Evaporative condenser water level control title graphic
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Evaporative Condenser Water Level Control Guide

Evaporative condenser water level control is the system that keeps the recirculating spray water basin within its operating range: filling it as water evaporates, alarming when the level leaves that range and, when specified, reporting status to the building automation system. The basin needs a dependable operating level whenever the equipment is running.

Too little water can create problems for the spray pump. Too much water can waste makeup water or cause overflow. A good level control specification addresses normal filling, alarm conditions and the information that operators need remotely.

Establish the Normal Basin Level

Begin with the evaporative condenser manufacturer’s approved operating water level.

Do not choose the fill stop point from the height of the overflow connection alone.

EVAPCO operation and maintenance literature states that the overflow sits above the normal operating level, and it lists different operating levels for different equipment lines.

The approved equipment drawings and manufacturer’s instructions should determine the final setpoints.

Replace Mechanical Makeup Control When Appropriate

Mechanical float valves remain common in evaporative equipment, but electronic control is also widely available.

EVAPCO states that a mechanical float valve assembly is standard equipment unless the unit is ordered with an optional electronic water level control package or arranged for a remote sump.

Waterline Controls manufactures cooling tower and evaporative condenser level controls for cooling towers, remote sumps, evaporative condensers and closed circuit fluid coolers.

Electronic level controls are an option for new projects and replacement work where electronic alarms and remote signaling are useful.

Add High and Low Level Alarms

The fill start and fill stop points define the normal operating band.

Alarm points should sit outside that band.

A high alarm can identify uncontrolled filling or another condition causing the basin to rise. A low alarm provides warning if water continues falling after the fill system should already have responded.

The WLC-5000 fill controller provides automatic fill with high and low alarms, using separate probes for fill start, fill stop, high alarm and low alarm.

Connect Useful Information to the BMS

Facility operators should not have to visit the condenser to discover that the water level is abnormal.

Dry contacts can report fill activity, high level, low level and controller power loss, depending on the selected Waterline Controls model.

The BMS point list should state exactly what each contact represents and whether the point is a normal status or an alarm.

This makes troubleshooting easier when a problem occurs overnight or during peak refrigeration demand. For a full point list, see which BMS points a water level controller should report.

Consider Winter Operation

Evaporative condensers operating in cold climates may also require basin heaters and low water protection.

BAC offers basin heater controls that supervise both water temperature and water level, including low water cutoff protection. On the level control side, the WLC-6100T controller with basin heater control combines fill, high and low alarms, basin heater cutoff and basin heater control in one panel.

If a heater is part of the project, coordinate its control with the condenser manufacturer’s requirements rather than treating it as a separate accessory.

Review Water Supply and Valve Operation

Electronic level control still depends on a reliable source of makeup water.

Check the valve, strainer, supply pressure and piping.

If a valve cannot deliver enough water during heavy evaporation, the controller may call for fill continuously while the basin still falls.

Likewise, a valve that leaks through after being de-energized can cause a high level condition even though the level controller is functioning correctly.

Commission Under Operating Conditions

Test the system with the condenser running.

Verify fill start, fill stop, high alarm and low alarm. Confirm the BMS receives the correct signals.

Where basin heating is installed, verify the associated low water protection according to the approved sequence.

Evaporative Condenser Fill, Alarm and Heater Controllers

Waterline Controls manufactures frequency-based electronic water level systems for evaporative condensers, cooling towers, remote sumps and closed circuit fluid coolers. Models are available with automatic fill, multiple alarms and BMS dry contacts, and basin heater control is available on the WLC-6100T. For remote sump arrangements, see the cooling tower remote sump level control guide. Call 480-905-1892 to discuss the condenser model, normal operating level, sensor arrangement and required control sequence.

References

Cooling tower and evaporative condenser level controls

WLC-5000 fill controller with high and low alarms

WLC-6100T fill, alarm and basin heater controller

EVAPCO: Operation and Maintenance Instructions for Closed Circuit Coolers and Evaporative Condensers

BAC: Basin Heater Controls

Cooling Towers, Water Level Controls
0
Pump panel retrofit with float switches replaced by electronic level sensing probes while the existing panel is kept
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Float Switch Replacement for an Existing Pump Panel

Float switch replacement in an existing pump panel changes how the panel senses water level while keeping the motor starters, overloads, disconnects and wiring that are still serviceable. A troublesome float switch does not automatically mean that every component in the pump control system has reached the end of its useful life.

If the existing power components remain suitable, it may be possible to update level sensing while retaining much of the existing control equipment. The retrofit still needs to begin with the existing sequence.

Document What Every Float Does

Before removing anything, identify each float and the condition it controls.

