomes NFC signal oil and destrokes the two pumps.
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Control valve operation is similar for all of the valves in the main control valve group. The following explanation is for the basic operation of all of the valves in the main control valve group. The variations in each individual valve will be discussed later in more detail. The control valve above is shown in NEUTRAL. The valve spool is spring centered in NEUTRAL when there is no pilot oil pressure directed to shift the spool. In the NEUTRAL position, the spool blocks the oil in Port A and Port B. Oil flows from the pump to the parallel feeder passage. The load check valve is seated because of the pressure differential and spring force present on the load check valve. In NEUTRAL, the valve spool allows oil to flow unrestricted through the center bypass passage, which directs a high NFC signal pressure to the pump control valve. The high NFC signal pressure causes the pump to destroke to a standby condition.
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When the operator begins to move the joystick to shift the control valve, metered pilot pressure causes the control valve to shift slightly. With the spool initially shifted, the center bypass passage begins to close. This movement causes NFC signal pressure to decrease, which causes the pump to begin to upstroke. The movement of the spool partially opens a passage allowing the oil from Port B to work with the load check valve spring to keep the load check valve seated. The load check valve prevents unexpected implement movements when a joystick is initially activated at a low pump supply pressure. The load check valve also prevents oil loss from a high pressure circuit to a lower pressure circuit. The combined force of the work port pressure from Port B and the force of the spring above the load check is greater than the pump supply pressure, causing the load check valve to remain closed.
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As the operator moves the joystick for a full shift, the pilot pressure on the end of the spool increases. This increased pilot pressure causes the spool to fully shift. The center bypass passage is fully closed, which blocks the oil flow to the NFC signal passage to the pump control valve. When the NFC signal pressure is fully reduced, the pump fully 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 workport pressure in Port B, which causes the load check valve to unseat. Oil flows out to Port B. The oil returning from Port A flows past the spool and returns to tank. NOTE:
The load check valve is a loose fit in the load check seat to allow leakage past the check valve from the spring chamber. A separate spring chamber vent passage is not required with this load check design.
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Text Reference Main Control Valve Group
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This illustration shows the operation of the main control valve when only the bucket spool has been shifted. All of the control valves in the left side are in the NEUTRAL position, and the center bypass passage is open. All of the flow from the idler pump flows through the center bypass passage to the NFC orifice. Because all of the oil flow from the idler pump is restricted by the NFC orifice, the NFC signal pressure is at maximum pressure. The NFC signal pressure flows through the control line to the idler pump control valve. The NFC signal pressure present at the pump control valve causes the swashplate to move to the minimum angle position. The output of the idler pump is decreased to STANDBY due to the increased NFC pressure. The bucket control spool is fully shifted by pilot oil when the joystick is fully moved. Flow from the drive pump flows into the right side of the main control valve and into the center bypass passage to the bucket control valve. Because the bucket control spool is fully shifted, all of the oil flow from the drive pump flows to the bucket cylinder. No oil flows to the NFC control orifice and no NFC signal pressure is generated. Because no NFC signal pressure flows to the pump control valve, the pump control valve moves the pump toward maximum angle. The drive pump flow output increases to maximum. The individual circuits of the main control valve group will be covered in more detail later.
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When the joystick is partially moved from the NEUTRAL position to perform a fine control operation, reduced pilot pressure shifts the control spool slightly to the left. The movement of the control spool partially opens a passage to Port B. The movement of the control spool also partially blocks the center bypass passage, which divides the flow from the one drive into two flow paths. A portion of the pump output flows through the center bypass passage to the NFC orifice at a reduced pressure. The remainder of the drive pump output flows through the parallel feeder passage and internal passages to Port B. Because the oil flow from the center passage to the NFC orifice decreases, the NFC signal pressure to the drive pump control valve decreases. The reduced NFC signal causes the drive pump to move toward maximum angle. The drive pump output increases proportional to the reduction in NFC signal pressure.
