How things work
How a spray bottle sprays
A working model of a trigger sprayer, cut in half. The liquid is not animated by hand: where it goes is worked out from how far the piston has moved.
The trigger
Things to try
Start with a new sprayer and count the pulls before anything comes out. Then block the vent and keep spraying.
What is simplified
- Sprayers differ. This one has a ball for each valve and a vent that the piston uncovers. Many real ones use a flexible flap or a small spring-loaded disc for the upper valve, and some open the vent with a separate seal. The order of events is the same.
- The nozzle parts are drawn larger than life so you can see them. A real swirl chamber and its hole are well under a millimeter across.
- Air is treated as if it did not compress, and the air in the cylinder is assumed to leave before any liquid does. A real sprayer coughs out a mix of both for a pull or two, and the number of pulls it takes to prime varies from one sprayer to the next.
- The bottle caving in with a blocked vent is exaggerated. A real bottle dents a little and the pump simply gets weaker.
- The valve balls, piston and spring are shown whole, standing out of the cut face, so they are easy to follow.
In short
A trigger sprayer is a small hand pump. Squeezing the trigger pushes a piston into a cylinder against a spring. Two small balls act as one-way valves. One lets liquid rise from the dip tube into the cylinder but not fall back, and the other lets it out toward the nozzle but not return. Releasing the trigger lets the spring pull the piston back, and the cylinder refills from below. Grooves behind the nozzle set the liquid spinning, so it leaves as a thin hollow cone that breaks into droplets. A small vent lets air into the bottle to replace the liquid.