19 Pumps, Valves & Plant Equipment Practice Questions & Answers

1. 1. An operator is manually bringing a high-head high-service centrifugal pump online. What should be done with the discharge valve?

   • A.Open the discharge valve wide before starting the motor, so that the pump never runs against a closed head
   • B.Throttle the suction valve during starting and hold the discharge valve wide open until the flow steadies
   • C.Leave the discharge valve shut for the first ten minutes of running so the casing can warm and self-vent
   • D.Start with the discharge valve closed or nearly closed, then open it slowly once the pump is up to speed✓ Answer

   A centrifugal pump draws its least power at shutoff head, so starting against a closed or nearly closed discharge valve limits starting current and protects the motor from overload; the valve is then opened slowly to avoid a surge. Axial-flow (propeller) pumps are the exception and are started with the discharge open.

   Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 1 — centrifugal pump startup proceduresReport a problem with this question

2. 2. A raw-water pump that ran normally yesterday now rattles as though it were pumping gravel, its discharge pressure swings, and its capacity has dropped; the wet well has been drawn down near its low-level mark. What is happening?

   • A.Cavitation, because suction pressure has fallen below the vapor pressure and the bubbles collapse on the impeller✓ Answer
   • B.Water hammer, because a pressure surge from a fast valve movement is travelling along the discharge main
   • C.Reversed rotation, because the impeller is turning backward and can develop only a fraction of its head
   • D.Air binding, because a pocket of air is trapped in the impeller eye and the pump is only churning that air

   The gravel-like rattle, fluctuating discharge pressure and lost capacity with a low wet well are the classic signature of cavitation: the low suction level drops the pressure inside the pump below the water's vapor pressure, vapor bubbles form and then implode against the impeller vanes, pitting them. Air binding is cured by venting the casing, and water hammer is a surge event, not a continuous noise.

   Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 1 — cavitation symptoms and causesReport a problem with this question

3. 3. The net positive suction head available at a pump must stay above the net positive suction head required that the manufacturer publishes for it. Which condition lowers the head available?

   • A.A second pump has been placed in series downstream, raising pressure in the discharge main
   • B.The wet well has been refilled, raising the water level well above the pump suction bell
   • C.The suction strainer has partly plugged, adding friction loss on the suction side of the pump✓ Answer
   • D.The discharge valve has been throttled back, cutting the flow the pump delivers to the system

   Head available is the absolute pressure at the pump suction minus the vapor pressure, so anything that reduces suction-side pressure — a clogged strainer or partly closed suction valve, greater suction lift, a low wet well, warmer water or higher elevation — lowers it and pushes the pump toward cavitation. Raising the wet well level and throttling the discharge both work in the opposite direction, and downstream pressure has no effect on the suction.

   Source: Hydraulic Institute standards for centrifugal pumps — NPSH available versus NPSH requiredReport a problem with this question

4. 4. Two identical high-service pumps normally run one at a time. When the operator starts the second pump in parallel with the first on a system with substantial friction head, what should be expected?

   • A.The combined discharge head roughly doubles while the flow stays close to that of one pump alone
   • B.The combined flow drops below what one pump delivered, because the two pumps work against each other
   • C.The combined flow rises but falls short of twice one pump's flow, because friction head grows with flow✓ Answer
   • D.The combined flow is exactly twice one pump's flow, because each pump keeps its own rated capacity

   Pumps in parallel add flow at a common head, but the system head curve rises as flow increases, so the new operating point sits at a higher head where each pump delivers less than it did alone. Adding head, not flow, is what pumps in series do.

   Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 1 — pump curves and parallel/series operationReport a problem with this question

5. 5. Why must a positive-displacement chemical metering pump be fitted with a pressure-relief valve on its discharge side?

   • A.It loses its prime as soon as the discharge is blocked, so the relief valve is what keeps the suction line full of chemical solution
   • B.It moves nearly the same volume per stroke whatever the pressure, so a blocked discharge raises pressure until something fails✓ Answer
   • C.It runs at a fixed pressure set by the drive motor, so the relief valve is what sets the feed rate the pump actually delivers
   • D.It cannot be started against a closed discharge, so the relief valve gives the pump an open flow path during every start-up

   A positive-displacement pump displaces a fixed volume per stroke and does not have a shutoff head, so if the discharge is valved shut or plugged the pressure climbs without limit until the piping, the pump head or the motor gives way. The relief valve is the required protection, and it must never be blocked or set above the weakest component's rating.

