Dynamic pumps Flashcards
What is specific gravity?
It is the ratio of the density compared to cool water. SG of water is 1. Less than 1 is lighter than water and more than 1 is heavier than water.
What is the conversion of psi to kpa?
1 psi = 6.9 kpa
What is the formula to determine pressure?
Pressure=force / area
What is atmospheric pressure?
14.7 psia
How much pressure is lost with elevation gain?
Approx 1/2 psi per 1000 feet gain
What is head pressure?
It is the height, in feet, of a column of water that is one foot square at the base
What does water weigh?
62.4 lbs/cubic foot
How much pressure is on One cubic foot of headwater?
.433 psi
What is differential pressure?
It is the difference between the discharge pressure and the suction pressure
What is vapour pressure?
It is the pressure at which a liquid flashes into a vapour at a given temperature
When the Pressure increases what happens to the boiling point?
The boiling point also increases
What are some causes of turbulent flow
Bends, abrupt changes in cross-section, fittings in the pipe, velocity that is too high
In Bernoulli’s principle, what are the two types of energy that make up total head?
Head pressure, velocity head
What is the difference between static head, and dynamic(or total) head
Static is the distance, and dynamic is the distance plus all the energy needed to move the fluid
What is net positive suction head?
It is a measure of head at the pump suction. It is commonly referred to as npsha or net positive suction head available
How is net positive section head required determined?
It is done by the pump manufacturers testing
The npsha should be at least how much more than npshr?
10% higher
What is another name for radial pumps?
Centrifugal pump
What creates the kinetic(speed,velocity) energy?
The impeller
Describe an axial pump
There is no change in the direction of flow. It is also known as a propellor pump. They produce low discharge head, but large volume of flow.
Describe a radial (centrifugal) pump.
Discharge is perpendicular to the intake, has reasonably high discharge head.
What is the only pump that has straight blades?
High speed peripheral pumps. They can reach 25,000 rpm and head capabilities of 12,000 feet
Where would you find a stripper?
They are in a regenerative turbine pump, Inbetween the suction and discharge ports
What is the most common centrifugal pump?
Single stage, end suction pump.
What is the benefit of the vertical single stage end suction pump?
It saves space because pump can be incorporated in the piping
What is benefit of a single stage double suction pump?
It has a single suction inlet that then splits to allow flow to both sides. The opposing forces on either side cancel each other out, so it limits axial thrust.
What pump handles the most amount of pressure?
Multi stage barrel pumps. Handles pressures up to 6500 psi and 20,000 gpm. It has a double casing
What are the three types of impellers?
Open, semi open, closed
What are the shaped lines running from the center outward on the back side of the impeller?
Pump out vanes
What is a drawback of the open impeller?
The vanes are weak and bend easily.
Where are the fixed bearings normally located?
Typically on the coupling end
What is the big benefit of a double suction impeller?
Because of the two suction intakes, it is hydraulically balanced, and has minimal axial thrust. Because it requires two stuffing boxes, it is not recommended for abrasive service.
What is considered the most efficient impeller design?
The Francis impeller. It has double curved vanes.
Describe an axial flow impeller.
Also known as a propeller. It moves the liquid parallel with the shaft. These move large quantities of liquid at low head
What are the four types of pump casings?
Volute, double volute, concentric, diffuser
In a volute casing how much can you vary the capacity?
The impeller can be trimmed by 20%
Describe a diffuser casing
It has a series of stationary curved beans with each space between the two vanes gradually expanding to slow the liquid down. This converts velocity head into pressure head and there is no radial thrust. The impeller can only be trimmed 5 to 10%
When should wear rings be replaced?
When they reach three times the initial clearance
Where would you find renewable sleeves on the shaft?
On medium and large pumps
What is the most common driver for centrifugal pumps
Electric motors
What is the difference between a dual drive or tandem drive pumps
Dual drives that have one of two drivers operating at one time, and tandem drives have two drives operating simultaneously
What position should gate valves be in?
