Hydraulic Pumps And Actuators Flashcards
Do Pumps Create Pressure or flow?
Flow.
Why are positive displacement pumps used for hydraulics?
Because flow is not affected by backpressure.
Does the volume of the pumping chambers expand or contract at the inlet?
Expands.
List three (3) methods of changing the output of a pump?
- Built-in flow control and relief
- Drive speed change
- Variable displacement
If a pump is mounted above the surface of the liquid, what provides the pressure to push the fluid up into the pump?
Atmospheric Pressure.
What are three (3) ways to push fluid into a pump besides using atmospheric pressure?
- Gravity
- Pressurized Reservoir
- Charge Pump
How is the stroke increased on an axial piston pump?
By increasing the swash plate angle.
Which swash plate control limits the maximum pressure in the system?
Pressure Limiting Compensator.
Which swash plate control regulates the flow to suit any given load?
Load Sensing Compensator.
What is the main reason for using the pressure compensator and the load sensing compensator?
To Save Energy
What would happen if you set the load sensing compensator at zero psi?
There would be no pressure to operate the bias piston and it would bring the pump back to full stroke.
What must you do to a new or rebuilt pump before you install it?
Fill the case with fluid?
How can you increase the stroke on a bent axis piston?
Increase the cylinder block angle to the shaft axis.
Which component of a rotary piston pump port the fluid in and out of the cylinders?
The Pintle.
How can you increase the flow from a rotary piston pump?
Move the reaction ring farther off centre.
Which part of a radial piston pump drives the piston?
An eccentric drive cam.
Does the space between the vane increase or decrease at the inlet?
Increases.
How is the output flow increased on an unbalanced vane pump?
By moving the cam ring off centre.
What two (2) Methods are normally used to hold the vane out against the cam ring on a vane pump?
- Centrifugal Force
* Fluid Pressure Under The Vanes
Which type of pump is more compact? Balanced vane or the unbalance vane?
Balanced Vane
What is the rotation of a factory rebuilt balanced vane pump?
Right Hand.
From which end of the pump is the direction of rotation defined?
Drive End.
How do you change the direction of rotation in a balanced vane pump?
Flip over the cam ring, rotor and flex plate assembly.
Name three (3) indications of contamination damage in a vane pump?
- Marks around the inside of the cam ring.
- Frosted appearance on the vanes.
- Circular marks on the flex plates.
Name two (2) indications of cavitation or aeration damage in a vane pump?
- Ripple marks inside the cam ring.
* Erosion at the ports.
On a gear pump, do the teeth go into or come out of mesh at the inlet?
Out Of Mesh.
What determines the volumetric efficiency of a gear pump?
The close fit between the gears, and between the gears and the casing and wear plates.
Why do gear pumps require heavy needle bearings?
Because they are hydraulically unbalanced, so the bearing must support high radial loads.
If the crescent seal in an internal gear pump becomes worn, what happens to the flow inside the pump?
Some of the discharge flow recirculate back to the inlet.
How can you change the output of a gear pump?
By changing the speed of the driver.
Name two (2) symptoms of wear from contamination in gear pumps?
- Wear plates scored.
* Sharp edges on tips of the gears.
What can you do to repair a gear pump if only the wear plates are scored and the tips of the teeth have sharp edges?
Change the wear plates and stone off the sharp edges.
What is the maximum efficiency that you can expect from a new gear pump?
85%
What is the basic operating principle of any positive displacement pump
Pumping chambers increase in volume at the inlet and then decrease as they push the fluid out the discharge ports.
What, if any, change should you expect in the output of a positive displacement pump as the backpressure increases?
Small Decrease.
why is it better to locate a pump below the level of the fluid than above the surface?
More pressure is available to ensure adequate inlet flow?
What condition occurs when the inlet flow is less than the discharge?
Cavitation.
List three (3) methods of ensuring adequate inlet flow?
- Gravity
- Pressurized Reservoir
- Charge Pump
Why is it worthwhile to examine a pump that you are about to replace?
To determine the root cause of failure.
How is the flow rate from an in-line axial piston pump increased?
By increasing the swash plate angle.
What is the purpose of the bias piston in a in-line axial piston pump?
To move the swash plate angle.
Which is the best pump to use if you have to locate it above the surface of the fluid; an in-line axial piston pump or a bent axis pump?
Bent Axis Pump.
How is the fluid ported in and out of a radial piston pump?
Through check valves in the pistons.
Does the space between the vanes and the cam ring increase or decrease at the discharge port in a vane pump?
It Decreases.
How many inlet ports and how many discharge ports would you see in a balanced vane pump flex plate?
Two Inlet and Two Outlet.
Which direction of rotation are factory rebuilt or new balanced vane pump assembled for?
Right Hand.
List two (2) root causes of heat discoloration on a cam ring that you should check?
- Aeration.
* Poor Quality Fluid.
Why is a very tight fit necessary between the teeth and the casing on a gear pump?
To prevent bypassing back to the inlet.
On an internal gear pump, should the inside gear have the same number of teeth as the outside gear or should it have fewer teeth?
Fewer Teeth.
Should you expect a new gear pump to be more efficient or less efficient than a piston pump?
Less Efficient.
What is a double acting cylinder?
A cylinder that exerts force in both directions.
Which seals are contained in the rod bushing?
Rod wiper seals and pressure seals.
What is caused by failed rod seals?
Dirt and air get into the system.
Which type of piston rings would you use if no creep could be tolerated?
Synthetic.
State two (2) reasons for using cast iron piston rings?
- Higher Temperatures
* Higher Pressures
Under what operating condition would you use cylinder cushions?
When the load can force the piston to hit the end of the cylinder.
When would you required a cushion bypass?
If the cylinder is loaded as it begins its stroke.
When would you need a stop tube?
When the rod has a long extension with some side load.
Why is an ORB fitting preferable to a tapered thread fitting?
It causes less stress and distortion.
Should you normally install a cylinder with the ports at the top or at the bottom?
At the top.
Why is it important to align a cylinder with the load to which it is attach?
To avoid undue wear on the cylinder walls and on the seals.
What is the most costly result of leaks in a cylinder?
Dirt and air get sucked into the system and damage components throughout the system.
How can you detect an internal leak in a cylinder?
By hot spots.
What is the operating principle of any hydraulic motor?
Fluid pushes on vanes, gear teeth or pistons to turn the drive the shaft.
Which three (3) types of motors are used for low speed and high torque?
- Radial Piston.
- Cam-Type Radial Piston.
- Roller Vane Gerotor.
Which type of motor can only turn part of a rotation?
A limited rotation motor.
Which type of limited rotation motor can be used for clamping?
Cylinder with bell crank.
Which three (3) specifications determine the torque in a motor?
- Inlet Pressure
- Surface Area Of The Motor Elements
- The Radius Of Rotation
What does a decease in mechanical efficiency indicate?
An increase in internal friction.
What does a decrease in volumetric efficiency indicate?
Internal Leakage.
On which two (2) factors does motor speed depend on?
- Displacement
* Flow Rate
Open loop hydra
3/4