A commercial sump may have separate points for pump stop, pump start, second pump start and high level alarm. Other systems may use floats for filling or low level protection.

Do not assume wire color identifies function.

Trace the circuits and compare them with the panel drawings. If the drawings no longer match the installation, update them before designing the replacement.

Keep Pump Power Separate From Level Sensing

The level sensing circuit tells the system what the water is doing. It does not necessarily carry the motor load itself.

Large pumps commonly operate through motor starters or contactors sized for the equipment.

Documentation for the WLC-9100 duplex pump-down level controller notes that its relays can be used as pilot relays for properly rated pump contactors.

That means the existing power hardware may remain part of the final design when it is in good condition and properly rated.

Match the Existing Sequence

A replacement level system should reproduce the required operating logic rather than simply copying the physical locations of old floats.

Waterline Controls offers simplex and duplex pump-down controllers, with high and low alarms available on selected models. Their dry contacts can report status to an existing control system.

If the old arrangement alternated pumps or used staged starts, select the new controls around that requirement. On the WLC-9000 A/C duplex pump-down controller, the A version is sequenced and the C version alternates. On the WLC-9100, A and B are sequenced and C and D alternate. Confirm which suffix matches the existing panel logic.

Check Sensor Cable Routing

Electronic sensing introduces its own installation requirements.

Waterline Controls installation instructions call for the sensor cable to run in earth-grounded metal conduit, separate from the conduit that carries high voltage lines, to reduce unwanted interference.

A retrofit is a good opportunity to correct questionable cable routing left from previous modifications.

Decide Which Signals Go to SCADA or BMS

Older float panels may provide only local lights or alarms.

An updated level control can add dry contacts for remote monitoring without requiring the BMS to control the pump sequence itself.

Possible points include pump calls, high level, low level and controller power loss, depending on the selected model.

Keep the local automatic sequence capable of doing its job even if remote monitoring is unavailable, unless the project design intentionally says otherwise.

Test Each Level Point

Commission the retrofit one function at a time.

Raise or simulate the water level and verify pump start, second pump operation, alarms and shutdown. Test manual controls separately.

Then verify the remote signals. For point-list details, see which BMS points a water level controller should report.

Where the selected controller has a press-to-test button, follow the model’s instructions to run the test sequence and confirm relays and connected devices respond.

Float Switch Replacement Controllers for Existing Panels

Waterline Controls manufactures frequency-based float switch replacement controllers for commercial sumps, lift stations, wastewater systems and other pump applications. Existing motor starters and panel components may be retained when the design and condition permit. For the cooling tower side of the same problem, see why float switches fail in cooling tower level control. Call 480-905-1892 to discuss the existing sequence, pump sizes, panel arrangement, alarm requirements and sensor locations before planning your retrofit.

References

Water and wastewater level controls

WLC-9100 A/B/C/D duplex pump-down controller with high alarm

WLC-9000 A/C duplex pump-down controller

Float switch replacement controllers

Float Switch, Pumping Stations, Water Level Controls
0
Level control during power loss title graphic
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What Happens to Level Control During Power Loss?

A level control’s power loss response is the state its valves, pumps and alarm contacts take when the controller itself loses power. It is one of the conditions a level control specification should address before equipment is installed.

The correct response is not identical for every application. A cooling tower fill valve, a wastewater pump and a fire water tank may have very different priorities. What matters is that the desired state is intentional and documented.

Define the Safe State for the Application

For many ordinary automatic fill systems, the conservative response to loss of controller power is to stop filling.

A common fail-safe arrangement uses a fill valve that closes when controller power is lost. That prevents a fill command from remaining active after the controller is no longer available to stop it.

That logic should not simply be copied into every project. The engineer must consider which failure creates the greater risk.

Pump Down Systems Have Different Concerns

A sump or lift station cannot remove incoming water if its pumps have lost electrical power.

The level controller may therefore be only one part of a larger emergency strategy involving standby power, remote alarms and available storage volume.

A high level alarm should be located with enough margin to provide a meaningful response if normal pumping is unavailable.

Power loss and high water are different conditions and should be reported separately where the control system allows it.

Send Power Loss to the Remote System

The WLC-5000 fill controller provides four remote dry contacts: one power loss contact and three contacts for its control functions. Its submittal identifies the normal and power loss state of the power contact.

That allows the BMS to identify that the controller itself is unavailable rather than assuming the water is normal. For the full list of points worth sending, see which BMS points a water level controller should report.

Fire Protection May Require Different Logic

Fire protection water storage deserves separate consideration.

The FPT-50 fire protection water level controller offers an optional Paragon valve arrangement that lets the fill operate automatically during power loss.

That illustrates why the phrase fail-safe cannot be reduced to one universal rule.

