Pumps & Booster Stations

Pumps are used throughout drinking-water distribution systems to move water, increase hydraulic head, maintain pressure, fill storage, and serve higher or remote pressure zones. Booster stations perform these functions at selected locations in the distribution network.

Operators should understand how pump performance interacts with system resistance, tank levels, valve positions, demand, pressure controls, and check valves. A pump can be mechanically healthy and still operate poorly if the surrounding hydraulic conditions are wrong.

Why Distribution Pumps Are Used

Distribution pumps may be used to:

• move finished water into the system;
• increase pressure;
• fill storage tanks;
• serve high-elevation areas;
• transfer water between pressure zones.

High-Service Pumps

High-service pumps commonly move finished water from a treatment plant or clearwell into the distribution system.

Their operation affects:

• system pressure;
• flow;
• tank filling;
• energy use.

Booster Pumps

Booster pumps increase hydraulic head in a portion of the distribution system.

They are commonly used when:

• elevation is high;
• distance is large;
• incoming pressure is insufficient;
• a separate pressure zone is required.

Booster Stations

A booster station may include:

• multiple pumps;
• motors;
• variable-frequency drives;
• check valves;
• isolation valves;
• pressure sensors;
• flow meters;
• controls and alarms.

Pumps Add Head

A pump increases hydraulic energy by adding head.

This can increase:

• pressure;
• flow capability;
• ability to overcome elevation;
• ability to overcome friction loss.

Total Dynamic Head

Total dynamic head represents the total head a pump must overcome while water is flowing.

It can include:

• elevation difference;
• required pressure head;
• friction loss;
• minor losses.

Static Head

Static head is the elevation-related head difference that exists without considering flow-related friction losses.

Friction Head

Friction head is the head lost as water flows through:

• pipe;
• valves;
• fittings;
• meters;
• other restrictions.

System Head Changes with Flow

As system flow increases, friction loss generally increases.

A pump may therefore produce different flow under different system conditions even when pump speed remains unchanged.

Pump Curve

A pump curve shows how pump head changes with flow.

For many centrifugal pumps:

• head is higher at lower flow;
• head decreases as flow increases.

System Curve

A system curve represents the head required by the system at different flow rates.

It reflects:

• static head;
• friction loss.

Operating Point

The actual pump operating point occurs where pump performance and system requirements balance.

If system resistance changes, the operating point changes.

Valve Restriction Changes the Operating Point

A partially closed discharge valve increases system resistance.

This generally causes:

• lower flow;
• higher pump discharge head.

Lower System Resistance

If a large flow path opens, such as a hydrant or large demand, system resistance may decrease.

The pump may move toward:

• higher flow;
• lower developed head.

Pressure and Head Conversion

For water:

1 psi ≈ 2.31 feet of head

and:

1 foot of head ≈ 0.433 psi

Head Example

A pump increases pressure by 50 psi.

Head added = 50 × 2.31

Head added = 115.5 ft

Pump Suction Conditions

Good suction conditions are essential for reliable pump operation.

Operators should monitor:

• suction pressure;
• source level;
• valve position;
• screen or strainer condition;
• air entry.

Low Suction Pressure

Low suction pressure can result from:

• low tank level;
• restricted suction pipe;
• closed or partially closed valve;
• high suction-side flow;
• blocked screen.

Cavitation

Cavitation can occur when local pressure falls low enough for vapor bubbles to form and then collapse within the pump.

Possible symptoms include:

• noise;
• vibration;
• reduced flow;
• reduced head;
• physical damage over time.

Cavitation Risk Factors

Risk can increase with:

• low suction pressure;
• high water temperature;
• excessive pump flow;
• restricted suction piping.

Priming

Pumps that are not designed to handle air generally require the pump casing and suction path to be properly filled with water before operation.

Loss of prime can cause:

• loss of flow;
• overheating;
• pump damage.

Discharge Pressure

Pump discharge pressure reflects both:

• head added by the pump;
• downstream hydraulic conditions.

High Discharge Pressure

Possible causes include:

• closed discharge valve;
• restricted downstream piping;
• high tank level;
• high system pressure;
• low flow.

