HYDRAULICS

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HYDRAULICS

• The life blood of all modern engineering
  equipment

SSgt Courie
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HYDRAULICS

• Purpose- To provide you with the knowledge
  necessary to service, troubleshoot, and repair
  hydraulic systems.

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HYDRAULICS

• Terminal
• Learning
• Objective

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HYDRAULICS

• Enabling
• Learning
• Objectives

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HYDRAULICS

• Method- Lecture
• Media- Student outline and power point

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HYDRAULICS

• Eval- Upon completion of this course there will
  be a 50 question, closed book, multiple choice
  examination

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Questions

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Principles of Hydraulics

• Liquids have no shape of their own

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Principles of Hydraulics

• Liquids are incompressible

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Principles of Hydraulics

• Transmit pressure in all directions

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Principles of Hydraulics
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1

• Provide great increase in workforce

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Principles of Hydraulics

• Pumps move the oil
• Oil moves the cylinder
• Pumps convert mechanical force to hydraulic
  power, while the cylinder converts the hydraulic
  power back to mechanical force to do the work

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Principles of Hydraulics

• Reservoirs store oil
• Check valves hold oil in cylinders between
  strokes
• Pumps transform rotary force into hydraulic
  energy
• Control valves direct the flow of oil.
• Relief valves protect the system from high
  pressure

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Definition of hydraulics

• The use of liquids under controlled pressure to
  do work

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Force

• Tends to cause something to move if at rest, or
  to change speed or direction if in motion

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Pressure

• The amount of force exerted on a unit of area

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Flow
Flow is simple, its the movement of fluid.
Flow is measured in gallons per minute G PM
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Flow vs Pressure
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HYDRODYNAMICS AND HYDROSTATICS
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Hydrodynamics

• The use of fluids at high speeds (on impact) to
  supply power.

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Hydrostatics

• The use of fluids at relatively low speeds but at
  high pressure to supply power.

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Hydraulic System
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Fluids

• 70 percent of hydraulic problems stem from the
  improper types of fluids, or fluids containing
  dirt or other contaminants.
• NEVER use brake fluid in a hydraulic system.

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Fluids

• Fluid must maintain proper viscosity through a
  wide temperature range.
• Capable of transmitting the power, lubricate
  moving parts, be stable over long periods of
  time, resist foaming and oxidation, and be able
  to separate itself from air, water and other
  contaminants.
• Be readily available and reasonably economical to
  use.

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Fluids

• Dirt and contamination are the worst enemies of
  any hydraulic system.
• Only fluid recommended by the manufacturer should
  be used
• It should also be checked and changed at the
  manufacturer's suggested intervals

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Fluids

• Oxidation of fluid doubles every 18 degrees.
• Emulsification

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Filters

• Cheaper to buy a good filter, than to replace
  hydraulic components
• Dirty oil can ruin close tolerance surfaces
• 1 grain of sand

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Full Flow Filter

• Mounted internally or externally

Filters the entire supply of oil each time it
circulates in the hydraulic system.
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Bypass filters

• This filter has a safety valve, which opens if
  the filter element becomes clogged.
• When the valve is open there is no filtration.

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Types of filters

• 2 types of filters
• - Surface
• - Depth

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Surface Filters

• Single surface that catches and removes dirt
  larger than holes in filter
• Particles smaller than the hole fall to the
  bottom and eventually will fill in the holes to
  prevent further filtration
• Made of wire mesh, stacked metal, paper disk ect

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Wire and Metal Edge
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Paper and Cotton
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Depth Filters

• Uses a large volume of filter to make oil move in
  different directions before it enters the
  hydraulic system
• Classified as absorbent or adsorbent depending on
  how they remove dirt

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Absorbent filters

• Oil passes through filter material leaving dirt
  trapped in the filter
• This type will remove particles suspended in the
  oil

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Adsorbent Filters

• Same as absorbent filter but are chemically
  treated to attract and remove contaminants
• Made of Charcoal, chemically treated paper or
  fullers earth
• May remove additives from the oil and are not
  commonly used because of this

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Degrees of filtration

• Measured in microns
• 25,000 microns make 1 inch
• 40 microns is smallest size that can be seen with
  the eyes
• 1 grain of salt is about 100 microns

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Contamination

• Liquids, metallic particles, non-metallic
  particles and fibers are all forms of
  contaminates
• Inside and outside of hydraulic system
• -air is the biggest sources of contamination
• During break-in bits of metal will contaminate
  the oil

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Questions

• What is the purpose of the baffles inside the
  hydraulic tank ?
• - Prevents hot oil from flowing directly to the
  outlet
• What type of a valve is in some hydraulic filters
  ?
• - Safety Bypass Valve

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Reservoirs

• Stores oil stores all the oil that can drain
  back into the reservoir
• Separates air from oil allows air and foreign
  matter to separate from oil.
• Maintains oil level maintains the oil level
  above the suction line opening.
• Remove heat from oil dissipates excess heat
  during normal operation. To serve its purpose,
  the reservoir must have several features.

