Beer too pressurised!

Hello,

I have just had another failed brew due to the over-pressurisation of the beer in my pressure barrel which led it to leak out from the seal around the tap.

I am going to buy a new barrel i think - probably a "king keg" with a tap at the top - but I was wondering whether there was any way of reducing the pressure inside the barrel without having to unscrew the lid? I have a valve in the lid of my barrel, but dont know if i can release pressure using it - i thought it just enabled CO2 to be pumped in?

Also - should I buy a pressure gauge so that i can monitor the pressure inside? What pressure should my beer be at if i dont want it to leak?

the king keg has a valve/pressure release valve in one. i've overpressurised mine before and the valve allows it to reduce to a "safe" pressure, i've certainly never seen it leak....
i don't have a pressure guage. on't know if there's any way of attaching it to the keg really....