Low Discharge Pressure

Possible causes include:

• pump wear;
• low suction pressure;
• wrong pump speed;
• high system demand;
• major leak.

Check Valves

Check valves on pump discharge lines help prevent reverse flow when the pump stops.

Failed Check Valve

A leaking or failed check valve can cause:

• reverse flow;
• pump reverse rotation;
• pressure loss;
• water hammer;
• repeated cycling.

Isolation Valves

Isolation valves allow a pump to be removed from service for maintenance.

Do Not Operate Against a Closed Discharge Indefinitely

Operating a centrifugal pump at or near zero flow can produce:

• heat buildup;
• vibration;
• internal recirculation;
• equipment damage.

Lead and Lag Pumps

Stations with multiple pumps often use:

• a lead pump;
• one or more lag pumps.

The lead pump normally starts first.

Lag pumps start when additional capacity is required.

Lead-Lag Sequencing

Sequencing can be based on:

• pressure;
• flow;
• tank level;
• time;
• SCADA logic.

Alternating Lead Pump

Systems may rotate which pump serves as lead to distribute operating hours more evenly.

Why Rotation Matters

Pump rotation can help:

• balance wear;
• verify standby equipment;
• reduce dependence on one pump.

Standby Pumps

A standby pump should be maintained in operable condition.

A pump that never runs may fail when finally needed.

Automatic Pump Start

Pumps may start automatically when:

• pressure falls;
• tank level falls;
• flow demand increases.

Automatic Pump Stop

Pumps may stop when:

• pressure recovers;
• tank level rises;
• demand decreases.

Control Deadband

A deadband is the difference between control start and stop points.

A deadband that is too narrow can cause excessive pump cycling.

Short Cycling

Short cycling occurs when pumps start and stop too frequently.

Possible causes include:

• narrow pressure band;
• small effective storage;
• unstable pressure signal;
• oversized pump;
• failed check valve.

Effects of Short Cycling

Short cycling can increase:

• motor starts;
• electrical stress;
• bearing wear;
• control wear;
• pressure fluctuations.

Variable-Frequency Drives

A variable-frequency drive, or VFD, changes motor speed.

In booster applications, this can help maintain pressure as demand changes.

Variable-Speed Pressure Control

A pressure sensor sends a signal to the control system.

The VFD can then:

• increase pump speed when pressure falls;
• reduce speed when pressure rises.

Benefits of Variable-Speed Operation

Potential benefits include:

• smoother pressure control;
• reduced throttling losses;
• lower energy use at reduced demand;
• less frequent pump cycling.

Pressure Sensor Location Matters

A sensor near the pump station may not represent pressure at a remote high-elevation customer.

Control strategy should reflect the hydraulic needs of the pressure zone.

Pressure Setpoint

A pressure setpoint should provide adequate service without creating unnecessarily high pressure.

Excessive pressure can increase:

• leakage;
• main breaks;
• energy use;
• stress on customer plumbing.

Low Pressure Setpoint

A setpoint that is too low can cause:

• poor customer service;
• insufficient high-elevation pressure;
• reduced fire-flow capability.

Pump Efficiency

Pump efficiency compares hydraulic power delivered to water with mechanical or electrical input power.

A pump operating far from its intended range can waste energy.

Energy Use as an Operating Indicator

Operators can trend:

• pump run time;
• flow;
• pressure;
• electric energy use.

Energy per Unit Water

A useful performance measure is energy used per unit volume pumped.

If energy per unit water rises, possible causes include:

• pump wear;
• greater pumping head;
• hydraulic restriction;
• lower efficiency.

Pump Flow Calculation

When volume and time are known:

Flow = Volume ÷ Time

Flow Example

A pump moves 180,000 gallons in 6 hours.

Convert time:

6 hr × 60 min/hr = 360 min

Then:

Flow = 180,000 ÷ 360

Flow = 500 gpm

Pump Production

If flow is constant:

Volume = Flow × Time

Production Example

A pump operates at 750 gpm for 4 hours.