The approved fire protection design, adopted standards and authority having jurisdiction determine the required behavior for that project.

Consider Normally Open and Normally Closed Devices

The valve or relay state matters as much as the controller program.

A normally closed fill valve typically requires energy to remain open. Losing that energy therefore stops the fill.

Other arrangements may be intentionally designed to fail in another position.

The electrical drawings should show the relay state, the controlled device and the expected result during power loss. Labels such as normally open should always be interpreted in relation to the actual relay or valve being described.

Test Power Failure Deliberately

Do not wait for the first outage to discover how the system behaves.

During commissioning, simulate loss of controller power and observe the valve or pump response. Confirm the BMS or fire panel receives the expected signal.

Restore power and verify the system returns to normal operation without creating an unintended pump start, overflow or missed alarm.

Record the result in the sequence of operation.

Power Loss Contacts, Relays and Fire Panel Signals

Waterline Controls manufactures frequency-based electronic level control systems with power relays, alarm functions and model-specific dry contacts for BMS, BAS and fire panel integration. Because the correct power loss response depends on the application, the safest approach is to define it before equipment is ordered. Call 480-905-1892 to review the desired sequence, controlled device, alarm points and remote signaling requirements for your project.

References

WLC-5000 fill controller with high and low alarms

FPT-50 fire protection water level controller

What BMS points should a water level controller report?

Fire Protection, Pumping Stations, Water Level Controls
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Water level sensor placement guide title graphic with Waterline Controls logo and piping illustration
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Water Level Sensor Placement Guide

Water level sensor placement is the choice of where each sensing point sits in a tank, basin, sump or reservoir, and it decides when filling starts and stops, when alarms activate and whether pumps are protected from low water. A water level control system can only respond to the information it receives, so a sensor in the wrong place can make a good controller ineffective.

Proper positioning is a vital part of designing or upgrading an automatic water level control system. The sensing points should reflect the actual operating range of the equipment.

Start With the Normal Operating Water Level

Before deciding where sensors belong, determine the normal operating level for the application. A cooling tower basin, fire protection tank, wastewater sump and storage tank do not necessarily require the same control range.

In a fill application, the fill-start sensing point identifies when additional water is needed. The fill-stop sensing point determines when filling should stop. These points are separated to form an operating range, instead of switching the equipment on and off as the water surface moves.

The fill-start point must allow enough water for normal operation, and the stop point must leave enough space below the overflow level.

Keep Sensors Away From Misleading Water Movement

Water inside a tank is not always calm. Incoming water, pump suction, recirculation, turbulence and splashing can cause the level around one part of a vessel to behave differently from the overall water level.

Installing a sensor directly beside a forceful inlet can cause unnecessary switching because the sensor may repeatedly become wet and dry. Similar problems can occur where strong turbulence affects the sensing area.

The best location is one that represents the true level of the vessel as consistently as possible. This matters particularly where equipment cycles frequently or water is continuously moving.

Protect Pumps From Low Water Conditions

Sensor placement also plays a role in pump protection.

Once the level has fallen below a safe point, pumps that need a sufficient water supply should not be allowed to run. Operating a pump below its required water level can damage components such as bearings and shaft seals, so use the selected pump manufacturer’s minimum level and dry running limits.

A correctly positioned low level sensor can provide the signal needed to stop equipment, activate an alarm or initiate another programmed response before the water reaches a damaging level.

Its exact position depends on the system, including the pump intake, required reserve volume and the level at which continued operation becomes undesirable.

Leave Space for High Level and Overflow Protection

The upper sensing point should not simply be placed as high as physically possible. Tanks and basins need room between their normal full level and the point where water can escape.

The U.S. Department of Energy states that properly operated cooling towers should not have leaks or overflows, and recommends checking float control equipment and system valves to confirm the basin level is being maintained.

Where high level alarms are used, their sensing point should provide useful warning before an overflow occurs. The normal fill stop point and the high level alarm should perform separate jobs rather than respond at essentially the same height. On the WLC-5000 water level controller, for example, fill start, fill stop, high alarm and low alarm each have their own probe length. The difference between a high water alarm and an overflow alarm is covered in high water alarm vs overflow alarm for level controls.

Review Sensor Position When Conditions Change

A system that worked well when first installed may need review after equipment changes. A replacement pump, altered flow rate, new basin configuration, different operating level or changing water demand can affect the most useful sensing positions.

That makes sensor placement worth checking during upgrades and recurring maintenance. Operators should also look for physical changes around sensors that could interfere with consistent detection.

