Soon after its introduction, the water gun took its place
among the most popular summer toys of all time, and it's easy
to see why: When you're a kid, or a kid at heart, what better
way to cool off on a hot afternoon than waging an epic water
battle against your friends and family?
Water guns have come a long way in the past
20 years. An ordinary squirt gun can only shoot water 8
or 9 feet, but a pump-action water blaster, like this
Super Soaker CPS 1200, can shoot water more than 50
feet.
Over the years, these toys have evolved considerably.
Thirty years ago, a typical water warrior was armed only with
a small squirt pistol, which had a fairly short range and an
even more limited ammunition reservoir. These days, you'll
find an entire arsenal of water weapons at most toy stores,
complete with water machine guns, water bazookas and even
water grenade launchers.
In this edition of HowStuffWorks,
we'll find out how these summertime staples produce their
drenching blasts. We'll trace the path of water guns from
traditional squirt pistols to motorized water Uzis and finally
to the pump-action water blasters that dominate the market
today.
The Classic Water Gun Before the 1980s,
water guns had fairly limited capabilities. Handheld pistols
could only shoot water a short distance. They shot a weak,
narrow stream and you had to run to a spigot to refill them
after every shoot-out. These guns are still terrific toys, of
course, and they're a wonderful demonstration of basic
plumbing principles.
In a classic squirt gun, there are just a few basic parts:
There is a trigger lever, which activates a small
pump.
This pump is attached to a plastic tube that
draws water from the bottom of the reservoir (in most
cases, the reservoir is the entire inside of the gun).
The pump forces this water down a narrow barrel
and out a small hole at the gun's muzzle.
The hole, or nozzle, focuses the flowing water
into a concentrated stream.
The only complex element in this design is the water pump,
and it's about as simple as they come. The main moving element
is a piston, housed inside a cylinder. Inside
the cylinder is a small spring. To operate the pump:
You pull the trigger back, pushing the piston into the
cylinder.
This compresses the spring, causing it to push the
piston back out of the cylinder when you release the
trigger.
These two strokes of the piston, into the
cylinder and out again, constitute the entire pump cycle.
The downstroke, the piston pushing in, shrinks the
volume of the cylinder, forcing water or air out of the pump.
The upstroke, the spring pushing the piston back out,
expands the cylinder volume, sucking water or air into the
pump. In a water gun, you need to suck water in from the
reservoir below and force it out through the barrel above. In
order to get all the water moving through the barrel, the pump
must only force water up -- it cannot force water back into
the reservoir. In other words, the water must move through the
pump in only one direction.
The device that makes this possible is called a one-way
valve. The one-way valve in a basic squirt pistol consists
of a tiny rubber ball that rests neatly inside a small
seal. There are two one-way valves: one between the
reservoir and the pump, and another between the pump and the
nozzle.
This pump design is beautiful in its simplicity, but it has
a two big limitations:
The amount of water in each blast is limited by
the size of the pump cylinder. The size of the pump
cylinder, in turn, is determined by the range of the trigger
mechanism. To compress and expand more water, you have to
push and pull the piston a greater distance, which means
pulling the trigger farther back.
The duration of the blast is also limited. Each
pull on the trigger creates only a small burst. To squirt
water continually, you have to keep squeezing and releasing
the trigger.
Throughout the history of water guns, designers have been
wrestling with these problems to create a better pumping
system. In the next section, we'll look at two simple
water-gun designs that increase the stream's range, pressure
and duration. Then we'll check out the gun design that blew
all other water weapons away.
Muscle and Motors In the last section, we
saw that the basic squirt gun uses a simple piston, a cylinder
pump and two one-way valves. Since the pump is activated by
moving the trigger back and forth, this design is fairly
limited in the size, range and duration of its bursts.
One easy solution to this problem is to increase the size
of the pump cylinder and the trigger. This is the basic idea
behind classic water bazookas like the one shown below.
In this design, the trigger mechanism isn't really a trigger
at all -- it's more like a syringe. Essentially, you
hold the piston in one hand and the cylinder in the other. To
suck water in from the reservoir, you pull the piston and
cylinder apart. To expel the water, you push them back
together.
