Actuators

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Actuators

• Converts fluid power to mechanical power.
• Single acting cylinders
• Double acting cylinders
• Vane Cylinders
• Rotary Cylinders (also non-rotating)
• Hydraulic and Air motors
• Oscillators (back and forth rotary motion)
• Telescoping Cylinders

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Hydraulic Cylinders
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Pneumatic Cylinders
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Double Acting Cylinders
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Non-Differential Cylinder
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Single Acting Cylinders
May be of the PUSH or PULL types. (Spring and
connection can be reversed)
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Cushions
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Telescoping Cylinder
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Cylinder Operation

• To hold the load, the fluid pressure must balance
  the load pressure.
• To move the load, fluid pressure must be greater
  than the minimum needed to balance the load
  pressure and overcome friction.

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Speed of an Air Cylinder

• The higher the air pressure, the faster the
  cylinder will move.
• Speed limited only by air resistance in lines and
  valves.
• 25 to 100 over-pressure is supplied but speed
  is adjusted by constricting air flow (designing
  to get a particular speed is not accurate)

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Speed of a hydraulic cylinder

• Volumetric flow from the pump limits the speed of
  the cylinder.

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Sizing a Cylinder

• Starting with air pressure 75 less than
  available air pressure, determine the bore needed
  to produce the desired force.
• Consult a handbook to select a combination of
  bore diameter and load balance pressure.

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Pneumatic Symbols
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Flow Control Valves
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Flow control

• Used to adjust speed of actuation
• Normally, only one flow control valve is needed
  for hydraulic cylinders.
• Normally two valves are used with air cylinders.
• Meter-out gives smooth control with high pressure
  on the piston throughout stroke
• Meter-in gives more gradual pressure rise as the
  piston advances against a load.

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Hydraulic meter-out
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Meter-In Air flow Control
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Cylinder Attachment Points

• Lug
• Flange
• Trunion
• Clevis

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Cylinder Cautions

• Side loading
• Rod Bearing Failure
• Barrel scoring
• Stop collar
• Alignment
• Column Strength
• Rod buckling occurs where the diameter of the rod
  is too slim for the length of stroke and the size
  of the load force.

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Air Motors Advantages

• Ease of speed control
• Tolerance of Environment
• Safety
• Can be Stalled indefinitely while holding torque
• Low first cost
• Less Maintenance
• Clean Leakage
• Speed and torque adjust to load
• Rapid acceleration
• Lower HP per pound than electric

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Air Motor Disadvantages

• Low operating efficiency
• Poor speed self-regulation
• Low power level.
• Variable torque
• Noisy

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Rotary Vane Air Motor
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Radial Piston Air Motors
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Axial piston with Planetary Reducer