BCIT: Millwright Level 3 (Hydraulics: Pumps - Basic)

Do pumps create pressure or flow?

Pumps create flow.

Why are positive deplacement pump used for hydraulics?

Positive displacement pumps are used for hydraulics because they can generate accurate and consistent flow rate without being affected by the back pressure in the system.

Does the volume of the pumping chambers expand or contract at the inlet?

The volume of the pumping chambers expands at the inlet, allowing fluid to enter the chamber.

List three (3) methods of changing the output of a pump.

Three methods of changing the output of a pump are adjusting the drive speed, using built-in flow control, and using 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?

If a pump is mounted above the surface, atmospheric pressure causes the fluid up into the pump.

What is the basic cause of cavitation?

The basic cause of cavitation in the lack of flow at the inlet of the pump.

What are three (3) ways to push fluids into a pump besides using atmospheric pressure?

Three methods of pushing fluid into a pump besides atmospheric pressure are gravity, a pressurized reservoir, and a charge pump.

How much internal leakage can you expect in a new pump?

In a new pump, you can expect between 5-15% internal leakage?

How is the stroke increased on an axial piston pump?

The stroke on an axial piston pump is increased by increasing the angle of the swash plate.

Which swash plate control limits the maximum pressure in the system?

The swash plate control that limits the maximum pressure in the system is the pressure compensator.

Which swash plate control regulates the flow to suit any given load?

The swash plate control that regulates the flow to suit any given load is the load-sensing compensator.

What is the main reason for using the pressure limiting compensator and the load-sensing compensator?

Pressure-limiting and load-sensing compensators are used to protect the system from excessive pressure and to improve efficiency by supplying only the flow required by the load.

What is the pressure at the compensator at zero psi?

At zero psi, there is no pressure at the compensator.

What must you do to a new or rebuilt pump before you install it?

A new or rebuilt pump must be primed before it is installed.

How can you increase the stroke on a bent axis piston pump?

The stroke on a bent axis piston pump can be increased by increasing the angle of the swash plate.

Which component of a rotary piston pump ports the fluid in and out of the cylinders?

The pintle ports the fluid in and out of the cylinders in a rotary piston pump.

How can you increase the flow from a rotary piston pump?

The flow from a rotary piston pump can be increased by moving the reaction centre further off-center.

Which part of a radial piston pump drives the pistons?

The pistons in a radial piston pump are driven by an eccentric drive cam.

Does the space between the vanes increase or decrease at the inlet?

The space between the vanes increases at the inlet.

How is the output flow increased on an unbalanced vane pump?

The output flow on an unbalanced vane pump is increased by moving the cam ring further off-center.

What two (2) methods are normally used to hold the vanes out against the cam ring on a vane pump?

Two methods the vanes are held against the cam ring are centrifugal force and fluid pressure.

Which type of pump is more compact, the balanced vane or the unbalanced vane pump?

The balanced vane pump is more compact than the unbalanced vane pump.

What is the rotation of a factory rebuilt balanced vane pump?

A factory rebuilt balanced vane pump rotates in the right-hand direction.

From which end of the pump is the direction of rotation defined?

The direction of rotation is defined from the drive end of the pump.

How do you change the direction of rotation in a balanced vane pump?

The direction of rotation in a balanced vane pump is changed by flipping the cam, rotor, and flex plate.

Name three (3) indications of contamination damage in a vane pump.

Three indications of contamination damage in a vane pump are frosted vane tips, score marks, and circular marks on the flex plate.

Name two (2) indications of cavitation or aeration damage in a vane pump.

Two indications of cavitation or aeration damage in a vane pump are ripple marks in the cam ring and erosion.

On a gear pump, do the teeth go into or come out of mesh at the inlet?

On a gear pump, the teeth come out of mesh at the inlet.

What determines the volumetric efficiency of a gear pump?

The volumetric efficiency of a gear pump is determined by the clearance between the gears, the casing, and the wear plates.

Why do gear pumps require heavy needle bearings?

Gear pumps require heavy needle bearings because they experience radial loads due to unbalanced forces.

If the crescent seal in an internal gear pump becomes worn, what happens to the flow inside the pump?

If the crescent seal in an internal gear pump becomes worn, the discharge flow escapes back to the inlet.

How can you change the output of a gear pump?

The output of a gear pump can be changed by adjusting the speed of the driver.

Name two (2) symptoms of wear from contamination in gear pumps.

Two symptoms of wear from contamination in gear pumps are worn wear plates and sharp tips on 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?

If only the wear plates are scored and the tips of the teeth are sharp, the wear plates should be replaced and the sharp edges of the gear teeth should be stoned.

What is the maximum efficiency that you can expect from a new gear pump?

The maximum efficiency expected from a new gear pump is approximately 85%.

What is the basic operating principle of any positive displacement pump?

The basic operating principle of a positive displacement pump is to increase volume at the inlet and decrease volume at the discharge.

What, if any, change should you expect in the output of a positive displacement pump as the backpressure increases?

As backpressure increases, the output of a positive displacement pump decreases slightly.

Why is it better to locate a pump below the level of the fluid than above the surface?

It is better to locate a pump below the fluid level because it allows easier inlet flow.

What condition occurs when the inlet flow is less than the discharge?

When the inlet flow is less than the discharge flow, cavitation occurs.

List three (3) methods of ensuring adequate inlet flow.

Three methods of ensuring adequate inlet flow are gravity feed, a charged or pressurized reservoir, and a charge pump.

Why is it worthwhile to examine a pump that you are about to replace?

It is worthwhile to examine a pump before replacing it in order to determine the cause of failure.

How is the flow rate from an in-line axial piston pump increased?

The flow rate from an in-line axial piston pump is increased by increasing the angle of the swash plate.

What is the purpose of the bias piston in an in-line axial piston pump?

The purpose of the bias piston is to move the swash plate to its maximum 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?

A bent axis piston pump is the better choice because it has check valves in the pistons.

How is the fluid ported in and out of a radial piston pump?

In a radial piston pump, the fluid is ported through two inlet ports and two discharge ports.

Does the space between the vanes and the cam ring increase or decrease at the discharge port in a vane pump?

The space between the vanes and the cam ring decreases at the discharge port.

How many inlet ports and how many discharge ports would you see in a balanced vane pump flex plate?

A balanced vane pump flex plate has two inlet ports and two discharge ports.

Which direction of rotation are factory rebuilt or new balanced vane pumps assembled for?

Factory rebuilt or new balanced vane pumps are assembled for right-hand rotation.

List some root causes of heat discoloration on a cam ring that you should check.

Some root causes of heat discoloration on a cam ring include aeration and poor-quality hydraulic fluid.

Why is a very close fit necessary between the teeth, and between the teeth and the casing on a gear pump?

A very close fit is necessary to prevent fluid from 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?

In an internal gear pump, the inside gear has fewer teeth than the outside gear.

Should you expect a new gear pump to be more efficient or less efficient than a piston pump?

A new gear pump is less efficient than a piston pump.