Pump Controls & Pump Stations

Pump stations combine pumps, controls, sensors, valves, electrical equipment, alarms, and standby systems into one operating unit. They may transfer drinking water, maintain distribution pressure, move wastewater from a wet well, or provide process flow within a treatment plant.

Operators should understand how pumps are started and stopped, how control signals are generated, how multiple pumps are sequenced, and what happens when normal automatic control fails.

Purpose of Pump Controls

Pump controls are used to match pumping operation with system demand.

Depending on the station, controls may respond to:

• wet-well level;
• tank level;
• system pressure;
• flow;
• time schedule;
• process demand;
• operator command.

The control strategy should keep the system within acceptable operating limits while avoiding unnecessary starts, stops, and hydraulic disturbances.

Automatic and Manual Control

Most pump stations provide both automatic and manual control modes.

In automatic mode, pumps respond to control logic and sensor inputs.

In manual mode, an operator directly commands equipment according to approved procedures.

Manual mode is useful for testing and troubleshooting, but equipment should not be left in manual unintentionally.

Lead Pump

The lead pump is the first pump scheduled to start when pumping is needed.

For example, in a wastewater lift station:

• wet-well level rises;
• lead start level is reached;
• lead pump starts;
• level begins to fall.

Lag Pump

A lag pump starts when the lead pump alone cannot meet demand or when a higher control point is reached.

The lag pump may start because of:

• higher wet-well level;
• low distribution pressure;
• high system demand;
• insufficient flow from the lead pump.

Multiple Lag Pumps

Larger stations may have:

• lead pump;
• lag pump;
• second lag pump;
• standby pump.

Each additional pump is normally started only when needed.

Lead-Lag Alternation

Control systems often alternate which pump is designated lead.

Alternation helps balance:

• run time;
• number of starts;
• equipment wear.

A pump should not remain permanently unused simply because another unit always starts first.

Duty and Standby Pumps

A station may be designed with:

• duty pumps that normally operate;
• standby capacity that is available if another pump fails.

Standby pumps should be tested regularly so their availability is known.

Level-Controlled Pump Stations

Wastewater lift stations commonly use wet-well level to control pumps.

A typical control sequence may include:

• pump stop level;
• lead pump start level;
• lag pump start level;
• high-level alarm;
• high-high alarm or emergency level.

The exact elevations depend on station design.

Why Separate Start and Stop Levels Are Needed

If a pump started and stopped at the same level, small fluctuations could cause rapid cycling.

Using different start and stop levels creates a control range, sometimes called differential or hysteresis.

This gives the pump time to run before stopping.

Example of Level Differential

A lead pump starts at 8 feet and stops at 4 feet.

The control differential is:

8 ft - 4 ft = 4 ft

The wet well must fall approximately 4 feet before the pump stops.

Float Switches

Float switches are simple level-control devices commonly used in pump stations.

A float changes position as liquid level rises or falls and can activate an electrical switch.

Floats may be used for:

• pump start;
• pump stop;
• lag start;
• high-level alarm.

Float Problems

Float switches may fail or give incorrect signals because of:

• ragging;
• grease;
• tangled cables;
• physical obstruction;
• switch failure;
• incorrect mounting.

Wastewater operators should inspect float movement where appropriate.

Level Transducers

Many stations use continuous level sensors instead of individual floats.

Examples include:

• submersible pressure transducers;
• ultrasonic level sensors;
• radar level sensors.

The measured level is sent to the control system, which compares it with programmed setpoints.

Continuous Level Control Advantages

A continuous level signal allows:

• multiple adjustable setpoints;
• trend recording;
• VFD control;
• more detailed alarms;
• SCADA display.

Pressure-Controlled Pump Stations

Booster stations often use system pressure as the control variable.

A typical sequence may be:

• pressure falls;
• lead pump starts or increases speed;
• demand continues to increase;
• lag pump starts;
• pressure is restored.

Pressure Setpoints

Pressure-control systems may use:

• start pressure;
• stop pressure;
• target pressure;
• high-pressure alarm;
• low-pressure alarm.

