The document discusses hydraulic systems used in construction equipment. It focuses on load sensing (LS) valves and pressure compensated (PC) valves that are used to control hydraulic pump discharge based on system pressures. The LS valve monitors differential pressure between the pump and workport to regulate pump flow, increasing it under load and decreasing it otherwise. The PC valve works to maintain equal power by reducing pump discharge if pressure rises too much. Diagrams show how these valves interface with hydraulic pumps and solenoids to optimize pump output based on changing load conditions.

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9. PC200-7
Material para Presentación de
Ventas

10. '90 '91 '92 '93 '94 '95 '96 '97 '98 '99 '00 '01
3 1 8 8
KOMATSU ◎ ○ ○ ◎
ＰＣ２００－５ ＰＣ２００－６ ＰＣ２００－７
3 6 7 3
CAT ◎ ◎ ○ ◎
３２０ ３２０Ｂ ３２０Ｃ
10 1 1 6
HITACHI ◎ ◎ ◎ ◎
ＥＸ２００－２ ＥＸ２００－３ ＥＸ２００－５ ＺＸ２００
CAT 320C HITACHI ZX200
KOMATSU PC200-7
Mercado
Japones

11. The maximum digging height of 10m is very effective for slope finishing and demolition
KOMATSU
PC200-7
KOMATSU
PC200-6
HITACHI
ZX200
CAT
320C
Max.digging Height mm 10,000 9,305 9,600 9,400
The maximum digging height of 10m is very effective for slope finishing and demolition
Max. digging height

12. E-OLSSSection 3.2
Charge Pump
Charge pump for the PC1250-7 excavator is mounted in a back of gear
pumps. The bank of pumps is found between the two work equipments and
swing pumps.
PPC/charge pressure Pump
After Cooler Fan Pump
PTO Lubrication Pump

13. CLSSSection 2.2
Hydraulic Pump
HPV95+95 VARIABLE DISPLACEMENT PISTON PUMPHPV95+95 VARIABLE DISPLACEMENT PISTON PUMP
112 CC PER PUMP MAX DISPLACEMENT112 CC PER PUMP MAX DISPLACEMENT
Controlled by 2 LS valves and 2 PC valvesControlled by 2 LS valves and 2 PC valves
With an LS EPC and PC EPCWith an LS EPC and PC EPC
mounted on the side of the pump bodymounted on the side of the pump body

14. CLSSSection 2.2
Hydraulic Pump.
Text
Front Pump
The two pumps can work independently or together as one.
Rear Pump

15. CLSSSection 2.2
Hydraulic Pump.
Input Shaft (front)
Input shaft (front)
Front Seal
Shaft Coupling Input shaft (rear)

16. CLSSSection 2.2
Hydraulic Pump.
Input Shaft (front)
Rocker Cam
Servo-piston
Rod.
(Connection between servo & swash plate)

17. CLSSSection 2.2
Hydraulic Pump.
Input Shaft (front)
Shoes Piston Cylinder Block
Valve Plate

18. CLSSSection 2.2
Hydraulic Pump.
Control of Discharge Amount.
Servo piston moves in a reciprocal movement, according to the signal
pressure from the LS or PC valves. This movement is transmitted through
the rod to the rocker cam to increase or decrease swash plate angle.

19. CLSSSection 2.2
Hydraulic Pump.
Operation of Pump.
Cylinder block is splined
onto input shaft and all
rotate together.
When the rocker cam is in
the minimum swash plate
angle. The volume in the
inlet and outlet chamber are
the same, discharging a
small flow of oil.
The rocker cam is moved
into the maximum position,
volume in the inlet chamber
become larger than the out-
let. Causing a greater flow of
oil.
The swash plate angle on
this pump never becomes 0
Minimum Discharge
Maximum Discharge

20. CLSSSection 2.2
LS Valve.
LS Valve: Detects the load and controls the pump
discharge amount.
The pump discharge or flow is proportional to
differential pressure.

