HOW IT WORKS

Imagine you have a syringe (without the needle!) filled with a little air and the tip sealed with your finger.

Now try this:

Pull the plunger back.
You’re giving the air inside more space. The air spreads out, and you can feel it pulling gently on your finger — that’s lower pressure.

Push the plunger in.
You’re squeezing the same air into a smaller space. The air can’t escape, so it pushes back harder against your finger — that’s higher pressure.

When you pull the plunger back you are creating a pressure drop which causes the air bubbles entrained in the water to expand. That’s what happens in your water system when pressure drops due to demand and air bubbles in your water pipes expand.

👉 This shows Boyle’s Law — when the volume goes down, the pressure goes up, and when the volume goes up, the pressure goes down (as long as the temperature stays the same).