   Source: CSUS Office of Water Programs, Water Treatment Plant Operation — positive-displacement chemical feed pumpsReport a problem with this question

6. 6. A pump's stuffing box is dripping steadily, roughly a drop each second, and the gland and shaft sleeve are cool to the touch. What should the operator do?

   • A.Tighten the gland nuts a little at a time until the dripping stops completely, then watch the sleeve
   • B.Replace the packing rings with a mechanical seal, because packing should never leak while in service
   • C.Leave the drip as it is, because that leakage is what lubricates and cools the packing and sleeve✓ Answer
   • D.Back the gland nuts off completely and let the box flush freely until the leaking water runs clear

   Stuffing-box packing is designed to leak a small, steady stream — a rate on the order of tens of drops per minute is commonly recommended — because that flow carries away frictional heat and lubricates the packing against the shaft sleeve. Tightening the gland until the drip stops burns the packing and scores the sleeve; a mechanical seal, by contrast, is the type of seal that should show no visible leakage.

   Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 2 — packing, gland adjustment and mechanical sealsReport a problem with this question

7. 7. A pump delivers 1,400 gpm against a total dynamic head of 120 ft, and its pump efficiency is 75%. Using brake horsepower = (gpm x head in ft) / (3,960 x pump efficiency), what brake horsepower does it require?

   • A.75.5 hp
   • B.56.6 hp✓ Answer
   • C.42.4 hp
   • D.31.8 hp

   (1,400 x 120) / 3,960 = 42.4 water horsepower, and dividing by the 0.75 pump efficiency gives 56.6 brake horsepower. Efficiency must divide, not multiply: 42.4 hp is the water horsepower with efficiency ignored, and 31.8 hp is what you get by multiplying by 0.75 instead.

   Source: WPI Formula and Conversion Table for Water Treatment — brake horsepower formulaReport a problem with this question

8. 8. A booster pump delivers 900 gpm against a total head of 78 psi. Taking 1 psi = 2.31 ft of water and water horsepower = (gpm x head in ft) / 3,960, what is the water horsepower?

   • A.7.7 hp
   • B.17.7 hp
   • C.94.6 hp
   • D.40.9 hp✓ Answer

   The head must be in feet before it enters the formula: 78 psi x 2.31 = 180.2 ft, and (900 x 180.2) / 3,960 = 40.9 hp. Feeding psi straight into the formula gives 17.7 hp, multiplying by 0.433 instead of 2.31 gives 7.7 hp, and applying the 2.31 factor twice gives 94.6 hp.

   Source: WPI Formula and Conversion Table for Water Treatment — water horsepower and the 1 psi = 2.31 ft conversionReport a problem with this question

9. 9. A four-pole three-phase induction motor is supplied at 60 Hz, and its nameplate full-load speed reads 1,750 rpm rather than the 1,800 rpm synchronous speed. Why?

   • A.The bearings are dragging, and that friction is what pulls the rotor below its synchronous speed
   • B.An induction motor must slip, because the rotor has to turn slower than the field to develop torque✓ Answer
   • C.The nameplate reports speed with the pump coupled, and an uncoupled motor would reach 1,800 rpm
   • D.The supply voltage is low, and a motor loses speed in direct proportion to any voltage it loses

   Synchronous speed is (120 x frequency) / number of poles, or 1,800 rpm here, and an induction motor's rotor must always lag that rotating field: the relative motion is what induces rotor current and produces torque, so the difference, called slip, is normal and increases with load. A motor turning at exactly synchronous speed would develop no torque at all.

   Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 2 — electric motor fundamentals, synchronous speed and slipReport a problem with this question

10. 10. A variable-frequency drive slows a centrifugal pump from full speed to 80% of full speed. What happens to its flow, head and power?

    • A.Flow falls to about 80%, head to about 64%, and the power drawn to about 51%✓ Answer
    • B.Flow falls to about 80%, head is unchanged, and the power drawn to about 64%
    • C.Flow falls to about 64%, head to about 51%, and the power drawn to about 41%
    • D.Flow falls to about 80%, head to about 80%, and the power drawn to about 80%

    The affinity laws state that flow varies directly with speed, head with the square of speed, and brake horsepower with the cube of speed, so at 0.8 speed the values are 0.8, 0.64 and 0.51 of the original. That cube relationship is why a variable-frequency drive saves far more energy than throttling a discharge valve, which instead adds head and wastes it as friction.

    Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 2 — pump affinity laws and variable-speed drivesReport a problem with this question

11. 11. An operator needs to hold a small stream of plant service water at a set rate and adjust that rate from time to time. Which valve suits that duty?

    • A.A gate valve, held part-open at whatever position gives the flow that is wanted
    • B.A globe valve, whose plug and seat are built to hold a set position against flow✓ Answer
    • C.A swing check valve, whose disc rides at the opening that the passing flow gives it
    • D.A plug valve, turned partway so its port passes only the flow that is wanted

    A globe valve throttles by seating a plug against a fixed orifice, which gives fine, stable control of flow at the cost of higher head loss when wide open. A gate valve is an isolation valve only: a partly open gate vibrates, chatters and erodes the seat, and a check valve or plug valve is likewise not designed to be parked in a throttling position.

    Source: AWWA Water System Operations, Water Treatment — valve types and their applicationsReport a problem with this question

12. 12. A large-diameter transmission main inside the plant is being drained for repair. Which appurtenance keeps the emptying pipe from collapsing?

    • A.A pressure-reducing valve, which holds the downstream pressure at a set value
    • B.A surge-relief valve, which opens to release pressure when a surge arrives
    • C.An air and vacuum valve, which admits a large volume of air as the water leaves✓ Answer
    • D.An air-release valve, which vents the small pockets that collect while in service

    Draining a full main pulls a partial vacuum behind the falling water, and atmospheric pressure on the outside can buckle the pipe unless a large opening lets air in; that is exactly the job of an air and vacuum valve, which also expels large volumes of air while the line is being filled. An air-release valve has only a small orifice sized to vent air that comes out of solution during normal operation.

    Source: AWWA Water System Operations, Water Treatment — air-release, air/vacuum and combination air valvesReport a problem with this question

13. 13. When a high-service pump trips on a power failure, a heavy bang is heard at the pump and a pressure surge runs back into the discharge main. What is the appropriate fix?

    • A.Fit an air-release valve at the pump so any trapped air can leave the discharge line
    • B.Fit a larger swing check valve so the disc can swing more freely when the pump trips
    • C.Fit a cushioned or spring-loaded check valve so the disc closes before flow reverses✓ Answer
    • D.Fit a foot valve on the suction line so the pump holds its prime after it has tripped

    The bang is check-valve slam: when the pump stops, the column reverses and drives an unassisted swing disc shut violently, and stopping that moving column generates the surge. A spring-loaded silent check or a cushioned slow-closing check closes as the flow decelerates, before reversal, so no column has to be stopped abruptly; a larger swing check would slam harder, not less.

    Source: AWWA Water System Operations, Water Treatment — check valves, valve slam and surge controlReport a problem with this question

14. 14. New plant yard piping includes several bends, a tee and a dead end. Why must those fittings be given thrust blocks or restrained joints?

    • A.Fittings carry more of the trench backfill load than an equal length of straight pipe does
    • B.Internal pressure pushes on the fitting with a force that no straight run of pipe has to carry✓ Answer
    • C.Fittings expand and contract more than straight pipe does as the water temperature changes
    • D.Fittings collect air pockets that must be held in place until a vent can release them safely

    Wherever a pressurized line changes direction or size or stops, the pressure acting on the projected area is no longer balanced by an equal and opposite force, and the resulting thrust tries to push the fitting out of the joint. Thrust blocks transfer that force to undisturbed soil and restrained joints carry it in the pipe itself; without either, the joint can pull apart under pressure.

    Source: AWWA C600, Installation of Ductile-Iron Mains and Their Appurtenances — thrust restraint at bends, tees and dead endsReport a problem with this question

15. 15. To reduce air to the filter air-scour header, an operator begins closing a valve on the discharge of a positive-displacement rotary-lobe blower. What will happen?

    • A.Discharge air flow will hold while the blower slows itself to the new back pressure
    • B.Discharge pressure will fall as the blower unloads back through its inlet air filter
    • C.Discharge pressure will climb until the relief valve lifts or the motor overloads✓ Answer
    • D.Discharge air flow will drop in step with valve position while pressure holds steady

    A rotary-lobe blower is a positive-displacement machine that moves a fixed volume of air per revolution, so throttling its discharge does not reduce flow; it only raises pressure until the required relief valve opens or the driver trips on overload. Air flow from such a blower is changed by changing its speed, whereas a centrifugal blower can be throttled.

    Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 2 — blowers and compressed air systemsReport a problem with this question

16. 16. During a finished-water storage tank inspection, four features are recorded. Which one is a sanitary defect that must be corrected?

