Content .. 11 12 13 14 ..

JCB 3CX, 4CX, 214e, 214, 215, 217 & VARIANTS Backhoe Loader. Service Manual - page 13

Section E

Hydraulics

Section E

3 - 32

Circuit Schematics

3 - 32

Precision Control (Servo)

* (Machines up to serial no. 931159)

A396210

9803/3280

Issue 2*

Section E

Hydraulics

Section E

3 - 33

Circuit Schematics

3 - 33

Precision Control (Servo)

(Machines from January 2003)

POWER SIDESHIFT

(OPTION)

HAMMER

(OPTION)

HAMMER

(OPTION)

A403921

9803/3280

Issue 1

Section E

Hydraulics

Section E

3 - 34

Basic System Operation

3 - 34

Hydraulic Circuit Schematic

Precision Control (Servo)

(Machines from January 2003)

The schematic shows the main system hydraulics for

Precision Control (Servo) machines. For the pilot circuit refer

to relevant pages.

Note: The boom and dipper services are interchanged for

the ISO control pattern.

Component Key:

Small letters on the schematic indicate port markings. Refer

to Technical Data pages at the begining of this section for

more information. Ports A and B are always identified as

service ports (feed and return from respective ram).

Tank

Hydraulic Oil Cooler

Return Filter

Anti Cavitation Check Valve

Suction Strainer

Lift Ram R.H.

Pump, Main Section

Lift Ram L.H.

Pump, Secondary Section

Shovel Ram R.H.

Loader Valve Block

Shovel Ram L.H.

Loader Lift Ram Spool

Clam Shovel Ram R.H.

Loader Shovel Ram Spool

Clam Shovel Ram L.H.

Clam Shovel Spool

Steer Mode Control Valve

Shovel Ram Head Side A.R.V.

Steer Unit

Shovel Ram Rod Side A.R.V.

AWS Power Track Rod Rams

Excavator Valve Block

2WS Power Track Rod Ram

Slew Spool

Unloader Valve

Boom Spool (Dipper ISO)

Priority Valve

Right Stabiliser Spool

Stabiliser Ram R.H.

Left Stabiliser Spool

Stabiliser Ram L.H.

Dipper Spool (Boom ISO)

Hydraclamps (Sideshift Only)

Bucket Spool

Boom Ram (Dipper ISO)

Extending Dipper Spool

Slew Ram R.H.

Hydraclamp Valve (Sideshift Only)

Slew Ram L.H.

Slew A.R.V.

Dipper Ram (Boom ISO)

Slew A.R.V.

Bucket Ram

Boom Ram Rod Side A.R.V.

Extending Dipper Ram

Boom Ram Head Side A.R.V.

Dipper Ram Head Side A.R.V.

Boom Ram Rod Side A.R.V.

Bucket Ram Head Side A.R.V. (Hammer Only)

Hammer Option:

Bucket Ram Rod Side A.R.V.

Hammer Flow Valve

Extending Dipper Ram Rod Side A.R.V.

Hammer Selector Valve

Extending Dipper Ram Head Side A.R.V.

Hammer Feed Coupling QR

Flow Regulator Valve

Hammer Return Coupling QR

Flushing Valve

Load Sense Relief Valve

Power Sideshift Option:

Power Sideshift Selector Valve

Power Sideshift Ram

9803/3280

Issue 1

Section E

Hydraulics

Section E

3 - 35

Basic System Operation

3 - 35

Hydraulic Circuit Schematic

Precision Control (Servo)

(Machines from January 2003)

The schematic shows the pilot circuit for Precision Control

(Servo) machines. For the main system hydraulics refer to

relevant pages.

Note: The boom and dipper services are interchanged for

the ISO control pattern.

Component Key:

Small letters on the schematic indicate port markings. Refer

to Technical Data pages at the begining of this section for

more information. Ports A and B are always identified as

service ports (feed and return from respective ram).

Excavator Valve Block

Stabiliser Ram R.H.

