50/Plumbing Engineer October 2021
it is the first thing anyone looks at when they wash their hands. The device that switches a hands-free faucet on is typically an infrared sensor. It includes an emitter and receiver, usually housed behind that little red window we wave at frantically when the faucet does not work. Sometimes the sensor device is cleverly tucked away at the end of a spout. According to the manufacturers I spoke with, sen- sor technology is not the leading cause of malfunction. While they said that the sensor is one of the first things people assume is the problem, they claim sensor technol- ogy is rather straightforward and dependable. Once the infrared beam from the sensor is reflected to the detector, a solenoid valve gets actuated. This is what allows water to flow through the spout. The solenoid is an electromechanical device subject to the most move- ment in the hands-free faucet assembly. For this reason, solenoid valves should be on a periodic maintenance schedule for facilities. Solenoid valve designs are different between manu- facturers. Common to the dependable operation of sole- noid valves is typically a pre-filter, sometimes shaped like a small wire-mesh cone. Solenoid valve assemblies can be sensitive to small grit and other water impurities. One of the more common reasons for sensor faucet failures is the improper installation of the solenoid filter and improper flushing of the domestic water system before startup. Some manufacturers include a "wiper spring" to clear out the solenoid after each use. Construction materials also play a factor in how long a solenoid lasts; silicon seals are commonly used for longevity. The solenoid is also the component using the most power. The power source for sensor-type faucets is one of the most unique and emphasized components of the faucet. For health-care designs, many of my colleagues specify sensor-type faucets using AC power on an emergency circuit. This would seem to create the highest level of dependability. When it comes to designs where DC power is the pre- ferred choice, each manufacturer has its strategy. Some manufacturers claim that standard AA batteries are the best choice since they are readily available and provide a better load distribution profile than custom-type batter- ies. The designs using lithium-type batteries will claim operational lives of eight, 10, 12 or even 15 years. One of the keys to battery life is how the circuitry of the faucet is designed. A hands-free sensor faucet's electronic features, including the sensor and the solenoid valve, can only operate through the power source. There will be a low, consistent power drain for the sensor and a larger power drain for the solenoid valve. Capacitors are typically employed in the design to help store an electric charge and dampen the spike in power demand when the solenoid is actuated. Photovoltaic cells or hydrogenerators may be used to help top off the power stored in the capacitor. The last electronic portion of hands-free faucets is the programmable component; this is sometimes referred to as the controller. Similar to many electronic devices, the controller seems to have gotten smaller over time. My question to many of the manufacturers I spoke to was: "Why can't the faucet just turn on when your hands are under it and turn off when you pull them away?". I didn't quite get a straight answer. Probably the most sat-
No ]}v 1 Gooseneck Spout 2 Ceramic Cartridge 3 Power Adapter (AC Only) 4 Pressure Valve Assembly 5 Sensor/Control Module Assembly
1 5 4 2 3
AC Powered Only
Sensor-operated mixing faucet assembly parts. Graphics: Hydrotek International 1.1 AUTOMATICALLY OPERATED LAVATORY FAUCETS A. NSF Standard: Comply with NSF 61 and NSF 372 for faucet materials that will be in contact with potable water. B. Lavatory Faucets - Automatic Type: Hardwired Electronic Sensor Operated: 1. Standards: ASME A112.18.1/CSA B125.1 and UL 1951. 2. Electrical Components, Devices, and Accessories: Listed and labeled as defined in NFPA 70, by a qualified testing agency, and marked for intended location and application. 3. General: Include hot- and cold-water indicators; coordinate faucet inlets with supplies and fixture hole punchings; coordinate outlet with spout and fixture receptor. 4. Body Material: Commercial, solid-brass, or die- cast housing with brazed copper and brass waterway. 5. Finish: Polished chrome plate. 6. Maximum Flow Rate: 0.5 gpm. 7. Drain: Not part of faucet.
A standard-based spec for lavatory faucets. Source: SmithGroup
Hands-Free
Previous Page