21. CLSSSection 2.2
LS Valve.
Differential Pressure.
PLS = PP – PLS.
PP Main pump Pressure.
PLS Control valve outlet Pressure
Main Pump Pressure
Spool
Control Valve Outlet
Pressure

22. CLSSSection 2.2
LS Valve
Control of Pump Discharge.
When Differential Pressure
PLS = 0 to 22
pump discharge increases.
PLS = 22 to 30
pump discharge is reduced.
PLS
PP PLS

23. CLSSSection 2.2
LS Valve
LS Valve Ports.
The LS valve is a three way selector valve.
Depending on the differential pressure this will determine the
position of the LS spool.
Pump Pressure
(PP)
LS EPC Solenoid Signal
(PSIG)
PC control Valve Input Port
(PPL)
LS Control Pressure
To Servo Piston Large end.
(PLP)
LS Pressure.
(PLS)
Pump Pressure.
(PP)

24. CLSSSection 2.2
LS Valve.
Increase Pump Discharge.
When the operator uses the work equipment LS pressure is introduced to
the LS valve. Pump pressure is always acting on the LS valve.
With LS pressure (PLS) introduce into the LS valve and with the assistance
of the spring and spool area surface is able to over come the pump
pressure (PP) pushing the LS spool to the Left, increasing pump
discharge.
PP - PLS = PLS
180 - 170 = 10 Kg/cm2
(Less than 22 Kg/cm2 pump will increase discharge)
PP = 180
Kg/cm2
PLS = 170
Kg/cm2

25. CLSSSection 2.2
LS Valve.
Decrease Pump Discharge.
When the operator reduces the speed of work equipment or stops working
LS pressure is reduced to the LS valve. Pump pressure is always acting
on the LS valve.
With LS pressure (PLS) reduced Pump Pressure is able to overcome LS
valve, spring tension and spool area surface. This will push the LS spool
to the Right, decreasing pump discharge.
PP - PLS = PLS
180 - 150 = 30 Kg/cm2
(Greater than 22 Kg/cm2 pump will decrease discharge)
PP = 180
Kg/cm2
PLS 150 Kg/cm2

26. CLSSSection 2.2
LS Valve.
LS Valve Balanced.
If the work load is maintained at the same flow and load the pump discharge
or flow will equalize to the load. When this occurs the pump in neither
increasing of decreasing its discharge. This is the benefit of having
CLSS, it will only deliver the oil flow that’s required.
LS pressure, spring tension is equal to Pump Pressure, the LS spool in
neither stroking or de-stroking the pump.
PP - PLS = PLS
180 - 158 = 22 Kg/cm2
PP = 180
Kg/cm2
PLS 158 Kg/cm2

27. CLSSSection 2.2
LS Valve
Control Levers in
Neutral.
When the levers are in
the neutral position
There is no LS pressure
(PLS) delivered to the LS
Valve.
Pump Pressure (PP) is
able to push the LS spool
to the left.
This will introduce PP
into the Large end to
servo-piston, because of
the difference in servo
piston surface area the
swash plate is moved to
minimum position.

28. CLSSSection 2.2
LS Valve
Reduce Flow
When the control leverWhen the control lever
reduces its stroke thereduces its stroke the
pump pressure increasespump pressure increases
and the LS pressureand the LS pressure
drops.drops.
PP pressure pushing LSPP pressure pushing LS
spool to the left.spool to the left.
Introducing PP to largeIntroducing PP to large
end of servo piston.end of servo piston.
The pump will reduce itsThe pump will reduce its
flow until the LS valve isflow until the LS valve is
balancedbalanced..
The LS EPC solenoidThe LS EPC solenoid
supplies a varyingsupplies a varying
pressure depending onpressure depending on
machine condition tomachine condition to
assist in reducing theassist in reducing the
pump flowpump flow

29. CLSSSection 2.2
LS Valve
Increase Flow.
When the machine is
in use, the LS
pressure (PLS) is
introduced to the LS
Valve. Able to
overcome Pump
Pressure (PP).
Pushing the LS spool
to the Right.
This will close off the
PP and open the port
back to tank.
Draining the Large
end to servo-piston
allowing the swash
plate is moved to
maximum position.

30. CLSSSection 2.2
LS Valve
Servo Piston
Balanced.
When the machine is
working at a even
load the pump
pressure (PP) will
equal LS pressure
(PLS) and spring (4).
At this point the
pump is delivering
the correct flow
required.
The LS spool is
neither introducing
PP to the large end of
the servo or draining
it off.
At this point the
pressure applied to
both ends of servo
piston is 3:5.

