How Automatic Faucets Work
Automatic faucets are created by combining four key components: Solenoid valve, sensor and control electronics, power source, and faucet. Although there are variations to this theme, these are key tools each with a distinct function that, once combined, constitute an automatic faucet. Here's an overview break down of these components:
- Solenoid operated diaphragm valve which is entrusted with the task of physically starting and stopping water flow. A small number of foreign manufacturers use geared motors to achieve valve opening and closing.
- Sensor and control electronics who's combined mission is to sense the presence of an object in front of the faucet (automatic faucets employ presence sensors and not motion sensors) and order the solenoid valve to initiate the flow of water. Then, when the object is no longer present, the sensor and control electronics order the solenoid valve to terminate the flow of water, but only after a predetermined time have passed. This "off delay" time is generally measured in seconds.
- Power source, generally batteries or AC transformer. Since both solenoid valve as well as sensor and control electronics require power source, this readily available component is crucial to insure faucet operation. Commonly used batteries are C, AA, 6Volt and 9Volt Lithium batteries. Automatic faucets using AC transformer as power source are generally inexpensive to produce and are priced accordingly in the marketplace. A notable exception to this cost basis detail is the type of automatic faucet specifically designed for either power source (MAC Faucets FA400 and FA444 series are clear examples).
- Faucet spout, for water delivery. Most automatic faucet spouts are design to house within them the sensor capsule, or in the case of a notable competitor, the faucet spout houses fiber optic cables to carry infrared signal from the sensor to the spout. Some spouts house within them the whole "enchilada" sensor, control electronics, solenoid valve, and even, batteries.
Component details is covered in Part II.
No credible explanation of the solenoid valve is complete without discussing the two hybrid technologies that, when combined, form a solenoid valve:
- Electromagnetism (solenoid)
- Fluid dynamics (diaphragm valve, AKA poppet valve). I will start by breaking the solenoid valve discussion into 2 sections, one that addresses the "solenoid" portion of the solenoid valve and one that addresses the "valve" portion of the solenoid valve.
A) Solenoids are electrical components that transform electrical energy into mechanical energy "motion". When energized a solenoid creates a magnetic field which exerts a linear force on an object called plunge or actuator. That's why solenoids are called "linear motors". Automatic faucets powered by batteries employ a type of solenoid called "magnet latching or bi-stable solenoid". These solenoids operate at low voltage, usually 6 volt DC, with some solenoids operating at 9 volt DC. The reason these solenoids are called "magnet latching" is that as the solenoid is initially energized to start the water flow, the plunger is driven into the range of a permanent magnet which in turn holds the plunger in the "open" position. This initial energizing of the solenoid is called "pulsing or inrushing" and takes place within a fraction of a second. In order to return the plunger into its original "closed" position the solenoid is once again "pulsed" but this time by reversing polarity (remember, we're working with DC voltage here). The reason behind this complex operation: Conserving battery power.
Faucets powered by AC transformers utilize standard, none latching solenoids. This type of solenoid requires constant energy to hold plunger in place, and when e-energized, the plunger naturally returns to its normal "closed" position with the help of a biasing spring.
I won't go into dizzying details here about the solenoid (or any of the four components discussed earlier) for that you have to stick around for act three.
In addition to Voltage specification, solenoids have Mill Watt specification. This last specification is especially important when dealing with battery powered automatic faucets since solenoids, by far, are the largest consumer of battery power in an automatic faucets. Mill Watt specification gives us a glance at solenoid's efficiency and the amount of current it needs to do its job. It's a sort of "miles per gallon" measurement, the more miles per gallon, given a specific size gas tank, the less gas stops we have to make on our journey. The same holds true in an automatic faucet, the more efficient the solenoid the less often we have to replace the batteries.
B) Diaphragm valves are often misunderstood and much maligned devices; however, they are commonly used in many household equipment such as toilets tanks, sprinkler valves, washers, dishwashers, ice makers and many more. I don't know who invented the first diaphragm valve but the guy (or it could as easily have been gal) is a genius. The basic premise behind the diaphragm valve is to control the flow of a large volume of water with a smaller, more manageable, water volume. The way in which this task is accomplished is nothing short of brilliant (like I said earlier, the original inventor must have been a genius). I want to ask you at this time to suspend your disbelief for a moment, read this paragraph through once, this'll make it easier to understand the next time around. The percentage values are used strictly for illustration purposes. We begin with a malleable rubber disc (today's diaphragms are much more sophisticated than that of course) which itself acts as a water valve as it seats itself against a solid valve seat no different from a standard faucet valve seat. This disc is located in an environment punctuated by three pressure zones locked into a constant battle to get the upper hand, like my dear nieces and nephews AKA The Trio of Terror. On one end we have supply pressure acting on 70% of the diaphragm area (the portion may be lesser or greater depending on the specific valve design) and pushing the diaphragm up and away from the valve seat, an act that would result in opening the diaphragm valve. Also on the same end we have atmospheric pressure which, for the purpose of this discussion, equals "0" psig and is unable to impact the diaphragm movement in either direction. This "0" psig zone represents the area inside the valve seat and occupies the other 30%. Why "0" psig you ask? The valve seat is plumbed directly into the faucet spout, "0" psig is the pressure in the faucet spout when no water is going through it. On the other end of this tug of war we have pressure that equals supply pressure (that's because it is supplied by supply pressure through a very small diameter hole often built into the diaphragm itself) acting on 100% of the diaphragm area, pushing the diaphragm the other way and firmly seating it against the valve seat, an act that would result in closing the diaphragm valve. Think of it this way: we have two arm wrestlers, equally strong in every way, yet one of them ate only 70% of his wheaties, and the other one finished the bowl. Who do you think is going to win the arm wrestling competition? If you guessed the guy who finished his bowl, you guessed right. In this case the guy who finished the bowl represents the pressure acting on 100% of the diaphragm area pushing the diaphragm tight against the valve seat.
