basics of hydraulics

1
POWER POINT PRESENTATION FOR HP
1JT12ME058
By
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Objectives

• Explain fundamental hydraulic principles.
• Apply the laws of hydraulics.
• Calculate force, pressure, and area.
• Describe the function of pumps, valves,
  actuators, and motors.
• Describe the construction of hydraulic conductors
  and couplers.

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Hydraulics

• The term hydraulics is used to specifically
  describe fluid power circuits that use
  liquidsespecially formulated oilsin confined
  circuits to transmit force or motion.
• Hydraulic circuits
• Hydraulic brakes
• Power steering systems
• Automatic transmissions
• Fuel systems
• Wet-line kits for dump trucks
• Torque converters
• Lift gates

4
Pascals Law

• Pressure applied to a confined liquid is
  transmitted undiminished in all directions and
  acts with equal force on all equal areas, at
  right angles to those areas.

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Fundamentals

• Hydrostatics is the science of transmitting force
  by pushing on a confined liquid.
• In a hydrostatic system, transfer of energy takes
  place because a confined liquid is subject to
  pressure.
• Hydrodynamics is the science of moving liquids to
  transmit energy.
• We can define hydrostatics and hydrodynamics as
  follows
• Hydrostatics low fluid movement with high system
  pressures
• Hydrodynamics high fluid velocity with lower
  system pressures

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Atmospheric Pressure

• A column of air measuring 1 square inch extending
  50 miles into the sky would weigh 14.7 pounds at
  sea level.
• If we stood on a high mountain, the column of air
  would measure less than 50 miles and the result
  would be a lower weight of air in the column.
• Similarly, if we were below sea level, in a mine
  for instance, the weight of air would be greater
  in the column.
• In North America, we sometimes use the term atm
  (short for atmosphere) to describe a unit of
  measurement of atmospheric pressure.
• Europeans use the unit bar (short for barometric
  pressure).

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Force

• Force is push or pull effort.
• The weight of one object placed upon another
  exerts force on it proportional to its weight.
• If the objects were glued to each other and we
  lifted the upper one, a pull force would be
  exerted by the lower object proportional to its
  weight.
• Force does not always result in any work done.
• If you were to push on the rear of a parked
  transport truck, you could apply a lot of force,
  but that effort would be unlikely to result in
  any movement of the truck.
• The formula for force (F) is calculated by
  multiplying pressure (P) by the area (A) it acts
  on.
• F P x A

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Pressure Scales

• There are a number of different pressure scales
  used today but all are based on atmospheric
  pressure. One unit of atmosphere is the
  equivalent of atmospheric pressure and it can be
  expressed in all these ways
• 1 atm 1 bar (European)
• 14.7 psia
• 29.920 Hg (inches of mercury)
• 101.3 kPa (metric)
• However, each of the above values is not
  precisely equivalent to the others
• 1atm 1.0192 bar
• 1 bar 29.530 Hg 14.503 psia
• 10 Hg 13.60 H2O _at_ 60 F

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Torricellis Tube

• Evangelista Torricelli (16081647) discovered the
  concept of atmospheric pressure.
• He inverted a tube filled with mercury into a
  bowl of the liquid and then observed that the
  column of mercury in the tube fell until
  atmospheric pressure acting on the surface
  balanced against the vacuum created in the tube.
• At sea level, vacuum in the column in
  Torricellis tube would support 29.92 inches of
  mercury.

10
Manometer

• A manometer is a single tube arranged in a
  U-shape used to measure very small pressure
  values.
• It may be filled to the zero on the calibration
  scale with either water H2O) or mercury (Hg),
  depending on the pressure range desired.
• A manometer can measure either push or pull on
  the fluid column. Examples
• Crankcase pressure
• Exhaust backpressure
• Air inlet restriction

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Absolute Pressure

• Absolute pressure uses a scale in which the zero
  point is a complete absence of pressure.
• Gauge pressure has as its zero point atmospheric
  pressure.
• A gauge therefore reads zero when exposed to the
  atmosphere.
• To avoid confusing absolute pressure with gauge
  pressure
• Absolute pressure is expressed as psia.
• Gauge pressure is usually expressed as psi or
  psig.