Controllers and Sensors for Defined Sensing Points

Reliable automatic control begins with accurate detection of the water level. Waterline Controls manufactures frequency-based level controllers and stainless steel sensors for cooling towers, tanks, sump systems, fire protection applications, HVAC equipment and other commercial uses. For help selecting a water level control system and setting sensing points for your application, call Waterline Controls at 480-905-1892.

References

U.S. Department of Energy: Best Management Practice #10, Cooling Tower Management

Waterline Controls water level control systems

WLC-5000 water level controller

WLC Checkpoint OEM sensor for liquid level controls

Water Level Controls, Water Tanks
0
High water alarm vs overflow alarm title graphic
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High Water Alarm vs Overflow Alarm

A high water alarm warns that the level has risen above its normal operating range. An overflow alarm is a project or code label for an alarm intended to warn of or prevent overflow, and specifications do not agree on where it sits. The actual sensor elevation and control sequence, not the label, decide whether either alarm gives useful response time.

An alarm that waits until water is already leaving the tank offers much less protection than one that warns while an operator or an automatic action can still respond.

Define the Normal Maximum First

Before locating the alarm, establish the normal fill stop level.

Automatic filling should stop at the intended operating level. The high alarm then sits above that point.

The WLC-5000 water level controller uses separate probes for fill stop and high alarm, allowing the controller to distinguish normal filling from an abnormal high water condition.

The distance between those points depends on the tank geometry and operating requirements.

High Level Means the Normal Sequence Has Been Exceeded

A high level alarm usually indicates that normal level control has not stopped the rise in water.

Possible causes include a leaking fill valve, a valve stuck open, incorrect control wiring or unexpected inflow.

The alarm therefore provides diagnostic information: the operator knows that the tank has moved beyond the normal control range. For that reason the high alarm should be a dedicated sensing point, independent of the points that run normal fill or pump control.

Overflow Is a Physical Condition

Overflow occurs when water reaches a path that allows it to leave the intended vessel.

That may be through an overflow pipe or over the edge of a basin.

Calling a sensor an overflow alarm does not necessarily tell the engineer whether it is located before, at or after that physical level.

The drawings should therefore show the actual sensor elevation instead of relying only on the alarm name.

Waterline Controls has previously discussed overflow alarms for cooling tower level control, including WLC models that combine high and low alarms with automatic level control. For tank applications, see the water tank level controller high water alarm guide.

Leave Enough Response Margin

The faster a tank can fill, the more important alarm margin becomes.

If the high alarm sits only a fraction below overflow during a high inflow condition, the facility may have little useful warning.

Consider the maximum inflow rate, available freeboard and whether the control system can automatically stop the incoming water.

An alarm intended only to summon an operator requires enough time for that person to respond.

Send the Alarm Somewhere Useful

A local light is valuable during maintenance, but it does little for an unattended mechanical room.

WLC controllers that include a high alarm, such as the WLC-5000, provide a dry contact that can send that condition to a BMS, BAS or other remote monitoring system. For the full point list, see which BMS points a water level controller should report.

The BMS alarm should identify the actual equipment and condition.

Avoid a generic message such as “Water Alarm” when “Cooling Tower 2 High Level” gives the operator much better information.

Test the Alarm Independently

During commissioning, confirm normal fill stops before the high alarm activates.

Then simulate the high level condition and verify the local indicator, remote contact and any connected audible alarm.

If the system is designed to close another valve or stop equipment at high level, verify that function as well.

Record the actual final elevation.

High Water Alarms and Level Controllers for Tanks and Towers

Waterline Controls manufactures frequency-based electronic water level systems with automatic filling, high and low water level controls and alarms and remote signaling for cooling towers, tanks, sumps and other commercial applications. Call 480-905-1892 to review your normal operating range, high water setpoint, freeboard and BMS requirements so the alarm provides useful warning before an overflow becomes a facility problem.

References

WLC-5000 water level controller with high and low alarms

Water level controls and alarms

Overflow alarms for cooling tower level control

Water tank level controller high water alarm

Cooling Towers, Water Level Controls, Water Tanks
0
Cooling tower remote sump with level sensor showing high alarm, fill stop, fill start and low alarm points
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Cooling Tower Remote Sump Level Control Guide

A remote sump is a separate tank that holds a cooling tower’s operating water, pump suction and makeup connection in place of the tower’s own cold water basin. A cooling tower does not always store circulating water in that basin. Some systems drain to a separate remote sump, where the pump suction, makeup water and operating storage are located away from the tower.

That changes where water level should be controlled. The useful measurement is the level that protects the remote sump and keeps the circulation system operating properly.

Understand What the Remote Sump Is Doing

During operation, water is moving through the cooling equipment, piping and spray system before returning to the sump.