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Reservoirs
VENTED CAP
OUTLET TO PUMP
RETURN LINE
OIL LEVEL GAUGE
BAFFLE
DRAIN
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Reservoirs

• Two types of reservoirs
• -Vented
• -Pressurized

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Vented Tanks

• Allows the tank to breathe as the oil expands and
  contracts.
• Has a filter to keep out dirt.
• The disadvantage of a vented tank is some
  contamination can still enter the system through
  the vent filter.

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Pressurized Tanks

• Keeps dirt out.
• Forces oil to the pump.
• Has two valves.
• Pressure relief valve opens if the tank pressure
  becomes too high.
• Atmospheric valve opens when the oil cools and
  air pressure outside the tank becomes greater
  than inside the tank.

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Oil Coolers

• 2 types of oil coolers
• Air - uses air to cool the oil
• Water - uses water to cool the oil
• Mounted near the cooling source

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Hoses

• Absorb vibration, rated in PSI and provide a path
  for fluid to flow to different components
• Inside must be smooth, flexible and able to
  resist heat
• Reinforced with wire or rope depending on the
  pressure required

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Three Parts Of A Hose

• Inner tube
• Reinforcement layers
• Outer cover

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Hoses

• Flow
• Pressure and Temperature
• Compatibility

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Hose Chart
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Hose installation rules

• Avoid Taut Hoses
• Avoid Loops
• Avoid Twisting
• Avoid Rubbing
• Avoid Heat
• Avoid Sharp Bends

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External Leakage
BOLT LEAKAGE
BORE LEAKAGE
GASKET LEAKAGE
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Seals

• All Hydraulics must have a proper seal to hold
  fluid under pressure
• Seals are used in two applications
• -Static- seals fixed parts
• -Dynamic- seals moving parts

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Seals

• Will it resist all pressures expected
• Can it withstand the heat of operation
• Will it wear out to rapidly
• Will it be harmed by the hydraulic fluid
• Does it fit without dragging
• Will it score or scratch polished metal or parts

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Seals

• Types
• O-Rings
• U and V Packings
• Spring Loaded
• Cup and Flange
• Mechanical and Metallic
• Internal leaks are the hardest to detect

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Cylinders
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Hydraulic Cylinders

• Piston Type Cylinders- Give straight movement.
• Vane Type Cylinders- Give rotary movement.

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Piston-Type Cylinders

• SINGLE-ACTING give force only one way. Needs an
  outside force to return the piston

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Single - Acting Cylinders
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Double - Acting Cylinders

• DOUBLE-ACTING Gives force in both directions.
  Fluid power will both extend and retract the
  cylinder.

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Double - Acting Cylinders

• Balanced cylinder has equal force in both
  directions
• Unbalanced cylinder total force on the rod side
  of the cylinder is less than on the blank side

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Stroke Control Cylinders

• A hydraulic stop is sometimes used to stop the
  piston at any point of its travel by shutting off
  the flow of outgoing oil.

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Slave Cylinders

• These cylinders can operate in unison or by
  delayed action.
• The poppet valve, allows oil to flow to the slave
  cyl during extension and to the reservoir during
  retraction.

MASTER CYLINDER
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Cushion Cylinder

• Their used as a hydraulic brake to protect
  against impact damage.

ORFICE
OIL OUTLET CLOSED
CUSHION AT END OF STROKE
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Vane Type Cylinders

• They produce circular motion.
• Used on the m-9 ace.
• Used for suspension systems.

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Questions

• Hydraulic actuators produce what types of motion?
• - Linear or rotary motion
• What are the two types of hydraulic actuators?
• - Piston and vane type cylinders
• What are the two types of piston cylinders?
• - Single and Double acting

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Questions

• What Does Hydraulic Cylinders Change?
• converts the hydraulic power back to mechanical
  force to do the work
• An unbalanced cylinder will have a rod coming out
  of how many ends?
• One

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Valve Types
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Hydraulic Valves

• Valves can be divided into three major types
• Pressure Control Valves
• Directional Control Valves
• Volume Control Valves

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Pressure Control valves

• Limit system pressure
• Reduce pressures
• Set pressure at which oil enters a circuit
• Unload a pump

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Pressure Control Valves

• Relief valves
• Pressure reducing valves
• Pressure sequencing valves
• Unloader valves

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Relief Valves

• The purpose of any relief valve is to protect the
  hydraulic system and its component parts from
  excessive pressure or damage.

