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Proportional, Priority, Pressure Compensated Hydraulic Systems Objectives: • Provide students with a comparison of a basic PPPC hydraulic system to a basic LS/PC hydraulic system • Explain PPPC hydraulics as it is used on representative Cat products
FLOW CONTROL VALVE PRESSURE REDUCING VALVE ORIFICE
Definition: Pressure Compensation A control system which results in constant implement speed for a given lever displacement. The system does this by maintaining a controlled pressure drop across the main control or directional spool in each circuit.
LOAD SENSING WITH SIGNAL NETWORK
ENGINE
RESOLVER
LOAD
300 PSI SPRING RESOLVER LOAD FLOW CONTROL VALVE RESOLVER 3000 PSI SPRING
A RELIEF VALVE
B
SIGNAL NETWORK
BOOM
ENGINE
SWING
LEFT RIGHT STABILIZER STABILIZER
BUCKET
STICK
PRIMARY RESOLVER SECONDARY RESOLVER
300 PSI SPRING
FLOW CONTROL VALVE
3000 PSI SPRING
TO IMPLEMENT CONTROL VALVES
RELIEF VALVE
Definition: Load Sensing A control system that maintains a pump supply pressure at a fixed value above the highest system pressure requirement.
VARIABLE DISPLACEMENT PUMP PUMP OUTPUT LARGE ACTUATOR
YOKE PAD SWASH PLATE
DRIVE FLOW COMPENSATOR ( MARGIN SPOOL)
PRESSURE COMPENSATOR (PRESSURE CUT-OFF)
SHAFT SMALL ACTUATOR & BIAS SPRING
LOAD SENSING / PRESSURE COMPENSATION
LOAD ENGINE
FIXED DISPLACEMENT PUMP DOUBLE CHECK VALVE
300 PSI SPRING
FLOW CONTROL VALVE
3000 PSI SPRING
50 PSI SPRING
PRESSURE REDUCING VALVE
CLOSED CENTER CONTROL VALVE
LOAD SENSING / PRESSURE COMPENSATION PUMP CONTROL VALVE
LOAD
ENGINE
VARIABLE DISPLACEMENT PUMP
DOUBLE CHECK VALVE
50 PSI SPRING
PRESSURE REDUCING VALVE
CLOSED CENTER CONTROL VALVE
LOAD SENSING TWO VALVE OPERATION MOTOR
LOAD
LOAD 300 PSI SPRING
3000 PSI SPRING
A
B
LS Only - Pressure Differentials Flow Needs Met Maximum Pump Flow = 30 gpm Valve A desired flow = 10 gpm Valve B desired flow = 10 gpm Margin Pressure is normal System Pressure = Valve A load plus margin pressure = 2300 psi
If Valve A load stayed the same and Valve B would vary as the load on the circuit varied, the operator would have to constantly shift the lever to maintain implement control.
LOAD SENSING / PRESSURE COMPENSATION TWO VALVE OPERATION ENGINE LOAD
300 PSI SPRING
LOAD 50 PSI SPRING
3000 PSI SPRING
A
50 PSI SPRING
B
LS/PC - Pressure Differentials Flow Needs Met Maximum Pump Flow = 30 gpm Valve A desired flow = 10 gpm Valve B desired flow = 10 gpm Margin Pressure is normal System Pressure = Valve A load plus margin pressure = 2300 psi
LS/PC - When Flow Demand Exceeds Available Pump Flow Maximum Pump Flow = 30 gpm Margin Pressure less than normal
ValveA @2000psi Valve B @ 1000 psi ValveC@500psi Total
Desired Flow 30gpm 20 gpm 10gpm 6g0pm
Available Flow 0gpm 20 gpm 10gpm 3g0pm
PPPC HYDRAULIC SYSTEM TWO VALVE OPERATION / FLOW NEEDS MET 2000 PSI
1000 PSI 10 GPM FLOW REQ'D
10 GPM FLOW REQ'D
VALVE B
VALVE A
PRESSURE COMPENSATING CHECK VALVE
FEEDER PASSAGE
BRIDGE PASSAGE
50 PSI SPRING
P I L OOTI L 300 PSI MARGIN SPRING PUMP 3500 PSI CUTOFF SPRING
30 GPM MAXIMUM FLOW
50 PSI SPRING DIRECTIONAL SPOOL
P I L OOTIL
SIGNAL LIMITER VALVE 3000 PSI SPRING
PPPC - Pressure Differentials Flow Needs Met Maximum Pump Flow = 30 gpm Valve A desired flow = 10 gpm Valve B desired flow = 10 gpm Margin Pressure is normal System Pressure = Valve A load plus margin pressure = 2300 psi
PPPC - When Flow Demand Exceeds Available Pump Flow Maximum Pump Flow = 30 gpm Margin pressure less than normal
ValveA @2000psi ValveB@1000psi ValveC@500psi Total
Desired Flow 30gpm 20gpm 10gpm 6g0pm
Available Flow 15gpm 10gpm 5gpm 3g0pm
Definition: Proportional, Priority, Pressure Compensated Hydraulic System Provides precise multiple circuit flow control whenever pump flow is exceeded. This is accomplished through post main spool pressure compensation, which results in proportional flow division.
