Fluid Power

1
Fluid Power

• Basic Principles

2
Links

• http//www.tpub.com/content/engine/14105/
• http//www.nfpa.com/default.asp?pid450
• http//machinebuilders.net/plans/gallery/Miscellan
  eous/Hydraulics20101.PDF
• The future of water systems
• http//www.nfpa.com/default.asp?pid76Role

3
ADVANTAGES  OF  FLUID  POWER

• Motion can be transmitted  without  the
• slack  inherent  in  the  use  of solid  machine
   
• parts.  

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ADVANTAGES  OF  FLUID  POWER

• Fluids  used  are  not subject to breakage as are
  mechanical parts, and the mechanisms are not
  subjected to great wear.

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ADVANTAGES  OF  FLUID  POWER

• The  different  parts  of  a  fluid  power  
• system can be conveniently located at widely
• separated points,  since  the  forces generated  
• are  rapidly transmitted  over  considerable  
• distances  with  small loss.

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ADVANTAGES  OF  FLUID  POWER

• Forces can be conveyed up and down or around
  corners with small loss in efficiency and without
   complicated  mechanisms.  

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ADVANTAGES  OF  FLUID  POWER

• Very large forces can be controlled by much
  smaller ones and can be transmitted through
  comparatively small lines and orifices.

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ADVANTAGES  OF  FLUID  POWER

• Smooth,  flexible,  uniform  action without
  vibration, and is unaffected by variation of
   load.  

9
ADVANTAGES  OF  FLUID  POWER

• In  case  of  an  overload,  an  automatic
  release  of  pressure  can  be  guaranteed,
   sothat  the system is protected against
  breakdown or strain.

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ADVANTAGES  OF  FLUID  POWER

• Can provide widely variable motions in both
  rotary and straight-line trans- mission of power
   

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ADVANTAGES  OF  FLUID  POWER

• The  need  for  control  by  hand can   be
    minimized.   

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ADVANTAGES  OF  FLUID POWER

• Fluid power systems are economical to
  operate. That explains why they are used in many
  applications where force is needed.

13
Pneumatics

• Power Typically 1/4 to 1 1/2 hp
• Noise Can be designed to be very quiet
• Cleanliness Very clean
• Speed Faster than hydraulic systems
• Operating Cost Heat loss is significant
• First Cost More costly than hydraulic
• Rigidity Not rigid.

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Hydraulics

• Power Level Typically greater than 1 1/2 HP
• Noise Usually noisier than pneumatics
• Cleanliness Oil spill is always a possibility.
• Speed Slower than pneumatics.
• Operating Cost More efficient than pneumatics
• First Cost Typically less than pneumatics
• Rigidity Very rigid.

15
Applications

• Hydraulic systems are slow but accurate (cutting
  tools). Pneumatic systems are quick but not as
  controlled.
• Hydraulic systems are well suited to moving a
  load against friction. Pneumatic systems would
  move erratically.

16
Pascal's Law

• Pressure transmitted throughout a confined fluid.
• Force from pressure acts at a right angle to the
  inside surfaces of the container

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Transmission of Force
18
Multiplication of Force
19
Differential Force in Cylinders
20
Compressibility of Hydraulic Fluid

• Hydraulic fluid compresses at approximately 1/2
  per 1000 PSI.
• For most hydraulic applications, the fluid is
  considered incompressible.
• Exceptions to this approximation are servo
  systems and where conductor runs are very long.

21
Compressibility of Air

• The absolute pressure of a confined gas varies
  inversely as its volume if the temperature is
  kept constant.
• Compressing a gas generates heat.

22
Pressure Measurement Units
The metric unit Pascal is too small. 1 bar
100,000 Pascals. Vacuum is measured in inches of
mercury. 30" Hg 14.7 PSI
23
Press Gauges

• Some presses have gauges calibrated in tons.
  This is based on FPxA and indicates the force
  developed by the press hydraulic system.

24
Units of Flow in Fluid Systems

• Gallons per minute (GPM).
• Cubic inches per minute (CIM)
• Cubic inches per shaft rotation (CIR)
• Standard Cubic Feet per Minute (SCFM)
• Standard conditions
• 14.696 PSIA
• 60O F
• 36 relative humidity

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VOLUME  AND  VELOCITY  OF  FLOW

• Q is the volumetric flow rate
• V is the velocity of the fluid
• A is the cross-sectional area of the conductor
• Expect the velocity to increase as the diameter
  of a conductor decreases.

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Force and Pressure
27
Fluid Flow through Conductors
28
Hydraulic fluid speed

• 10 ft/sec at 1000PSI
• 15 ft/sec at 1000 to 2000 PSI
• 20 ft/sec at 2000 to 3500 PSI
• 30 ft/sec above 3500 PSI
• 2 4 ft/sec for return lines

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Typical Restrictions

• Sharp bends
• Conductor Fittings
• T's, L's
• hose fittings

30
Pressure Loss through Conductors
31
Pressure Losses in a Conductor

• Any major restriction
• Diameter must be large enough
• Not more than 1 PSI per 100 feet of conductor
• Viscosity of fluid must be normal
• Some pressure losses are desirable and
  intentional (next slide)

32
Delayed Sensor Activation
33
Pipe Size for Compressed Air
SCFM
PSI
For concept only. Consult handbooks for reliable
data. Use Schedule 40 black pipe with dry-seal
threads (NPTF) or O-ring.
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Types of Conductors for Compressed Air

• Black Pipe
• Must be a material that does not rust.
• Used for long runs

35
Types of Conductors for Compressed Air

• Tubing
• Copper work hardens
• Plastic not considered permanent
• Brass, Aluminum, Stainless are OK but difficult
  to flare.

