Pumps (Positive Displacement) Flashcards
Where are positive displacement pumps used?
Used where constant flow or a measure amount of flow is critical.
Reciprocating
Rotary
What are the two classifications of displacement pumps?
Reciprocating
Rotary
Define volumetric efficiency of a displacement pump?
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%
What are the two types of reciprocating pumps? What type of flow is produced?
Piston/plunger
Diaphragm
They both increase and decrease the area of the cavity, which pumps the fluid
What does the volume of liquid per stroke depend on?
Cross sectional area of the piston, plunger, or diaphragm and on the length of stroke.
What is the difference between plunger and piston pumps?
Plunger pump has its plunger sliding inside packing
Piston pump has its packing sliding with its piston
Describe the operating principle of a single acting plunger/piston pump?
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
Described operating principles of a double acting piston pump?
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
What type of packing are used to promote efficient operation of plunger/piston pumps?
V or U packing for plunger type
And
Cast iron rings or cup or u ring packing
Why is a diaphragm pump used?
Separates the pumped fluid from the mechanism
What are the different types of check valves used?
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
What types of flow do rotary pumps produce?
Fixed delivery
Variable delivery
What is a rotary pump used for?
Fuel, lubricants, hydraulic oil and other liquids of various viscosity’s
What is fixed delivery?
Always delivery the same volume at a given speed.
What is variable delivery?
Delivering volumes varying from zero to a given maximum.
Describe the action of of external and internal gear pumps?
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.
Describe the action of sliding vane pumps?
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.
What is the difference between balanced and unbalanced vane pumps?
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
What is special about the variable capacity vane pump?
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.
What vane pump has a oval rotor rotating centrally in the housing?
External vane pump
What are the applications for the flexible tube pump, flexible liner pump and the flexible vane pump?
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
Which pump uses different sets of lobes timed to mesh together and move liquid?
Lobe pump
What type of pump can have multiple screws?
Screw pumps
How does a axial piston pump work?
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
How is capacity regulated in a positive displacement pump?
By varying their speed.
Why/how is pressure relieved from a positive displacement pump.
If a line were to become blocked the pump would stall and be damaged.
A pressure relief valve is installed
What is the correction needed if the pump is leaking around the shaft?
Inspect the bearing and replace if needed. Replace shaft seal as specified.
What is the symptom and the correction needed if the oil viscosity is to high for the pump to pick up and prime?
Pump does not deliver fluid
Use thinner oil and follow recommendations for temperature and service
Heat oil for cold weather start up
What corrective action should be taken if oil is freely re-circulating to the tank through the system?
Check the directional control valve.
The valve return line may be open
How would you test for a small air leak on the pump suction line?
Pour pumped fluid on the joints while listening for a change in sound of operation
What are the symptoms of a partially clogged intake line or filter?
And how do you repair it?
Pump makes unusual noise
Clean lines and filter to prevent cavitation