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Hydraulic Levers (1 of 2)

• Hydraulic levers can be used to demonstrate
  Pascals law
• Pressure equals force divided by the sectional
  area on which it acts.
• (PF\A)
• Force equals pressure multiplied by area.
• ( F P x A)

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Hydraulic Levers (2 of 2)

• One of the cylinders has a sectional area of
  1sq. and the other 50 sq.
• Applying a force of 2 lbs. on the piston in the
  smaller cylinder would lift a weight of 100 lbs.
• Applying a force of 2 lbs. on the piston in the
  smaller cylinder produces a circuit pressure of 2
  psi.
• The circuit potential is 2 psi and because this
  acts on a sectional area of 50 sq., it can raise
  100 lbs.
• If a force of 10 lbs. was to be applied to the
  smaller piston, the resulting circuit pressure
  would be 10 psi and the circuit would have the
  potential to raise a weight of 500 lbs.

14
Flow

• Flow is the term we use to describe the movement
  of a hydraulic fluid through a circuit.
• Flow occurs when there is a difference in
  pressure between two points.
• In a hydraulic circuit, flow is created by a
  device such as a pump.
• A pump exerts push effort on a fluid.
• Flow rate is the volume or mass of fluid passing
  through a conductor over a given unit of time.
• An example would be gallons per minute (gpm).

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Flow Rate and Cylinder Speed

• Given an equal flow rate, a small cylinder will
  move faster than a larger cylinder. If the
  objective is to increase the speed at which a
  load moves, then
• Decrease the size (sectional area) of the
  cylinder.
• Increase the flow to the cylinder (gpm).
• The opposite would also be true, so if the
  objective were to slow the speed at which a load
  moves, then
• Increase the size (sectional area) of the
  cylinder.
• Decrease the flow to the cylinder (gpm).
• Therefore, the speed of a cylinder is
  proportional to the flow to which it is subject
  and inversely proportional to the piston area.

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Pressure Drop

• In a confined hydraulic circuit, whenever there
  is flow, a pressure drop results.
• Again, the opposite applies. Whenever there is a
  difference in pressure, there must be flow.
• Should the pressure difference be too great to
  establish equilibrium, there would be continuous
  flow.
• In a flowing hydraulic circuit, pressure is
  always highest upstream and lowest downstream.
  This is why we use the term pressure drop.
• A pressure drop always occurs downstream from a
  restriction in a circuit.

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Flow Restrictions

• Pressure drop will occur whenever there is a
  restriction to flow.
• A restriction in a circuit may be unintended
  (such as a collapsed line) or intended (such as a
  restrictive orifice).
• The smaller the line or passage through which the
  hydraulic fluid is forced, the greater the
  pressure drop.
• The energy lost due to a pressure drop is
  converted to heat energy.

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Work

• Work occurs when effort or force produces an
  observable result.
• In a hydraulic circuit, this means moving a load.
  
• To produce work in a hydraulic circuit, there
  must be flow.
• Work is measured in units of force multiplied by
  distance, for example, in pound-feet.
• Work Force x Distance

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Bernoullis Principle (1 of 2)

• Bernoullis Principle states that if flow in a
  circuit is constant, then the sum of the pressure
  and kinetic energy must also be constant.
• Pressure x Velocity IN Pressure x Velocity OUT
• When fluid is forced through areas of different
  diameters, fluid velocity changes accordingly.
• For example, fluid flow through a large pipe will
  be slow until the large pipe reduces to a smaller
  pipe then the fluid velocity will increase.

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Bernoullis Principle (2 of 2)
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Laminar Flow

• Flow of a hydraulic medium through a circuit
  should be as streamlined as possible.
• Streamlined flow is known as laminar flow.
• Laminar flow is required to minimize friction.
• Changes in section, sharp turns, and high flow
  speeds can cause turbulence and cross-currents in
  a hydraulic circuit, resulting in friction losses
  and pressure drops.

