Hydraulic Pumps And Actuators Exam Review Flashcards
List the three (3) main styles of pumps (based on pumping elements)?
- Piston Pump
- Vane Pump
- Gear Pump
What is required at the pump inlet in order for oil to flow into the inlet port?
Pressure Differential.
Explain why hydraulic pumps are required to be positive displacement pumps?
To maintain pressure by positive sealing, inlet to discharge. (eliminating backpressure)
Explain the difference between a pressure compensation and load sensing in a pump. And Which one is more efficient?
Pressure Compensation Pump: Is to reduce flow, but maintain self operating pressure.
Load Compensating Pump: It adjust pump stroke to maintain only required flow and required pressure drop. plus (200 to 400 psi)
Load Compensating is more efficient.
Explain the difference in Operation between an in-line axial piston pump and a bent-axis piston pump?
An in-line piston pump has a swash plates which can be adjusted to an operating degree. The bent-axis has a bent shaft and can be adjusted by a block.
Explain the difference in operation between a radial piston pump and a rotary piston pump?
The difference is that the rotary piston pump the pistons are rotating
What is the purpose of the intra-vane in a pump? And in what type of vane pump would you find one in?
Explain the difference between a balanced cam pump and an unbalanced vane pump?
- Balance Cam Pump: is more compact and has an eccentric cam.
- Unbalanced Vane Pump: Is a variable pump.
Explain the differences between an internal gear pump and an external gear pump?
- External Gear Pumps: They have two (2) meshing gears together.
- Internal Gear Pumps: Internal has a crescent seal.
Gerotor gear pumps do not have seals. What is required for Gerotor pumps to be a positive displacement pump and where are they found?
- Sliding Creates sealing
* They are found on charged pumps
Explain the operation of a cylinder cushion?
It’s purpose is to provide cushion when it hits the end of stroke.
Explain the factors that affect torque and speed in hydraulic motors?
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Why should dynamic seals have some leakage?
For Lubrication
How can you determine the proper torque value when you are assembling a hydraulic component?
Consult the service manual.
What type of sealant should be used on tapered pipe threads in hydraulic systems?
Liquid PTFE (Teflon)
When static O-ring gaskets are used, what percentage must they project from the mating surface?
10%
What method is used to ensure that you have achieved your target cleanliness code for a hydraulic system?
Use a particle counter
Which filter must be rated at the relief valve pressure of the system?
Pressure line filter.
What is the recommended micron size filter for a reservoir breather?
3 Microns
What is the efficiency of a filter with a Beta Ratio of 10?
90%
what is the main purpose of an accumulator?
To store pressurized hydraulic fluids.
What extra safety precaution must be taken when working on a system with an accumulator?
Completely depressurize and block out accumulator.
Which type of gas could be used in a gas accumulator?
Nitrogen.
What is the main disadvantage of a spring type accumulator?
Cannot maintain a constant pressure as they discharge.
What component in a reservoir reduces turbulence, aids in cooling, and promotes settling of contaminants?
The Baffle
The oxidation rate of petroleum based hydraulic oil doubles every 10°C above?
60°C
What condition can occur should the inlet strainer on a pump be clogged?
Cavitation
What size is an open circuit reservoir when compared to the capacity of the pump?
2 - 3 times larger
What condition can occur should the pump shaft seal fail?
Aeration
In addition to transmitting power, what are the other functions must hydraulic fluid must do?
- Lubricate
- Cool
- Seal
- Clean
Viscosity Index (VI) of oil is defined as?
Stability of an oil viscosity over a temperature range.
Built in contamination in a hydraulic system can happen when?
When the components are assembled and repaired.
What is the main cause of oxidation in a hydraulic fluid?
*Heat
Which filter location is the most efficient in a hydraulic system?
Permanent off-line
A rotating mechanical seal that allows controlled leakage for flushing and cooling purposes would be classified as?
Positive/Dynamic
What is the proper accumulator Pre-charge if used for shock absorption purposes?
75% of normal working pressure
Cavitation can be the result of?
Running a pump at too high a speed.
An example of dynamic pump would be
Impeller
A cylinder which is extended by force and retracted by spring or gravity is known as
Single Acting
The flow produced by a pressure compensated pump during cylinder extension is at
Load Pressure
The flow produced by a pressure compensated pump at the end of stroke is at
No flow produced
The purpose of a cylinder cushion is to?
Reduce mechanical shock
The pump in a hydraulic system produces?
Fluid Flow
An unbalanced vane pump can be identified by its?
Off-Centre cam ring
Variable displacement vane pumps control fluid flow by?
Shifting the cam ring
The vanes of a pump maintain contact with the cam ring by?
Centrifugal Force / Fluid Pressure
A balanced vane pump would have?
Sets of inlet and outlet ports opposing each other
The displacement of a bent-axis piston pump can be varied by?
Pivoting the cylinder block to change angle to shaft
The torque of hydraulic motor is dependent upon?
Inlet pressure, surface area and radius of rotation
If a cylinder had internal leakage it would affect?
Speed
Hydraulic motors are driven by?
Fluid flow and pressure
Which component prevents contamination from entering a cylinder?
Rod Wiper
Which type of cylinder accelerates during extension?
Telescopic
Balanced vane motors maintain vane contact by?
Fluid Pressure / Springs
In an in-line axial piston motor, speed can be increased by
Decreasing swash plate angle
The purpose of a stop tube is?
Reduce side load when extended
In a rotary piston pump the fluid is ported in and out of cylinders through the?
Pintle
The output flow of gear pumps can be adjusted by
Changing RPM of prime mover
A radial piston motor can be classed as?
Low Speed / High Torque
O-ring boss port connections have which type of threads?
Straight
