Pump Theory Flashcards
Positive displacement pumps are mechanical devices capable of?
Increasing the volume of the chamber. Water is drawn into the chamber as the volume is increased and in turn is forced out as the volume is decreased
What is the theory of positive displacement based on?
That water is a non-compressible fluid and will, therefore, occupy a volume directly proportional to the weight
Slip is?
Leakage between internal parts of the pump
True or false
Air as well as water can be drawn into and expelled by a positive displacement pump. These pumps are, therefore, capable of producing sufficient vacuum prime themselves
True
Piston pumps are used for?
Pumping small volumes of water at extremely high pressures
Rotary type positive displacement pumps consist of
A casing divided into separate suction and discharge chambers by a rotor
In a positive displacement pump, as speed increases
The amount of water pumped increases proportionately
Rotary pumps take pressure advantage of
Hydrants
Displacement factors:
Theoretical displacement is?
Every time the pump turns over once, it moves a certain amount of water from the suction side to the discharge side of the pump
Displacement factors:
Actual displacement is
Pressure on the discharge side pushes some water back into the suction. Water slips back through pump clearances.
Displacement factors:
Volumetric efficiency
= Actual displacement x 100
Theoretical displacement
Rotary pumps are not good for high-pressure; most manufacturers do not recommend pressures higher than?
300 psi
Rotary gear pumps
Two intermeshing gears or cams revolving in opposite directions within a close fitting casing.
Rotors move away from each other on the suction side and toward each other on the discharge side.
Rotary vane pumps
Consists of a single rotor within, and eccentric to, a casing. A series of slots in the rotor permit sliding vanes to move in and out, maintaining contact the surface of the casing by means of centrifugal action in rotation of the rotor.
Centrifugal means
To proceed away from the center, to develop outward; the energy to impel an object outward from a center rotation.
Diffusion impellers
Diffusion: water directed toward the discharge outlet by means of a series of stationary diffusion vanes fastened to or part of the inner wall of the pump casing.
Volute impeller
Spiral shaped casing
Combination impeller
Spiral shaped casing with stationary diffusion vanes
The volute principle
To enable the pump to handle the increasing quantity of water, at the same time permitting the velocity of the water to remain constant
The impeller
creates a velocity in the water which is converted into pressure as it approaches the confining space of the discharge pipe.
Displacement factors in centrifugal pumps
- When pumping at constant pressure, the quantity of water is directly proportional to speed of the pump
New quantity = new pump speed
——————— X old quantity
Old pump speed
Displacement factors in centrifugal pumps
2 when pumping at constant quantity, pressure is directly proportional to the square of the speed
2
New pressure = (new pump speed)
———————- X old pressure
(Old pump speed )
Has the priming line discharge above the eye of the impeller
Waterous pump
Has the priming line discharge at the eye of the impeller
Hale pump
