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Millwright 4th Year > Dynamic Pumps > Flashcards

Dynamic Pumps Flashcards

1
Q

What is S.G.?

A

Specific gravity, the ratio of the density of a substance to that of water.

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2
Q

What is gauge pressure if the gauge reads 20 psi?

A

20 psig

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3
Q

What is the absolute pressure if the gauge reads 20 psig?

A

34.7 psia

20+14.7

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4
Q

What is head pressure?

A

The height in feet of a column of water that is one foot square at the base.

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5
Q

What is the formula for head pressure?

A

Psi= ft x 0.433 x S.G.

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6
Q

What is vapour pressure?

A

Pressure at which a liquid flashes into a vapour (boil) at a given temperature.

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7
Q

What is cavitation?

A

When the pressure of a liquid is reduced to or below it’s vapor pressure, small bubbles or pockets of vapor called cavitation begin to form as these vapor bubbles move to regions of higher pressure they collapse ore implode.

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8
Q

What is aeration?

A

Where a partial vacuum is created at the pump inlet, which can draw in air and reduce the pumps capacity.

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9
Q

What is Bernoulli’s principle?

A

That as a liquid or gas passes through a pipe, if it comes to a larger section of pipe the velocity will decrease while the pressure increases.

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10
Q

What is velocity head?

A

Energy in a system due to the liquids velocity.

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11
Q

What is friction head?

A

The friction the liquid has while passing through the pipes reducing the amount of head or pressure available.

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12
Q

What is suction head?

A

When the level of the supply liquid is above the centreline of the pump.

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13
Q

What is a positive suction head?

A

It means the weight of the liquid and the atmospheric pressure are able to push the fluid into the pump.

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14
Q

What is total suction head?

A

Is the static suction head on the pump suction line above the pump centreline minus all the frictional losses.

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15
Q

What is suction lift?

A

Where the supply reservoir is located below the pump.

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16
Q

What is static discharge head?

A

The vertical distance from the centre of the suction eye to the surface of the liquid in the discharge tank.

17
Q

What is total head?

A

The measure of the work the pump foes to raise the liquid from the level in the suction tank to the level in the discharge tank for a given flow.

18
Q

What is net positive suction head?

A

Suction head in feet absolute above the vapour pressure of the fluid at the pump suction.

19
Q

What is the net positive suction head required? (NPSHR)

A

Amount of head used to overcome friction and increase the velocity of the fluid as it flows from the suction flange of the pump through the eye of the impeller and onto the vanes.

20
Q

What are the 4 main categories of dynamic pumps?

A
  1. Radial-flow centrifugal pumps
  2. Axial-flow pumps
  3. Mixed-flow pumps
  4. Peripheral pumps
21
Q

How does a radial-flow centrifugal pump work?

A

The water that flows through the centre of the impeller follows the path dictated by the blades in the casing. The centra fugal force flings it outward so it gains velocity. The liquid then enters the collector, a casing that surrounds the impeller, which slows the liquid to a useable velocity and converts the kinetic or velocity energy into pressure energy.

The 2 basic forms of the collector are the volume and the diffuser.

22
Q

Characteristics and main parts behind an axial-flow pump?

A
  • No radial component to the discharge from its impeller.
  • Produces it’s head by the pushing action of the vanes on the liquid.
  • No change in the direction of flow, which moves through the purple like casing parallel to the shaft.
  • Relatively low discharge head but produces large flow.
23
Q

Characteristics and main idea of a mixed-flow pump?

A
  • Have both radial and axial components to the discharge from there impellers.
  • Develops it’s discharge by using centrifugal force and the lifting action of the vanes on the liquid.
24
Q

Characteristics and types of peripheral pumps?

A
  1. High speed pumps
  • Run at extremely high speeds.
  • liquid enters the eye of the impeller and makes a number of rotations within the forced vortex. The orbits gradually increase until the liquid exits the concentric housing and the diffuser nozzle that converts that velocity head into the head pressure.
  1. Regenerative turbine pumps
  • Relatively high heads and low flow applications
  • Generally a solid disk with a double row of straight cut or impulse type buckets cut around his periphery
25
Q

What is a Single stage end suction pump and what are there characteristics?

A

Used for low capacities and specific speeds or special applications.

Horizontal version and vertical version.

26
Q

Vertical column pit pumps?

A

Run submerged in their own liquid. Have long shafts and may incorporate plain bearings when running in a compatible liquid.

Sometimes use cantilever shafts that are normally heavier to prevent excessive impeller-end vibration.

27
Q

Single stage double suction pumps?

A

Axially (horizontally) split for head and capacity ratings exceeding those of the previous single overhung designs.

Cast casing
Includes a single suction inlet that splits to allow equal flow to each side of the impeller and a volute that continues around both the top and bottom halves of the casing.

Opposing forces that balance out axial loads.

28
Q

Multi stage horizontal pumps?

A

Pressure increases progressively as the liquid moves from one end to the other, axial thrust must be balanced out using thrust bearings or special balancing discs or drums.

Diaphragm or stage piece is used to isolate the different pressures.

29
Q

Multi stage barrel pumps?

A

Multi stage pump installed in a one piece outer casing that has radially split ends and retains any hazardous leaks that the pump fluid may produce.

30
Q

Single stage axial flow pumps

A

Frequently called a propeller pump, handles large capacities at low heads.

31
Q

Vertical turbine pumps?

A

Consist of a series of conventional impellers (radial or mixed flow) separates by diffusers or bowls.

Impellers are held in place by split tapered bushings also called Collets

32
Q

What are the effects of viscosity on a pump curve?

A

Pumps curves are usually generated using water if the viscosity of the fluid being pumped is similar to water, there is no effect on the curve.

Viscosity is defined as resistance to flow, increasing the viscosity of a fluid affects the efficiency of a pump therefore, an increase can also affect the pump curve.

33
Q

What is the head curve or head-capacity curve?

A

Efficiency is the ratio of output (hydraulic) horsepower to input horsepower.

34
Q

What is the best efficiency point?

A

Where the flow rare and total head developed by the pump coincide with the maximum efficiency.

Millwright 4th Year (15 decks)

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