This document provides training materials on truck hydraulics for logging operators. It discusses the basic components and functions of hydraulic systems used in logging trucks, including: - Two independent closed-loop hydraulic circuits that power the winch and alternator motor. - Key components like variable displacement pumps and motors, relief valves, filters, and charge pumps that replenish fluid. - Operating principles like Pascal's law, variable displacement, and how pumps and motors work using swash plate and bent axis designs. - Safety systems like relief valves and mooring control for maximum line tension control when logging up. The document aims to help operators understand the why and how of truck hydraulics systems

1. OH043.1
Internal Use Only
Basic Logging Truck
Hydraulics

2. OH043.2
Internal Use Only
Basic Logging Truck
HYDRAULICS
As a logging operator you will
have to run the Winch.
This basic course will help you
understand why and how of the
Truck Hydraulics

3. OH043.3
Internal Use Only
Why Hydraulics
• Transmission of power is very easy and flexible using
Hydraulics. Pumps and Motors are connected by
flexible hoses
• It is safe in the sense that it does not have fire or
electrical hazards. Remember we need to switch OFF /
Disconnect the Truck Alternator during Explosive
related operations yet the Winch has to move.
Hydraulics can be run from the Truck 12 V Battery
• It is relatively maintenance free. Just keep changing
Oil & Filters regularly as scheduled in PM manuals
• Hydraulic operations are smooth and noiseless.
• The ease with which one can control Speed, Torque,
Direction of the winch by operating just one Joy Stick

4. OH043.4
Internal Use Only
Hydrostatic laws
• If pressure is applied
on surface of the same
area, the forces which
are produced are the
same size.
• Forces depend on
height of liquid not on
the shape of the
container in which
liquid is placed.
• Hydrostatic laws
assume an ideal fluid
which is
incompressible,
frictionless and
without mass.

5. OH043.5
Internal Use Only
Pascal’s law
• The effect of a force
acting on a stationery
liquid spreads in all
directions within a
liquid.
• The amount of
pressure in the liquid
is the equal to the
weight force, with
respect to the area
being acted upon.
• The pressure always
acts at right angles to
the limiting surface of
the container.

6. OH043.6
Internal Use Only
Pressure due to external force
• P = F1/A1
• F2 = P.A2
• F1/A1 = F2/A2
• As such a small force
applied on the small
area side can result in
much larger force on a
large area.

7. OH043.7
Internal Use Only
Important characteristics of hydraulic
circuits
• Transfer of large forces
• Operations may commence from rest under full load.
• Smooth adjustments of the following is easily achieved:
• Speed
• Torque
• Force
• Change of Direction (no engaging reverse gear)
• Simple protection against overloading.
• Suitable for both quick and very slow controlled
sequence of movements.
• Decentralized transformation of mechanical/electrical
to hydraulic and hydraulic to mechanical energy is
possible

8. OH043.8
Internal Use Only
Logging Truck hydraulics
There are 2 Independent* Closed Loop Hydraulic circuits in
a Logging Truck (or Skid)
* These two independent circuits share a common Prime Mover
and a common Hydraulics oil tank
1.Controls direction, Speed and
Torque of the Winch
2.Runs the Alternator at a constant
speed of 1800 rpm under changing
load conditions

9. OH043.9
Internal Use Only
Closed Loop Hydraulic circuit- Electrical analogy
Current
source
A
V
R
I
V= IR , I = V/R
Power = V * I
The current source feeds
power while the Resistor
dissipates Power
Pressure = Flow*Load
Power = Pressure * Flow , Torque *
RPM
The Pump converts mechanical
energy to hydraulic energy while the
Motor converts hydraulic energy
back to mechanical energy

10. OH043.10
Internal Use Only
Closed Loop Hydraulic circuit components
Prime Mover (M) Source - Truck/Skid Diesel Engine
Hydraulic Pump (2)
Hydraulic Fluid (1)
Hydraulic Motor (4)
Various accessories like Hoses, Filters, Controls,
Valves etc.
Pump Motor
Pressure Gauge
Fluid Flow
Mechanical energy turns
the Pump, which sucks
hydraulic fluid from a
tank and pushes it out
under pressure. The
pressurized fluid is taken
to the motor in a hose. The
pressurized fluid turns the
motor, looses energy and
returns to tank

11. OH043.11
Internal Use Only
Well, It’s not that simple
Pump Motor
Pressure Gauge
Fluid Flow
What will happen if
1. The load on the motor
increases
2. How to stop the motor without
stopping the engine
3. The Hydraulic oil heats up, gets
dirty with metal dust
1. If the load on the motor increases, pressure will increase. It may
burst the hoses, stall the pump and engine, cause mechanical
damage
2. Variable Displacement is the answer
3. When hydraulic oil heats up, it might loose its properties and start
burning, spoil the rubber seals and gaskets. Metal dust has to be
filtered