EVAPCO engineering information for remote sump arrangements notes that additional water has to remain in the remote sump to cover the pump suction and strainer during operation. Its remote sump arrangements use an enlarged outlet so water can drain from the evaporative equipment to the separate sump.

The engineer therefore needs to consider both stored water and water that is temporarily in circulation.

Control Level at the Actual Storage Point

If the operating water is held in the remote sump, the level sensor should normally supervise that vessel rather than an inactive basin elsewhere in the system.

Waterline Controls specifically lists remote sumps among the HVAC applications for its electronic water level controllers. The same product family is used for cooling tower basins, evaporative condensers and closed circuit fluid coolers.

The sensor elevations should be based on the sump geometry and approved operating level.

Allow for Water in Transit

When circulation begins, some water leaves the sump and occupies the piping and cooling equipment.

The sump level may therefore fall even when the system has not lost water. Waterline Controls covers this effect in more detail in water in transit and cooling tower level control.

If the makeup control is set without considering that normal change, it may add more water than the system needs. When the pumps stop and circulating water drains back, the sump can then rise considerably.

The sequence should be reviewed under both running and shutdown conditions.

Protect Pump Suction

The low operating point needs to leave enough water over the pump suction for reliable operation.

EVAPCO’s engineering guidance specifically tells designers to allow additional water in the remote sump to cover the pump suction and strainer.

A separate low level alarm point can provide warning before the usable reserve reaches an unacceptable condition.

The pump manufacturer’s minimum submergence and suction requirements should also be followed.

Add a High Level Alarm

A high level alarm can identify excess makeup, a fill valve that does not close, heavy drainback or a blocked overflow.

The alarm should normally sit above the regular fill stop level so ordinary makeup operation does not create nuisance alarms.

The WLC-5000 level controller combines automatic fill with high and low alarms and provides dry contacts for BMS monitoring.

Those discrete outputs allow the BMS to report fill, high alarm, low alarm and power loss status.

Consider Shutdown and Winter Operation

A remote sump arrangement may also be selected to move water indoors or into a protected location during cold weather.

EVAPCO’s remote sump notes say the unit’s spray pump, suction strainer and associated piping are omitted from the unit and provided at the remote sump instead, and an oversized outlet is used so the equipment can drain to the sump. EVAPCO also describes a remote sump as a way to keep recirculating water out of the basin in cold weather. Shutdown and freeze protection still have to be designed for the whole system.

Level control should therefore be coordinated with the entire seasonal operating sequence.

Test the System in Both Conditions

Commission the system with circulation operating and again as the system shuts down.

Confirm the normal operating level, makeup start and stop points, low alarm, high alarm and the level reached after drainback.

Record those observations for future operators.

Level Control for a Cooling Tower Remote Sump

Waterline Controls manufactures frequency-based electronic water level control systems for cooling towers, remote sumps, evaporative condensers and closed circuit fluid coolers. Systems are available with automatic fill, high and low alarms and dry contacts for building automation. Basin heater control is a separate option and is often unnecessary when the sump is indoors. Call 480-905-1892 to review your remote sump dimensions, operating levels, sensor arrangement and BMS requirements.

References

Cooling tower level controls

EVAPCO: Closed Circuit Coolers Engineering Data

Cooling Towers, Water Level Controls
0
Slow closing fill valve and Y strainer on a tank fill line with a Waterline Controls level controller
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Why Slow Closing Fill Valves Matter

Water hammer is a pressure surge that occurs when moving water is stopped too quickly. The level controller may tell a fill valve exactly when to close, but the valve still has to stop the water in the pipe.

When a large flow is stopped very quickly, the resulting pressure change can create water hammer. Operators may hear a bang in the piping, but the concern goes beyond noise. Repeated pressure shock can place unnecessary stress on piping, fittings and valves.

For automatic tank and cooling tower fill systems, valve behavior deserves attention during design.

Fast Closure Can Create Pressure Shock

Water has momentum while it is moving through a pipe. A quick closing valve changes that velocity rapidly.

Watts, in its water hammer arrestor literature, explains that a sudden stop from a fast closing valve creates a shock that can damage pipes and appliances. The same surge occurs on large makeup lines.

Higher flow velocity and rapid valve closure increase surge risk, so pipe length, diameter, material, operating pressure and closure time should be evaluated together.

The required valve and surge control method depend on system pressure, pipe size, velocity and layout.

Slow Closing Solenoid Valves Reduce the Sudden Change

A slow closing valve does not simply delay the controller command. It changes how the valve physically reaches the closed position.

Emerson’s ASCO 221 series is specifically designed as a slow closing water solenoid valve. ASCO documentation states that its closing mechanism reduces the pressure spike associated with water hammer.

Waterline Controls offers slow closing valves for level control systems as accessories for its electronic level control systems.