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10 Additional Components
The main relief valve (1) is located in the left half of the main control valve group. The main relief valve limits the maximum operating pressure of the the travel and implement hydraulic circuits. For the NACD market the 300D Series main relief valve has two settings. One setting is for the standard maximum pressure and the other setting is for Heavy Lift. In all other markets Heavy Lift is optional. When energized the heavy lift solenoid (not shown) sends a pilot signal through the line (2) at the top of the relief valve to increase the pressure setting of the main relief valve. When heavy lift is selected, the Machine ECM limits engine speed to speed dial 6 and activates the heavy lift solenoid The heavy lift solenoid directs pilot oil to the main relief valve to increase the relief valve setting. At the same time the Machine ECM increases the power shift pressure to decrease the pump output flow. Decreasing the pump output flow provides increased controlability and hydraulic smoothness during a heavy lift operation. The Heavy Lift Mode limits the pumps to a maximum of approximately 60% of the normal hydraulic horsepower. Heavy Lift Specs: - Engine rpm for Heavy Lift is the engine speed dial 6 setting. - Hydraulic horsepower is limited to 60% of full power during Heavy Lift. - Main relief maximum pressure during Heavy Lift is 36000 kPa ± 490 kPa (5225 ± 70 psi).
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Heavy lift is activated by pressing the heavy lift switch (1) on the soft switch panel (2) in the operators station. The heavy lift switch is an input to the Machine ECM. The heavy lift solenoid (3) is located near the hydraulic tank and below the main control valve group.
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The drive pump oil flow enters the main control valve group through the upper delivery line. The idler pump oil flow enters the main control valve group through the lower delivery line. The drive pump oil and idler pump oil pressures work against the two check valves. The oil from both pumps is directed to the appropriate passages by the straight travel valve. The check valves ensure that only the higher pressure from the idler or the drive pump flows to the main relief valve. The check valves also ensure that flow from the highest supply pressure circuit does not enter the other supply pressure circuit if the pressure is lower. For example, if the bucket was being closed at a high pressure and no other function was active, the lower check valve would close. The check valve would prevent the drive pump oil from flowing through the center bypass in the left circuit. This action ensures that the higher supply pressure is always sensed at the relief valve. The relief valve will open when a circuit is stalled, limiting the maximum system pressure.
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Text Reference Main Control Valve Group
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The above illustration shows the pilot operated main relief valve equipped with the heavy lift solenoid. At lower system pressures the poppet is held against the the seat by the force of the spring. System pressure in the passage flows through the orifice into the spring chamber above the unloading spool. When the force applied by system pressure is less than the value of the upper spring, the poppet remains seated, causing the oil pressure in the lower spring cavity to equal system pressure. The combined force of the lower spring and system pressure holds the unloading spool down. As the system pressure nears the main relief valve pressure setting, the force of the system pressure in the lower spring chamber overcomes the force of the upper spring. This causes the poppet to unseat, allowing system oil to flow around the poppet to the return passage. As the oil in the lower spring chamber flows around the poppet, additional system pressure oil flows through the orifice into the lower spring chamber at a reduced pressure. System pressure overcomes the force of the oil pressure in the lower spring chamber and the spring, causing the unloading spool to move upward. As the unloading spool moves upward, system pressure oil is allowed to flow to the return passage.
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Text Reference Main Control Valve Group
The amount of spring force acting on the poppet determines the main relief valve pressure setting. Adjustments to the main relief valve pressure setting are made by changing the spring force of the upper spring. Heavy Lift increases the maximum system pressure. When the Heavy Lift is activated, the Heavy Lift solenoid is energized sending pilot hydraulic oil to the top end of the main relief valve. The pilot hydraulic oil pushes the piston down compressing the poppet spring to increase the maximum system pressure. To adjust the maximum system pressure turn the adjustment nut in or out. To adjust the Heavy Lift pressure setting, the spindle must be turned in or out. The Heavy Lift pressure setting should be adjusted first before adjusting the normal relief pressure.
