301 B - Hydraulic Pump Fundamentals Flashcards
What number of pistons does a piston pump have? Why?
They use an odd number to control pulsations from the pump.
What are some characteristics of a Gear Pump?
Cheaper Simple More Rugged Fixed Displacement Bi-Directional
What sort of efficiency does a piston pump have?
94-98%
What are the two pistons called that control pressure compensation in a piston pump?
A Bias piston constantly achieves max angle Stroking piston changes angle to minimum angle when outlet pressure rises enough.
What are some characteristics of Vane Pumps?
Variable displacement More expensive More efficient More susceptible to contamination Square Case
What is the Volumetric Efficiency of a pump?
Expresses how well it generates flow.
What is the most commonly used pump in the mobile hydraulics area?
An axial piston pump.
Why is a gear pump a fixed displacement?
The pockets created by the moving gear teeth never change.
What is the purpose of a hydraulic pump?
To change rotary mechanical motion into Hydraulic power.
What two designs of vane tips can be used within a Vane Pump?
Bevelled Tip Rounded Tips (Bi-Directional)
How is the displacement of an fixed displacement axial piston pump determined?
The displacement is the volume displaced by the largest stroke, times the number of pistons.
What would a PSI Atmosphere Gauge read at sea level?
14.7 PSI A
What is pump slip? What does it cause?
Oil leaking from the outlet side to the inlet side. Causes a reduction in volumetric efficiency.
When does maximum displacement within a vane pump occur?
When the cam ring is pushed its maximum distance off centre of the rotor.
What causes a pump to be unbalanced?
As long as the inlet pressure and outlet pressure are different the pump is considered unbalanced.
What pressures do Vane Pumps run at?
3500-4000 PSI
What are pressure plates within pumps used for?
To control the leakage rate and maintain better volumetric efficiency.
What best describes a Fixed displacement pump?
Delivers a constant volume as long as there is constant input.
How efficient are Vane Pumps?
92-95%
What pressure does a Gear pump run at?
2500 PSI or less
What is the typical volumetric efficiency of a Gear Pump?
85-87%
How can a pump be described as balanced?
If the pump has 2 or more inputs and equal amounts of outputs, then the pump becomes balanced.
What is the mechanical efficiency of a pump?
The power required to overcome internal friction.
On a variable swash plate piston pump, what is the condition of the swash plate at maximum flow?
Maximum angle of the pump.
What would a PSI G gauge read at sea level?
0 PSI
What is the specific gravity of oil?
0.40 Pounds / Vertical Foot
How does a variable vane pump change its displacement?
The cam ring is shifted to create larger or smaller pockets for the vanes to shuttle oil.
What speed is required to enable a Vane Pump’s vanes to be thrown against the cam ring?
600 RPM
How does a piston pump achieve pressure compensation?
A set of pistons act upon the swash plate to change the angle in relation to outlet pressure.
What sort of pressures does a Piston Pump operate at?
3500-5000 PSI
What is a rotating group in a piston pump?
The cylinder barrel, and pistons are called a rotating group.
What are the three types of efficiency regarding Hydraulic Pumps?
Mechanical Volumetric Overall
Why is a minimum and maximum operating speed of a pump given?
To provide adequate lubrication but prevent cavitation.