The valve still needs to be sized for the actual application.

Match the Valve to the Water Supply

Do not select an automatic fill valve solely from the pipe diameter shown on a sketch.

Review required flow and Cv, minimum and maximum differential pressure, valve pressure rating, electrical supply and the time available to refill the basin or tank.

An oversized valve can raise velocity and overshoot the stop level while it closes, while an undersized valve can make recovery unnecessarily slow.

The project engineer should also confirm any requirements for backflow prevention and water supply protection.

Protect the Valve From Debris

Automatic valves work better when debris is kept out of the internal components.

Waterline Controls drawings commonly show a Y strainer upstream of the fill valve. The company also provides strainers and valve accessories for its systems.

A strainer still needs inspection and cleaning. A blocked strainer can reduce makeup flow and create a low level problem even when the controller and valve are operating correctly.

Watch for More Than Water Hammer

A fill problem can show up in several ways.

A valve that does not close completely may cause the level to creep upward after the controller has stopped calling for water. A valve that opens slowly or has inadequate flow may allow the basin to fall toward the low alarm during heavy demand.

The control system should therefore be commissioned as an assembly rather than testing the sensor and valve independently.

Verify the Complete Fill Cycle

Operate the system through a full cycle.

Confirm the controller calls for fill at the correct level, the valve opens fully, the water level recovers and the valve closes without excessive shock.

Then confirm that the high and low alarms remain outside the normal operating range.

If the BMS receives fill status, verify that point as well.

Fill Controllers, Slow Closing Valves and Strainers

Waterline Controls manufactures frequency-based electronic fill controllers for cooling towers, tanks, fire protection water tanks and other commercial applications, including the WLC-5000 fill controller with high and low alarms. The company also supplies valves, strainers and related accessories. If your project requires reliable automatic filling or you are dealing with repeated valve problems or piping shock, call 480-905-1892 to discuss the controller, valve type, operating levels and system requirements.

References

Slow closing valves for level control systems

Level control accessories

Watts: Water Hammer Arrestors

Emerson: ASCO Series 221 Slow Closing Water Solenoid Valve

Water Level Controls, Water Tanks
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Pump and level sensor at a sump illustrating water level control pump short cycling
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Why Water Level Control Pumps Short Cycle

Short cycling means a pump starts again before it has finished a useful run, often many times an hour. Those repeated starts can overheat motors, wear relays and contactors, increase maintenance and hide a level sensing problem. In a tank, sump or lift station, the correct run time depends on inflow, pump capacity and the distance between the start and stop levels.

The first step is to confirm that the cycling is abnormal. Then the operator can separate a pump problem from a sensor, controller or hydraulic problem.

Record What the System Is Doing

Count how many times the pump starts during a normal hour and note how long each run lasts. Record the water level at start and stop, whether both pumps are affected and whether the pattern changes during rain, process demand or heavy building use.

Xylem describes a case in which unrealistic level spikes caused two pumps to start and stop hundreds of times per day. Because both pumps were affected equally, the evidence pointed toward the level sensor or controller rather than two pump failures.

Check the Distance Between Start and Stop Levels

A pump needs enough drawdown between the start and stop points to complete a useful cycle. If the sensing points are too close, a small change in level can stop the pump almost immediately. Water returning through the discharge pipe may then raise the level enough to start it again.

Review the operating band, tank dimensions and pump rate before moving sensors. A wider separation may reduce cycling, but it must not allow overflow, low water damage or an unsuitable process level.

Look for Turbulence and Wave Action

Water entering near the sensor can create splashing, waves and temporary changes. A float may bounce, or another sensor may see movement that does not represent the average level.

Inspect the sensor location while the system operates. In a cooling tower basin, surge tank or active sump, the answer may involve repositioning the sensing assembly, using a suitable time delay or selecting a controller designed to compensate for wave action. Waterline Controls states that its cooling tower level controls are designed to compensate for wave action in a basin. That is surface stability for fill control, not the start to stop distance a pump needs.

Inspect Sensors and Wiring

Mechanical floats can catch on piping, cables, grease or debris. Probe systems should be checked for secure mounting, correct depth and intact wiring. Loose terminals, damaged insulation or intermittent power can create false transitions.

Do not assume the pump has failed because it receives repeated start commands. Check whether the controller LEDs or BMS points show rapid level changes. If the indicated level jumps while the water remains steady, focus on the sensing and control circuit.

Check Valves and Flow Conditions

A leaking check valve can allow discharged water to return after the pump stops. Restricted piping can cause the pump to move less water than expected. In a fill application, a valve that leaks through may raise the level after the controller has closed it.

