PART
II
Solenoid valve.
No credible explanation of the solenoid valve is complete
without discussing the two hybrid technologies that, when
combined, form a solenoid valve:
1. Electromagnetism (solenoid)
2. 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 de-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.
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