This gives you much more water to work with in each shot.
If you push the piston into the cylinder with great force, you
can shoot the water a good distance. If you push it more
slowly, you can expand the duration of the blast. Some water
bazookas don't have an attached water reservoir: To load them,
you must suck in water through the barrel, as you would fill a
syringe.
Obviously, this design requires a lot more work from the
shooter than the conventional squirt gun, so it's not
particularly user-friendly. The 1980s saw the arrival of a new
sort of water gun that did almost all the work itself. You can
see in the diagram below that these guns work in basically the
same way as the conventional squirt gun, except the pump is
powered by a small motor rather
than by the trigger. The trigger is only a switch that
completes an electrical circuit so that the battery
can power the motor. The motor moves a series of gears, which
move a small cam. The rotating cam has an extended
lever that catches the piston, pulls it back and then releases
it, allowing a spring to push it forward. In this way, the
motor moves the piston in and out of the cylinder, drawing
water in from the reservoir on the upstroke and driving it
down the barrel in the downstroke.
Since the pump is activated by a turning motor rather than
a trigger, the design can have a slightly expanded cylinder
size without making it more difficult to shoot. This extends
the blast range somewhat. But the real advantage of this
design is that the shooter doesn't have to keep pumping the
trigger to continually shoot water. If you hold down the
trigger, the motor keeps pumping, emitting a rapid series of
bursts, like the continual fire of a machine gun.
Both of these gun designs are a substantial step up from
the ordinary squirt pistol, but they still have significant
limitations. Blasting the bazooka requires a good bit of
muscle power from the shooter, and the motorized gun's water
stream is still fairly weak. In the next section, we'll look
at the water-gun design that revolutionized the industry,
building blasts that reach 50 feet (15 m) or more.
Under Pressure As we saw in the last two
sections, the main problem with conventional water guns is
that they don't produce a very powerful stream. This is
because the water pressure must be generated with each shot,
either by the shooter or by a motorized system. It's not
feasible to produce a high-pressure stream because it would
mean applying a great deal of force in a short amount of time.
In 1982, a nuclear scientist named Lonnie Johnson
came up with an ingenious solution to this problem. In his
spare time, he was working on a new heat-pump system that
would use moving water to regulate temperature. Late one
night, he attached a model of the pumping mechanism to the
bathroom sink, and was startled by the powerful water blast
that shot across the room. In that instant, he was struck by
the idea for a water gun that would use compressed air to
provide pressure for a water blast.
The CPS 1200 Super Soaker has two water
reservoirs, an expandable water bladder and a
hand-operated pump
system.
To make his idea a reality, Johnson enlisted the help of an
accomplished inventor named Bruce D'Andrade. Together,
D'Andrade and Johnson came up with the basic design that would
become the Super Soaker.
Super Soakers are built around a pump mechanism, but moving
the pump doesn't actually drive water out of the gun; it
serves to build up water pressure before the blast. In
the first wave of Super Soakers, you built up this pressure by
pumping air directly into a single water reservoir. As you
pumped in more air, it became more and more compressed and so
applied greater pressure to the water inside.
In later models, you built pressure by pumping water
instead of air. In the diagram below, you can see how the
pieces of this sort of gun fit together.
Unlike its predecessors, this gun has two water reservoirs
(labeled A and B), which are connected together
via a network of tubes. To load the gun, you fill the larger
reservoir (A) with water. To prime the gun for a blast, you
pull the pump handle (C) in and out several times. The pump
handle is connected to a long, narrow piston (D), which moves
back and forth inside a cylinder (E). This pump is similar to
the one in a squirt-gun pistol, and it relies on the same
one-way-valve system to control the direction of water flow.
The first valve (F) is positioned between the large water
reservoir and the pump mechanism, and the second valve (G) is
positioned between the pump and the smaller water reservoir,
which feeds into the barrel of the gun (H).
Inside the body of a Super Soaker, you'll
find a network of plastic tubes. This is something like
the plumbing system that pumps water throughout your
house.