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Types of Hydraulic Systems

• Hydraulic systems can be grouped into two main
  categories
• Open-center systems
• Closed-center systems
• The primary difference between open-center and
  closed-center systems has to do with what happens
  to the hydraulic oil in the circuit after it
  leaves the pump.

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Open-center Systems

• In an open-center system, the pump runs
  constantly and oil circulates within the system
  continuously.
• An open-center valve manages flow through the
  circuit. When this valve is in its neutral
  position, fluid returns to the reservoir.
• An example of an open-center hydraulic system on
  a truck is power-assisted steering.

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Closed-center Systems

• In a closed-center system, the pump can be
  rested during operation whenever flow is not
  required to operate an actuator.
• The control valve blocks flow from the pump when
  it is in its closed or neutral position.
• A closed-center system requires the use of either
  a variable displacement pump or proportioning
  control valves.
• Closed-center systems have many uses on
  agricultural and industrial equipment, but on
  trucks, they would be used on garbage packers and
  front bucket forks.

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Calculating Force

• In hydraulics, force is the product of pressure
  multiplied by area.
• Force Pressure x Area
• For instance, if a fluid pressure of 100 psi acts
  on a piston sectional area of 50 square inches it
  means that 100 pounds of pressure acts on each
  square inch of the total sectional area of the
  piston. The linear force in this example can be
  calculated as follows
• Force 100 psi x 50 sq. in. 5000 lbs.

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Hydraulic Components

• Reservoirs
• Accumulators
• Pumps
• Valves
• Actuators
• Hydraulic motors
• Conductors and connectors
• Hydraulic fluids

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Reservoirs

• A reservoir in a hydraulic system has the
  following roles
• Stores hydraulic oil
• Helps keep oil clean and free of air
• Acts as a heat exchanger to help cool the oil
• A reservoir is typically equipped with
• Filler cap
• Oil-level gauge or dipstick
• Outlet and return lines
• Baffle(s)
• Intake filter
• Oil filter
• Drain plug

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Gas-loaded Accumulators

• The gas and hydraulic oil occupy the same chamber
  but are separated by a piston, diaphragm, or
  bladder.
• When circuit pressure rises, incoming oil to the
  chamber compresses the gas.
• When circuit pressure drops off, the gas in the
  chamber expands, forcing oil out into the
  circuit.
• Most gas-loaded accumulators are pre-charged with
  the compressed gas that enables their operation.

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Fixed-Displacement Pumps

• A fixed-displacement pump will move the same
  amount of oil per revolution with the result that
  the volume picked up by the pump at its inlet
  equals the volume discharged to its outlet per
  revolution.
• This means that pump speed determines how much
  hydraulic oil is moved.
• Fixed-displacement pumps are commonly used for
  applications such as
• Lift pumps
• Power steering pumps
• Transmission pumps
• Lube pumps

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Variable-displacement Pumps

• Variable-displacement pumps are positive
  displacement pumps designed to vary the volume of
  oil they move each cycle even when they are run
  at the same speed.
• They use an internal control mechanism to vary
  the output of oil usually with the objective of
  maintaining a constant pressure value and
  reducing flow when demand for oil is minimal.

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Gear Pumps

• Gear pumps are widely used in mobile hydraulics
  because of their simplicity.
• They are also widely used to move fuel through
  diesel fuel subsystems and as engine lube oil
  pumps.
• Three types of gear pumps are used
• External gear
• Internal gear
• Rotor gear

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External-gear Pumps

• Two intermeshing gears are close-fitted within a
  housing.
• One of the gears is a drive shaft and this drives
  the second gear because they are in mesh.
• As the gears rotate, oil from the inlet is
  trapped between the teeth and the housing, and is
  carried around the housing and forced from the
  outlet.

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Internal-gear Pumps

• A spur gear rotates within an annular internal
  gear, meshing on one side of it.
• Both gears are divided on the other side by a
  crescent-shaped separator.
• When an external gear is in mesh with an internal
  gear, they both turn in the same direction of
  rotation.
• As the gear teeth come out of mesh, oil from the
  inlet is trapped between the teeth and the
  separator and is carried to the outlet and
  expelled.

