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