PPPC HYDRAULIC SYSTEM TWO VALVE OPERATION / CUTOFF CONTROLS MAX. PRESSURE 3500 PSI
1000 PSI 10 GPM FLOW REQ'D
VALVE B
VALVE A
PRESSURE COMPENSATING CHECK VALVE
FEEDER PASSAGE
BRIDGE PASSAGE
50 PSI SPRING
50 PSI SPRING DIRECTIONAL
PILOT OIL 300 PSI MARGIN SPRING PUMP 3500 PSI CUTOFF SPRING
30 GPM MAXIMUM FLOW
SPOOL
PILOT OIL
SIGNAL LIMITER VALVE 4000 PSI SPRING
PPPC - Pressure Differentials Pressure Cutoff Controls Maximum System Pressure Maximum Pump Flow = 30 gpm Valve A desired flow = Stalled Valve B desired flow = 10 gpm Actual Flow = 0 gpm Margin pressure = 0 System Pressure = Controlled by Pressure Cutoff = 3500 psi
Valve A@ 3500 psi Valve B @ 1000 psi
∆PD irectional Spool 35 00 - 350 0 = 0 p s i 35 00 - 350 0 = 0 p s i ∆Pt he Same
∆PC ompensator 3500 - 3550 psi = -50 psi 1 000 - 355 0 p s i = -2 550 p s i Neg ∆PV aries = No Flow
Telehandlers PPPC Hydraulic System
IMPLEMENT AND STEERING SYSTEM BOOM EXTEND/RETRACT
COMPENSATING CYLINDERS
HYDRAULIC PUMP
BOOM
COMPENSATING
RAISE/LOWER
FORKS
VALVE
SIGNAL LINE DIRECTIONAL
JOYSTICK
CONTROL VALVES
ATTACHMENT CARRIER ROTATE TILT
FILTER
FRAME LEVEL CONTROL HMU
VALVE
FRAME LEVEL
TANK SELECTOR VALVE MANIFOLD TO BRAKE BOOST CYLINDER
DIFFERENTIAL LOCK
MANUAL OVERRIDE
BOOM RAISE
BOOM LOWER
BOOM RETRACT
BOOM EXTEND
TILT BACK
TILT FORWARD
HYDRAULIC SYSTEM
RETURN FROM OTHER VALVES
SIGNAL RELIEF VALVE STEERING VALVE
BOOM RAISE/LOWER CONTROL VALVE
BOOM RETRACT/EXTEND CONTROL VALVE
TILT CONTROL VALVE
SIGNAL FROM OTHER VALVES
PRESSURE REDUCING VALVE
TO OTHER VALVES
DIFFERENTIAL LOCK
PUMP SERVICE BRAKE BOOST CYLINDER
SELECTOR VALVE MANIFOLD
JOYSTICK PILOT CONTROL VALVE
STEERING AND IMPLEMENT PUMP
COMPENSATOR VALVE
CONSTANT FLOW
BIAS
ACTUATOR PISTON
SIGNAL
SPRING
SWASHPLATE
PRESSURE
TO CONTROL VALVE GROUP
PRESSURE CUTOFF SPOOL
MARGIN SPOOL
RESOLVER
BOOM RAISE
BOOM LOWER
BOOM RETRACT
BOOM EXTEND TILT BACK
HYDRAULIC SYSTEM
TILT FORWARD
IMPLEMENTS IN HOLD
TO HMU RETURN FROM OTHER VALVES
SIGNAL RELIEF VALVE
SIGNAL FROM OTHER VALVES
PRESSURE REDUCING VALVE
TO OTHER VALVES
STEERING PRIORITY VALVE
PRESSURE COMPENSATING CHECK VALVE
DIFFERENTIAL LOCK
PUMP SERVICE BRAKE BOOST CYLINDER
SELECTOR VALVE MANIFOLD
JOYSTICK PILOT CONTROL VALVE
RETURN TO TANK
DIRECTIONAL CONTROL SPOOL
IMPLEMENT CONTROL VALVE HOLD
PUMP SUPPLY
PORT A
BRIDGE PASSAGE
FEEDER PASSAGE
PORT B PRESSURE COMPENSATING CHECK VALVE
RESOLVER VALVE
A
SIGNAL PASSAGE TO NEXT VALVE
FROM PILOT SYSTEM
B
RESOLVED SIGNAL
FEEDER PASSAGE
RETURN TO TANK
DIRECTIONAL CONTROL SPOOL
IMPLEMENT CONTROL VALVE SHIFT
PUMP SUPPLY
PORT A
BRIDGE PASSAGE
FEEDER PASSAGE
PORT B PRESSURE COMPENSATING CHECK VALVE
RESOLVER VALVE
A
SIGNAL PASSAGE TO NEXT VALVE
FROM PILOT SYSTEM
B
RESOLVED SIGNAL
FEEDER PASSAGE
