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4th Year Millwright JD > Dynamic pumps > Flashcards

Dynamic pumps Flashcards

1
Q

What is specific gravity?

A

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.

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2
Q

What is the conversion of psi to kpa?

A

1 psi = 6.9 kpa

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3
Q

What is the formula to determine pressure?

A

Pressure=force / area

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4
Q

What is atmospheric pressure?

A

14.7 psia

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5
Q

How much pressure is lost with elevation gain?

A

Approx 1/2 psi per 1000 feet gain

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6
Q

What is head pressure?

A

It is the height, in feet, of a column of water that is one foot square at the base

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7
Q

What does water weigh?

A

62.4 lbs/cubic foot

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8
Q

How much pressure is on One cubic foot of headwater?

A

.433 psi

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9
Q

What is differential pressure?

A

It is the difference between the discharge pressure and the suction pressure

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10
Q

What is vapour pressure?

A

It is the pressure at which a liquid flashes into a vapour at a given temperature

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11
Q

When the Pressure increases what happens to the boiling point?

A

The boiling point also increases

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12
Q

What are some causes of turbulent flow

A

Bends, abrupt changes in cross-section, fittings in the pipe, velocity that is too high

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13
Q

In Bernoulli’s principle, what are the two types of energy that make up total head?

A

Head pressure, velocity head

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14
Q

What is the difference between static head, and dynamic(or total) head

A

Static is the distance, and dynamic is the distance plus all the energy needed to move the fluid

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15
Q

What is net positive suction head?

A

It is a measure of head at the pump suction. It is commonly referred to as npsha or net positive suction head available

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16
Q

How is net positive section head required determined?

A

It is done by the pump manufacturers testing

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17
Q

The npsha should be at least how much more than npshr?

A

10% higher

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18
Q

What is another name for radial pumps?

A

Centrifugal pump

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19
Q

What creates the kinetic(speed,velocity) energy?

A

The impeller

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20
Q

Describe an axial pump

A

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.

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21
Q

Describe a radial (centrifugal) pump.

A

Discharge is perpendicular to the intake, has reasonably high discharge head.

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22
Q

What is the only pump that has straight blades?

A

High speed peripheral pumps. They can reach 25,000 rpm and head capabilities of 12,000 feet

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23
Q

Where would you find a stripper?

A

They are in a regenerative turbine pump, Inbetween the suction and discharge ports

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24
Q

What is the most common centrifugal pump?

A

Single stage, end suction pump.

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25
What is the benefit of the vertical single stage end suction pump?
It saves space because pump can be incorporated in the piping
26
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.
27
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
28
What are the three types of impellers?
Open, semi open, closed
29
What are the shaped lines running from the center outward on the back side of the impeller?
Pump out vanes
30
What is a drawback of the open impeller?
The vanes are weak and bend easily.
31
Where are the fixed bearings normally located?
Typically on the coupling end
32
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.
33
What is considered the most efficient impeller design?
The Francis impeller. It has double curved vanes.
34
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
35
What are the four types of pump casings?
Volute, double volute, concentric, diffuser
36
In a volute casing how much can you vary the capacity?
The impeller can be trimmed by 20%
37
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%
38
When should wear rings be replaced?
When they reach three times the initial clearance
39
Where would you find renewable sleeves on the shaft?
On medium and large pumps
40
What is the most common driver for centrifugal pumps
Electric motors
41
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
42
What position should gate valves be in?
Valves should be only fully open or fully closed and never used for throttling
43
How big should a inverted suction strainer be?
Ideally they are four times the surface area of the pipes ID
44
What is another name for the inverted cone suction strainer
Witches hat
45
What is the purpose of an expansion joint
They help eliminate pipe strain on the pump flanges due to thermal growth or misalignment
46
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
47
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
48
What is a simple test to check for cavitation?
Throttle the discharge valve.
49
What does increasing the impeller eye size do?
Increases the capacity, or GPM
50
What does increasing the OD of the impeller do?
It increases the pressure, and to a smaller extent the capacity.
51
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
52
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
53
How big should the foundation be relative to the pump?
It should be 2.5 times the mass of the pump
54
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 ```
55
How much should compression pickings leak, as a rule of thumb?
40 drops per minute
56
If performance gradually decreases, what is likely the problem.
Component wear. An abrupt failure could be something broke, plugged, or a valve accidentally closed
57
How can a suction or discharge line be isolated, before maintenance is performed?
By using blinds (pancake or spectacle). Never trust a valve
58
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"
59
What should never be used to loosen a stuck impeller?
Heat
60
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
61
Describe NPSH
The amount of energy in the liquid, measured at the suction eye center line
62
Describe total static head
The vertical distance from supply liquid level, to liquid discharge level
63
What are inducers used for?
High speed pumps. It feeds flow into the eye of impeller
64
Name two styles of peripheral pumps
High speed and regenerative
65
Name for single stage end suction pump casing types
Volute Double volute Concentric - produces the highest radial load Diffuser- no radial loading
66
When should wear rings be replaced?
When the clearances reach three times the minimum clearance
67
What is a thrust pot?
It is an extra bearing housing usually used in turbines to support the shaft
68
Where is suction lift or section head measured from?
From the fluid surfaces to the centreline of the pump
69
.Between balance disc, drums, combination disk and drum which is the simplest?
The balance drum
70
Which balancing device uses an intermediate relief chamber?
The combination disk and drum
71
How can the flow be changed on some reciprocating plunger pumps?
Either the stroke or the speed can be changed
72
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
73
Does the diaphragm pump require a relief valve?
Yes unless it indicated that it is only run at shop air pressure
74
Can a plunger pump be double acting?
No
75
How many pumping chambers does a triplex pump have?
3
76
What kind of positive displacement pump has a rotor and elastomeric stator?
Progressive cavity
77
If you have a double-acting duplex pump how many times will fluid be delivered per revolution?
4
78
Two pumps can be referred to as peristaltic what are they?
The progressive cavity, and flexible tube
79
If a pump has suction lift what is used to help prime the pump?
Foot valve
80
When discharge pressure exceeds air pressure on the air powered diaphragm pump, what happens?
It stops

4th Year Millwright JD (14 decks)

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