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Rotor-gear Pumps

• A rotor-gear pump is a variation of the
  internal-gear pump.
• An internal rotor with external lobes rotates
  within an outer rotor ring with internal lobes.
• No separator is used.
• The internal rotor is driven within the outer
  rotor ring. The internal rotor has one less lobe
  than the outer rotor ring, with the result that
  only one lobe is fully engaged to the rotor ring
  at any given moment of operation.
• As the lobes on the internal rotor ride on the
  lobes on the outer ring, oil becomes entrapped
  as the assembly rotates, oil is forced out of the
  discharge port.

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Vane Pumps

• Vane pumps are also used extensively in hydraulic
  circuits.
• Truck power-assisted steering systems use vane
  pumps.
• A slotted rotor fitted with sliding vanes rotates
  within a stationary liner known as a cam ring.
  There are two types
• Balanced
• Unbalanced

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Balanced Vane Pumps

• As the rotor rotates, centrifugal force moves the
  vanes outward.
• Fluid is trapped between the crescent-shaped
  chambers formed between vanes.
• The size of these chambers are continually
  expanding and contracting as the rotor turns.
• Oil from the inlet is trapped in the space
  between two vanes.
• As the rotor continues to turn, the chamber
  contracts until it is aligned with the outlet and
  the oil is expelled.
• This action repeats itself twice per revolution
  because there are a pair of inlet ports and a
  pair of discharge ports.

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Unbalanced Vane Pumps

• This has the same principle as the balanced
  version, with the exception that the operating
  cycle only occurs once per revolution because it
  has only one inlet and one outlet port.
• The disadvantage of the unbalanced vane pump is
  the radial load caused by high pressure that is
  acting on the discharge side of the rotor and
  none on the inlet side because the inlet oil is
  under little or no pressure.

38
Piston Pumps

• There are a wide variety of piston pumps,
  beginning with the most simple and including some
  of the more complex pumps used in hydraulic
  circuits.
• There are three general types of piston pump
• Plunger pumps
• Axial piston
• Radial piston
• Plunger-type pumps are seldom found on hydraulic
  circuits, but the latter two are used on systems
  that demand high flow and high-pressure
  performance.

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Plunger Pumps

• A bicycle pump is an example of a plunger pump as
  are the fuel hand-priming pumps used on many
  diesel fuel systems.
• A plunger reciprocates within a stationary
  barrel. Fluid to be pumped is drawn into the pump
  chamber formed in the barrel on the outward
  stroke of the plunger.
• This fluid is then discharged on the inboard
  stroke of the plunger.

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Axial Piston Pumps

• A rotating cylinder with piston bores machined
  into it rides against an inclined plate.
• The pistons are arranged parallel with the pump
  drive.
• The base of each piston rides against a tilted
  plate known as a swashplate or wobble plate which
  does not rotate.
• They provide a method for controlling the tilt
  angle of the swashplate.
• Fluid is charged to each pump element as the
  piston is drawn to the bottom of its travel.
• As the cylinder head rotates, the piston follows
  the tilt of the swashplate and is driven upward
  forcing fluid out of the discharge port.

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Radial Piston Pumps

• Radial piston pumps are capable of high
  pressures, high speeds, high volumes, and
  variable displacement. However, they cannot
  reverse flow.
• Radial piston pumps operate in two ways
• Rotating cam
• Rotating piston

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Valves

• Valves are used to manage flow and pressure in
  hydraulic circuits.
• There are three basic types of valves used in
  hydraulic circuits.
• Pressure control
• Directional control
• Volume (flow) control

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Directional Control Valves (1 of 3)
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Directional Control Valves (2 of 3)

• Directional control valves direct the flow of oil
  through a hydraulic circuit. They include
• Check valves
• Rotary valves
• Spool valves
• Pilot valves

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Directional Control Valves (3 of 3)

• Check valves
• A check valve uses a spring-loaded poppet. It
  permits flow in one direction and prevents flow
  in the other.
• Rotary valves
• A rotary spool turns to open and close oil
  passages. Rotary valves are commonly used as
  pilots for other valves in systems with multiple
  sub-circuits.
• Spool valves
• A sliding spool within a valve body to open and
  close hydraulic circuits. Spool valves are used
  extensively in hydraulic systems and automatic
  transmissions.
• Pilot valves
• Pilot valves may be controlled mechanically,
  hydraulically, or electrically.