Setpoints should be appropriate for the pressure zone and approved operating strategy.

Variable-Speed Pump Control

VFD-controlled stations can vary pump speed instead of using only on-off operation.

For pressure control, the VFD may:

• increase speed when pressure falls;
• decrease speed when pressure rises.

This can provide smoother control and reduce some hydraulic transients.

VFD Control by Wet-Well Level

A wastewater station may use VFDs to maintain wet-well level within a selected range.

As level rises:

• pump speed increases;
• pump flow increases.

As level falls:

• speed decreases;
• pump flow decreases.

Minimum Pump Speed

A VFD should not automatically be assumed safe at any low speed.

Minimum speed may be limited by:

• motor cooling;
• minimum pump flow;
• solids transport;
• hydraulic stability;
• manufacturer requirements.

Control Signal Failure

If a level or pressure signal fails, the station may:

• stop pumping;
• run continuously;
• switch to backup control;
• generate an alarm;
• use a programmed fail-safe state.

Operators should know the designed failure response.

Backup Level Controls

Critical wet wells may have independent high-level floats in addition to the normal continuous level sensor.

The backup device may:

• start pumps;
• activate an alarm;
• provide emergency protection if the main sensor fails.

Pump Start Permissives

A control system may require certain conditions before allowing a pump to start.

These conditions are sometimes called permissives.

Examples include:

• adequate liquid level;
• required valve open;
• motor available;
• no active trip;
• seal system ready;
• power available.

Interlocks

An interlock prevents or changes equipment operation when a specified condition occurs.

Examples include:

• low wet-well level stopping a pump;
• high motor temperature tripping a pump;
• closed discharge valve preventing startup;
• low suction pressure stopping a booster pump.

Interlocks Protect Equipment and Process

Operators should not bypass an interlock casually.

If an interlock prevents operation, determine why the condition exists before overriding protection.

Pump Alarms

Common pump-station alarms include:

• high wet-well level;
• low wet-well level;
• high pressure;
• low pressure;
• pump fail;
• motor overload;
• seal leak;
• high motor temperature;
• power failure;
• generator failure;
• communication failure.

Alarm Versus Trip

An alarm warns that attention is required.

A trip automatically stops equipment or prevents operation to protect the system.

An alarm does not always mean the pump has stopped.

A trip does not always identify the root cause by itself.

High Wet-Well Alarm

A high wet-well alarm can indicate:

• pump failure;
• insufficient pump capacity;
• blocked pump;
• high inflow;
• control failure;
• force-main problem;
• power failure.

The operator should determine whether level is still rising and whether additional pumping capacity is available.

Low Wet-Well Alarm

Unexpected low level may indicate:

• pump failing to stop;
• incorrect level signal;
• control setpoint problem;
• abnormally low inflow.

Very low level may cause vortexing, air entrainment, or insufficient pump submergence.

Pump Fail Alarm

A pump fail alarm may mean that a start command was issued but the system did not confirm successful operation.

Possible causes include:

• motor trip;
• starter failure;
• power problem;
• control circuit failure;
• mechanical pump problem.

Motor Overload

An overload device protects a motor from excessive electrical load.

Possible reasons for an overload trip include:

• mechanical binding;
• blocked pump;
• electrical fault;
• high motor load;
• incorrect voltage conditions.

Do not repeatedly reset an overload without investigating the cause.

Seal Leak Alarms

Submersible pumps may contain moisture or seal-leak detection.

A seal leak alarm can warn that moisture has entered an area intended to remain dry.

Ignoring the alarm can allow further damage.

High Motor Temperature

High motor temperature can result from:

• overloading;
• poor cooling;
• frequent starts;
• electrical problems;
• mechanical problems.

SCADA

Supervisory Control and Data Acquisition, or SCADA, allows operators to monitor and sometimes control remote pump stations.

SCADA may display:

• pump status;
• wet-well level;
• pressure;
• flow;
• motor current;
• VFD speed;
• alarms;
• generator status.

