OIT OIT Pumping Systems and Hydraulics 2 — Questions and Answers
Question 1: What is water hammer and what causes it?
- Excessive pump speed causing bearing failure
- Pressure surge caused by rapid change in fluid velocity, such as sudden valve closure (Correct answer)
- Vibration from an unbalanced pump impeller
- Air trapped in suction piping during priming
Correct answer: Pressure surge caused by rapid change in fluid velocity, such as sudden valve closure
Water hammer is a pressure surge or wave caused by a sudden change in fluid velocity, commonly triggered by rapid valve closure or pump shutdown.
Question 2: What is the function of a pressure relief valve in a pumping system?
- To maintain a constant flow rate through the pump
- To automatically release excess pressure and protect system components from overpressure (Correct answer)
- To prime the pump before startup
- To reduce friction losses in the suction line
Correct answer: To automatically release excess pressure and protect system components from overpressure
A pressure relief valve automatically opens to discharge fluid when system pressure exceeds a set limit, protecting pipes and equipment from damage.
Question 3: What does pump efficiency measure?
- The ratio of water delivered to water withdrawn from the source
- The ratio of hydraulic power output to shaft power input (Correct answer)
- The ratio of motor horsepower to pump horsepower
- The percentage of time the pump operates without failure
Correct answer: The ratio of hydraulic power output to shaft power input
Pump efficiency is the ratio of the hydraulic power imparted to the fluid to the mechanical shaft power supplied to the pump.
Question 4: If a pump is operating to the right of its best efficiency point (BEP) on its curve, what is likely happening?
- The pump is operating at too high a head
- The pump is moving more flow than its design point, potentially causing cavitation and overheating (Correct answer)
- The pump is running backwards
- The motor is underpowered for the system
Correct answer: The pump is moving more flow than its design point, potentially causing cavitation and overheating
Operating to the right of BEP means the pump is moving excess flow, which can lead to cavitation, motor overloading, and reduced pump life.
Question 5: What is the purpose of a variable frequency drive (VFD) on a pump motor?
- To increase the pump's maximum flow capacity
- To adjust pump speed to match varying system demand and save energy (Correct answer)
- To provide emergency power during outages
- To prevent motor overheating by reducing voltage
Correct answer: To adjust pump speed to match varying system demand and save energy
A VFD varies the motor speed (and thus pump output) to match system demand, saving significant energy compared to running pumps at full speed constantly.
Question 6: What is the affinity law relationship between pump speed and flow rate?
- Flow rate varies as the square of speed
- Flow rate varies directly (linearly) with speed (Correct answer)
- Flow rate varies as the cube of speed
- Flow rate is independent of pump speed
Correct answer: Flow rate varies directly (linearly) with speed
According to the affinity laws, flow rate varies directly (proportionally) with pump speed — doubling speed doubles flow rate.
OIT OIT Pumping Systems and Hydraulics 2
What is water hammer and what causes it?