Stabiliser Ram L.H.

Hydraclamps (Sideshift Only)

Boom Ram (Dipper ISO)

Slew Ram R.H.

Slew Ram L.H.

Dipper Ram (Boom ISO)

Bucket Ram

Extending Dipper Ram

Joystick Controller L.H.

Servo Pressure Supply Valve

Joystick Controller R.H.

Stabiliser Control R.H.

Stabiliser Control L.H.

Footpedal Control (Extending Dipper)

9803/3280

Issue 1

Section E

Hydraulics

Section E

3 - 36

Circuit Schematics

3 - 36

Precision Control (Servo)

(Machines from January 2003)

A405700

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 1

Circuit Descriptions

5 - 1

Hydraulic Pump - Fixed Flow

Component Key:

Single Pump - Operation

A Spur Gear - Idler

The hydraulic pump is a gear type. The basic principle of the

B Spur Gear - Driven

pump depends on the meshing of the two spur gears A and

C Channel

B, one of which is engine-driven whilst the other is an idler.

D Recess

Oil is picked up on the inlet side of the pump by the gears

Main Section

and carried round between the gear teeth and the pump

Secondry Section

body. As the gears come into mesh the oil is forced through

the pump outlet port.

Lubrication is provided by the hydraulic oil which is directed

around the unit, via special oil ways, by the motion of the

meshing gears.

Double Pump - Operation

Both sections P1 and P2 operate as described below:

The basic principle of the gear pump depends on the mesh-

ing of two spur gears A, one of which is engine driven while

the other is an idler.

Oil is picked up by the gear teeth on the inlet side of the

pump and carried around betwwen the teeth and the pump

body. As the gears come into mesh, the space carrying the

oil is filled by a gear tooth on the mating gear, forcing the oil

out of the space and the through the pump outlet.

The wear plates B are loaded towards the gears by pres-

surised oil which is fed to the backs of the wear plates via

channels C. This ensures that the clearance between the

wear plates and gears is prevented from becoming exces-

sive as outlet pressure rises.

The side of each wear plate that faces the gears has two

recesses D. The recess on the inlet side of the pump assists

the flow of oil into the gear spaces, thus raising the cavitation

threshold of the pump. The recess on the outlet side vents oil

trapped between meshing gear teeth to prevent compres-

sion loads on the bearings.

9803/3280

Issue 1

Section E

5 - 2

Circuit Descriptions

5 - 2

Key to Oil Flow & Pressure

Full Pressure

Pressure

Servo

Neutral

Exhaust

Cavitation

Lock Up

A390630

A396380

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 3

Circuit Descriptions

5 - 3

Hydraulic Pump - Variable Flow

Operation

Component Key:

The pump is a variable displacement axial piston type.

Pump

Displacement of oil is achieved by the continuous operation

Cylinder Barrel

of nine pistons. Pump fluid output is controlled by a tilting

Drive Shaft

cam (swashplate), the angle of which is regulated to ensure

Kidney Plate

that only the amount of fluid necessary to satisfy load

Axial Piston

conditions is delivered. If a load condition is such that no

Swashplate

flow is required, only sufficient fluid for cooling and

Shoe Plate

lubrication is provided.

Stroking Piston

Control Piston

Main components of pump P are a cylinder barrel 1 splined

Pressure/Flow Compensator Valve

to a drive shaft 2 which is held against a kidney plate 3.

Contained in the cylinder barrel are the axial pistons 4, each

having an articulated shoe that is in held contact with the

swashplate 5 by an attachment plate 6. The tilting action of

the swashplate is exercised by a stroking piston 7 and a

control piston 8, the latter fed by servo pressure. Fitted to

the pump exterior is the valve block 9 housing the

pressure/flow regulators that provide servo control.

Rotation of the cylinder barrel causes linear movement of the

axial pistons and fluid from the suction port is drawn into the

pump through the kidney plate to fill a developing vacuum

behind the piston. As the cylinder barrel rotates the fluid is

carried from an elongated suction kidney to an elongated

pressure kidney where linear movement starts to return the

piston into the cylinder barrel. Fluid is forced from the pump

through the pressure port.