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Text Reference Main Control Valve Group
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The above illustration shows a combination line relief and makeup valve in the closed, relief, and makeup positions. At lower system pressures, the poppet is held against a seat by the force of the upper spring. The circuit pressure in the passage flows through a cross-drilled orifice in the piston to the spring chamber above the inner spool. When the force applied by system pressure is less than the value of the upper spring, the poppet remains seated, causing the oil pressure in the lower spring cavity to equal system pressure. The combined force of the lower spring and system pressure keep the inner spool seated. As the system pressure nears the line relief valve pressure setting. The force of the system pressure in the lower spring chamber overcomes the force of the upper spring. This causes the poppet to unseat, allowing system oil to flow around the poppet to the return passage. As the oil in the lower spring chamber flows around the poppet, additional system pressure oil flows through the orifice in the piston from the lower spring chamber at a reduced pressure. System pressure overcomes the force of the oil pressure in the lower spring chamber and the spring, causing the inner spool to move upward. As the inner spool moves upward, system pressure oil is allowed to flow to the return passage.
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Text Reference Main Control Valve Group
The amount of spring force acting on the poppet determines the line relief valve pressure setting. Adjustments to the line relief valve pressure setting are made by changing the spring force of the upper spring. The position of the adjustment screw determines the spring force of the upper spring. The makeup function of the line relief valve prevents cavitation and voiding in the various circuits of the hydraulic system. Under normal operating conditions, the outer spool of the line relief valve is seated. The valve is held in the seated position by spring force and the hydraulic pressure in the spring chamber above the inner spool. If hydraulic circuit pressure becomes lower than the tank pressure, the pressure in the spring chamber is reduced. Tank pressure surrounds the outer spool, and creates a force on the step of the outer spool. This force unseats the outer spool and oil flows from the return system to the lower pressure hydraulic circuit.
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A NFC relief valve and orifice is located in the housing at each end of the main control valve group. The NFC relief valve on the right half of the main control valve group controls the NFC signal to the drive pump. The NFC relief valve on the left half of the main control valve group controls the NFC signal to the idler pump. The two reliefs work similarly. Oil enters the NFC orifices from the center bypass passage. The returning oil flows through the NFC orifices to the return passage when the system is in STANDBY. The orifices restrict the flow back to tank, which causes an increase in pressure through the center bypass passages. This NFC signal is sent to the pump control valve of the main hydraulic pump. When a hydraulic function is activated in the main control valve group, the center bypass passage is blocked. The NFC pressure at the pump control valve bleeds off through the NFC orifices to tank. The NFC relief valve is normally closed by spring force. The NFC relief valve is not adjustable. NOTE:
The left and right NFC relief valves can NOT be swapped from one end of the main control valve group to the other for diagnostic testing purposes.
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Text Reference Main Control Valve Group
The NFC relief valve only opens under sudden pressure spikes in the return system, which would occur if the pump was fully upstroked and a control valve was returned suddenly to NEUTRAL. A sudden pressure spike in the return system would cause high flow through the center bypass passage. The high volume of oil could not flow quickly enough through the NFC orifice to the return system. The high pressure generated in the center bypass passage would open the NFC relief valve, which would relieve the sudden pressure spike. The relief valve would close again once the pressure spike was diminished.
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Return Hydraulic System
The return hydraulic system transfers all of the hydraulic oil that has been used in the system to do work back to the hydraulic tank. The return hydraulic system has the following components: - slow return check valve - cooler bypass check valve group - hydraulic oil cooler - hydraulic oil filters - hydraulic oil tank
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The slow return check valve and the bypass check valve are in the cooler bypass valve group (arrow). The slow return check valve restricts return oil flowing from the main control valve, which maintains a constant back pressure in the return hydraulic system. The back pressure ensures that oil is available when needed for makeup in the various machine hydraulic circuits. The bypass check valve regulates return oil flow through the hydraulic oil cooler.