TELEHANDLER IMPLEMENT VALVE GROUP SIGNAL RELIEF VALVE
PRESSURE REDUCING VALVE
PUMP SUPPLY
PILOT OIL
AUX. VALVE
A
B
A
B
BOOM EXTEND/RETRACT VALVE
A
B
BOOM RAISE/LOWER VALVE
A
B
TILT VALVE
STEERING VALVE
RESOLVER SIGNAL TO PUMP CONTROL
LINE RELIEF VALVE
RESOLVER
BOOM RAISE
BOOM LOWER
BOOM RETRACT
BOOM EXTEND TILT BACK
HYDRAULIC SYSTEM
TILT FORWARD
BOOM RAISE
TO HMU RETURN FROM OTHER VALVES
SIGNAL RELIEF VALVE
SIGNAL FROM OTHER VALVES
PRESSURE REDUCING VALVE
TO OTHER VALVES
STEERING PRIORITY VALVE
PRESSURE COMPENSATING CHECK VALVE
DIFFERENTIAL LOCK
PUMP SERVICE BRAKE BOOST CYLINDER
SELECTOR VALVE MANIFOLD
JOYSTICK PILOT CONTROL VALVE
'H' Series Motor Graders PPPC Hydraulic System
STEERING AND IMPLEMENT HYDRAULIC SYSTEM HAND METERING UNIT
LEFT VALVE BANK
RIGHT VALVE BANK
ACCUMULATOR
PUMP
TANK
COMBINATION COMPENSATOR VALVE VALVE
H-SERIES HYDRAULIC SYSTEM
RIGHT VALVE BANK HAND METERING UNIT
TO IMPLEMENT CYLINDERS
STEERING ACCUMULATOR
COMBINATION VALVE TO STEERING CYLINDERS
IMPLEMENT SIGNAL LINE
TO IMPLEMENT CYLINDERS LEFT VALVE BANK
STEERING SIGNAL LINE
COMPENSATOR VALVE FILTER
PUMP
PUMP AND COMPENSATOR OPERATION CONSTANT FLOW
SIGNAL
PUMP OUTPUT REDUCED PRESSURE
SIGNAL NETWORK RIGHT BLADE LIFT
LEFT BLADE LIFT
SIDE SHIFT
CIRCLE DRIVE BLADE TIP
CENTER SHIFT ARTICULATION
WHEEL LEAN
RIGHT BLADE LIFT
TO COMPENSATOR VALVES
SIGNAL RESOLVER VALVE
FROM STEERING HAND METERING UNIT
FROM PRIORITY AND STEERING RELIEF VALVE
SIGNAL CHECK VALVE
TO SIGNAL BLEED AND SIGNAL PRESSURE RELIEF VALVES
COMBINATION VALVE TO PUMP COMPENSATOR VALVE
LEFT IMPLEMENT CONTROL VALVES HOLD
SIDE SHIFT
BLADE TIP
LEFT BLADE LIFT CIRCLE DRIVE
RIGHT IMPLEMENT CONTROL VALVES HOLD
ARTICULATION
CENTERSHIFT
WHEELLEAN
RIGHTBLADELIFT
LOCK VALVE SEATS
PORT A
LOCK VALVE PISTON
TYPICAL IMPLEMENT VALVE PORT B
LOCK VALVE POPPET
HOLD LOCK VALVE POPPET COMPENSATOR VALVE
TO TANK TO TANK CENTERING SPRING
ROTARY ACTUATOR COUNTERBALANCE CONTROL FROM SPRING STEM PUMP
SIGNAL CHECK BALL TO COMBINATION VALVE MANIFOLD
LOCK VALVE POPPET
TO LOCK VALVE SEATS TO HEAD END ROD END LOCK VALVE PISTONS
BLADE LIFT VALVE HOLD LOCK VALVE POPPET
COUNTERBALANCE TO SPRING TANK
COMPENSATOR VALVE ROD END LINE RELIEF VALVE TO TANK
ROTARY ACTUATOR
DETENT SPRING
CONTROL STEM
FROM PUMP
SIGNAL CENTERING CHECK BALL SPRING
TO COMBINATION VALVE MANIFOLD
PORT A
PORT B
BLADE LIFT VALVE FULLY SHIFTED TO THE RIGHT
COMPENSATOR VALVE
CONTROL STEM
FROM PUMP
SIGNAL CHECK BALL
TO COMBINATION VALVE MANIFOLD
TYPICAL IMPLEMENT VALVES IMPLEMENT VALVE WITH LOWEST LOAD
IMPLEMENT VALVE WITH HIGHEST LOAD PORT A
PORT B
PORT A
PORT B
COMPENSATOR VALVE
COMPENSATOR VALVE
TO TANK
FROM PUMP
SIGNAL CHECK BALL (OPEN)
CONTROL STEM FROM PUMP
SIGNAL CHECK BALL (SEATED) TO COMBINATION VALVE MANIFOLD