John Deere

1
2500 Gas (Petrol) Diesel Triplex Greens Mower
Hydraulic System

2
2500 Slide Index
(Left Click Selection Box)
Steering/Charge Pump
Steering Valve
Hydrostatic Pump
Lift Valve - Neutral
Wheel Motors
Floating Orifice Operation
Hydro-Build the System
Lift Valve - Raise
Hydro-Normal Operation
Lift Valve - Lower
Hydro-Dynamic Brake
Hydraulic Pump
Hydro-Dump Valve
Reel Drive - Build the System
Rear Wheel Assist Option
Backlap Valve Operation
3
Charge Pump It is the most forward pump of the
triple pump assembly. The charge pump operates in
an Open Center Series type hydraulic system
consisting of the Steering and Hydrostatic drive
systems.
4
Steering/Charge Pump

• Functions
• Hydrostatic Steering
• Provides Oil Flow Through Oil Filter and Cooler
• Provides Makeup for Internal Leakage
• Keeps Back Pressureon Pump Pistons

5
The pump is direct coupled to the engine flywheel
and is mounted to the frame under the
seat. Directional control, forward or reverse, is
controlled by varying the direction of fluid flow
out of the hydrostatic pump by varying the
direction of rotation of the swash plate in the
pump. Control of the rotation is provided by two
foot pedals. The left pedal controls forward
motion, the right pedal controls reverse
motion. Speed is controlled by the angle of the
swash plate. The greater the angle of the swash
plate from the vertical position (neutral) the
greater the volume of fluid the pump will
displace and the faster the vehicle will travel.
Speed is governed by depressing the foot
pedals. The Hydrostatic Pump provides hydraulic
fluid to the axle and motors though hydraulic
lines and fittings. The hydraulic fluid in the
power train circulates in a closed loop. Fluid
leaves the pump and flows through the motor and
is returned to the pump, not the reservoir. Fluid
that leaves this closed loop circuit, such as
case drain, is replenished by fluid from the
Charge Pump located on the front of the triple
pump assembly.
6
Hydrostatic Pump

• Eaton Model 70144 Axial Piston Pump

7
Wheel Motors

• Parker-Ross Geroler TorqMotors(Same as 2653A)
• Third Wheel Drive Option

8
1. Bring in the Pumps and Motors that were
discussed in Hyd Fundamentals. 2. Connect the
Hydro Pump to the Motors 3. Students should now
recognize that this is the same type system as
that explained in hydraulic fundamentals. 4.
Point out the Pressure Regulating Valve
Inlet Checks Dump or TOW valve
9
Hydrostatic System

• Build the System

10
The hydrostatic pump provides hydraulic fluid to
the wheel motors though hydraulic lines and
fittings. The hydraulic fluid in the power train
circulates in a closed loop. Fluid leaves the
pump and flows through the motor and is returned
to the pump, not the reservoir. Fluid that leaves
this closed loop circuit, such as case drain, is
replenished by fluid from the charge pump located
on the end of the triple pump assembly.
11
Hydrostatic System

• NormalOperation

12
Notice that the motors want to act like pumps,
because forces (whether gravity or something
pushing the machine) attempt to make the drive
wheels rotate. The hydro pump is NOT rotating,
thus it is NOT providing oil and blocks the oil
path to the other side of the closed loop. There
is NO WHERE for the oil to go, thus the drive
wheels are locked. NOTE 1. There will be
some leakage past the hydro pump and motors
allowing the wheels to rotate slightly. 2.
Plus, it is possible for a piston in the hydro
axial pump to be in a position so that it will
leak oil through a lubrication orifice allowing
oil to escape back to sump which results in the
wheels turning. Moral of the Story Hydros
provide dynamic braking, they are NOT designed as
a parking brake. Always set the park brake when
exiting a machine equipped with a hydrostatic
transmission to be sure that it wont run-away.
13
Hydrostatic System
Motors Want to Act Like Pumps

• Dynamic Brake

14
The purpose of the dump (or TOW) valve is to
allow the movement of a disabled vehicle or if
you want to just push it a short distance,
without starting the engine. If an attempt is
made to push the vehicle the hydrostatic motors
become pumps, trying to pump oil through the
system. This creates a hydraulic lock between the
motor and pump. To overcome this condition, a
dump valve has been installed between the inlet
check valves. The dump valve is a plug that
contains a rotating stem which has a flat spade
end that fits between the two ends of the inlet
check valves. When the dump valve is in the
closed position, the inlet check valves are also
in the closed position. When the dump valve stem
is rotated 90, the flat spade end spreads the
inlet check valves to the open position. This
allows the oil in the hydrostatic closed loop to
by-pass around the inlet check valves inside the
pump backplate. The by-passing of oil inside the
pump backplate will allow the motor to rotate
freely when the vehicle is moved a short
distance. The dump valve is intended only for
moving a vehicle a very short distance and not
intended for towing the vehicle long distances
behind a truck or tractor!!
15
Hydrostatic System
Motors Want to Act Like Pumps