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Relief Valves Types

• Direct Acting- open / closed valves
• Pilot Operated- controls the main relief valve

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Direct Acting Relief Valve
OUTLET
OUTLET
INLET
INLET
OPEN
CLOSED
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Direct Acting Relief Valve

• These valves are used mainly where volume is low,
  and for less frequent operations.
• They have fast response, making them ideal for
  relieving shock pressure.
• They are often used as safety valves to prevent
  damage to components.

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Pilot Operated Relief Valve

• Because these valves dont start to open until
  almost full-flow pressure, the efficiency of the
  system is protected-less oil is released.
• These valves are best for high-pressure, high
  volume systems.
• Although slower to operate than direct acting
  valves, the pilot operated relief valve keeps
  system oil at a more constant pressure while
  releasing oil

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Pressure Reducing Valves Types

• Constant reduced pressure valve
• Fixed amount reduction valve

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Constant Reduced Pressure Valves

• They supply a fixed pressure regardless of main
  circuit pressure. (So long as it is higher)

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Constant Reduced Pressure Valve
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Fixed Amount Reduction Valves

• They supply a fixed amount of pressure reduction,
  which means that it varies with the main circuit
  pressure.
• For example,the valve might be set to give a
  reduction of 500 PSI. If system pressure was 2000
  PSI, the valve would reduce pressure to ________
  PSI.

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Fixed Amount Reduction Valve
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Pressure Sequence Valves

• They are used to control the sequence of flow to
  various branches of a circuit.
• Usually the valves allow flow to a second
  function only after a first has been fully
  satisfied.

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Pressure Sequence Valve
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Unloading Valve

• This valve directs pump output oil back to the
  reservoir at low pressure after system pressure
  has been reached.
• They may be installed in the pump outlet line
  with a tee connection.

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Valve Types

• Pressure control valves
• Directional control valves
• Volume control valves

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Directional Control Valves

• Direct the flow of oil in the system
• Types of valves
• - Check valves
• - Rotary valves
• - Spool valves
• - Pilot controlled poppet valves
• - Electro-hydraulic valves

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Check Valves

• One way valves, only allow fluid to flow in one
  direction
• The valve is open by system pressure
• The valve closes when inlet pressure drops
• Usually installed in oil line

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Rotary Valve

• This valve allows pressurized oil from the pump
  to enter one port, flow through the valve, and
  out another port to the work

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Rotary Valve

• This valve also allows oil from another working
  port to flow through the valve and return to the
  reservoir.

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Rotary Valves

• Used as pilot valves to direct flow to other
  valves
• Can be modified to operate as two, three, or four
  way valves
• Done by relocating parts, altering passageways,
  or adding and removing oil routes

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Spool Valves

• Most common is open center and closed center
• Directs oil to start, operate, and stop actuating
  units
• Dirt can cause these valves to stick or work
  erratically

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Spool Valves

• open center allows fluid to flow thru the center
  when in neutral and return to tank
• Closed center stops the flow of oil in neutral
• Used as a control valves

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Spool Valve (Stacked)
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Spool Valve (Unibody)
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Pilot Controlled Poppet Valves

• May be mounted close to the function it controls
• Eliminates the need for routing hydraulic pipes
  and hoses over long distances for every control
  function
• Reduces valve leakage (i.e. cylinder drift)
• Adjustable to vary amount of oil flow

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Electro-Hydraulic Valves

• Actuated by an electric solenoid

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Valve Types

• Directional control valves
• Pressure control valves
• Volume control valves

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Volume Control Valve Types

• Flow control.
• Flow divider.

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Flow Control Valves

• Restricts flow in or out of the component whose
  speed is being regulated.
• These valves are noncompensated.

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Bypass Flow Regulator

• This valve works by diverting flow away from the
  component whose speed is being regulated.
• These valve are usually compensated.

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Volume Control Valve Types

• Flow control.
• Flow divider.

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Priority Flow Divider

• Allows oil to feed two different circuit.
• Example,steering circuit and loader circuit.
• Pump output 10 gpm.
• Steering 2 gpm.
• Loader 8 gpm.

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Proportional Flow Divider

• Divides a single flow of oil to two circuits.
• Can divided oil flow in ratios from 50-50 to
  90-10.

