How to push fit fittings work?

[blun]

Hi,

I want to have a go at replacing the sink and taps in my kitchen, and I'd also like to add isolating valves for the 2 pipes.

Currently looking at a couple of these:

http://www.screwfix.com/prods/10931/Plumbing/Push-Fit-Fittings/JG-Speedfit-Chrome-Isolating-Valve

I was just wondering:

1) How do these actually work? What stops the water pressure forcing the connection off?

2) Do I then just need a tap connector to attach to the flexible tap pipes? Something like:
http://www.screwfix.com/prods/48168...edfit-Straight-Tap-Connector-15mm-x-Pack-of-5

Thanks for the help

 

[seco services]

their is a grab ring inside that will only slide one way on not off unless the teeth get damaged.
below that is a o ring that stops water passing.

you must always use inserts on any plastic pipe before pushing into fitting.