In order to open the diaphragm valve all we need to do here is to release the pressure that is pinning the diaphragm against the valve seat. This is a job assigned to the solenoid valve. Remember the solenoid's plunger we spoke about earlier in this discussion? The plunger, which is driven by the solenoid is yet another miniature water valve who's sole mission is to open and release the pressure that is pinning the diaphragm against the valve seat (the pressure acting on 100% of the diaphragm area), and close and allow the pressure supplied by supply pressure through a very small diameter hole (we spoke about that earlier) to build up "behind the diaphragm" pinning the diaphragm back against the valve seat.
While on the subject of diaphragm valves, it is inappropriate to move on to the next subject without discussing briefly "particle filters" and the type of relationship they have with diaphragm valves. There are 2 realities in plumbing systems that we all have to live with. 1. Water flowing in plumbing supply lines contain loose particles. 2. Diaphragm valves are defenseless against them. If allowed to enter a given diaphragm valve (regardless of whether the valve is involved in a faucet application or any of the numerous applications outlined above), particles present in water supply lines will damage the valve. Did you notice that I didn't say "if"? This damage often takes place immediately after installation or within a few days afterwards. Regardless of the time laps, allowing loose particles to enter diaphragm valves will cause valve damage, I cannot stress that enough. The damage mostly manifests itself in a leaky faucet or one that simply does not shut off, even though the solenoid did its job by driving the plunger into a closed position. This last condition called "runaway faucet" is a specially menacing condition that could possible cause severe flood damage to the area surrounding the faucet. Particle filters are an integral component of an automatic faucet. All automatic faucets are shipped with particle filters, these filters must not be removed and discarded.
Part II Continuted...
Sensor and Control Electronics
If the diaphragm is misunderstood and maligned, the electronic sensor component of automatic faucets by comparison is mired by hate and loathing of many in the plumbing industry. There seems to be an aura of mystery surrounding these sensors somewhat reminiscent of that exhibited towards personal computers and cellular phones when they first came into use. Well I'd like to do my part in dispelling this mystery first by taking it away on a long, hopefully entertaining, explanation, and then by bringing it all home to you. Feel free to email me and let me know if I did a good job, no hate letters please.
Automatic faucets are presence sensors and not motion sensors. They employ Active Infrared technology which senses "presence" and not "movement" of objects. Active infrared technology, like the name implies is actively emitting infrared light and actively waiting for this light to come back to it. On the frequency spectrum, infrared light lies between radio waves and light waves that are visible to the human eye. To achieve the task of emitting and receiving, faucet sensors employ 2 key components: an emitter AKA transmitter and a collector AKA receiver each about 1/4" in diameter and 5/16"long or smaller. These components are housed within the sensor capsule that is located either at the neck of the faucet spout, in a separate sink hole to the side of the faucet spout, or in a special compartment up next to the aerator. The emitter is constantly emitting infrared light in a blinking method, that is, the emitter is constantly blinking in the same way that turn signals on automobiles blink when the turn signal lever is engaged. The collector on the other hand, is always ready to receive (collect) this blinking light, and when it does, the control electronics take a factory preset action, in the case of battery powered faucets, the control electronics send an electrical pulse to the solenoid valve asking it to open. When the collector no longer receive the blinking light, the control electronics will then send yet another electrical pulse to the solenoid, this time, asking the solenoid to close. Since the emitter emits infrared light in a narrow and focused beam (imagine the focusing apparatus on a common household flash light), and since the collector also receives infrared light in a straight and narrow beam, and since both emitter and collector point in the same direction never in plane view of one another, the only way that the collector can receive the blinking light that is emitted by the emitter is to place a reflective object in the path of the beam, in most cases human hands.