Compare the actual drawdown or refill time with previous operation. A major change may point to a blocked line, worn pump, altered inflow or valve problem rather than a controller setting.

Make Sure the Pump Is Properly Sized

An oversized pump may remove the available water so quickly that each run is extremely short. An undersized pump may run almost continuously during peak inflow and still allow the level to rise. Pentair’s residential sump pump FAQ notes that oversizing and undersizing can shorten pump life through short cycling or continuous running. The same mechanisms apply to commercial sumps, where the motor’s rated starts per hour still govern.

Pump selection, operating level and control range have to work together. Changing one without reviewing the others may move the problem rather than solve it.

Test the Complete Sequence

After repairs or adjustments, observe several full cycles. Confirm start, stop, alarm and power loss indication. For duplex systems, verify the specified lead and lag sequence and, where applicable, pump alternation.

Document the final sensor locations and normal cycle time. A future technician can then identify a real change instead of guessing what the system used to do.

Level Controllers for Duplex Pump Down Stations

Waterline Controls supplies frequency-based electronic level controllers for tanks, wells, cooling towers, sumps, wastewater and dual pump applications, including the WLC-9100 dual pump down level controller for duplex stations. Its stainless steel sensing probes, local status lights, alarm options and dry contact outputs are designed for reliable level control without moving floats. Call 480-905-1892 to review short cycling, the required pump sequence and the applicable controller functions.

References

Water and wastewater system level controls

Water tank level sensors and controllers

Xylem: Very Short Pump Cycles

Pentair: Sump Pump Info FAQ

Pumping Stations, Water Level Controls
0
Lead lag duplex pump control with WLC-9100 dual pump controller, alternation and high level alarm
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Lead Lag Pump Control System Planning Guide

A two pump station needs more than a second pump sitting beside the first. The control sequence has to decide which pump starts first, when the second joins it and what happens if the water continues to rise. A well planned lead lag arrangement spreads operating hours, handles changing inflow and gives the facility a clearer response when one pump cannot keep up.

Understand Lead, Lag and Alternation

The lead pump is the first unit called during a normal cycle. The lag pump starts at a higher level if inflow exceeds the capacity of the lead pump or the level continues rising. When demand falls, the pumps stop according to the selected sequence.

Alternation changes which pump becomes lead on the next cycle. Grundfos explains that alternation divides operating hours between two pumps, while the second can start when demand exceeds the capacity of one. This avoids one pump carrying nearly all routine use while the other remains idle.

Choose the Shutdown Sequence

Two common questions are whether the pumps should stop one at a time as the level falls or stop together at a lower point. Both approaches can be useful, depending on the tank, inflow and desired drawdown.

Waterline Controls offers WLC-9100 dual pump controller variations with sequence on and sequence off operation, as well as versions in which both pumps stop together. Alternating models change the first pump each cycle so wear is shared.

The sequence should be shown on the control drawing. Operators need to know which level starts the lead pump, which starts the lag pump, where the high alarm activates and how the pumps shut down.

Set Levels Around the Actual System

Sensor positions cannot be chosen from tank height alone. The engineer should consider useful volume, inflow rate, pump capacity, minimum submergence, freeboard and the time available before overflow.

The lag point should be high enough to avoid unnecessary two pump operation during ordinary cycles but low enough to give the second pump time to respond. The high alarm should provide meaningful warning rather than activating when the station is already in danger.

A narrow control band can create short cycling. A band that is too wide may allow excessive level variation. The correct range balances pump protection, storage and process needs.

Plan for One Pump Being Unavailable

A duplex station is often selected for redundancy, but redundancy only exists when the controls can respond to a failed or unavailable pump. The design should consider overloads, disconnect position, maintenance isolation and whether the lag pump can become lead when the other unit is out of service.

The operator should also know whether an alarm confirms that a pump was commanded or that it actually ran. A command signal does not prove that water was moved.

Include a High Level Alarm

The high level alarm is the final warning that normal pumping has not controlled the water. It should be visible locally and, where required, reported to the BMS, SCADA system or remote alarm panel.

Waterline Controls combines dual pump down control with a high alarm in the WLC-9100. Its models provide dry contacts for remote signaling, including power loss and control functions. Remote point names should distinguish lead pump, lag pump, high alarm and controller trouble where those signals are available.

Commission Under Realistic Conditions

Startup testing should confirm more than manual pump rotation. Raise or simulate the level through each operating point. Confirm the lead pump starts, the lag pump joins at the correct point, the alarm activates and the pumps stop in the intended order.

Repeat the cycle to verify alternation. Test power loss indication and BMS or SCADA points. If the system uses check valves, verify that backflow does not restart the pumps immediately after shutdown.