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Return oil from the main control valve flows from the return line into the housing for the slow return check valve as shown above. The return oil flows to the slow return check valve and to the makeup line for the swing motor. motor. The back pressure created by the slow return check valve ensures that makeup oil is available at the swing motor and the various makeup valves in the hydraulic system. After flowing through the slow return check valve, oil flows to the cooler inlet line and the bypass check valve. v alve. At low temperatures, the high viscosity of the oil flowing through the hydraulic oil cooler causes the pressure pressure to rise. The rising pressure causes the bypass check valve to open. Most of the oil flows through the bypass check valve. Because only a small amount of oil flows through the cooler, the oil temperature increases. As the oil temperature increases, the bypass check valve begins to close and a greater portion of the oil flows through the hydraulic hydraulic oil cooler. cooler. The bypass check valve maintains the oil at the the optimum operating temperature. The plug located below the makeup line to the swing motor can be removed to install a minimal back pressure return for a hydraulic attachment, such as a hydraulic hammer.
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The hydraulic oil cooler (1) is part of the cooling package (2) on the left side of the machine at the rear. The hydraulic oil cooler reduces the temperature of the hydraulic oil in the system. Oil enters the hydraulic oil cooler from the slow return check valve. After passing through the cooler, oil flows to the hydraulic return filter.
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Return oil flow from the hydraulic oil cooler flows into the return filter (1), which is mounted at the rear of the hydraulic tank on smaller smaller machines. On larger machines, the filter filter is inside the hydraulic tank. The return filter has a bypass valve that directs the return return oil to the hydraulic tank if the filter becomes plugged. The tank has a vacuum breaker to limit the maximum tank pressure to 55 kPa (8 psi). psi). The breaker opens at 13 kPa (-2 psi) to prevent preven t damage to the tank. Oil in the hydraulic tank flows through the suction screen located inside the tank before being delivered to the main hydraulic pump group. The hydraulic tank sight gage (3) is located to the right of the return filter. The case drain filter (4) receives case drain oil from the swing motor, idler and drive main hydraulic pumps, and left and right travel motors. On the 330D/336D the filter also also receives case drain oil from the fan motor. Oil from the case drain filter filter flows into the hydraulic tank. The purpose of the case drain filter filter is to reduce hydraulic contamination to the hydraulic system if a pump or motor fails.
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Text Reference Implements
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INTRODUCTION
This presentation covers in more detail each implement circuit used for the 320D-336D Hydraulic Excavators. The circuits to be covered include: - boom - stick - bucket The idler pump provides oil to the boom 2 and stick 1 control valves. The drive pump provides flow to the bucket, boom 1, and stick 2 control valves. The boom, stick, and bucket control valves are shifted by pilot oil from the joystick pilot valves when they are activated. NOTE:
The main control valve group and return system are covered in another presentation. The attachment/auxiliary circuits will be covered in the electronic or tool control section. The ISO schematics were created primarily from "325D Hydraulic Schematic" (KENR6157). Hydraulic schematics for other 320D-336D excavators may/will have variations from illustrations shown.
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The boom circuit uses two control valves to control the boom operation, boom 1 (1) and boom 2 (2). Both spools shift when fast boom movement is required. Both pumps provide flow to the boom for this condition. Boom 1 valve provides single pump flow, whenever the boom is shifted for slow movement. The stick circuit also uses to two control valves to control the stick operation, stick 1 (3) and stick 2 (4). Both spools shift when fast stick movement is required. The boom circuit and stick circuits also use regeneration valves and drift reduction valves. The regeneration valves (not shown) provide improved efficiency and require less engine horsepower for BOOM LOWER and STICK IN. The drift reduction valves reduce cylinder drift when the boom or stick are in NEUTRAL. Only one control valve is required to control the bucket. The bucket circuit is supplied with oil only from the drive pump.