• Dump ValveOperation

16
Three Wheel Drive Solenoid Valve The Three Wheel
Drive solenoid valve is a electrically operated,
spring return shuttle valve. The solenoid is
energized whenever the mow switch is engaged.
When energized, fluid from the Forward side of
the Hydrostatic Pump is directed to the rear
wheel motor for added traction. When de-energized
fluid in the rear motors and lines circulate in a
closed loop allowing the rear wheels to freewheel
17
2500Hydrostatic System
Three Wheel Drive Solenoid Valve
Forward
Rear Wheel
Motor
Reverse
Freewheeling
Valve
Front Wheel Motors

• Rear Wheel Drive OFF

Hydraulic Filter
From Steering Valve
Bypass Valve
Oil Cooler
17
18
2500Hydrostatic System
Three Wheel Drive Solenoid Valve
Forward
Rear WheelMotor
Reverse
(
Freewheeling
Valve
Front Wheel Motors

• Rear Wheel Drive ON

HydraulicFilter
From the
TowValve
Steering Valve
Oil Cooler
18
19
2500Hydrostatic System
Three Wheel Drive Solenoid Valve
Forward
Rear Wheel
Motor
Reverse
Freewheeling
Valve
Front Wheel Motors

• Rear Wheel Drive in Reverse or Freewheeling

Hydraulic Filter
From the
Tow Valve
Steering Valve
Oil cooler
19
20
It is the forward pump of the triple pump
assembly. The steering pump operates in an Open
Center Series type hydraulic system consisting
of the Steering and Hydrostatic drive systems.
In this series circuit, the first valve
(steering) takes priority over charge pressure.
21
Steering/Charge Pump

• Functions
• Steering
• Provides Oil Flow Through Oil Filter and Cooler
• Provides Makeup for Internal Leakage
• Keeps Back Pressureon Pump Pistons

22
Function Offer hydraulic steering for ease of
operation. Theory of OperationOil is pressurized
by the steering/charge pump and routed through
the steering valve. The Steering system is
protected by the 1500 PSI relief valve located in
the steering valve. The steering system goes over
relief in full right hand or left hand
turns.Excess oil dumps across the relief and
returns to reservoir via filter.
23
Steering System
R
L

• Neutral

Gerotor
Mechanical Link
Steering/ChargePump
Control
1050 psi
P
Inlet
On to Filter, Cooler and Charge
24
Function Offer hydraulic steering for ease of
operation. Theory of Operation When the steering
wheel is turned, pressurized oil is routed
through the steering valve to the balanced
steering cylinder through the pressure hoses. The
steering cylinder converts the hydraulic flow to
mechanical movement to turn the wheel as desired.
25
Balanced Steering System

• A Rod on Both Sides of the Piston
• Equal Volumes on Each Side of the Cylinder
• Steering Speed Same in Either Direction
• Equal Effort in Either Direction

26
Lift Pump It is the second pump of the triple
pump assembly. The lift pump operates in an Open
Center Series type hydraulic system
27
Lift System Pump

• Functions
• Hydraulic Lift Circuit
• With 1500 PSI Relief Valve

28
Theory of Operation Oil is drawn out of the
reservoir through a 100 mesh filter screen by the
lift pump. It is then routed to the HIC
(Hydrostatic Integrated Circuit). The lift
system is protected by the 1500 PSI relief valve
located in the lift valve.
29
Lift Valve
Lift Valve

• Neutral Position

30
Floating Orifice

• Restricts Oil Flow in OneDirection and not the
  OtherDirection

Top View
Side View
Front Cylinder
31
Floating Orifice

• Does NOT Restrict Oil Flow in This Direction
  Because Oil is Able to Flow Through and Around
  the Orifice

Top View
Side View
Front Cylinder
32
Floating Orifice

• Restricts Oil Flow in This Direction Because the
  Oil Must Flow Through the Orifice

Top View
Side View
Front Cylinder
33
Lift Pump It is the second pump of the triple
pump assembly. The lift pump operates in an Open
Center Series type hydraulic system
34
Lift Valve
Lift Valve

• Raise Position

35
Lift Pump It is the second pump of the triple
pump assembly. The lift pump operates in an Open
Center Series type hydraulic system
36
Lift Valve
Lift Valve

• Lower/Float Position

37
Hydraulic Pump It is the third pump of the
triple pump assembly(closest to hydro). The reel
pump operates in an Open Center Series type
hydraulic system. Oil is drawn out of the
reservoir through a 100 mesh filter screen by the
reel pump and then routed to the control valve.
38
Reel Drive Pump