Document Normal Operation

Leave a sequence of operation in the facility records. Record sensor heights, pump assignments, relay functions and expected cycle behavior. This makes future troubleshooting much faster.

Operating staff should know how to place one pump out of service without defeating alarms or leaving the station without automatic control.

Specify Lead Lag Control With Waterline Controls

Waterline Controls manufactures dual pump level controllers for lift stations, sumps, wastewater systems, tanks and other pump down applications. The WLC-9100 provides several sequencing and alternation choices with high level alarm and remote signaling options. Call 480 905 1892 to review pump capacity, sensor levels, sequence and BMS requirements for your project.

References

WLC-9100 dual pump down level controller

Water and wastewater system level controls

Pumping Stations, Water Level Controls
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What to Specify for Fire Water Tank Level Monitoring
Regular Post
Written by Waterline Controls

Fire Water Tank Level Monitoring Guide

A fire water storage tank is not an ordinary process tank. Its level has to remain available for an emergency, while abnormal conditions must be reported clearly enough for facility staff to act. A gauge that only shows one condition at the tank may not provide the supervision, automatic filling and remote signaling expected for the project.

The final design depends on adopted codes, the fire protection plan and the authority having jurisdiction. A useful specification gives that team clear options instead of treating level control as a late plumbing accessory.

Confirm the Required Operating Level

Begin with the fire protection engineer’s required usable water volume and normal level. Controller setpoints should relate to that design, tank geometry and the elevations shown on the approved drawings.

NFPA guidance for fire protection water storage tanks addresses maintaining the required water level and supervising tank conditions. The local fire marshal may apply a particular adopted edition and local amendments, so the specification should not rely on a generic online diagram.

Define High, Low and Low Low Conditions

A low level alarm warns that available fire water has fallen below normal. A high level alarm can identify a fill valve problem or another condition that may cause overflow. Some projects also use a low low point for additional protection or heater cutoff.

Alarm descriptions should be specific. “Tank trouble” gives the operator little direction. Separate high, low, low low and power loss signals allow the remote system to display the actual condition.

Waterline Controls offers FPT fire protection tank level controllers with combinations of high alarm, low alarm, low low alarm, automatic fill and heater cutoff. The correct model depends on the approved sequence and which functions are handled elsewhere.

Decide Whether Filling Is Automatic

An automatic fill controller can open a valve when the level falls and close it after the normal level returns. That function should be coordinated with the water supply, valve type, backflow protection and municipal requirements.

Automatic filling does not replace supervision. A valve can fail, the supply can be interrupted or the tank can lose water faster than it is replaced. The remote system still needs to report abnormal conditions.

Plan Remote Fire Panel Connections

The level controller should connect to the approved remote fire panel or supervisory system using the required contact arrangement. Waterline Controls states that its FPT series integrates with existing remote fire panels. Potter also offers a float operated supervisory switch specifically for sprinkler supply tanks, showing that tank level is treated as a dedicated supervisory function.

Create a point list showing each signal, normal contact state and destination. Include controller power loss when required. The fire alarm contractor, electrical contractor and level control supplier should review the interface before installation.

Protect Against Power Loss and Cold Conditions

A level system that loses power should not appear normal. Decide how the panel will indicate loss of controller power and whether the remote signal is fail safe.

In cold climates, a tank heater or related equipment may need protection when water falls to a critical level. Waterline Controls offers the FPT-61T level controller with heater cutoff alongside high and low alarms. Heater operation and low water protection should follow the project design and equipment instructions.

Choose Sensor Locations Carefully

Sensor elevations should be measured from a fixed tank reference and documented on the approved drawing. Avoid placing the sensing assembly where incoming water creates misleading turbulence or where internal piping or maintenance work can damage it.

The sensor material and mounting assembly should suit the tank and water. Future access also matters. A technician must be able to inspect and test the system without removing unrelated equipment.

Commission Every Function

Testing should simulate each level condition and confirm local indication, fill valve response, remote panel signal and alarm restoration. Test power loss and any heater cutoff or low water interlock.

Record the final sensor elevations, relay states and sequence of operation. Facility staff should know how to use the test feature and how often the system must be inspected under the applicable fire protection program.

Specify Fire Tank Controls With Waterline Controls

Waterline Controls manufactures electronic FPT level control systems for fire water tanks, including alarm only models and configurations with automatic fill, high and low alarms, low low indication and heater cutoff. The systems are assembled in the United States and designed for remote panel integration. Call 480 905 1892 to discuss the approved sequence, tank dimensions, sensor arrangement and municipal requirements for your project.

References

Fire protection water tank level controls (FPT series)

FPT-61T fire tank level controller with heater cutoff

Fire Protection, Water Level Controls, Water Tanks
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