46
Actuators

• Hydraulic actuators convert the fluid power from
  the pump into mechanical work.
• A hydraulic cylinder is a linear actuator.
• A hydraulic motor is a rotary actuator.

47
Single-acting Cylinders

• Hydraulic pressure is applied to only one side of
  the piston.
• Single-acting cylinders may be either
• Outward-actuated When an outward-actuated
  cylinder has hydraulic pressure applied to it,
  the piston and rod are forced outward to lift the
  load. When the oil pressure is relieved, the
  weight of the load forces the piston and rod back
  into the cylinder.
• Inward-actuated When an inward-actuated cylinder
  has hydraulic pressure applied to it, the rod is
  pulled inward into the cylinder.
• One side of a single-acting cylinder is dry. The
  dry side must be vented so that when oil pressure
  on the pressure side is relieved, air is allowed
  to enter, preventing a vacuum.
• A ram is a single-acting cylinder in which the
  rod serves as the piston.

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Double-acting Cylinders

• Double-acting cylinders provide force in both
  directions.
• Pressure is applied to one side of the piston to
  either extend or retract the cylinder the oil on
  the opposite side returns to the reservoir.
• Double-acting cylinders may be balanced or
  unbalanced.
• Balanced double-acting cylinder
• The piston rod extends through the piston head on
  both sides, giving an equal surface area on which
  hydraulic pressure can act.
• Unbalanced double-acting cylinder
• A piston rod is located on one side of the
  piston. There is more surface area on the side
  without the rod because the rod occupies part of
  the space on the other side.

49
Vane-type Cylinders

• Vane-type cylinders may be found in some much
  older hydraulic systems.
• A vane-type cylinder provides rotary motion.
• Double-acting vane-type cylinders can be used in
  applications such as backhoes because they enable
  a boom and bucket to swing rapidly from trench to
  pile.
• An alternative to one double-acting vane cylinder
  for this application would be a pair of opposing
  cylinders.

50
Hydraulic Motors (1 of 2)

• The function of hydraulic motors is the opposite
  of hydraulic pumps
• Pump
• It draws in oil and displaces it, converting
  mechanical force into fluid force.
• Motor
• Oil under pressure is forced in and spilled out,
  converting fluid force into mechanical force.

51
Hydraulic Motors (2 of 2)

• There are three categories of hydraulic motors
• Gear motors
• Vane motors
• Piston motors
• All hydraulic motors rotate, driven by incoming
  hydraulic oil under pressure.

52
Gear Motors

• External gear
• An external-gear motor is driven by pressurized
  hydraulic oil forced into the pump inlet, which
  acts on a pair of intermeshing gears, turning
  them away from the inlet, with the oil passing
  between the external gear teeth and the pump
  housing.
• Internal gear
• An internal-gear motor is similar to an
  internal-gear pump. The motor drive shaft is
  connected to the inner rotor.

53
Conductors and Connectors

• The hydraulic fluid has to be conveyed to
  various components.
• Mobile hydraulic equipment uses hoses as
  hydraulic conductors because they
• Allow for movement and flexing
• Absorb vibrations
• Sustain pressure spikes
• Enable easy routing and connection on chassis

54
Hydraulic Hoses (1 of 2)

• The size of any hydraulic hose is determined by
  its inside diameter.
• This is sometimes indicated as dash size in
  1/16-inch increments.
• Each dash number indicates 1/16 inch,
• a 4 dash hose would be equivalent to 4/16 inch
  or 1/4 inch.
• Dash size Nominal diameter
• 4 1/4 inch
• 6 3/8 inch
• 8 1/2 inch
• 10 5/8 inch
• 12 3/4 inch
• A large-diameter internal hose has to be stronger
  to sustain the working pressures of a hydraulic
  circuit.

