Pumps Flashcards
What is the work of pumping
Discharging a quantity of liquid or gas against a resistance. The force exerted on the fluid increases its velocity or pressure.
In what ways do pumps exerted force?
Centrifugal force
Jet or propulsion force
Displacement
The amount of force required to move a substance depends on?
The materials density, height it must be raised, friction in the piping, and the pressure pumped against.the forces which a pump must overcome is called total pump head.
Gravity and non- gravity fed pumps
Gravity fed is self priming
Non gravity fed must utilize check valves on the suction or inlet to prevent backlog once the pump is stopped.
What happens to pressure in the suction line of a pump when it is started?
When the pump is started and the discharge line opens, the displacement of fluid decreases pressure in the suction line.the pressure must be so much as to allow the liquid to vaporize.
What is vaporization?
Vaporization occurs when the pressure in the suction line becomes lower than vapor pressure of the water at that temp.
(IE: restricted inlet valve and wide open discharge ) once past the restriction the steam flashes back into liquid under the increased pressure at the pump .
How much resistance does a 90° bend have?
As much as 16 ft. of straight pipe
Name the different types of pumps according to operation.
Reciprocating
Rotary
Jet
Centrifugal
Pumps classified by use.
Lift Force Circulating Vacuum Compressing
What are simplex, duplex, and triplex pumps.
These terms define how many cylinders the pump uses.
What is the most common cause of reciprocation pump failure?
Sticking or improper seating of suction or discharge valves.
Explain jet pumps.
They exert pumping action to move fluids. Jet pumps have no moving parts. Utilizes a fluid under high velocity by putting the fluid under high pressure and restricting it through a nozzle. The fluid around is sucked into the stream due to the effect of venturi.
Advantages of centrifugal pump (non positive displacement)?
Balanced rotation motion, absence of valves and pistons, uniform pressure and flow, freedom from shock, ability to handle dirty water, capable of high rpm ( direct coupling )p
What is work?
Work is said to be done when a body, acted upon by a force, moves in the direction the force is acting.
What is potential energy?
The energy which a body or system of bodies has by virtue of stresses, or “ the energy of postion”
What is kinetic energy?
The energy which a body has by virtue of its velocity.
What effect does going through the impeller and scroll case have on water?
The water leaving the periphery of the impeller retains the energy imparted to it by the driver of the pump, the pump transforms energy from kinetic energy to potential energy.
Classifications of centrifugal pumps?
Volute pumps- 2 parts - impeller secured to a shaft and casing having a spiral forming conforming to the curve known as the volute.
Diffusion ring or turbine pumps- 3 parts - impeller. Diffusion ring ( carries the diffusion vanes) and a casing. Purpose of the diffusion vanes are the same as the volute, to reduce velocity and increase the pressure of the water leaving the impeller.
Which classification of centrifugal pump should be used in high/low head situations.
The volute pump is best at handling large volumes of water at low heads and the diffuser ring type is used in high head situations.
The scroll case does what to the water?
Provides the means to convert the kinetic to potential ( pressure ) energy.
What is the function of rotating element in the pump?
Create and maintain the flow of liquid through the pump by converting mechanical power input to kinetic energy imparted to the fluid.
Describe the Impeller.
Sometimes referred to as the wheel or runner, it is the heart of the centrifugal pump.
What are the impeller types?
2 basic kinds single suction and double suction. Double suction runs more balanced and exerts no end thrust on the pump shaft.
Whats the purpose of clearance and labyrinth rings?
To increase efficiency of the pump by sealing the spaces between the impeller and casing and from the discharge to suction side of the impeller, also between stages.
Explain a stuffing box
A stuffing box is used at the casing and shaft connection. Uses packing in the glad and is cooled by clean water supplied through a seal or injection water inlet where it passes through a seal or lantern ring which distributes the water around the shaft.
What are the hydraulic functions of the pump casing?
To confine the liquid leaving the impeller, direct it to the discharge nozzle, and allow conversion from kinetic to potential or pressure energy.
What is head measured in?
Head is always measured in feet of liquid because the velocity formula is measured in feet.
One foot of pump head is?
The static force exerted by a column of water on foot high on an area of one square inch. Equal to .434 lbs of pressure
Total head of a pump?
Total head is the force needed to overcome the conditions which can change. Common causes of pump head change drive unit not keeping speed, pump wear, changes in piping, valves, load change or leakage, and change in temp and pressure.one foot of water pressure is .434 psi
What is Specific speed?
Rpm at which a geometrical similar impeller would operate if it were scaled down to discharge one gpm against one foot of head.
What is the purpose of the Francis vane?
To produce a high speed impeller of small diameter with sufficient vane surface to impart the required energy to the liquid to be pumped.
What are common causes of loss of efficiency in centrifugal pumps?
Loss due to recirculation from the impeller discharge to the impeller inlet, or through the space in between the impeller and pump casing. In multi stage pumps there are losses between stages as well. That is where clearance or labret rings are used.
Where is there common leakage on centrifugal pumps?
Leaking at the stuffing box. The direction of the leak depends on the internal and external pressure, it could result in loss of prime of the pump.
How tight should pump glands be tightened?
They must be adjusted enough the prevent air from entering the pump but tight enough to allow water to seep around the shaft. Too tight, and it will impose extra load on the pump.
Overview of pumps
Impeller. Specific speed. Capacity. Head
Radial. 200-2000. Small. High
Francis. 1800-2500. Medium. Medium
Mixed flow. 2000-3600. Large. Low
Propeller. 3000-7500. Larger. Lower
Screw. 6000-11000. Largest. 10ft or under
What is net positive suction head?
The pressure above vapor pressure of a liquid being pumped. Since centrifugal pumps cannot handle air pockets in the pump.
Describe a screw pump.
It has only three moving parts. A power rotor and two idler rotors.