The stroke length of the pistons and consequently the output

of fluid is directly related to the swashplate angle. The

swashplate is normally held in its maximum displacement

angle by the stroking piston spring and system pressure

inside the stroking piston.

S271440

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 4

Circuit Descriptions

5 - 4

Neutral Circuit Pressure

Pressure Generated by

Operation of a Service

Trapped Oil

Exhaust

A275730

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 5

Circuit Descriptions

5 - 5

Hydraulic Pump - Variable Flow

Pressure/Flow Regulator Valve

The pressure and flow regulator valve assembly is mounted

to the pump. The valve maintains the pump pressure and

flow rate in accordance with demand at the service valve

blocks.

Load Sensing - Stand-by Position

Stand-by is when the machine is running but the control

levers are in neutral position, i.e. no implements are being

used. There is no pressure or flow demands on the pump,

therefore there will be no pressure signal .

With the engine switched off, spring 1 holds swashplate 2 at

the maximum angle. When the engine is started and the

pump begins to turn, oil begins to flow and pressure builds in

the closed centre hydraulic system.

Valve 5 houses a flow regulator spool 4 and pressure

regulator spool 3. Pressure which is building in the closed

centre system is sensed at port P of the regulator valve. The

increasing pressure pushes flow compensating spool 4 up

against its spring 6. This movement creates a flow path from

port P to port A. Oil now flows from the flow regulator valve

(via port A) to swashplate control piston 7.

The control piston now moves the swashplate 2 towards its

minimum angle. As the piston moves towards its full travel

position, cross-drilled holes 8 are uncovered allowing oil to

drain.

A275760

The cross-drilled holes limit the travel of the control piston -

when the holes are exposed, pump flow is insufficient to

make up for leakage through the holes and maintain the

pressure behind the control piston. Therefore the piston

moves back to partially cover the cross holes thus

maintaining enough flow to cater for normal system leakage

whilst establishing a system stand-by pressure (see

Technical Data for pressure).

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 6

Circuit Descriptions

5 - 6

Neutral Circuit Pressure

Pressure Generated by

Operation of a Service

Trapped Oil

Exhaust

A275740

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 7

Circuit Descriptions

5 - 7

Hydraulic Pump - Variable Flow

Pressure/Flow Regulator Valve

Load Sensing - Maximum Flow

When a service is operated, the signal pressure from the

loader (or backhoe) valve 13 increases. The increase in signal

pressure combined with the force of spring 6 moves spool 4

down. Oil in control piston 7 is allowed to drain back to the

tank via restrictor 9 and passage 10.

The force of spring 1 is now sufficient to increase the angle

of swashplate 2. The increased angle of the swashplate

increase the output of the pump.

The pump output pressure will continue to increase,

eventually the pressure will move flow regulating spool 4

against the force of spring 6 and the signal pressure in cavity

11. Pump output pressure is now sent to control piston 7 via

port A. Control piston 7 will overcome the force of spring 1.

The pump swashplate angle decreases and therefore the

pump outlet decreases. Eventually the pressure in the load

sense line and the force of spring 6 will move spool 4 down

and the ‘metering’ cycle starts again.

The up and down movement of the spool 4 keeps the

pressure on both ends of the spool equal. Spring 6 is

equivalent to 20 bar (290 lbf/in²), therefore the pump

pressure should be this amount greater than the signal

pressure (except when at maximum pressure - see Load

Sensing - Maximum Pressure (no flow).

A275770

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 8

Circuit Descriptions

5 - 8

Neutral Circuit Pressure

Pressure Generated by

Operation of a Service

Trapped Oil

Exhaust

A275750

9803/3280

Issue 1

Section E

Hydraulics

Section E

5 - 9

Circuit Descriptions

5 - 9

Hydraulic Pump - Variable Flow

Pressure/Flow Regulator Valve

Load Sensing - Maximum Pressure (no flow)

When a service ram reaches the end of its stroke or the

service meets resistance (for instance tearing out), the signal

pressure from the loader (or backhoe) valve 13 will increase

to the same pressure as pump output pressure.