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Questions

• What are the three types of hydraulic valves?
• - Directional, pressure and volume control
• Check valves are designed too ?
• - Allow fluid to flow in one direction
• Whats the purpose of a relief valve?
• - Protect the hydraulic system and components

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Break
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Hydraulic Pumps

• The pump is the heart of the hydraulic system.
• The pump is the generating force of the hydraulic
  system, it creates the flow of fluid which
  supplies the whole circuit.
• Pumps convert mechanical energy to hydraulic power

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Pump Classification

• Two classifications of pumps
• Fixed Displacement
• Variable Displacement

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Types Displacement

• Fixed
• -Moves the same volume of fluid with each cycle

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Variable Displacement Pumps

• Changing Displacement- this is accomplished by
  changing the angle of the swashplate.
• Swash Plate Positioning - The position is
  controlled by one of two ways.
• - A small hydraulic cylinder called a servo
  
• - A spring loaded cylinder called a pressure
  compensator

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Types Of Pumps
GEAR
PISTON
VANE
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Types Of Pumps

• Gear (rotary)
• Internal
• External
• Vane (centrifugal)
• Balanced
• Unbalanced
• Piston (reciprocating)
• Axial
• Radial

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Gear Pumps

• Simple Design.
• Economical.
• Fixed Displacement.
• Used as charging pumps for larger system pumps.

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Gear Pump Side Plates

• Some gear pumps are equipped with pressurized
  plates on both side of the gears. These plates
  are used to prevent cavitation. The plates seal
  tightly when the pump is under a load and relax
  when there is no load.

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Internal Gear Pumps

• The internal gear is the drive gear, which is
  meshed with the outer ring gear and traps fluid
  between the gear teeth on both gears and the
  separator, which is fixed.

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External Gear Pump

• Oil is trapped between the gear teeth and flows
  around the outer perimeter of the pump housing,
  not through the middle of the meshing gears.

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Gear Pump Advantages

• Most widely used.
• Easiest to manufacture.
• Produces a large volume of oil for its size.
• Tolerant to dirt.
• Inexpensive to manufacture.

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Gear Pump Disadvantages

• Noisier than other types of pumps.
• Fixed displacement only.

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Vane Pumps

• Balanced Vane Pump
• - Fixed Displacement only.
• - Equalized force increases bearing life.
• Unbalanced Vane Pump
• - Either Fixed or Variable Displacement.
• - Frequent bearing failure.

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Balanced Vane Pump
PRESSURE HERE

• Balanced pumps are preferred because they allow
  an even load of oil around the circumference of
  the pump shaft, this reduces the wear on the pump.

PUMP HOUSING
VANE
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Unbalanced Vane Pump

• As the name implies only one side of the pump
  forces oil through, causing the oil load to shift
  to one side of the pump.

INLET
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Vane PumpAdvantages

• Quiet.
• They are self compensating for wear.

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Vane PumpsDisadvantages

• Not as tolerable to dirt as gear pumps.
• Low volume output.
• Low pressure output.

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Piston Pumps

• Radial piston pumps
• Rotating cam.
• Rotating piston.
• Axial piston pumps
• Inline axial.
• Bent-axis axial.

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Radial Piston Pump(Rotating Cam)

• Pistons are driven outward to discharge oil by
  the shaft cam, they move inward to take in oil by
  the force of their springs.
• Normally designed as a 4 or 8 piston model.

SPRINGS
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Radial Piston Pump(Rotating Piston)
INLET PORTS

• As the cylinder rotates pistons are thrown out
  against the housing by centrifugal force. A
  partial vacuum is created in the piston bores and
  oil flows into the inlet ports to fill the bores.

FIXED SHAFT
ROTATING CYLINDER
PISTON
PISTON BORE
OUTLET PORTS
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Radial Piston Pump(Rotating Piston)

• As the cylinder keeps turning, the pistons are
  pushed back into the bores and force the oil out
  the ports on the outlet side.

OUTLET PORTS
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Axial Piston Pumps

• The axial flow of fluid provides a more compact
  design and is the second most widely used pump in
  the industry next to the gear pump.
• Inline axial piston pump.
• Bent-axis axial piston pump

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Axial Piston Pumps(Inline)

• Pump can be variable displacement.
• Swashplate directs the intake and discharge of
  flow.
• Piston, draws and discharges the fluid.
• Cylinder block, holds the piston and rotates them
  from inlet to outlet ports.

OUTLET
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Axial Piston Pumps(Bent-axis)

• Fixed displacement.
• Rotating drive member directs the intake and
  discharge of flow.
• Piston, draws and discharges the fluid.
• Cylinder block, holds the pistons and rotates
  them from inlet to outlet ports.