12. OH043.12
Internal Use Only
Case 1 – Safety from High
Pressure
A simple relief valve may consist of nothing but a ball or poppet held seated in the valve body by
the compressive force of a heavy spring. When the pressure at the inlet is insufficient to
overcome the force of the spring the valve remains closed and hence it is very often referred as
a normally closed valve. When the preset pressure is reached, the ball unseats and allows flow
through the outlet to tank. In most of these valves, an adjusting screw is provided to vary the
spring force. Thus the valve can be set to open at any pressure within the specified range. The
pressure at which the valve first opens is called the cracking pressure. A relief valve should NOT
be allowed to operate in Relief mode for long.
Relief Valve – Operates much like a Zener Diode
Pump Motor
Pressure Gauge
Fluid Flow

13. OH043.13
Internal Use Only
Case 2 – Displacement (just like Gears)
Displacement of a Pump (or Motor) is the amount of
fluid moved per Rotation. Displacement is measured
in cc. For example a Pump could be 90cc (meaning that for
each complete rotation of the Pump shaft 90cc of oil will come out) and a
Motor could be 120cc.
Pump Motor
Pressure Gauge
Fluid Flow
In our example let
Pump = 90 cc
Motor = 120 cc
If the engine rpm (ω1)
is 1200 then what is
the rpm of the motor
(ω2)?

14. OH043.14
Internal Use Only
Case 2 – Variable Displacement
Think of Variable Displacement as being able to adjust the angle
of a Fan’s blades. If we make the Blades FLAT (angle=0) then
even if the Fan rotates no flow will take place.
What will happen if the angle is revered?
In a Logging Truck, we use
Variable Displacement
Pumps
Pump 0-90 Motor
Pressure Gauge
Fluid Flow

15. OH043.15
Internal Use Only
Case 2 – Changing Direction of the motor
•To change the direction of rotation of the motor the Fluid flow
direction MUST change to reverse. Fluid Flow direction is controlled
by Pumps
•Fluid Flow direction can be changed smoothly by Axial Piston design
Variable Displacement Pumps that can achieve this even while
turning in the same direction at the same rpm (much like the Fan
example of last slide)
The Displacement of the Pumps
(or motors) can be controlled by
a simple Electrical Joystick
Lever.
In Logging Trucks/Skids the
Winchman’s Joystick sends a DC
Current to Solenoid coils
mounted on the Hydraulic Pump.

16. OH043.16
Internal Use Only
Case 2 – Over center Variable Displacement Pumps
Axial Piston Variable Displacement Pumps can also change the
direction of Fluid Flow. Such pumps are called Over-center pumps
This means on such Pumps there is NO HIGH pressure Port and NO
LOW pressure port. Instead there are 2 ports (A and B) when one is
HIGH the other is LOW.
Notice that Motors can be variable displacement too but displacement can never be zero (or close
to zero). Why?

17. OH043.17
Internal Use Only
Case 3 – Cooling and Filtration of Hydraulic Fluid
As both ports (A & B) can be HI pressure (though not at the same
time), we must create a separate Port (C) where pressure will
always be LOW. This port is called CASE DRAIN. Some portion of the
oil is intentionally leaked out of the main circuit, collected and sent
back into a Tank. But before it reaches the Tank we cool it in a
radiator.
A
B B
A
C
C

18. OH043.18
Internal Use Only
Case 3 – Cooling and Filtration
As we have removed
some Oil, we must
replenish the same,
else the hydraulic
circuit will soon
starve. This is done by
a separate pump
called Charge Pump
and a Charge circuit.
A Charge Pump sucks
CLEAN, COOLED,
FILTERED Oil from the
tank and pushes it
back into the main
circuit by injecting oil
in the low pressure
side.

19. OH043.19
Internal Use Only
Hydraulics so far….
• Logging Hydraulics systems are closed loop
systems.
• There are 2 independent systems (Winch,
Alternator)
• Pumps used in both these two circuits are Over
center Variable Displacement Axial Type
• Controls to the Pump and Motors are electrical (12V
DC)
• System pressure is limited to 5500 psi by relief
valves
• Charge Pumps are Gear type pumps that are
mounted along with the main pumps. Since we
have 2 main pumps we also have 2 charge pumps
• Hydraulic oil must be filtered and cooled

20. OH043.20
Internal Use Only
Simple Hydraulics Diagram of
Truck/Skid

21. OH043.21
Internal Use Only
Advanced Truck Hydraulics
In this section you will learn about the practical
aspects of the Hydraulics system as used in a
Logging Truck or Skid

22. OH043.22
Internal Use Only
Lets start with the Engine and PTO
1. Once the Truck is correctly spotted, it is kept at Neutral.
2. Make sure the Drum Brakes are ON and Winch man’s Joystick in Neutral
3. Inside the drivers cabin, engage the PTO. A PTO (Power Take Off) is an
auxiliary gearbox, usually much smaller. Depending on the type of PTO, the
Truck diesel engine rpm is slowly increased to about 1500 rpm (1200 old)
4. The PTO (when engaged) drives the 2 Hydraulic Pumps (along with their 2
Charge Pumps) via a drive shaft. In most new Halliburton Trucks the PTO rpm
is equal to engine rpm
5. Both Pumps always start at Zero displacement. The Charge pumps builds the
system pressure to around 400 psi.