The force of spring 6 is sufficient to move spool 4 down. The

pressure in the system is also sufficient to move spool 3 up

against the force of spring 12, this creates a connection from

the pump outlet to control piston 7 via port A.

Control piston 7 moves thus decreasing the angle of

swashplate 2. Pump output flow now decreases whilst the

system pressure is maintained at maximum setting. There is

now no flow but maximum system pressure.

A275780

9803/3280

Issue 1

Section E

Hydraulics

Section E

6 - 1

Circuit Descriptions

6 - 1

Loader Valve - Neutral Circuit

Component Key:

The loader valve is mounted on the chassis frame, right

hand side (when viewed from the rear).

Parallel gallery

Gallery

It includes the lift ram spool 3C, shovel ram spool 3D and

Drilling

auxiliary spool 3E. Linkage rods connect the spool ends to

Tank Port

the control levers.

Pump Inlet (section P1)

High Pressure Carry Over

In neutral circuit hydraulic oil from the pump section P2

Pump Inlet (section P2)

enters the loader valve at 1C via the steering priority valve.

Main Relief Valve

On entering the valve block, oil flows around the waisted

LIft Ram Spool

section of the unloader valve 3L, past check valve 3N and

Shovel Ram Spool

joins the flow from pump section P1.

Auxiliary Spool

Unloader Valve Spool

Oil from pump section P1 enters the loader valve at 1A.

3M Unloader Pilot Valve

3N Check Valve

Combined oil flow from P1 and P2 passes the main relief

Spring Cavity

valve (MRV) 3B and fills the parallel gallery B. From the

Solenoid Valve

parallel gallery the oil flows around the waisted central

portions of spools 3C, 3D and 3E (all in neutral position) and

flows on to feed the excavator valve via high pressure carry

over line 1B.

Pressure in inlet gallery C is sensed by pilot valve 3M via the

bore of spool 3L. At pressures below the setting of the

unloader valve, both pilot valve 3M and spool 3L remain

closed.

Loader Valve - Unloader Operation

Unloader spool operation protects the engine from being

overloaded if a service is being worked particularly hard, for

example when using the excavator to tear out. It does this

by dumping the oil from the pump section P2 to tank,

allowing engine power to be applied fully to the main pump

section P1.

If the pressure in the inlet gallery C rises to the setting of the

pilot valve 3M, this valve will open, allowing oil in spring

cavity 3P to escape more quickly than it can be replaced by

oil entering through the small drilling D.

This creates a pressure differential between the spring cavity

3P and gallery C. Higher pressure in gallery C acts on the

face of spool 3L causing the spool to be moved off its seat.

Oil entering the valve block from pump section P2 now flow

directly to tank T.

High pressure in gallery C also holds check valve 3N firmly

closed, preventing oil from pump section P1 from also being

dumped.

When pressure in inlet gallery C falls, for example if the

excavator has stopped tearing out, pilot valve 3M will close.

This means oil in spring cavity 3P will be at the same

pressure as oil in gallery C, spring pressure will move spool

3L back onto its seat, closing pump section P2 connection

to tank.

9803/3280

Issue 1

Section E

6 - 2

Circuit Descriptions

6 - 2

1B T

1C(P2)

Key to Oil Flow & Pressure

Full Pressure

1A(P1)

Pressure

Servo

A401150

Neutral

Exhaust

Cavitation

Lock Up

A390630

3N P1

A401160

9803/3280

Issue 1

Section E

6 - 3

Circuit Descriptions

6 - 3

1C(P2)

1A(P1)