Valves should be only fully open or fully closed and never used for throttling
How big should a inverted suction strainer be?
Ideally they are four times the surface area of the pipes ID
What is another name for the inverted cone suction strainer
Witches hat
What is the purpose of an expansion joint
They help eliminate pipe strain on the pump flanges due to thermal growth or misalignment
What are some common problems that could result in low flow?
Blockage, pump needs to be primed, air leaks, motor turning the wrong rotation, insufficient NPSHA, worn parts, inadequate foot valve size
How should an elbow be in relation to the straight piping on the suction side?
A minimum of 10X the pipe diameter of straight pipe between the elbow and the pump suction to avoid swirl or uneven flow
What is a simple test to check for cavitation?
Throttle the discharge valve.
What does increasing the impeller eye size do?
Increases the capacity, or GPM
What does increasing the OD of the impeller do?
It increases the pressure, and to a smaller extent the capacity.
What is water hammer? How can you help control it?
Opening, or closing a valve too quickly cause a shock wave to travel up and down a pipe. A long stem gate valve will take a long time to close and slow down how fast the flow is stopped
What is hydraulic slap?
When a pump stops with the discharge valve left open. The pressure difference between the suction head discharge head quickly closes the check valve creating the slap
How big should the foundation be relative to the pump?
It should be 2.5 times the mass of the pump
What are some causes of excessive power consumption?
Tight packing Tight mechanical seals High viscosity, or specific gravity Bent shaft Wrong rotation Faulty motor windings excessive flow
How much should compression pickings leak, as a rule of thumb?
40 drops per minute
If performance gradually decreases, what is likely the problem.
Component wear. An abrupt failure could be something broke, plugged, or a valve accidentally closed
How can a suction or discharge line be isolated, before maintenance is performed?
By using blinds (pancake or spectacle). Never trust a valve
Where should readings take place to determine wear?
Shaft radial runout
Shaft radial movement
Stuffing box squareness
Shaft axial movement
As a rule of thumb, none of these should be more than .003”
What should never be used to loosen a stuck impeller?
Heat
What does NPSH stand for?
Net positive suction head. It can either be
a for available or
r for required. NPSHa must be higher than NPSHr
Describe NPSH
The amount of energy in the liquid, measured at the suction eye center line
Describe total static head
The vertical distance from supply liquid level, to liquid discharge level
What are inducers used for?
High speed pumps. It feeds flow into the eye of impeller
Name two styles of peripheral pumps
High speed and regenerative
Name for single stage end suction pump casing types
Volute
Double volute
Concentric - produces the highest radial load
Diffuser- no radial loading
When should wear rings be replaced?
When the clearances reach three times the minimum clearance
What is a thrust pot?
It is an extra bearing housing usually used in turbines to support the shaft
Where is suction lift or section head measured from?
From the fluid surfaces to the centreline of the pump
.Between balance disc, drums, combination disk and drum which is the simplest?
The balance drum
Which balancing device uses an intermediate relief chamber?
The combination disk and drum
How can the flow be changed on some reciprocating plunger pumps?
Either the stroke or the speed can be changed
Name some benefits of a diaphragm pump?
They are self priming, they can be used to vary output through metering, there is no contamination because it’s self contained and they can be run dry
Does the diaphragm pump require a relief valve?
Yes unless it indicated that it is only run at shop air pressure
Can a plunger pump be double acting?
No
How many pumping chambers does a triplex pump have?
3
What kind of positive displacement pump has a rotor and elastomeric stator?
Progressive cavity
If you have a double-acting duplex pump how many times will fluid be delivered per revolution?
4
Two pumps can be referred to as peristaltic what are they?
The progressive cavity, and flexible tube
If a pump has suction lift what is used to help prime the pump?
Foot valve
When discharge pressure exceeds air pressure on the air powered diaphragm pump, what happens?
It stops