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The two joysticks in the cab are used to control the movements of the boom, stick, swing and bucket circuits. - right joystick (1) to control the bucket and boom (SAE excavator pattern) - left joystick (2) to control the swing and stick (SAE excavator pattern)
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Boom Circuit
The boom circuit consists of the following major components: - boom 1 spool - boom 2 spool - two boom cylinders - drift reduction valve - Heavy Lift solenoid - boom priority valve (pressure reducing) - boom lowering control valves (if equipped - not shown)) - boom regeneration valve - SmartBoom™ (if equipped - not shown)) NOTE:
325D Hydraulic Schematic (KENR6157) was used to develop the ISO schematics.
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Text Reference Implements
Boom 1 Spool: The boom 1 spool controls oil flow from the drive pump. The boom 1 spool receives a BOOM RAISE pilot signal on the bottom of the valve, and a BOOM LOWER pilot 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 BOOM RAISE pilot signal from the joystick on the top of the valve stem, when active. The boom 2 spool does not operate during BOOM LOWER. 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. Heavy Lift Solenoid: The heavy lift solenoid is activated to increase the maximum system pressure for lifting. (Refer to the "Main Control Valve Group and Return Group" for more details on Heavy Lift operation.) Boom Priority Valve: The boom priority valve (pressure reducing) is used to reduce the pilot pressure to the stick 2 valve whenever both the BOOM RAISE and STICK IN are activated at the same time. The higher the boom pilot pressure to the boom priority valve the less pilot pressure is available to shift the stick 2 control valve, resulting in more pump flow going to the boom cylinders. 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 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. 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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As previously discussed, the control valve operation is similar for all of the valves in the main control valve group including the boom, stick, and bucket valves. Pump flow is provided by the drive and/or idler hydraulic pump. Which pump is used depends on the circuit. The centering spring force holds the valve spool to NEUTRAL when there is no pilot oil pressure directed to shift the spool. In NEUTRAL the valve spool allows oil to flow unrestricted through the center bypass passage, which directs a high NFC pressure signal to the pump control valve. The high NFC pressure causes the pump to destroke to a standby condition, as explained previously.
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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 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 NFC relief valve. Less oil to the NFC relief valve results in a reduced NFC signal to the drive pump. The drive pump control valve causes the pump to upstroke to provide flow to operate the boom. A BOOM 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 to shift the boom 1 control valve, metered pilot pressure causes the control valve to shift slightly. With the spool initially shifted, the center bypass passage is partially closed. This movement causes NFC pressure 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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A BOOM 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.
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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 2 control valve does not handle any of the return flow for the boom circuit. NOTE:
valve.
The swing priority valve does not affect the operation of the boom 2 control
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During combined operations of BOOM RAISE and STICK IN, the boom raise pilot oil pressure shifts the pressure reducing valve for 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 pressure reducing valve for the boom priority to gradually shift. A portion 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.
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Text Reference Implements
The stick 2 control valve shifts toward the NEUTRAL position. 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 pressure reducing valve for boom priority reduces pilot pressure to the stick 2 control valve. NOTE:
If the joysticks are fully shifted for BOOM RAISE and 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. When the joystick is shifted pilot oil moves the boom 1 control spool down, the regeneration valve right, and unlocks the drift reduction 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 regeneration valve and the boom 1 control valve. The boom 1 control valve restricts the return oil flow. Whenever the return oil pressure is higher than the supply pressure in the rod end of the cylinders, the return oil from the boom cylinder head ends unseats the check valve above the regeneration valve. 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 regeneration 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 boom pilot oil flow from 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 NFC signal. 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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The boom regeneration valve has two components, the boom regeneration valve itself and the check valve. During a slow BOOM DOWN, the low pilot pressure is not able to move the regeneration valve down so return oil from the the boom cylinder head ends is not able to flow to the boom cylinder rod ends.