4 hr × 60 = 240 min

Volume = 750 × 240

Volume = 180,000 gallons

Pump Run Time

When required volume and flow are known:

Time = Volume ÷ Flow

Run-Time Example

A tank needs 300,000 gallons and the pump delivers 1,000 gpm.

Time = 300,000 ÷ 1,000

Time = 300 minutes

300 min ÷ 60 = 5 hours

Parallel Pumps

Pumps operating in parallel can provide increased flow.

Total flow is not always equal to the simple sum of each pump's individual flow because system resistance changes as combined flow increases.

Series Pumps

Pumps arranged in series primarily add head.

This arrangement is less common in ordinary distribution booster stations than parallel operation but may be used in specialized systems.

Parallel-Pump Troubleshooting

If the second pump starts but total station flow increases only slightly, investigate:

• high system resistance;
• restricted piping;
• valve position;
• pump condition.

Oversized Pumps

An oversized pump can create:

• short cycling;
• high pressure;
• poor efficiency;
• difficulty maintaining stable control.

Undersized Pumps

An undersized pump may:

• run continuously;
• fail to maintain pressure;
• fail to refill storage during high demand.

Pump Wear

Wear can reduce:

• flow;
• head;
• efficiency.

Possible Wear Areas

Depending on pump design, wear can involve:

• impeller;
• wear rings;
• bearings;
• seals;
• shaft.

Seal Problems

Seal problems can cause:

• leakage;
• air entry on certain suction arrangements;
• equipment damage.

Bearing Problems

Bearing problems may produce:

• noise;
• heat;
• vibration;
• higher energy use.

Vibration

Unexpected vibration can result from:

• cavitation;
• misalignment;
• bearing problems;
• imbalance;
• loose mounting.

Motor Current

Motor amperage can provide useful operating information.

An unexpected current change should be interpreted with:

• flow;
• pressure;
• pump speed;
• equipment condition.

Low Motor Current

Possible causes can include:

• low hydraulic load;
• loss of prime;
• low flow;
• mechanical problem.

High Motor Current

Possible causes can include:

• excessive flow;
• mechanical binding;
• electrical problem;
• incorrect operating condition.

Station Alarms

Useful booster-station alarms can include:

• low pressure;
• high pressure;
• pump failure;
• motor overload;
• low suction pressure;
• power failure;
• communication failure.

Alarm Acknowledgment Is Not Troubleshooting

When an alarm occurs, operators should determine:

• what condition triggered it;
• whether the reading is real;
• what effect it has on the distribution system.

Power Failure

A booster-station power failure can cause rapid pressure loss if:

• no elevated storage is available;
• alternate supply paths are limited.

Emergency Power

Critical pump stations may have:

• standby generators;
• alternate power sources;
• emergency operating procedures.

Water Hammer

Rapid flow changes can create pressure transients or water hammer.

Possible causes include:

• rapid pump shutdown;
• check-valve slam;
• rapid valve closure;
• power failure.

Transient Effects

Pressure transients can contribute to:

• pipe damage;
• valve damage;
• main breaks;
• temporary low pressure.

Slow and Controlled Changes

Where design allows, controlled pump starts and stops can reduce abrupt hydraulic changes.

SCADA

SCADA may provide:

• pump status;
• speed;
• suction pressure;
• discharge pressure;
• flow;
• motor current;
• alarms.

Verify SCADA Data

If displayed conditions do not match field behavior, investigate:

• sensor calibration;
• signal scaling;
• communication;
• actual pump condition.

Example: Pump Running but No Flow

Review:

• suction source;
• prime;
• suction valve;
• discharge valve;
• check valve;
• flow meter.

Example: Low Flow and High Discharge Pressure

This pattern commonly suggests increased downstream resistance.

Review:

• closed or partially closed valve;
• restricted piping;
• high tank level;
• PRV or control-valve condition.

Example: High Flow and Low Discharge Pressure

Possible causes include:

• high system demand;
• large open flow path;
• main break;
• pump operating far to the high-flow side of its curve.

Example: Low Suction Pressure

Review:

• source level;
• suction valve;
• screen or strainer;
• upstream pressure;
• pump flow.

