How Does a Squirt Gun Work?

The Parts of a Squirt Gun

Squirt guns are as simple as they are fun on a hot summer day. The largest component of most squirt guns is a hollow, watertight body. This gives the gun its recognizable shape, but it also serves as the water reservoir for the entire gun. On the tip of the barrel, a squirt gun has a small plastic nozzle that focuses the stream of water. This nozzle is connected to a plastic tube that runs the length of the barrel and attaches to one end of a simple pump. In the middle of this pump, there is a plastic piston. The piston is held in place with a spiral spring and is connected to a plastic movable trigger. On the side of the pump opposite the barrel tube, there is another tube extending out into the water reservoir. This tube is usually directed down into the butt of the gun, because that is where the last of the water tends to collect when the gun starts running low.

The Pump Design

The pump mechanism itself is the only moderately complicated element of the squirt gun design. The pump is a hollow plastic chamber, and the largest part on the inside of the pump is a plastic piston. The piston and the squirt gun trigger are typically one solid piece of molded plastic; when you squeeze the trigger, it pushes this piston into the chamber of the pump. The spiral spring that holds the piston in place depresses when you do this, and it expands to its original length when you release the trigger, which pushes the trigger back out. There are plastic tubes on both ends of the pump - one leading to the nozzle and the other leading to the reservoir - and these tubes are both separated from the center of the pump chamber by one-way valves. In most squirt guns, the one-way valve is just a small plastic ball nested inside a small plastic ring. Like the name implies, the valve allows water to travel in one direction by not in the other.

What Happens When the Trigger is Pulled

When a squirt gun is filled with water and you pull the trigger, it forces the piston into the pump chamber. On the first squeeze, you may not see any water come out; this is because it takes one pump of the piston to bring water into the pump chamber. The initial pump forces air out of the chamber and through the nozzle, but when you release the trigger and the spring pushes the piston back out, it creates a vacuum that sucks air in through the reservoir tube. Now the pump chamber is filled with water. When you pull the trigger again, the piston goes back into the pump chamber, forcing water out through the nozzle of the gun (the one-way valve prevents this water from being forced out through the reservoir tube and back into the reservoir). Again, when the trigger is released and the piston is pushed back out, a vacuum is created and more water is sucked into the pump chamber. This process continues until there's no more water left to pump.