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When boom lower pilot pressure increases, the boom regeneration valve is pushed down, a passage is opened allowing boom head end oil to flow to the check valve. If the boom rod end pressure is lower than the boom head end oil pressure, then the check valve opens allowing boom head end oil to be directed to the boom rod end. The check valve closes if the boom rod end oil pressure is higher than the boom head end oil pressure, such as when the boom is being powered down.
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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:
- shuttle valve - lock check valve - 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 lock check valve. Oil pressure from the boom control valves acts on the other end of the lock check valve. The lock 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 BOOM LOWER, the shuttle valve is opened by pilot oil from the joystick. The shuttle valve allows oil from the spring end of the lock check valve to return to tank. Oil pressure from the boom cylinder head end opens the lock check valve. The lock check valve allows oil flow from the head end of the boom cylinders to return to the boom control valve.
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2 6
18 Boom Lowering Control Valves: The boom lowering control valves (1 and 2) are mounted on the head end of the boom cylinders. If the machines are equipped with the optional boom lowering valves, the drift reduction valve for the boom is not installed on the machine.
The boom lowering control valves serve several purposes: - prevent the boom from falling rapidly in case of hose failure - provide BOOM LOWER 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. A pilot 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. A hose (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.
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When the boom circuit is equipped with boom lowering control valves (or load control valves), the lowering control valves are attached directly to each of the boom cylinders. The following major components are used in the boom lowering control valves : - boom head end line relief - check valve - boom lowering control valve spool - orifice - manual lower
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Text Reference Implements
Boom Head End Line Relief: The boom head end line relief protects the boom head end circuit from damage if the pressure in the circuit exceeds the line relief setting. Check Valve: The check valve holds the high pressure of the boom cylinder head end from leaking off. Because the weight of the boom, stick, and work tool are always applied to the head end of the boom cylinder, the check valve is needed to prevent the high pressure from leaking off and allowing the boom to drift. The check valve also provides an unrestricted means for the high pressure/high flow oil from the main control valve to enter the boom cylinder head end during BOOM UP. Boom Lowering Control Valve Spool: The infinitely variable boom lowering control valve spool controls the flow of oil exiting the boom cylinder head end. The top of the spool receives pilot pressure from the boom lower joystick. When the valve opens, oil flows from the head end back to the main control valve. Because the valve is infinitely variable and controlled by boom lower pilot pressure, the speed that the boom lowers is controlled by the boom lowering control valve spool. Orifice: The boom lowering control valves on each cylinder are connected by a small hose. The hose ensures that pressure is always equal in the two cylinders. The orifice in each of the boom lowering control valves restricts the amount of oil that flows from one cylinder to the other. The restriction created by the orifice will allow control over the boom in the event that the hose ruptures. Under normal operation the orifice plays no role in boom operation. Manual Lower: Manual lower allows the boom to be lowered if the engine will not run. The valve allows the oil pressure in the head end of the cylinder to bleed to the tank. NEUTRAL: When no boom function is performed the boom lowering control valve is in NEUTRAL. In NEUTRAL no oil flows to or from the boom cylinders, and the boom does not move.
In NEUTRAL, the check valve is seated by the combination of the spring force and the high pressure oil in the head end of the boom cylinders. The boom lowering control valve spool is seated by spring force. The boom lowering control valves have no effect on the flow of oil to/from the rod end of the boom cylinders. NOTE:
Manual lower may be done differently depending on the lowering control valves used. Some machines may have a manual lowering valve separate from the lowering control valves.
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The schematic above shows the two lowering control valves and the boom circuit control valves in NEUTRAL. Both pumps are destroked. NOTE:
The stick circuit may also be equipped with a single lowering control valve. Operation of the stick lowering control valve will be similar. With only a single stick cylinder there is no need for an equalization passage.
