Pumps (Positive Displacement)

Question 1

Where are positive displacement pumps used?

Answer 1

Used where constant flow or a measure amount of flow is critical.

Reciprocating

Rotary

Question 2

What are the two classifications of displacement pumps?

Answer 2

Reciprocating

Rotary

Question 3

Define volumetric efficiency of a displacement pump?

Answer 3

In theory a pump expels the same amount of liquid or gas it takes in. But due to internal leakage this is not true.

The degree of which this happens is called volumetric efficiency.

Volumetric efficiency = actual output/theoretical output x 100%

Question 4

What are the two types of reciprocating pumps? What type of flow is produced?

Answer 4

Piston/plunger

Diaphragm

They both increase and decrease the area of the cavity, which pumps the fluid

Question 5

What does the volume of liquid per stroke depend on?

Answer 5

Cross sectional area of the piston, plunger, or diaphragm and on the length of stroke.

Question 6

What is the difference between plunger and piston pumps?

Answer 6

Plunger pump has its plunger sliding inside packing

Piston pump has its packing sliding with its piston

Question 7

Describe the operating principle of a single acting plunger/piston pump?

Answer 7

Only one side of the plunger/piston is doing the pumping.

Plunger extends
-outlet valve opens
-inlet valve closes
-fluid is forced out of the chamber

Plunger retracts
-outlet valve closes
-inlet valve opens
- fluid is sucked into the chamber

Question 8

Described operating principles of a double acting piston pump?

Answer 8

Both side of pump moves fluid

Piston extends
-drawn in left side of cylinder
-forced out the right side

Piston retracts
- drawn in the right side of cylinder
-forced out the left side

Question 9

What type of packing are used to promote efficient operation of plunger/piston pumps?

Answer 9

V or U packing for plunger type

And

Cast iron rings or cup or u ring packing

Question 10

Why is a diaphragm pump used?

Answer 10

Separates the pumped fluid from the mechanism

Question 11

What are the different types of check valves used?

Answer 11

Ball check valves: used where free opening of suction and discharge is needed.

Stem guided check valves: used for low pressures

Wing guided check valves: moderate or high pressures

Flap check valves: low pressures and free flow semi solids

Question 12

What types of flow do rotary pumps produce?

Answer 12

Fixed delivery

Variable delivery

Question 13

What is a rotary pump used for?

Answer 13

Fuel, lubricants, hydraulic oil and other liquids of various viscosity’s

Question 14

What is fixed delivery?

Answer 14

Always delivery the same volume at a given speed.

Question 15

What is variable delivery?

Answer 15

Delivering volumes varying from zero to a given maximum.

Question 16

Describe the action of of external and internal gear pumps?

Answer 16

Fluid enters the pump at the inlet port into the space between the gear teeth

It is then carried around the casing to the discharge port.

At the discharge port the meshing of the teeth restrict the oil from returning to the inlet.

Question 17

Describe the action of sliding vane pumps?

Answer 17

Fluid is drawn into the chambers at the inlet side and carried around by vanes

As the chamber passes over the outlet the chamber reduces in size and the fluid is forced out.

Question 18

What is the difference between balanced and unbalanced vane pumps?

Answer 18

Balanced vane pumps have a two inlets and two outlets. Fluid is drawn in and discharged during each half revolution.

Unbalanced pumps need heavy duty bearings

Question 19

What is special about the variable capacity vane pump?

Answer 19

When the rotor is centred there is no pumping action.

When the ring is at its highest point it’s suction and discharge are opposite then when it is at its lowest point.

Question 20

What vane pump has a oval rotor rotating centrally in the housing?

Answer 20

External vane pump

Question 21

What are the applications for the flexible tube pump, flexible liner pump and the flexible vane pump?

Answer 21

Flexible tube pump used for: measured flow of liquids such as food products, paint, chemicals, slurry, sludge and pulp

Flexible liner pump is similar to flexible tube pump.

Flexible vane pump is used to: transfer liquids

Question 22

Which pump uses different sets of lobes timed to mesh together and move liquid?

Answer 22

Lobe pump

Question 23

What type of pump can have multiple screws?

Answer 23

Screw pumps

Question 24

How does a axial piston pump work?

Answer 24

The drive shaft rotates the cylinder block and pistons

When the housing angle is other then 0 degrees the distance between the piston and valves continually change.

Each piston moves away from the valve surface causing suction and inflow.

Each piston valve moves toward the valve surface during the second half of revolution causing compression and discharge

Question 25

How is capacity regulated in a positive displacement pump?

Answer 25

By varying their speed.

Question 26

Why/how is pressure relieved from a positive displacement pump.

Answer 26

If a line were to become blocked the pump would stall and be damaged.

A pressure relief valve is installed

Question 27

What is the correction needed if the pump is leaking around the shaft?

Answer 27

Inspect the bearing and replace if needed. Replace shaft seal as specified.

Question 28

What is the symptom and the correction needed if the oil viscosity is to high for the pump to pick up and prime?

Answer 28

Pump does not deliver fluid

Use thinner oil and follow recommendations for temperature and service

Heat oil for cold weather start up

Question 29

What corrective action should be taken if oil is freely re-circulating to the tank through the system?

Answer 29

Check the directional control valve.

The valve return line may be open

Question 30

How would you test for a small air leak on the pump suction line?

Answer 30

Pour pumped fluid on the joints while listening for a change in sound of operation

Question 31

What are the symptoms of a partially clogged intake line or filter?

And how do you repair it?

Answer 31

Pump makes unusual noise

Clean lines and filter to prevent cavitation