Pumps

Question 1

Give the equation of heads and what do the components stand for?

Answer 1

Hs=hss+hps+hvs-hfs.

Hs is the total suction head. hss is the static suction head. hps is the pressure suction head. hvs velocity suction head. hfs is frictionsuction head

Question 2

Name the three classes of pumps

Answer 2

Centrifugal, axial flow, positive displacement pumps

Question 3

Which is the most popular class of pump on ships and why?

Answer 3

Centrifugal pumps. Can be used an all systems. Convert energy of prime mover first into kinetic energy then into pressure energy.

Question 4

Name the two main outs of a centrifugal pump

Answer 4

Impeller and volute (diffuser). Impeller rotating part and volute is the stationary part

Question 5

What is capacity and what does it depend on?

Answer 5

The flow rate with which the liquid is moved/pushed by the pump. Depends on: liquid characteristics, size of pump and inlet and outlet sections, impeller size, impeller rpm, size and shape of cavities between vanes

Question 6

Giv ethe dynamic pressure equation

Answer 6

0.5ρV^2

Question 7

What is NPSH

Answer 7

Net positive suction head

Question 8

What is static suction head?

Answer 8

The head resulting from elavation of the liquid relative to the pump centre line

Question 9

Give some impacts of cavitation on pumps

Answer 9

Reduction in capacity if pump, decrease in devolved head, damage to pump parts, mechanical deformations, sounds vibrations, corrosion (erodes protective layers so then corrosion)

Question 10

Give the equation for NPSHa and for a pump to work what is the condition between NPSHr and NPSHa?

Answer 10

NPSHa=Hs-hvp.

NPSHa>NPSHr
Actual>required