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When BOOM UP is performed the boom lowering control valve allows oil to pass from the main control valve to the head end of the boom cylinders. High pressure oil from the main control valve enters the boom lowering control valve. As the supply pressure increases, the check valve opens and allows oil to flow to the head end of the boom cylinder. The boom lowering control valve spool remains seated due to spring force.
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For BOOM UP, the pilot pressure shifts both boom spools. Besides oil from the drive pump, supply oil may also be available from the idler pump for raising the boom. Other circuits not shown, operating at lower pressures than the boom will receive the idler pump flow first. The regen valve has no affect on the operation of the lowering control valves for BOOM UP.
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When the boom is slowly lowered, the boom lowering control valve allows oil to flow at a controlled rate from the head end of the boom cylinders to the return system. The boom lower pilot oil from the operator joystick enters the boom lowering control valve above the boom lowering control valve spool. The pilot pressure moves the spool down against the spring force. The movement of the spool partially opens a passage to allow flow from the boom cylinder head end to the return system. Since this flow is restricted by the spool, the boom lowers at a controlled rate. The farther the joystick is moved, the higher the pilot pressure on the spool, the greater the movement of the spool, and the greater the flow from the boom cylinder head end to the tank past the boom control valve. The check valve remains closed.
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For a slow boom down, with boom lowering valves, the boom 1 spool is only partially shifted by a reduced pilot pressure. The NFC signal to the pump is reduced, so the drive pump only partially upstrokes. The boom 2 spool does not shift. As long as the pilot pressure does not move the regen valve to the right, regeneration does not occur. Oil metered through the lowering valves to tank flows back to the tank through the boom 1 spool.
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For a full BOOM DOWN, the lowering control valve allows oil to flow with little restriction from the boom lowering control valve. The full boom lower pilot signal from the operator joystick enters the lowering control valve above the boom lowering control valve spool. The pilot moves the spool fully down against the spring force. The movement of the spool fully opens the passage to allow oil to flow from the boom cylinder head end to flow to the regen valve and to the boom control valve. The check valve remains closed.
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For a fast BOOM DOWN, the pilot pressure fully shifts the boom 1 spool, both lowering control valves, and the regen valve. With the regen valve shifted, head end return oil flows through the regen valve to mix with the supply oil from the drive pump to fill the cylinder rod ends. This action results in the boom lowering rapidly and more efficient operation of the excavator due to only one pump is providing flow and by using the return oil to supplement the supply oil.
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Stick Circuit
The stick circuit consists of the following major components: - stick 1 spool - stick 2 spool - stick cylinder - stick regeneration valve - stick unloading valve - stick lowering control valves (not shown) - stick drift reduction valve NOTE:
The stick priority systems and the stick drift reduction valve will be discussed in more detail later in this presentation.
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Text Reference Implements
Stick 1 Spool: The stick 1 spool controls oil flow from the idler pump. The stick 1 spool receives a STICK OUT pilot signal on the bottom of the valve, and a STICK IN pilot signal on the top of the valve. Stick 2 Spool: The stick 2 spool controls oil flow from the drive pump. The stick 2 spool receives a STICK IN pilot signal from the joystick on the top of the valve stem. The stick 2 spool receives a STICK OUT pilot signal from the joystick on the bottom of the valve stem. Stick Cylinder: When oil is supplied to the head end of the stick cylinder, the stick will extend for a STICK IN. When oil is supplied to the rod end of the stick cylinder, the stick will retract for a STICK OUT. Stick Regeneration Valve: The stick regeneration valve opens during STICK IN to allow returning oil from the rod end of the stick cylinder to be directed to the head end of the stick cylinders during STICK IN. Regeneration is used to reduce "stick wag" and increase the stick in speed. Stick Unloading Valve: The unloading valve allows the oil to return to the tank when regeneration is not necessary. Stick Drift Reduction Valve: The stick drift reduction valve is placed in the stick circuit between the main control valve and the stick cylinder. The stick drift reduction valve prevents oil from leaking from the rod end of the stick cylinder. The stick drift reduction valve also incorporates the line relief valve for the rod end of the stick cylinder. NOTE:
Approximate spring setting values have been provided to use as reference values only. The values have been provided to assist in explaining stick operation. Different pilot pressures are required to shift the stick 1 and the stick 2 control valves.