23. OH043.23
Internal Use Only
Various Pumps on Halliburton Trucks and Skids
1. Over center Variable Displacement 90 cc Axial Pump
for the Winch. Model Rexroth AA4VG90EL
2. Over center Variable Displacement 56 cc Axial Pump
for the Alternator. Model Rexroth AA4VG56EL
3. Along with each of the above 2 pumps are 2 Charge
Pumps. The Charge Pumps are simple Gear type
pumps stuck together along with the main pumps
The entire block of 4 pumps is then made into 1 assembly having a common drive shaft running
thru and thru
Charge
Pump
Charge
Pump

24. OH043.24
Internal Use Only
The Charge Pump
A charge pump is a simple gear pump
necessary for our system because of
the following:
• To supply system with cool fluid
• To supply fluid to compensate for
leaks
• To keep the system under pressure
As the gears rotate oil is trapped and
pushed from one port (Low) to another
(High)
A Charge Pump will NOT work if rotated in the opposite direction

25. OH043.25
Internal Use Only
The Rexroth AA4VG__EL Axial Pumps
Both the main Pumps (90cc and
56cc) are of similar design called
the Axial Piston Pumps
Both the main Pumps are Over
center variable displacement type
Both pumps are controlled by
Electrical 12V DC signals
So how do these pumps
work?
Swashplate principle

26. OH043.26
Internal Use Only
Swash-Plate principle

27. OH043.27
Internal Use Only
Motors used in Halliburton Trucks and Skids
Alternator Motor
Rexroth AA2FM32
Fixed Displacement
of 32 cc
Winch Motor Rexroth
AA6VM80EL
Variable Displacement
from 25cc to 80cc.
No signal Default 80cc
*Some Skids may have 55 cc motors
depending on Planetary Gear-Box
Both Motors are Bent Axis type Axial Piston Motors

28. OH043.28
Internal Use Only
The Bent Axis Principle
The Winch Motor
displacement
depends on the Axis
angle can vary from a
min to give 25 cc to a
max to give 80cc
The Alternator
Motor Axis angle
is fixed to give
32 cc
displacement
*Decreasing Swivel Angle decreases Displacement (therefore
increases RPM) but Hydraulic Motors cannot have 0 cc displacement
of as that would mean Infinite RPM and Zero Torque

29. OH043.29
Internal Use Only
Hydraulics Diagram of Truck/Skid
Winch Pump Winch Motor
2 Speed
Planetary
Gearbox
Reel
120V 60Hz
Alternator
Variable
Displacement
80cc Motor
Fixed
Displacement
32cc Motor
Variable
Displacement
56cc Pump
Variable
Displacement
90cc Pump
Oil Filters Heat exchanger
Case Drain
Diesel
Engine

30. OH043.30
Internal Use Only
Mooring Principle (Max Line Tension Control)
• It is basically a line tension control valve mounted on
the Winch man's control panel.
• In essence it is a system pressure regulator.
• The line tension valve can also control (and override
the Joy-Stick control) the swash plate angle of Winch
pump and when the set pressure is reached it forces
the pump to stop pumping in fluid.
• However the set pressure is maintained.
• This prevents the cable from breaking accidentally
while the tool is being logged UP (only) and there is a
Tight pull.
• On Floaters Mooring Control is a MUST

31. OH043.31
Internal Use Only
Mooring
Control –
How does
it work?
Charge
pressure
line

32. OH043.32
Internal Use Only
Max Line Tension – Why is it important?
As the Logging Tool goes deeper the Cable weight
(and therefore Tension) increases with depth and
conversely as the Tool is coming up the Cable
weight decreases.
Consider what will happen if we were Logging UP
and the Tool got stuck (at some deep depth) and
the Winch man is NOT paying attention

33. OH043.33
Internal Use Only
Requirements of a good hydraulic fluid
• Lubrication and anti-wear characteristics
• Appropriate viscosity (with respect to pressure)
• Stability against shearing
• Stability against thermal loads
• Should have low compressibility (little change due to
temperature)
• Fire resistant-does not burn
• Good protection against corrosion
• No formation of sticky substances
• Good filtration capability
• Cost and availability

34. OH043.34
Internal Use Only
Review and Questions
• Theory.
• Applications
• The Hydraulic Circuit
• Hydraulic pumps & motors
• PM1 issues
• Max Line Tension.

35. OH043.35
Internal Use Only
Thank You