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Hydraulic Hoses (2 of 2)

• Another consideration for hose selection is that
  the hose must be compatible with the hydraulic
  fluid used in the system.
• There are four general types of hoses used in
  hydraulic circuits
• Fabric braid
• Single-wire braid
• Multiple-wire braid (up to 6 wire braid)
• Multiple-spiral wire (up to 6 wire spirals)

56
Couplers (Connectors)

• Hydraulic hose couplers (also known as connectors
  and fittings) are made of steel, stainless steel,
  brass, or fiber composites.
• Hose couplers or fittings can either be reusable
  or permanent.
• Hose fittings are installed at the hose ends and
  the mating end consists of either a nipple (male
  fit) or socket (female fit).
• Adapters are separate from the hose and are used
  to couple hoses to other components such as
  valves, actuators, or pumps.

57
Permanent Hose Fittings

• These fittings are crimped or swaged onto the
  hose.
• When a hose fitted with permanent hose fittings
  fails, the hose must be replaced either as an
  assembly or one must be made up using stock hose
  cut to length fitted with either crimp-type or
  reusable fittings.

58
Reusable Hose Fittings

• Reusable fittings are common in truck shops
  because a hose assembly station, some stock hose,
  and an assortment of reusable fittings can
  replace many of the hundreds of different types
  of hose used on various OEM truck chassis.
• When a hose with reusable fittings wears out, the
  fittings can be removed and assembled onto new
  stock hose.
• Reusable fittings are usually screwed onto hose,
  although some types of low-pressure hose may use
  press fits.

59
Assembling Hose Fittings

• Sealing fittings
• Fittings can be sealed to couplers using the
  following
• Tapered threads
• O-rings
• Nipple and seat (flair)
• When making hydraulic connections, ensure that
  the coupler fittings are compatible with each
  other.
• Adapters
• Adapters are separate from the hose assembly.
  They have the following functions
• To couple a hose fitting to a component
• To connect hydraulic lines in a circuit
• To act as a reducer in a circuit
• To connect a pair of hoses on either side of a
  bulkhead

60
Caution

• Separation of a fitting and hose at high pressure
  can be dangerous!
• Never reuse a suspect fitting and observe the
  manufacturer assembly procedure to the letter.

61
Coupling Guidelines

• When making hydraulic connections, the following
  guidelines should be observed
• Torque the fitting on the hose, not the hose on
  the fittings.
• Couple male ends before female ends.
• Ensure the sealing method of each fitting to be
  coupled is the same.
• Use 45- and 90-degree elbows to improve hose
  routing.
• Use hydraulic pipe seal compound only on the male
  threads, and on thread-seal unions.
• Use two wrenches when tightening unions to avoid
  twisting hose.
• Never over-torque hydraulic fittings.

62
Shop Talk

• When tightening the fittings on a pair of
  hydraulic couplers, always use two wrenches to
  avoid twisting hoses or damaging adapters.

63
Pipes and Tubes

• Pipes used in hydraulic circuits are generally
  made from cold-drawn, seamless mild steel.
• They should never be galvanized because the zinc
  can flake off and plug up hydraulic circuits.
• Tubing can also be used.
• It has the advantage of being able to sustain
  some flex hence its use in vehicle brake
  systems.
• Tubing should be manufactured from cold-drawn
  steel if used in moderate-to-high-pressure
  circuits.
• When used in low-pressure circuits, copper or
  aluminum tubing may be used.

64
Flared Fittings

• 45 degrees (SAE standard -- Society of Automotive
  Engineers)
• 37 degrees (JIC standard -- Joint Industry
  Committee)
• Inverted flare
• A 45-degree flare is formed inside of the
  fitting.
• Two-piece flare
• A tapered nut aligns and seals the flared end of
  the tube.
• Three-piece flare
• A three-piece flare fitting consists of a body,
  sleeve, and nut and fits over the tube. The
  sleeve free-floats, permitting clearance between
  the nut and tube and aligning the fitting. When
  tightened, the sleeve is locked without imparting
  twist to the flared tube.
• Self-flaring
• These fittings use a wedge-type sleeve that, as
  the sleeve is tightened, is forced into the tube
  end, spreading it into a flare.