DRIVE SHAFT
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Piston PumpsAdvantages

• Able to withstand high pressure.
• Capable of variable displacement.

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Piston PumpsDisadvantages

• Very low tolerance to dirt.
• More difficult to manufacture.
• Most expensive to manufacture.

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Questions

• What are the three types of pumps?
• - Gear, Piston and Vane
• What will change the displacement of the piston
  pump?
• - Angle of the swashplate
• What is the purpose of the side plates in the
  gear type pump ?
• - These plates are used to prevent cavitation

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Questions

• Which pump can vary its displacement?
• - Piston
• What are the two types of vane pumps?
• - Balanced and unbalanced
• Which pump is more tolerant to dirt?
• - Gear

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Break
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HYDRAULIC MOTORS
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Hydraulic Pump and Motor

• A pump drives its fluid, while the motor is
  driven by its fluid.

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Hydraulic Motors

• A motor is a rotary actuator that rotates in a
  full circle.
• The work output of a motor is called torque.
• They convert hydraulic energy to mechanical
  energy.

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Hydraulic Motors

• Fixed displacement motors- have variable speed
  but fixed torque
• Variable displacement motors- have variable
  speeds and torques

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Hydraulic Motors (Types)

• Gear motors.
• Vane motors.
• Piston motors.

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Accumulators

• A spring is the simplest accumulator. When
  compressed, its a potential source of power.
  Hydraulic accumulators work in much the same way,
  basically they are containers which store fluid
  under pressure.

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Accumulators

• Stores energy to relieve the load on the pump.

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Accumulators

• Acts as a shock absorber.

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Accumulators

• Builds pressure gradually.

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Accumulators

• Maintains system pressure under a load.

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Types of Accumulators

• Pneumatic (gas loaded)
• Weighted
• Spring loaded

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Accumulator ( Pneumatic )

• Piston type
• A free-floating piston separates the gas from
  the oil.
• With double packings, a bleed hole is needed to
  relieve pressure of any oil seeping into the
  center area between the two packings.

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Accumulator (Pneumatic )

• Bladder type
• A flexible bag or bladder made rubber contains
  the gas and separates it from the hydraulic oil.

PROTECTIVE BUTTON
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Accumulator (Pneumatic)Advantage

• Can be precharged with gas before use in a
  system.
• Offers a high power output for their size.
• Very accurate in operation.

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Accumulator (Pneumatic)Disadvantages

• Require careful service to prevent leakage.
• Uses only dry nitrogen.

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Accumulators ( Weighted )

• This accumulator uses a piston and cylinder, but
  heavy weight on the piston does the job of
  loading or charging the oil. It is loaded by
  gravity.

PISTON
PACKING
CYLINDER
PRESSURE OIL
TO HYDRAULIC SYSTEM
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Accumulator (Weighted)Advantage

• It can provide constant pressure.

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Accumulator(Weighted)Disadvantage

• They are bulky in size.
• They are heavy in weight.
• There is little use for the gravity accumulators
  for mobile machines.

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Accumulator ( Spring Loaded )

• Internal spring type.
• In operation,pressure oil loads the piston by
  compressing the spring. When pressure drops,the
  spring forces oil into the system.

LOADING
DISCHARGE
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Accumulator ( Spring Loaded )

• In this design a disk on the end of the piston
  mounts several rods which hold the springs. As
  oil pressure raises the piston,the springs are
  compressed against the solid shoulder of the
  cylinder.

PISTON
PACKING
DOUBLE SPRING ACCUMULATOR
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Accumulator(Spring Loaded)Advantage

• They never have to be precharged or recharged.

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Accumulator(Spring Loaded) Disadvantage

• They are to bulky when designed for high volume
  or high pressure systems.
• They are only used for low volume or low pressure
  systems.

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CAUTION !

• Always read the service manual before
  disassembling an accumulator.
• Never charge a gas pressurized accumulator with
  oxygen or acetylene or any other gas except dry
  nitrogen.

157
Questions

• What does a motor convert?
• - They convert hydraulic energy to mechanical
  energy.
• What is the difference between a pump and a
  motor?
• - A pump drives its fluid, while the motor is
  driven by its fluid

158
Questions

• What are the three types of accumulators?
• - Spring loaded, Weighted and Pneumatic (gas
  loaded)
• When charging accumulators you must use what gas
  ?
• - Dry nitrogen
• What functions do accumulators perform?
• - Store energy, maintain pressure, act as shock
  absorber and build pressure gradually

159
Break