31. CLSSSection 2.2
PC Valve
PC Valve
The PC Valve will maintain equal horse power control so that the horse power
absorption by the pump does not exceed the engine horsepower.
If the load during operation increases and pump discharge rises, the PC valve
will reduce the pump discharge.

32. CLSSSection 2.2
PC Control Pressure.
(PPL)
PC Control Pressure.
(PPL)
PC Valve
PC Valve Ports.
The PC valve is a three way hydraulic valve situated inside the Servo
piston. The valve is regulated by pump controller via an EPC solenoid in
order to reach optimum matching between the load (pressure P) and the
flow (Q).
Second Pump Pressure
PP2
Pump Pressure
PP1
PC Mode Select Pilot Pressure
(PM)
Pump Pressure.
(PP1)
Drain Port.
(PT)

33. CLSSSection 2.2
PC Valve
No load conditionNo load condition
When the servo piston is atWhen the servo piston is at
maximum flow the springmaximum flow the spring
pressure from springs 4 &6pressure from springs 4 &6
is low. The spool 3 is forcedis low. The spool 3 is forced
to the right by springto the right by spring
pressure.pressure.
PP1 or PP2 pressure is notPP1 or PP2 pressure is not
high enough to over comehigh enough to over come
the spring tension.the spring tension.
This allows the connection CThis allows the connection C
from the LS valve to go tofrom the LS valve to go to
tank , through the centre oftank , through the centre of
spool 3 .spool 3 .
The PC EPC output which isThe PC EPC output which is
controlled by the controllercontrolled by the controller
varying the pressure actingvarying the pressure acting
on spool 3.on spool 3.
Will change the pump torqueWill change the pump torque
output.output.

34. CLSSSection 2.2
PC Valve
High PressureHigh Pressure
The pump pressures hasThe pump pressures has
increased enough pushincreased enough push
the PC spool against thethe PC spool against the
springs to close off port Csprings to close off port C
(Return to tank) and(Return to tank) and
introduce Pump pressure.introduce Pump pressure.
This pressure returns toThis pressure returns to
the large end of the servothe large end of the servo
piston via the LS valve.piston via the LS valve.
As the servo piston isAs the servo piston is
being pushed back tobeing pushed back to
reduce the pumps flow, atreduce the pumps flow, at
the same time the springsthe same time the springs
are being compressingare being compressing
Eventually the springEventually the spring
tension will equal thetension will equal the
pump pressure allowingpump pressure allowing
the optimum flow at thatthe optimum flow at that
particular pressure.particular pressure.

35. CLSSSection 2.2
Pump Discharge: Pressure and Flow
LS Valve
in control
Engine horse-power
unable to maintain
pump out put.
PC Valve
Springs

36. CLSSSection 2.2
LS & PC EPC Solenoids
PC Prolix Switch
ON
If there is a failure in the
pump controller, the
Prolix Switch can be
switch on to switch to
the resistor side, by
pass the controller.
When this is done the
current becomes
constant so the force
pushing the PC valve is
constant. There is no
pump sensing.

37. CLSSSection 2.2
LS & PC EPC Solenoids
EPC Valves
When the solenoid receives a signal
from the controller it generates the
EPC out-put pressure in proportion
to the electrical signal.
The higher the signal an increased
pressure is applied to the LS and PC
valves, this will back the pump off
earlier.
LS EPC
PC EPC

38. CLSSSection 2.2
LS & PC EPC Solenoids
Operation: No Signal.
When there is no signal
current flowing from the
controller the coil is de-
energized.
The spool is pushed across to
the left by spring (3).
Allowing the signal oil to
drain back to tank.

39. CLSSSection 2.2
LS & PC EPS Solenoids
Operation: Signal from Controller
When a signal current flows to the
coil, energizes the coil and
propulsion force is generated which
pushes the plunger (4).
Moving the spool to the right against
the spring.
Opening the oil supply (PEPC) to
flow to the LS or PC valve.
As the pressure raises in PSIG plus
spring force this will push spool (3)
to close and maintain a set pressure
going to the LS & PC valves.