inflating and deflating a air bladder continuously?

I am interested in a project however what i need to do is to inflate and deflate a air bladder repeatedly on a continuous cycle (so inflation and the deflation). This making me think of a piston style pump hooked up to a motor which I can control through use of a variable resistor. Is there any piston style pump i can use or is there a alternative which would be better. (I do have a budget of around 70usd)

What volume of air ? What pressure ? How fast ?

You don't control motor speed with variable resistors, if you want acceptable performance. .
mute86 (author)  steveastrouk4 years ago
volume of the bladder will be 561.5325319999995 (it is a cylinder type shape that has a radius approximately 2.08 cm and a height of 17.8 cm) may make it smaller. The pressure I do not care about a slong as it can fill the space in say 1or2 second and I would like to vary the speed.

Thanks for your reply
In that case, look at peristaltic pumps, reversing them makes them suck, controlling the speed changes the volume flow rate.

THere are a bunch of cheap ones in Ebay.

Incidentally, quoting the approximate volume to one part in 10^15 isn't helpful.....