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Types of Conductors for Compressed Air

• Hose
• Widely used for short connections.
• Purchased with fittings attached to both ends

37
Types of conductors for Hydraulic Systems

• Not recommended
• Copper, brass
• Aluminum
• Plastic
• Low carbon steel tubing is ordinarily used.
• Specify hydraulic grade soft

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Advice on Tubing

• Low carbon except at high pressures.
• Specified by wall thickness and O.D.
• Connector Flared (if softness permits)
• Flare (use flaring tool)
• Ferrule (ring grips tubing)
• Brazing (where flaring may crack tubing)

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Ferrule Design
40
Flare Design
41
Flareless
Ferrule bites into tubing
42
Petroleum Hydraulic Oil

• Lubricates
• Light weight
• Strong film strength
• Motor oil works
• Additives for rust, foam, viscosity index
• Transmission oil works except in gear pumps
• Not brake fluid! Incompatible with rubber seals
  used in hydraulic components.

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Viscosity

• Greater at low temperatures
• Measured in SSU Saybolt Second Universal.
• 60 cc
• 100 degrees F.
• 0.0695 inch diameter opening
• Use pump specs to determine proper viscosity.
• Should be between 45 and 4000 SSU
• 100 to 750 SSU in most systems

44
High Viscosity Effects

• High pressure (5000 PSI) and low temperature
  both tend to increase viscosity (fluid thickens).
• Greater loading of pump motor
• Cavitation
• Cylinder slow-down
• Erratic operation of cylinders

45
Low Viscosity Effects

• Slip results in power loss
• Oil heating
• Erratic operation of pistons

46
Viscosity Index

• V.I. is a rating that indicates viscosity
  variability with temperature.
• High V.I. ratings are preferred (95).
• High V.I. indicates least amount of viscosity
  change as the temperature changes.

47
High Operating Temperature

• Useful oil life is cut in half for every 20
  degrees of temperature rise.
• Oil oxidation deteriorates the oil. Products of
  oxidation coat internal metal surfaces, clog
  filters and small passages.
• Oil oxidation reduces lubricity and causes
  premature failure of components. Causes leaks
  and sticking parts.

48
Low Operating Temperature

• Most systems are designed to work 60 degrees
  above the environment temperature.
• Cavitation damage occurs when the pump is
  required to draw cold oil into its inlet.
• Electric heating may be necessary.

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Oil Contaminants

• Built-in contaminants
• Wear and tear contaminants
• Oxidation contaminants
• Dirt from outside (glands, quick disconnects,
  reservoir)

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Testing Oil for Serviceability

• Changes in color is significant
• Grit felt between finger tips
• Commercial testing is available.
• If replacing oil, siphon off the clear layer and
  use as a flush.
• Install a micronic filter if necessary

51
Anti-Foaming Additives

• Improper oil
• Insufficient reservoir capacity
• Excessive velocity of oil
• Leak of air into components or plumbing

52
Anti-Oxidation Additives

• High operating temperature
• Foaming
• Presence of Copper and copper alloys
• Water

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Rust Inhibitors

• Water condenses in the reservoir
• Demulsifying agents keep water from mixing with
  the oil so it settles to the bottom of the
  reservoir.

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Other Fluids

• Fire resistance
• May be required by MIOSHA and other governmental
  agencies.
• Most water-based fluids work OK at low pressures.
• Higher power loses
• Cavitation
• Larger filters
• Larger pipes
• Temperature range 40 to 120 degrees.
• Close monitoring of quality.
• See vendor for latest developments.
• http//www.dow.com/polyglycols/index.htm

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How about water?

• Water costs less
• Safety hazards reduced
• Lower insurance costs
• Easy availability
• Disposal costs less
• Environmental compliance costs less
• Reduced product contamination
• Green image enhanced

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Water Challenges

• low viscosity
• turbulent flow
• bacteria can corrode (Oxygen, Sulfur)
• limited temperature range (2-50 degrees)
• Biodegradeable antifreeze?
• microorganisms
• clogged filters and foul smells
• water hammer effect
• low lubricity

57
Water instead of Oil? Maybe!

• made in limited quantities
• may cost more than those used in comparable
  oil-based systems
• initial costs can be justified by factoring in
  savings from operating costs over time

58
Vacuum

• A form of fluid power
• Force depends on atmospheric pressure
• Hoses are small bore and reinforced to prevent
  collapse
• Some pneumatic components work well on vacuum but
  receivers may collapse.
• A pumped vacuum is imperfect but useable to 20
  inches of mercury.

59
Uses of the Vacuum

• Vacuum cups for lifting
• Compression in printing
• Vacuum forming
• Vacuum chucking of non-magnetic materials

60
Evacuation Time

• T Time
• V Volume
• D pump displacement SCFM
• A deadhead vacuum of pump
• B Desired vacuum level in Hg.