SCADA Does Not Replace Field Inspection

A station can appear normal on SCADA while field conditions show:

• leakage;
• noise;
• vibration;
• odor;
• corrosion;
• blocked ventilation;
• housekeeping problems.

Remote monitoring should complement field inspection.

Communication Failure

A lost SCADA connection does not necessarily mean the station has stopped operating.

Local controls may continue to operate automatically.

Operators should know whether the station can operate independently during communication loss.

Local Control Panel

A local control panel commonly provides:

• hand-off-auto selector switches;
• start and stop controls;
• status lights;
• alarm indication;
• VFD interface;
• motor protection.

Hand-Off-Auto Switch

A Hand-Off-Auto, or HOA, selector commonly provides three control modes:

• Hand for local manual operation;
• Off to stop or disable the pump;
• Auto for normal automatic control.

An HOA switch left in Hand or Off can prevent the station from responding as expected.

Check Control Mode During Troubleshooting

When a pump fails to start automatically, verify:

• HOA position;
• control power;
• active alarms;
• level or pressure signal;
• permissives;
• motor availability.

Wet-Well Volume and Pump Cycling

Wet-well working volume influences how frequently pumps start.

If the start-stop volume is too small, pumps may cycle excessively.

If it is too large, wastewater detention time may increase.

Pump Cycle Time

Pump run time and off time depend on:

• inflow;
• pump flow;
• wet-well working volume;
• start and stop levels.

Tracking cycle frequency can help identify changing station conditions.

Increasing Pump Run Time

If inflow remains similar but a pump takes longer to lower the wet well from start level to stop level, possible causes include:

• reduced pump capacity;
• increased force-main resistance;
• pump wear;
• blockage;
• incorrect valve position.

Short Cycling

Short cycling means a pump starts and stops too frequently.

Possible causes include:

• small control differential;
• incorrect setpoints;
• bad level sensor;
• oversized pump;
• check-valve leakage;
• small effective wet-well volume.

Check-Valve Leakage and Cycling

If a check valve leaks after pump shutdown, pumped liquid can flow backward into the wet well.

The level rises again and may restart the pump quickly.

This can create repeated short cycling.

Standby Power

Pump stations may require standby power because loss of pumping can quickly create:

• low distribution pressure;
• loss of water supply;
• wet-well overflow;
• sanitary sewer overflow;
• process interruption.

Emergency Generators

Generator systems may include:

• engine;
• generator;
• fuel system;
• battery;
• charger;
• cooling system;
• automatic transfer switch.

All components must be maintained for reliable emergency operation.

Automatic Transfer Switch

An Automatic Transfer Switch, or ATS, detects loss of normal power and transfers the electrical load to emergency power when the generator is ready.

When normal utility power returns, the ATS transfers the load back according to its programmed sequence.

Generator Testing

Standby generators should be exercised and inspected according to facility procedures.

Operators may check:

• fuel level;
• battery condition;
• oil;
• coolant;
• alarms;
• transfer operation;
• run condition.

Fuel Supply

A generator with insufficient fuel is not reliable standby power.

Fuel planning should consider:

• expected generator load;
• fuel consumption;
• required emergency duration;
• delivery availability.

Pump Station Ventilation

Dry pump rooms and electrical spaces may require ventilation for:

• motor heat;
• equipment cooling;
• worker comfort;
• hazard control.

Wastewater structures may also involve hazardous atmospheres and require appropriate safety procedures.

Flood Protection

Pump-station reliability can be affected by flooding.

Operators should know the vulnerability of:

• motors;
• control panels;
• generators;
• fuel systems;
• electrical equipment;
• access roads.

Pump Station Housekeeping

Good housekeeping supports reliable operation.

Operators should watch for:

• water leaks;
• oil leaks;
• loose materials;
• blocked access;
• corrosion;
• standing water;
• damaged cables.

Station Inspection

A routine pump-station inspection may include:

• wet-well or tank level;
• pump status;
• flow;
• pressure;
• motor current;
• VFD speed;
• alarms;
• valve position;
• noise;
• vibration;
• leakage;
• generator condition;
• housekeeping.