    • A.The overflow pipe is piped directly into a storm drain below the tank✓ Answer
    • B.The roof hatch is locked, curbed and has an overlapping gasketed cover
    • C.The overflow pipe ends above a splash pad and carries a screened flap
    • D.The roof vent is turned downward and covered with a corrosion-resistant screen

    An overflow that is hard-piped into a storm drain or sewer is a direct cross-connection: if that drain surcharges, contaminated water can be forced back into the finished-water tank. The overflow must discharge through an air gap over a splash pad and be fitted with a screen or flap valve, exactly as the other three findings describe acceptable practice for hatches and vents.

    Source: AWWA Manual M42, Steel Water-Storage Tanks, and AWWA C652, Disinfection of Water-Storage Facilities — sanitary protection of vents, hatches and overflowsReport a problem with this question

17. 17. During a monthly generator test the utility feed is opened. The engine cranks, starts and runs at rated speed and voltage, but the plant stays without power until the utility returns. Where should the operator look first?

    • A.At the automatic transfer switch, which never moved the plant load onto the generator✓ Answer
    • B.At the block heater, which leaves a cold engine unable to hold its rated load for long
    • C.At the starting batteries, which are the usual reason a standby set fails to start at all
    • D.At the fuel filter and water separator, which can starve an engine of clean, dry fuel

    The engine did everything asked of it, so the failure lies downstream of the set: the automatic transfer switch is what senses the outage, signals the start and then transfers the load, and a set that runs while the plant stays dark points squarely at a transfer failure. This is why standby power must be tested by transferring load, not merely by starting the engine.

    Source: NFPA 110, Standard for Emergency and Standby Power Systems — transfer switch operation and load-transfer testingReport a problem with this question

18. 18. Monthly vibration readings on a high-service pump have climbed steadily above the baseline taken when it was rebuilt, so its bearings are scheduled for replacement. How is this work best classified?

    • A.Reactive maintenance, because the work follows a change the operator did not plan for
    • B.Corrective maintenance, because the bearings are being repaired before they can seize
    • C.Preventive maintenance, because the vibration readings are taken on a fixed schedule
    • D.Predictive maintenance, because a measured condition, not the calendar, triggered it✓ Answer

    Predictive, or condition-based, maintenance schedules work only when a measured indicator trends toward failure, and the trend against a baseline — not any single reading — is the trigger; vibration analysis specifically detects imbalance, misalignment, looseness and bearing wear. Preventive maintenance would replace the bearings at a fixed interval regardless of their condition, and corrective maintenance repairs after a failure has occurred.

    Source: CSUS Office of Water Programs, Water Treatment Plant Operation, Volume 2 — preventive, predictive and corrective maintenance programsReport a problem with this question

19. 19. A pump must be opened up so its impeller can be pulled. What does the operator do first?

    • A.Close the suction and discharge valves, drain the pump casing, and hang a warning tag on it
    • B.Check the motor leads with a meter, then chain the breaker handle in the off position
    • C.Isolate every energy source, apply a personal lock and tag, and then try to start the pump✓ Answer
    • D.Open the motor starter, tell the shift supervisor about it, and begin removing the coupling

    Lockout/tagout comes before any other step: notify affected staff, shut down normally, isolate all energy sources including electrical, hydraulic, pneumatic and stored gravity or pressure energy, apply an individual lock and tag, release stored energy, and then verify zero energy by attempting to operate the equipment. Only the worker who applied a lock may remove it, and a tag alone or a supervisor's word is not isolation.

    Source: OSHA 29 CFR 1910.147, The Control of Hazardous Energy (Lockout/Tagout) — energy isolation and verification of zero energyReport a problem with this question

Practice questions written against the standardized Water Treatment Operator Need-to-Know Criteria published by Water Professionals International (formerly the Association of Boards of Certification) and standard references from the CSUS Office of Water Programs and AWWA. This site is not affiliated with or endorsed by WPI/ABC, AWWA, or the US EPA. Operator certification is issued by your state's certifying authority, which sets plant classification tiers, operator grades, eligibility, and the passing standard — confirm those with your state before testing. Contaminant limits and monitoring requirements are set federally and are revised over time, so no answer here should be relied on as a current regulatory value; consult the regulations in force for your system. This bank covers the drinking-water treatment exam only — wastewater treatment, wastewater collection, and water distribution are separate certifications. About the Need-to-Know Criteria →