301D: Hydraulic Actuator Fundamentals Flashcards
Hydraulic motors convert hydraulic energy into:
Rotary mechanical energy
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What are three category types of hydraulic motors?
- Gear: External, Gerotor, Geroller/Orbital
- Vane
- Piston motors.
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The construction between hydraulic pumps and hydraulic motors is significantly different. (T/F)
False
In most cases, the construction of hydraulic motors is very similar to the construction of hydraulic pumps.
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What does reversing oil flow through a hydraulic motor do?
Reverses output shaft rotation
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What is a major disadvantage of gear type motors?
Poor torque generators due to their unbalanced design.
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In a ram type cylinder, pressurized oil is allowed to flow past the piston tube end and to its sides. (T/F)
True
The guide ring supports the inner end of the piston tube, but does not seal the piston in the cylinder barrel.
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What advantage does a telescoping cylinder offer?
Additional stroke length is gained from a relatively compact size
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Why are double-acting cylinders are often referred to as differential cylinders?
There is a difference in the speed and force generated in extension versus retraction
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The difference between a differential and non-differential cylinders is:
Non-differential cylinders have equal piston area and equal volume on both sides of the cylinder.
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The function of a cylinder rod wiper is to:
Prevent contamination from entering the cylinder when retracting
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The purpose of a piston relief valve is to:
Allow oil flow to bypass through the piston at the end of it’s stroke.
Allows the oil to return to the reservoir instead of having pump oil flow over the main system releif valve. Results in lower system pressure and reduces overheating.
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In reference to hydraulic cylinder operation, the term regeneration refers to:
Supplementing pump oil flow to the base end of a double-acting cylinder with oil from the rod end which increases cylinder extension speed.
By use of quick drop valves
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The speed of a motor driveshaft depends upon what two factors?
- Inlet flow rate
- Motor displacement
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Over time, internal clearances in a motor increase due to wear. What else does this increase?
Leakage and oil flow through the drain line
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Which one of the folloring factors does not influence motor torque generation:
a) inlet flow rate
b) inlet pressure
c) motor displacement
Inlet flow rate
Flow rate affects speed.
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Why are external gear motors such poor torque generators?
Due to counteracting forces, torque is generated by inlet pressure acting on the surface area of just one tooth.
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Gerotor motors are considered to be high-speed low torque motors. (T/F)
False
Low speed, high torque motors
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Gerotor motors require a spool valve to:
Direct oil to and from the valleys in the gerotor element.
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Balanced vane motors are good torque generators because:
Can operate at higher pressures due to their balanced design.
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Why must some vane motors be equipped with spring-loaded vanes?
Ensure good vane-to-cam ring contact at start-up
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Pressure compensated, variable displacement motors vary their displacement in response to changes in motor load. As the load on the motor output shaft increases, the motor displacement:
Increases
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Why are variable displacement motors prevented from reaching the zero displacement position?
The motor will hydrostatically lock and stall (freewheel) in the zero displacement position
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In a piston motor, the cylinder barrel and pistons are often referred to as:
Rotating group
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What are three types of piston motors?
- Axial
- Bent axis
- Radial
In a piston motor, the amount of torque generated is determined by the force generated by the pistons and the distance between the centreline of the pistons and centre line of the driveshaft. What is this refered to?
Torque arm
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Unlike variable displacement pumps, variable displacement axial piston motors have a limited working swash plate angle range. What degrees from perpendicular should the swash plate stay within?
6.5 to 19 degrees
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If a hydraulic motor’s swash plate goes into a perpendicular position, what could happen?
The circuit would go into a hydrostatically locked situation allowing motor to freewheel.
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How is maximum torque achieved in a piston pump?
With the swash plate at a minimum angle, producing little flow, but high torque.
What are the differences between a piston and ram type single-acting hydraulic cylinder?
Piston Type: Consists of a piston and rod
Ram Type: Consists of a large diameter rod (piston tube)
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With a telescoping hydraulic cylinder, what stage will produce the greatest force output?
First stage as it has the largest surface area for oil pressure to act on
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With a telescoping hydraulic cylinder, what stage will generate the fastest extension speed?
Final stage. Smallest volume to fill with oil.
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What is component #1 in the following diagram of a double-acting cylinder?
Cylinder Barrel
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What is component #4 in the following diagram of a double-acting cylinder?
Piston
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What is component #10 in the following diagram of a double-acting cylinder?
Rod end cap
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What is component #15 in the following diagram of a double-acting cylinder?
Rod
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What is component #14 in the following diagram of a double-acting cylinder?
Rod wiper
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What considerations should be made when selecting hydraulic cylinder seals? (7)
- Operating pressures & temperatures
- Fluid compatibility
- Cylinder speed
- Clearances to be sealed
- Internal friction
- Finish of the sealing surface
- Acceptable seal life
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When does pressure intensification refer to in hydraulic cylinders?
When oil leaking past the seals acts on both sides of the piston. The effective result is the same as having the piston removed and the load supported by only the surface area of the rod end.
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What are hydraulic cylinder cushions used for?
To slow down the cylinder as it reaches the end of its stroke.
Done by restricitng the return oil from the cylinder, creating backpressure.
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What are two types of hydraulic cylinder cushions?
- Cushion plunger
- Return drillings
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Describe the flow of oil in the quick drop valve when the dozer blade is being raised.
- Oil enters at 1 and flows to rod end of cylinder
- Pressure created by orifice 3 is transmitted through orifice 2 to the valve spring cavity
- Spool valve is held to the right, closing the connection between the rod end and base end of cylinder
- Return oil from base end returns to reservoir through directional control valve
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Describe the flow of oil in the quick drop valve when the directional control valve is in the full lower position.
- As the blade quickly lowers, oil begins to return to reservoir through orifice (3)
- Pressure created by orifice (3) alows oil to act on the right sside of spool valve, pushing it left
- Valve movement opens a path (13) for oil to enter the valve outlet to the base end of cylinder (11)
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Describe the flow of oil in the quick drop valve when the directional control valve is in the full lower position after the blade has contacted the ground.
- Return oil flow is reduced which allows the valve spring to force the valve to the right, closing the passage (13) to the base end of the cylinder
- Increased pressure in the cylinder base end side of the circuit increases
- This pressure, through passage (13) acts on the back side of the valve, maintaining the force to keep it closed
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What determins the amount of torque output from a hydraulic motor? (2)
- Inlet pressure
- Motor displacement
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A variable displacement bent axis piston motor has its displacement altered by moving ____ in relation to _____.
By moving the cylinder block in relation to the motor driveshaft.
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What are the three components in the following motor?
- Output shaft
- Rotor
- Rollers
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