Compare Run Hours

In stations with alternating identical pumps, large differences in accumulated run hours may indicate:

• failed alternation;
• one pump unavailable;
• control problem;
• one pump producing less capacity.

Compare Starts

Start counts can also reveal operating problems.

A large increase in starts may indicate:

• short cycling;
• changing demand;
• bad level control;
• check-valve leakage.

High-Level Response

If wet-well level continues rising toward overflow, operators may need to:

• verify all available pumps;
• place standby pumps in service;
• check power and controls;
• check force-main condition;
• check pump blockage;
• call maintenance or emergency support;
• make required notifications.

The exact emergency response should follow facility procedures.

Low-Pressure Response

At a drinking water booster station, low pressure may require checking:

• pump availability;
• tank level;
• system demand;
• suction pressure;
• valve position;
• VFD speed;
• main breaks or major leaks.

Do Not Reset Repeated Trips Without Investigation

If a pump repeatedly trips, repeated resetting can cause additional damage.

The operator should determine whether the problem involves:

• electrical load;
• blocked pump;
• overheating;
• seal condition;
• control failure;
• hydraulic condition.

Control Setpoint Changes

Changing level or pressure setpoints can affect:

• pump cycling;
• wet-well storage;
• system pressure;
• energy use;
• lag-pump operation;
• hydraulic transients.

Setpoints should be changed only under approved procedures.

Common Pump-Control Mistakes

• Leaving a pump in Hand or Off unintentionally.
• Ignoring failed lead-lag alternation.
• Allowing short cycling to continue.
• Assuming a high-level alarm is only a sensor problem.
• Resetting repeated overload trips without investigation.
• Ignoring seal-leak or temperature alarms.
• Assuming SCADA communication loss means the station stopped.
• Failing to test standby pumps.
• Failing to maintain generator fuel and batteries.
• Changing control setpoints without understanding system effects.
• Relying only on remote data without field inspection.

A Practical Pump Station Inspection Sequence

1. Review active alarms.
2. Confirm control mode.
3. Check level or pressure.
4. Verify lead and lag pump status.
5. Review pump run hours and starts.
6. Review flow and pressure.
7. Check motor current and VFD speed.
8. Inspect for noise, vibration, leakage, or overheating.
9. Check valves and check-valve operation.
10. Verify standby pump availability.
11. Inspect generator and emergency power status.
12. Document abnormal conditions.

A Practical High Wet-Well Troubleshooting Sequence

1. Confirm the level reading is real.
2. Determine whether the level is still rising.
3. Verify lead pump operation.
4. Verify lag and standby pumps.
5. Check power and control mode.
6. Review motor trips and alarms.
7. Check pump flow or run time.
8. Check force-main pressure and valve position.
9. Investigate blockage or hydraulic restrictions.
10. Escalate according to the emergency procedure if overflow risk remains.

What to Remember for the Exam

• Pump controls match pump operation with system demand.
• The lead pump is normally the first pump to start.
• A lag pump provides additional capacity when demand increases.
• Lead duty may alternate to balance run time and wear.
• Different start and stop setpoints help prevent rapid pump cycling.
• Float switches and continuous level sensors are common wet-well controls.
• Pressure sensors are commonly used at booster stations.
• VFDs can vary pump speed to control pressure, flow, or level.
• Permissives are conditions that must be satisfied before operation is allowed.
• Interlocks protect equipment or process by preventing or stopping operation under specified conditions.
• An alarm warns of a condition; a trip stops or prevents equipment operation.
• HOA means Hand-Off-Auto.
• Short cycling increases equipment wear and may indicate control or hydraulic problems.
• Increasing pump run time for the same level change can indicate reduced pump capacity or increased system resistance.
• Check-valve leakage can cause repeated pump cycling.
• SCADA supports remote monitoring but does not replace field inspection.
• Standby pumps should be tested and maintained.
• Emergency generators require fuel, batteries, controls, and transfer equipment to be maintained.
• Repeated trips should be investigated rather than repeatedly reset.
• Control setpoint changes can affect pressure, storage, cycling, and hydraulic response.