A401170

Key to Oil Flow & Pressure

Full Pressure

Pressure

Servo

Neutral

Exhaust

Cavitation

Lock Up

A390630

9803/3280

Issue 1

Section E

Hydraulics

Section E

6 - 4

Circuit Descriptions

6 - 4

Loader Valve

Component Key:

- Hydraulic Speed Control (HSC)

B Parallel gallery

C Gallery

Solenoid valve 3Q allows the operator to control the

D Drilling

unloader spool movement (to dump flow from the hydraulic

T Tank Port

pump section P2) using a switch. There are two main

1A Pump Inlet (section P1)

applications for this operation:

1B High Pressure Carry Over

1C Pump Inlet (section P2)

More tractive force can be applied to the loader end

3B Main Relief Valve

when entering a stock pile. This is because more power

3C LIft Ram Spool

is available from the engine as flow from pump section

3D Shovel Ram Spool

P2 is being dumped directly to tank.

3E Auxiliary Spool

3L Unloader Valve Spool

More power can be made available from the engine

3M Unloader Pilot Valve

whilst the machine is travelling on the highway. Again,

3N Check Valve

this is because flow from pump section P2 is being

3P Spring Cavity

dumped directly to tank.

3Q Solenoid Valve

When the solenoid valve 3Q is de-energised its spool is

moved by spring pressure. This spool movement makes a

connection from the unloader spool chamber 3P to tank.

Because the unloader chamber is now connected to tank,

and so at exhaust pressure, pressure in gallery C (neutral

shown) acts on the face of unloader spool 3L causing the

spool to be moved off its seat. Oil entering the valve block

from pump section P2 now flows directly to tank.

When solenoid valve 3Q is energised its spool closes the

connection from the unloader valve spool chamber to tank.

Spool 3L is once again controlled by system pressure.

9803/3280

Issue 1

Section E

Hydraulics

Section E

6 - 5

Circuit Descriptions

6 - 5

Loader Valve - Load Hold Check Valves

Component Key:

Operation 1

1A Pump Inlet

The illustration shows 'arms raise' being selected by the lift

B Parallel Gallery

ram spool 3C.

D Service Line

3C Lift Ram Spool

The weight of the loaded shovel, as indicated by the arrows,

3J Load Hold Check Valve

produces a higher pressure in service line D than in the

Lift Ram

parallel gallery B.

Lift Ram

This pressure differential causes load hold check valve 3J to

close, thus preventing the load from dropping.

Operation 2

As the neutral circuit has been blocked by the central land of

the selected spool 3C, the pressure in parallel gallery B

increases until it is greater than that in service line D.

At this point, load hold check valve 3J opens, allowing oil to

flow from the parallel gallery into the service line and operate

the lift rams 33 and 34.

9803/3280

Issue 1

Section E

6 - 6

Circuit Descriptions

6 - 6

A396410

Key to Oil Flow & Pressure

Full Pressure

Pressure

Servo

Neutral

Exhaust

Cavitation

Lock Up

A390630

A396420

9803/3280

Issue 1

Section E

6 - 7

Circuit Descriptions

6 - 7

A396390

Key to Oil Flow & Pressure

Full Pressure

Pressure

Servo

Neutral

Exhaust

Cavitation

Lock Up

A390630

A396400

9803/3280

Issue 1

Section E

Hydraulics

Section E

6 - 8

Circuit Descriptions

6 - 8

Loader Valve

Arms Lower

Component Key:

A Spool Waists

When a spool is selected as shown at 3C, the central land of

B Parallel Gallery

the spool C blocks the neutral circuit. Oil from the pump,

C Central Land

entering at 1A, is diverted into the parallel gallery B, opens

D Spool Waist

the load hold check valve 3J, and flows around the waisted

E Lower Waist

section of the spool D and out to the rod side of lift rams 33

1A Pump Inlet

and 34.

3C Lift Ram Spool

3J Load Hold Check Valve

The lower land of the selected spool E blocks the flow from

Lift Ram

the parallel gallery to the head side port and oil returning

Lift Ram

from the rams is diverted into the exhaust gallery.

