All electronic water level controllers have two major failure points - the relay in the controller that drives the solenoid valve, and the solenoid-actuated valve itself. Typically, these are the only moving parts in an electronic water level control system. The field technician or facility maintenance person needs to be able to quickly diagnose which part has failed.
The relay and valve fail for different reasons. The contacts on the relay fail after many years of operating the valve. However, when properly matched to the valve, they can last up to two million strikes before they fail - typically, seven to 20 years, depending upon the environment.
The solenoid valve has two failure points: the coil and the plunger inside the valve. This part takes the brunt of the work and should be rebuilt every five years as part of a proper maintenance schedule.
Here are the three things to look for in an electronic water level controller so you can rely on it over the lifespan of the cooling tower.
1. Integrated Diagnostics to Ease TroubleshootingA field technician or facility maintenance person should be able to easily diagnose the problem without taking the entire unit apart. To ease troubleshooting, look for a controller with the diagnostics built into the controls. Look for a controller that uses LED lights that go on when the relay and solenoid valve are operating and off when they are not operating.
The controls also should include an onboard test switch to allow the controller to automatically sequence through the functions as the operator watches the lights come on, hears the relays activate and sees the valves turn on. This type of system helps the technician successfully diagnose the problem in the field and does not require any other technical knowledge.
2. Modular PartsOnce the technician has identified what is wrong with the controller, now he or she needs to fix it, preferably in the field. The entire water level control system should be designed so a field technician can remove and replace only the necessary parts - not the entire unit.
The relay that operates the solenoid valve is the main component that fails inside the controller. Look for a controller that eases access to the relays and allows them to be removed and replaced.
It should be possible to rebuild the solenoid valve without removing it from the piping system. The valves manufacturers have rebuild kits, so be sure you know what company manufactured the valve as well as the part number for the valve and rebuild kit. Keep one on hand because you never really know when it is going to fail.
Other parts of the water level control system can also fail, but they do not do so not as often. However, these parts - transformers, printed circuit boards and sensor - also should be field replaceable. Look for a product with a modular design so you can replace only individual parts that have failed or worn out rather than the entire product. It may be cost prohibitive to own a water level controller that does not have interchangeable parts that the operator cannot replace.
3. Safety Certification by a Third PartyAnother important aspect of controls is the third-party validation, which often is required by the building department inspector or other authority having jurisdiction. A properly listed product means that an independent third party has tested and evaluated the product - as a system - to be safe to use for the application intended. When a product or system is not listed, there can be safety issues. Electronic water level controllers fall under the UL508 standard for industrial control systems.
Third-party validation is labeled as a listed product for a system by UL, CSA or ETL in the United States and Canada. Some cooling towers manufacturers have in the past asserted that the “cooling tower system” is certified or listed; therefore, the electric water level controller is listed as well. But recently, CSA rejected this idea and required cooling tower manufacturers to remove the electrical water level controller until they had third-party certification with a listing as a system or a controller that is certified and listed by a third party.
Remember, electronic water level controls for cooling towers are certified under the UL508 standard and/or the equivalent standard for CSA. Listed products carry a logo mark of the agency which listed it directly on the device.