• Functions
• Provides Oil Flow to Drive the Cutting Units

39
REEL DRIVE SYSTEM THEORY OF OPERATION The Mow
valve is a solenoid actuated, pressure limiting
shuttle valve. It is used to control the flow to
the reel motors. The mow valve is energized
through the control module during mowing
operations. It limits pressure in the reel drive
circuit to 3000 PSI. The flow control valve,
located in the backlapping valve assembly, is a
manually operated flow restrictor. It is used to
control reel speed when backlapping. It is
adjusted by rotating the knob clockwise to
restrict and counterclockwise to increase
flow. The backlapping valve or directional valve
, located in the backlapping valve assembly, is a
hydraulically operated, three position,self
centering, closed center spool valve that changes
fluid flow direction. The knob, when pushed in,
directs the fluid flow to the motors for forward
cutting. When pulled out, the cutting units will
reverse direction for backlapping. The motors are
Danfoss.
40
Backlap Valve
(
Reel Pump
40

• Build the System

41
Mow OFF/ Neutral
In the neutral Position, oil simply flows through
valve assembly and back to tank. Notice oil is
free to travel out to the directional valve.
The center position of the directional valve is
closed and prevents oil traveling through the
reel motor circuit, so the oil takes the path of
least resistance and flows back to the reservoir
(out port T).
42
Backlap Valve

• Off

) (
)(
)(
42
43
When the mow solenoid valve is energized pressure
and flow are now routed to the flow control valve
and logic element. The flow control valve
determines the rpm of the reels. Pressure in the
reel circuit will vary according to the amount of
resistance that the cutting units are generating.
The logic element, compares pressure at the inlet
and outlet ports of the flow control valve. As
the flow is restricted, pressure builds on the
input side of the flow control valve to a value
higher than that on the output side. This forces
the logic element to open and dump excess flow to
the tank. As flow returns to the reservoir,
pressure to the input side of the flow control
valve drops and the logic element closes. The
logic element will continue this cycle as needed
to equalize pressure on both sides of the flow
control valve. After leaving the flow control
valve, fluid enters the top of forward/reverse
valve. The pressure oil shuttles the spool valve
down to allow hydraulic oil to the forward side
of the reel motors. When the mow valve is
de-energized pressure oil is then routed the
path of least resistance which is back to tank.
The flow control valve will then shuttle back to
the off position. Thus blocking the path for oil
to flow to the cutting units and stopping the
possibility of reel creep or wind milling. After
leaving the backlapping valve, flow is directed
to the forward side of the reel motors. The reel
motors are connected in series starting with the
left front, right front then center.
44
Backlap Valve

• Mow

MowValve
)
)
(
)
PortB
PortP
VariableOrifice
(
(
(
(
PortA(Mow)
LogicElement
(
44
Port T
45
Reel Momentum OFF
The purpose of the reel momentum off is to allow
the reels to gradually slow down. If we abruptly
stopped our reels we would run the chance of
damaging the reel motors.(cavitation) When the
mow valve is de-energized the reels continue to
spin momentarily. While they continue to spin
the motors become pumps thus keeping pressure in
the system and holding the directional valve in
the down position. As the reels slow down,
pressure decreases and the springs on the
directional valve then center the spool to the
OFF position. This all happens in a matter of
seconds.
46
Backlap Valve

• Off - Reel Momentum

MowValve
)
)
(
)
PortB
PortP
VariableOrifice
(
(
(
PortA(Mow)
LogicElement
(
(
46
Port T
47
Lets look at just the pressure sensing, flow
compensating, variable reel speed control,
Micro-Backlap valve for short. The pressure
sensing, flow compensating aspect of the Backlap
valve is accomplished with the logic element.
During backlapping the reel speed is turn down to
1 or 2 on the reel speed control knob. This
causes pressure/restriction, opening the logic
element, the excess oil is now dumped back to
tank through the logic element. When we apply
backlapping compound to the reels this causes
pressure/restriction on the other side of our
reel speed control. The logic element senses
this through the pilot line and compensates the
flow by closing the path to tank, thus sending
more oil to our cutting units, keeping a more
consistent reel speed. Giving us pressure
sensing, flow compensating
48
Backlap Valve

• Backlap

(
48
49
Backlapping Valve The backlapping valve, located
in the backlapping valve assembly, is a three
position, self centering closed center spool
valve that changes fluid flow direction. The
knob, when pushed in, directs the fluid flow to
the motors for forward cutting. When pulled out,
the cutting units will reverse direction for
backlapping, and a switch is actuated to energize
the Mow Valves. Pushing the knob in stops the
cutting unit rotation Flow Control Valve The
flow control valve, located in the backlapping
valve assembly, is a manually operated flow
restrictor. It is used to control reel speed when
backlapping. It is adjusted by rotating the knob
clockwise to restrict and counterclockwise to
increase flow. The logic element, compares
pressure at the inlet and outlet ports of the
flow control valve. As the flow is restricted,
pressure builds on the input side of the flow
control valve to a value higher than that on the
output side. This forces the logic element to
open and dump excess flow to the tank. As flow
returns to the reservoir, pressure to the input
side of the flow control valve drops and the
logic element closes. The logic element will
continue this cycle as needed to equalize
pressure on both sides of the flow control valve.
50
Backlap Valve

• Over Relief

MowValve
)
)
(
)
PortB
PortP
VariableOrifice
(
(
(
(
PortA(Mow)
LogicElement
(
50
Port T