Float

The float facility is provided to allow the arms to move up

and down so that the shovel can follow the surface contours

as the machine is driven over uneven ground.

This is achieved by moving the lift spool 3C down beyond

'arms lower' into the 'float' detent, when the feed from the

parallel gallery to the service ports is blocked and the neutral

circuit is re-opened. Both service ports are connected to

exhaust via the spool waists A.

Oil can then be displaced from either end of the lift rams 33

and 34 into the exhaust gallery, allowing the rams to open

and close as required.

9803/3280

Issue 1

Section E

Hydraulics

Section E

6 - 9

Circuit Descriptions

6 - 9

Loader Valve - A.R.V. Operation

Component Key:

Under normal operating conditions, with the shovel in the

'carry' position, the mechanical linkage keeps the shovel

1A Pump Inlet

level as the arms are raised, to prevent spillage of the load.

3C Lift Ram Spool

3D Shovel Ram Spool

If, as illustrated, the shovel is fully tipped when the arms are

3F ARV - Head Side

being raised, the shovel is unable to tip further, producing

3G ARV - Rod Side

back pressure in the head side of the shovel rams 31 and

Shovel Ram

32 and cavitation in the rod side.

Shovel Ram

As the arms continue to rise, the back pressure increases

until it reaches the setting of A.R.V. 3F. This A.R.V. then

opens, allowing the excess back pressure to be dumped to

exhaust and prevent the rams and linkage from being

damaged.

The rod side A.R.V. 3G senses a higher pressure in the

exhaust gallery than in the service port and therefore opens

to allow exhaust oil to overcome the cavitation.

9803/3280

Issue 1

Section E

6 - 10

Circuit Descriptions

6 - 10

A396370

Key to Oil Flow & Pressure

Full Pressure

Pressure

Servo

Neutral

Exhaust

Cavitation

Lock Up

A390630

9803/3280

Issue 1

Section E

6 - 11

Circuit Descriptions

6 - 11

A401180

Key to Oil Flow & Pressure

Full Pressure

Pressure

Servo

Neutral

Exhaust

Cavitation

Lock Up

A390630

9803/3280

Issue 1

Section E

Hydraulics

Section E

6 - 12

Circuit Descriptions

6 - 12

Main Relief Valve (MRV) - Operation

The main relief valve (M.R.V.) 3B, situated in the loader valve

Component Key:

block, provides control of both loader and excavator

pressures.

Main Plunger

Valve Seat

Valve at Rest

Spring

Chamber

The illustration 1 shows a loader service selected by spool

Drilling

3D causing pressure to rise in the service line and back

Pilot Valve

through the loader valve to the pump via line 1A. The service

Spring

is operating under light load and the pressure is not

Exhaust Gallery

sufficient to cause any response in the M.R.V.

Pump Inlet

Main Relief Valve

The main plunger A is held on its seat B by the combined

Shovel Ram Spool

effect of spring C and the pump pressure which enters

chamber D through the small drilling E. Pump pressure

outside the chamber is not high enough to lift the plunger off

its seat.

Pilot Valve Opens

If, as shown in view 2, pump pressure rises high enough to

force the pilot valve F from its seat (against spring G), the

pressure in chamber D is vented into the exhaust gallery H.

Unless the pressure continues to rise, plunger A will remain

on its seat.

Valve Moves off its seat

In view 3, pump pressure at 1A has risen to the setting of

the main relief valve but pressure in chamber D has not risen

because the seat orifice of pilot valve F is larger than small

drilling E and oil is unable to fill the chamber as quickly as it

is being exhausted.

Pressure acting on the upper faces of main plunger A is

therefore greater than the combined force of spring C and

the pressure in chamber D. The plunger then moves off its

seat, allowing pressure to be released to the exhaust gallery.

As the pump pressure decreases, the pilot valve is able to

reseat and pressure in chamber D assists spring C to force

the main plunger A back onto its seat.

9803/3280

Issue 1

Content .. 11 12 13 14 ..