65
Caution

• Never attempt to cross-couple SAE and JIC
  fittings.
• The result will be to damage both.

66
Flareless Fittings

• Ferrule fittings
• Consist of a body, a compression nut, and a
  ferrule.
• A wedge-shaped ferrule is compressed into the
  fitting body by the compression nut, creating a
  seal between the tube and the body.
• Compression fittings
• These are used with thin-walled tubing and are
  sealed by crimping the end of the tube to form a
  seal.
• O-ring fittings
• The principle is similar to ferrule-type fittings
  except that a compressible rubber compound O-ring
  replaces the ferrule.
• As the fitting nut is torqued, the O-ring is
  compressed, forming a seal between the tube and
  the fitting body.
• Several different types of O-rings are used,
  including round section, square section,
  D-section, and steel-backed.

67
Quick-release Couplers

• When hydraulic lines have to be frequently
  connected and disconnected, a quick release
  coupler is used.
• A quick coupler is a self-sealing device that
  shuts off flow when disconnected.
• Quick-release couplers consist of a male and
  female coupler. There are four types
• Double poppet.
• Sleeve and poppet
• Sliding seal
• Double rotating ball

68
Hydraulic Fluids (1 of 2)

• Hydraulic fluids used in truck hydraulic systems
  may be
• Specialty hydraulic oils
• Engine oil
• Transmission oil
• Always check when adding to or replacing
  hydraulic oil.
• Synthetic hydraulic oils are commonly used in
  todays hydraulic circuits because they have
  wider temperature operating ranges and offer
  greater longevity.

69
Hydraulic Fluids (2 of 2)

• Hydraulic oils must
• Act as hydraulic media to transmit force
• Lubricate the moving components in a hydraulic
  circuit
• Resist breakdown over long periods of time
• Protect circuit components against rust and
  corrosion
• Resist foaming
• Maintain a relatively constant viscosity over a
  wide temperature range
• Resist combining with contaminants such as air,
  water, and particulates
• Conduct heat

70
Safe Practice (1 of 2)

• Truck hydraulic circuits are designed to run at
  high pressures and support high loads. It is
  essential that you work safely around chassis
  hydraulic equipment. Some basic rules
• Never work under any device that is only
  supported by hydraulics.
• A raised dump box or chassis hoist must be
  mechanically supported before you work under it.
• Just as when using a floor jack, you must use
  some means of mechanically supporting any raised
  equipment or components.

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Safe Practice (2 of 2)

• Hydraulic circuit components can retain high
  residual pressures.
• The system does not have to be active for this to
  be a hazard.
• Ensure that pressures are relieved throughout the
  circuit before opening it up.
• Crack hydraulic line nuts slowly and be sure to
  wear both safety glasses and gloves.

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Summary (1 of 3)

• Fundamental hydraulic principles include Pascals
  Law, Bernoullis Principle, and how force,
  pressure, and sectional area are used in
  hydraulic circuits to produce outcomes.
• A typical simple hydraulic circuit consists of a
  reservoir, pump, valves, actuators, conductors,
  and connectors.
• Hydraulic pumps convert mechanical energy into
  hydraulic potential.

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Summary (2 of 3)

• Valves manage flow and direction through a
  hydraulic circuit.
• Actuators such as hydraulic cylinders and motors
  convert hydraulic potential into mechanical
  movement.
• Hydraulic oil is used to store and transmit
  hydraulic energy through a hydraulic system.
• ANSI and ISO graphic symbols are used to
  represent hydraulic components and connectors in
  hydraulic schematics.

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Summary (3 of 3)

• Maintenance procedures on truck hydraulic
  systems begin with ensuring the system is clean
  both inside and outside the circuit.
• Routine replacement of hydraulic fluid, sometimes
  accompanied by system flushing, is recommended to
  minimize system malfunctions and downtime.
• Hydraulic circuit testers are used to analyze
  hydraulic circuit performance.
• A hydraulic tester consists of flow gauge,
  pressure gauge, temperature gauge, and gate
  valve.

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THANK U/.,,,,,