Question

best answer (select only the best or closest answer)

1. what type of pump is not seriously damaged if the discharge valve is close for a short time when the pump is running.

a centrifugal pump
b lobe pump
c piston pump
d positive cavity pump

1. why are check valves used in conjunction with centrifugal pumps?

a. to prevent wastewater in the suction line from flowing back into the wet well
b. to regulate the rate of wastewater flow through the discharge pipe
c. to equalize the pressure on both of the impellers
d. to prevent wastewater in the discharge line from flowing back into the wet well

1. a pump is delivering less than expected rate of discharge. what causes this to happen?

a. discharge head too low
b. discharge head too high
c. pump is primed
d. check valve open

1. a positive displacement sludge pump should never be placed into operation

a. none of the below
b. with the discharge valve open
c. with the discharge valve closed
d. without being primed

Explanation:

1. Centrifugal pumps can handle short - term closure of the discharge valve as they have a different operating principle compared to positive displacement pumps (lobe, piston, positive cavity). Positive displacement pumps are more prone to damage if discharge is blocked.
2. Check valves with centrifugal pumps prevent back - flow from the discharge line (higher pressure side) to the wet well. Option a is about suction line which is not the main function here. Option b is for regulating flow (not check valve's main role). Option c is incorrect as it's not about impeller pressure equalization.
3. A high discharge head (resistance) can cause a pump to deliver less flow. A low discharge head would allow more flow (if other factors are constant). If the pump is primed (option c), it should operate better. A check valve open (option d) is normal for flow.
4. Positive displacement sludge pumps should not be operated with the discharge valve closed as it can cause excessive pressure build - up. Operating without priming (option d) is also an issue, but in the context of the question, the main concern among the options is the discharge valve.

Answer:

1. a. Centrifugal pump
2. d. To prevent wastewater in the discharge line from flowing back into the wet well
3. b. Discharge head too high
4. c. With the discharge valve closed