Pumps/Actuators A

Question 1

Controlling the output of a piston pump

Answer 1

-output can be varied by controlling the length of the stroke

Question 2

Internal leakage

Answer 2

-thinner oil could cause it

Question 3

Changing the output of a pump

Answer 3

• use of flow control
• change the speed of the driver by using a frequency drive
• use a variable displacement pump (adjusting the swash plate)

Question 4

Positive displacement pump vs. Dynamic

Answer 4

-positive displacement has a positive seal between the inlet and outlet

Question 5

Load compensator pump

Answer 5

-less pressure when extension, more on retraction
-no flow on extension or retraction after pressure “required” (plus moving the check valve spring) is achieved
-

Question 6

Pressure compensator pump

Answer 6

-no flow after reaching max pressure needed to move load or

Question 7

In-line axial piston pump

Answer 7

• swash plate controls flow by changing its angle

- has the bias piston

Question 8

Type of positive displacement pumps

Answer 8

• piston
• vane
• gear

Question 9

Difference between rotary and radial

Answer 9

• radial uses a stationary block instead of rotating block like the rotary
• rotary has the pintle that injects fluid and the radial fluid is ported by check valves in the Pistons

Question 10

Rotary piston pump

Answer 10

• cylinder rotates around stationary pintle
• the housing is eccentric so when the cylinder is in the middle there is no stroke and no flow, as it moves out of the centre the flow increases.

Question 11

Bent axis piston pump

Answer 11

• controlling the stroke by adjusting the angle between the cylinder and the drive shaft
• can handle high vacuum so it can be mounted above fluid level

Question 12

Bias piston

Answer 12

• holds swash plate at max angle when needed

- when pressure builds it overcomes bias piston and lowers angle of swash plate

Question 13

Unbalanced vane pump

Answer 13

• hydraulic forces not balanced
• circular cam is off centre with respect to the rotor
• advantages: able to give you variable displacement by rotating the cam ring
  disadvantage: very large to support the large radial force

Question 14

Balanced vane

Answer 14

• much more compact because it has two pumping chambers that are 180 apart so the forces at one outlet act against the forces on the opposing outlet.
• high performance balanced vane pumps have intra-vane

Question 15

Intra vane

Answer 15

• slotted rotor with intra vane passage have outlet pressure constantly applied to small intra vane area of vane
• pressure on the intra vane along with centrifugal pressure force vanes to maintain constant with cam ring.
• more stable, less noise, less maintenance than regular vanes
• found on cartridge style balanced vane pumps

Question 16

Cam ring (unbalanced Vane)

Answer 16

• thickness of the cam ring determines the amount of fluid displaced on each revolution
• vanes are held against the cam ring by centrifugal force and hydraulic pressure

Question 17

Pintle (Rotary piston)

Answer 17

-a stationary shaft that shoots the fluid in and out of the cylinder

Question 21

Gear pumps

Answer 21

• use gear meshing for pumping action
• two styles: external and internal
• cannot have adjustable displacement (without fluid bypass or VFD)
• less efficient (85%) than piston pumps (95%) because of internal leakage

Question 21

External gear pumps

Answer 21

• unbalanced forces
• spur, helical, or Herrington
• simple design
• most dirt tolerant

Question 21

Internal gears

Question 21

Gerotor internal

Answer 21

• no crescent seal and is star shaped rotor with one less tooth than the lobes on the outer gear
• less dirt tolerant