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How Does a Spray Bottle Work?

Dec. 13, 2021

Spray Bottles


How does a sprayer allow liquid to flow in only one direction from the reservoir to the nozzle? It does so with simple check valves made of two pieces of plastic, a spring, and a small sphere.

 

What is the one-way flow?

It’s often useful to restrict flow to only one direction. One simple use case is in a spray bottle. Let’s think of a simplified sprayer with three main components: the reservoir where we store the fluid, the staging area for the fluid that’s about to be sprayed, and the nozzle that connects it to the space outside where we’ll dispense our fluid. We want to take fluid from the reservoir, put it in the staging area, and dispense it to the outside.

 

Fluid sounds like a technical term, but it’s an important one in this context. Fluid refers to anything that flows, meaning its particles aren’t fixed. This means that both gases and liquids are fluids. We want to pay attention to particles that can move, as they’re the ones that move and push around on their own.

 

The main user interface for the spray bottle is the trigger. This is a simple lever with a plunger that extends into the staging area. When the trigger is pressed, it pushes on the fluid that is in the staging area, which then travels out of the nozzle. When the trigger is relaxed, a spring pushes it back out, creating a vacuum effect that pulls fluid from the reservoir into the staging area, allowing the cycle to continue with the next pull of the trigger.

 

Why does this work?

There are two important things happening here. First, as the plunger applies pressure to the fluid, it must move only through the nozzle to the exterior. If the fluid only went back to the reservoir, we would have a simple machine that draws water from its reservoir and pushes it back in. Not very helpful.

 

Also, when the trigger is drawn back out, it must refill the staging area from the reservoir, not from any fluid from the outside. In the case of a water sprayer, the outside fluid is air. If it refilled the staging area with air, attempting to spray would just shoot the air back out of the nozzle. This would also be a simple machine that just sprayed a small amount of air. Again, not very helpful.

 

The spring keeps the ball pushed against the circular hole. This means that any fluid on the spring side doesn’t fit through the hole, as the ball is in the way. Both the pressure from the spring and any pressure from fluid on the right pushes the ball tighter against the hole, ensuring that there’s no space for fluid to flow to the left.

 

Now, let’s apply pressure on the left side with a plunger, which causes the fluid on the left to push against the ball. If that pressure is more than the pressure from the right (from the spring and the right fluid), it will push the ball back, allowing some fluid from the left to escape around it through the hole. Fluid now successfully flows from the left to the right. When we stop applying pressure, the pressure from the right once again dominates, and the ball is pushed tightly back against the hole forming a seal.

 

We are a micro sprayer supplier, please contact us if you need them!

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