How do bike tire pumps work?

Question

The ones that you pump the plunger up and down, filling your bike tires with air?

what i don't understand is how they can get air into the tire, but when you pull up on the plunger, it doesn't suck air out of the tire... will someone enlighten me?

Answer 1

it's just like a scuba mask on an air tank.  You breathe in the oxygen from the tank through a one-way valve and when you breathe out, the passageway back to the tank is blocked.

With the bike pump, when you push it down, it forces the air from the hollow part  of the tube into the tire through the valve.  When you pull up, that valve closes and the one that takes air from the outside opens.  It keeps switching when you pull up or push down.

Answer 2

That's all I ever use.

I can't tell you exactly how they work, though.  I'm sure the concept is pretty basic and crude, though.  The technology has been around forever.

Answer 3

Part of the pump is a device called a check valve.  Your heart has them too.

Have you ever seen those flappy plates on top of truck exhaust pipes?  its kinda like that....when you push down on the pump it pushes a check valve open, when you stop pushing down the tire pressure pushes it back the other way and closed the flap....

meanwhile there is another check valve that pops open on another hole into the pump champber when you pull the pump back up.....that one closes again when  you push back down....