This video dates from the pre-broadband era, and is therefore highly compressed
Kate: Now you both looked at me in absolute horror, but is it really going to be that hard to supply me with air when I'm underwater?
Kathy: Well if you were just a little way underwater, you know 10, 20 centimetres, we could just give you a snorkel.
Kathy: But the problem is, the deeper you go, the bigger the water pressure. So we have to provide air at the right pressure for you to breathe.
Kate: Why is that though?
Jonathan: Well basically it's all the water above you is squashing everything.
Jonathan: So your whole body is at higher pressure and I think your your lungs just can't expand to breathe normally. So the only way that they can, you can breathe normally is if we supply you with air at the pressure of the water that you're at.
Jonathan: So that means the air that we feed to you has to be compressed basically. So we have to build a pump.
Kate: So, I mean how does - just looking at this I don't think I've ever seen inside a pump. How does it actually work?
Jonathan: It's really simple, you have a tube with this piston on.
Kate: Yeah. Yeah.
Jonathan: And when you push it along the tube, it compresses the air. Which obviously forces it out.
Jonathan: There's actually a little plastic ring here.
Jonathan: Which when you push it, compresses the air, and when you pull it back it lets air in. It's a really clever little thing. It's very simple but it allows you to basically compress the air.
Kate: Right, but - also allow air constantly to come in to then be compressed again?
Jonathan: That's right. I mean if you block the thing, it will just compress the air. But if you have a tube that goes down into your breathing apparatus it will push the air down there, but a higher pressure.