Dynamic Pumps

Question 1

What is S.G.?

Answer 1

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

Question 2

What is gauge pressure if the gauge reads 20 psi?

Answer 2

20 psig

Question 3

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

Answer 3

34.7 psia

20+14.7

Question 4

What is head pressure?

Answer 4

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

Question 5

What is the formula for head pressure?

Answer 5

Psi= ft x 0.433 x S.G.

Question 6

What is vapour pressure?

Answer 6

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

Question 7

What is cavitation?

Answer 7

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.

Question 8

What is aeration?

Answer 8

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

Question 9

What is Bernoulli’s principle?

Answer 9

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.

Question 10

What is velocity head?

Answer 10

Energy in a system due to the liquids velocity.

Question 11

What is friction head?

Answer 11

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

Question 12

What is suction head?

Answer 12

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

Question 13

What is a positive suction head?

Answer 13

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

Question 14

What is total suction head?

Answer 14

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

Question 15

What is suction lift?

Answer 15

Where the supply reservoir is located below the pump.

Question 16

What is static discharge head?

Answer 16

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

Question 17

What is total head?

Answer 17

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.

Question 18

What is net positive suction head?

Answer 18

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

Question 19

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

Answer 19

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.

Question 20

What are the 4 main categories of dynamic pumps?

Answer 20

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

Question 21

How does a radial-flow centrifugal pump work?

Answer 21

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.

Question 22

Characteristics and main parts behind an axial-flow pump?

Answer 22

• 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.

Question 23

Characteristics and main idea of a mixed-flow pump?

Answer 23

• 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.

Question 24

Characteristics and types of peripheral pumps?

Answer 24

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.

2. 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

Question 25

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

Answer 25

Used for low capacities and specific speeds or special applications. Horizontal version and vertical version.

Question 26

Vertical column pit pumps?

Answer 26

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.

Question 27

Single stage double suction pumps?

Answer 27

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.

Question 28

Multi stage horizontal pumps?

Answer 28

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.

Question 29

Multi stage barrel pumps?

Answer 29

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.

Question 30

Single stage axial flow pumps

Answer 30

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

Question 31

Vertical turbine pumps?

Answer 31

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

Question 32

What are the effects of viscosity on a pump curve?

Answer 32

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.

Question 33

What is the head curve or head-capacity curve?

Answer 33

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

Question 34

What is the best efficiency point?

Answer 34

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