Example: Pump Cycles Too Frequently

Review:

• pressure deadband;
• storage volume;
• pressure sensor;
• check valve;
• pump sizing.

Example: Pump Runs Continuously

Review:

• system demand;
• pressure setpoint;
• pump capacity;
• leakage;
• pump wear;
• pressure-sensor accuracy.

Example: Second Pump Starts but Pressure Still Falls

Possible causes include:

• demand exceeds station capacity;
• main break;
• restricted suction supply;
• one pump is not producing expected flow;
• incorrect valve position.

Example: Pressure Surges When Pump Stops

Review:

• check-valve closure;
• pump shutdown speed;
• system transient protection;
• valve operation.

Example: Energy Use Increasing

At similar flow and pressure, increasing energy use can suggest:

• pump wear;
• motor problem;
• mechanical friction;
• declining efficiency.

Common Pump and Booster-Station Mistakes

• Looking at discharge pressure without suction pressure.
• Assuming pump flow is constant regardless of system conditions.
• Ignoring system resistance and valve position.
• Ignoring cavitation symptoms.
• Ignoring check-valve condition.
• Using a pressure sensor location that does not represent the critical part of the zone.
• Allowing excessive short cycling.
• Failing to exercise standby pumps.
• Ignoring energy-use trends.
• Trusting SCADA data without verifying abnormal readings.

A Practical Pump Performance Review

1. Review suction pressure.
2. Review discharge pressure.
3. Review flow.
4. Review pump speed.
5. Review motor current.
6. Review vibration and noise.
7. Compare with normal historical operation.
8. Review system demand and valve positions.

A Practical Low-Pressure Booster Review

1. Verify the pressure sensor.
2. Review suction pressure.
3. Review pump status and speed.
4. Review station flow.
5. Review lag-pump operation.
6. Review check valves and isolation valves.
7. Check for high demand or major leakage.
8. Compare with storage level and pressure-zone conditions.

A Practical Pump-Cycling Review

1. Review start and stop setpoints.
2. Review pressure deadband.
3. Review storage influence.
4. Review pump size relative to demand.
5. Verify pressure-sensor stability.
6. Inspect check valves for reverse flow.
7. Review VFD control logic where applicable.
8. Adjust controls according to approved procedures.

A Practical Pump-Efficiency Review

1. Measure or review flow.
2. Review suction and discharge pressure.
3. Determine approximate head added.
4. Review motor power or energy use.
5. Compare energy per unit volume with historical values.
6. Inspect for mechanical and hydraulic restrictions.
7. Compare performance with expected pump operation.
8. Schedule maintenance if efficiency has deteriorated.

What to Remember for the Exam

• Distribution pumps add hydraulic head to move water and maintain pressure.
• Booster stations commonly serve high-elevation, remote, or separate pressure zones.
• Total dynamic head includes elevation, pressure requirements, friction losses, and other hydraulic losses.
• A pump curve shows the relationship between pump flow and head.
• A system curve represents the head required by the system at different flows.
• The pump operating point occurs where pump performance and system requirements balance.
• Increasing system resistance generally reduces pump flow.
• For water, 1 psi is approximately equal to 2.31 feet of head.
• Low suction pressure can contribute to cavitation.
• Cavitation can cause noise, vibration, reduced performance, and equipment damage.
• Check valves help prevent reverse flow when pumps stop.
• Lead-lag sequencing allows additional pumps to start as demand increases.
• Rotating lead pumps can balance operating hours and verify standby equipment.
• VFDs can adjust pump speed to maintain pressure as demand changes.
• A pressure-control sensor should represent the hydraulic needs of the zone.
• Short cycling increases mechanical and electrical wear.
• Parallel pumps primarily increase available flow, but combined flow is affected by system resistance.
• Energy use per unit water can help identify deteriorating pump efficiency.
• Pump troubleshooting should compare suction pressure, discharge pressure, flow, speed, motor current, system demand, and valve position together.
• Good booster-station operation requires coordinated pumps, controls, valves, sensors, alarms, energy monitoring, and hydraulic understanding.