On the upstroke of the pump cycle, when you pull the pump
handle out, the receding piston pulls in water from the large
reservoir above. The second one-way valve (G) keeps water from
flowing up from the smaller reservoir (B). On the downstroke
of the pump cycle, when you push the pump handle in, the
plunging piston drives the water out of the cylinder, through
the second one-way valve (G) and into the small reservoir (B).
The first one-way valve (F) keeps the pressurized water from
flowing back up into the large reservoir (A).
But what is all this accomplishing? In the next section,
we'll put the pieces together to see how the Super Soaker
builds such a powerful blast.
All Wet The purpose of the pumping system in
a Super Soaker is to compress air. Each time you drive
water from the large reservoir into the small reservoir, it
pushes up against all of the air inside. Air is a compressible
fluid -- you can decrease its volume by squeezing it -- but
water is not. When you add more and more water to the small
reservoir, it takes up a greater and greater volume. Since
there is a limited amount of space in the reservoir, these
larger volumes of water compress the air inside the gun so
that it has a much higher pressure than the air outside the
gun. This cushion of high-pressure air pushes on all of the
water in the reservoir; the water presses on the sides of the
gun, trying to get outside to restore pressure balance.
The only thing keeping the water inside the gun is the
trigger mechanism. The trigger is simply a lever
secured to the gun housing. A stiff length of metal attached
to the housing holds the top part of this lever against the
flexible plastic tube leading to the gun's barrel, pinching it
so no water can get through. When you pull the trigger back,
the metal piece bends, and the lever releases the plastic
tube. With this passageway open, the pressurized air can push
all of the water out of the gun, reestablishing a pressure
equilibrium with the air outside. If you build up enough
pressure, the water is expelled at a very high velocity.
Since each bit of water further compresses the air cushion,
the force of the blast depends on how much water you pump into
the small reservoir. At a high-enough pressure level, the
outward force of the compressed air and pressurized water
might exceed the structural integrity of the plumbing in the
gun, causing it to leak. To prevent this from happening, the
trigger mechanism is designed to let some water through when
the pressure reaches a certain level. This "leak level"
is determined by the strength of the metal that holds the
trigger down. Essentially, this piece of metal is like an
ordinary spring, and its springiness is determined by its
composition. If the metal is more rigid, it will take a higher
water-pressure level to push it out of the way. If you have a
more flexible piece, the gun will let some water leak at a
lower pressure.
Super Soaker's Constant Pressure System, or
CPS, pressurizes water by pumping it into a small,
expandable
bladder.
In the late 1990s, a new wave of Super Soaker guns came out
that boasted higher pressure levels. These guns, developed by
Bruce D'Andrade, feature the Constant Pressure System,
or CPS. The main component in this system is a simple water
bladder. This bladder is like a balloon, but it is made of
much more rigid material. These guns have the same sort of
pump as other Super Soakers, but the water and air are driven
into the water bladder rather than into a plastic reservoir.
As you pump more water in, the bladder expands, in the same
way a balloon expands as you blow more air into it. When it is
stretched, the bladder wants to return to its natural shape,
so it applies a good deal of inward pressure on the water.
When you pull the trigger and open up the passageway to the
gun barrel, this pressure drives all of the water out of the
gun. This allows for much more powerful water blasts than can
be achieved with compressed air alone.
Photo courtesy Larami
Ltd. Some of the Super
Soakers in the 2001 line Click on each picture to see
a larger
image.
These are just two sorts of pump-based water guns. Lonnie
Johnson and Bruce D'Andrade's first Super Soaker and the later
addition of the water bladder have launched an entire line of
water weapons. For extra ammunition, some designs hook up to a
huge water reservoir that you wear like a backpack. Other guns
are configured so you can shoot forward, backward and sideways
at once. This has altered the world of water guns drastically.
In the past, kids knew exactly what to expect when they went
to the toy store for a new water gun. These days, the shelves
are stocked with a wide range of new designs every summer.
Unless you've been to the toy store recently, you have no idea
what your neighbors might bring to the next big water fight.
For lots more information, check out the links on the next
page.