I promised you earlier that I will bring it all home to you. The reason that I want to do so is that some may read the earlier paragraph and immediately conclude that this automatic faucet "thing" is advanced technology, too complicated for plumbing purposes, maybe even extreme, and should never be used in any consumer level products. This assessment by some is simply unfair and, more notably, far from the truth. In fact this technology has been in the palm of your hand, literally, for well over twenty year. I am talking about TV remote control, man's new best friend, we all have them, we all love them, and some of us, can't live without them. Your TV remote control employs the same active infrared technology that your automatic faucet does, sometimes the same exact emitter and collector component. In the case of a remote control the emitter is located inside the remote control itself and at the end that points at the TV, whereas the collector is located inside the TV generally hidden behind an amber color transparent plastic guard. If you think that faucet sensor and control electronics are complex .. think again. Whereas faucet sensor and control electronics act as an On Off switch, a remote control designed for an entertainment centers, for example, sends and receives coded messages that are 100,000 to 1,000,000 times more complex than that of the simple on-off function that faucet electronics perform. Aren't some of us lucky we're in the plumbing business and not in the TV business?
Batteries and/or Wall A.C.
Automatic faucets draw power from two popular sources: Six Volt seems to be the standard voltage for battery powered faucets (for now), although 9 volt is not uncommon. Battery powered faucets generally employ the services of AA batteries, C batteries, standard 9 Volt alkaline batteries, or lithium batteries. These batteries have storage capacities measured in milliamp/Hour, 1000 milliamp/hour is equivalent to 1 amp/hour which is enough energy to light up a 1 amp bulb for 1 hour. Larger size batteries exhibit greater energy capacity than smaller size batteries, similar to an automobile's gas tank, the larger the tank the more fuel you can put in it, but only efficient cars get the longer haul. Which brings us back to automatic faucets, no discussion of battery powered faucets is complete without briefly touching on faucet efficiency. How often you need to replace the batteries depends largely on how fast or slow the faucet consumes the energy stored within its batteries. This principally is a none-issue for AC powered faucets since wall AC is an inexhaustible power source, until the power goes out of course. AC powered faucets will be discussed in length later in this chapter. It is worth mentioning here that the Faucet Automator model FA100sca is the only faucet automation device- to the best of our knowledge with a true AC/DC automatic switchover feature. With the batteries installed and AC transformer plugged in the device automatically switches over to AC power from battery power, however, should the power in the wall go out the device switches back over to batteries for continuous, uninterrupted service. If anyone out there is aware of another faucet automation device that has this feature, please let me know and I will be glad to revise this writing to include the brand name of that faucet.
AC powered faucets employ transformers and switching adapters (more on those later) that plug into/or are hard wired to the wall. Transformers and switching adapters transform wall AC into 24, 12, 9, or 6 Volt AC or DC depending on the application. These are generally the 4 voltage ratings that automatic faucets operate on, at least here in the USA. Transformers and switching adapters measure their output capacity in VAC, higher VAC transformers and switching adapters are capable of delivering steady current at rated voltage to loads that require more "juice", in this case faucet electronics and solenoids. To better understand the relationship between VAC and power consumption by load, one only needs to look at automobile engines. The larger the engine, the larger the carburetor and fuel line that feed the engine. The larger the solenoid and electronics, the larger the VAC rating should be.
I mentioned switching adapters earlier which are commonly employed for the purpose of supplying power to electronic equipment. They are generally found along side laptops and cell phones. There are key reasons why switching adapters are the power supply of choice for electronic equipment manufacturers, automatic faucets are no exception. When employing standard transformers to supply power to modern electronic equipment, use of these transformers can lead to power quality degradation and heating problems, here are some of the reasons why:
- Single phase electronic loads can cause excessive transformer heating.
- Electronic loads draw "non-linear" currents, resulting in momentary low voltage supply and output voltage distortion.
- Oversizing for impedance and thermal performance can result in a transformer with a significantly larger footprint, and weight.
Switching adapters by contrast, are specifically designed for non-linear loads and incorporate substantial design improvements that address both thermal and power quality concerns. Such devices are low impedance, compact, and have better high frequency performance than standard transformers.
Automatic faucet spoutare not dissimilar to standard faucet spouts. They're mainly constructed of brass or in some cases, Zink. It is proper to state a disclaimer here that all MAC faucets are constructed of brass, MAC faucets does not build faucets or faucet components out of Zink. Some automatic faucets are machined, for example: European style faucets, (the MAC 200spl), some are die cast with the water passage made of copper tubing, and yet some are made of brass that is sand cast, this type is generally referred to as solid brass for the large brass content in it. We will discuss the various forms of castings in Part III.
Automatic faucet spouts are designed for several applications: standard bathroom fixtures, lab or bar sink faucets, and splash mount faucets chiefly for food service applications. Beyond delivering water, spouts mainly encompass an aesthetic purpose. Style and finish combined are the number one reason why buyers choose one faucet over the next, therefore much attention is focused on creating a faucet fixture that is aesthetically pleasing.