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When the stick hydraulic circuit is operated independently of other hydraulic circuits, stick 1 control valve and stick 2 control valve are used for both the STICK IN and STICK OUT operation. When the stick 1 control valve and the stick 2 control valve are shifted, the supply oil from the idler pump and the drive pump is combined. The supply oil from both pumps flows to the stick cylinder. The supply oil from the drive pump flows through the parallel feeder passage in the main control valve group to the stick 2 control valve. The supply oil from the idler pump flows through the center bypass passage in the main control valve group to the stick 1 control valve. When the joystick for the stick is moved to STICK OUT, the pilot oil flows from the pilot control valve to the stick 1 control valve and the stick 2 control valve. The pilot oil shifts the stick 1 and stick 2 control valve spools. Supply oil is directed from both spools to the stick drift reduction valve. The lock check valve in the drift reduction valve shifts and combined pump oil flows to the rod end of stick to retract the cylinder. Return oil from the head end of the stick cylinder flows back to the stick 1 and stick 2 control valves and to the tank.
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Slow STICK IN - No Regeneration: Depending on the position of the stick, for a slow stick in, regeneration may not be required due to the supply oil from the pump being able to fill and pressurize the head end of the stick cylinder to force the stick in.
For a slow STICK IN the pilot signal is reduced and will only partially shift the stick 1 spool. The stick 2 control valve may or may not shift. Shifting of the stick 2 spool is determined by how high the pilot pressure to the stick 2 valve is. Different minimum pilot pressures are required to shift the stick spools. When pilot pressure is less than approximately 860 kPa (125 psi), the pilot oil is not able to shift the regeneration valve to the left. A reduced NFC signal is sensed at the idler pump, and the pump upstrokes to provide flow. Most of the supply oil from the idler pump is directed to the stick cylinder head end through the stick 1 control spool.
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Text Reference Implements
Return oil from the rod end flows to the drift reduction valve. The lock check valve in the drift reduction valve is unseated and return oil flows back to the tank through the stick 1 control valve. Though the return oil is restricted through the stick 1 control spool, to provide precise control of slow STICK IN.
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The stick 1 spool restricts the return oil from the stick rod end. The restriction at the stick 1 spool creates a back pressure in the stick cylinder rod end return circuit. The restriction prevents the stick cylinder from cavitating due to the force of gravity trying to lower the stick when the stick is being moved from a raised stick out position to a lowered position. Due to low pilot pressure the regeneration valve does not shift. Since the regeneration valve has not shifted to allow rod end oil to flow to the check valve, the check valve remains closed and the rod end and head oil does not mix. Regeneration does not occur. A drain passage in the stick regeneration valve vents the upper passage between the stick unloading valve and the regeneration valve to the tank.
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Fast STICK IN - Regeneration: Pilot pressure is increased for a fast STICK IN.
The boom 1 circuit has been activated as well, to show the importance of the stick regeneration valve. With the boom circuit activated the boom priority valve reduces the pilot pressure to the stick 2 valve, preventing the stick 2 valve from shifting. Only one pump flow from the idler pump is available to supply the stick 1 circuit. The higher stick pilot pressure causes the regeneration valve to shift to the left. Return oil from the rod end flows through the regeneration valve to the check valve. The check valve unseats due to the return oil pressure being higher than the pump supply pressure from the stick 1 control valve. When the check valve unseats, the return oil is added to the supply oil going to the head of the stick cylinder. The regeneration valve allows the excavator to operate more efficiently. The main pump supply oil not required to shift the stick in is available to operate another circuit.
