I received a new king keg(top tap) this week, having read all the issues regarding loss of pressure/air leaking out I decided to give it a good test yesterday before using properly for the 1st time(later today),
Initially I just assembled it as the instructions described, simply just smearing some Vaseline around the rubber seal inside the cap, I then filled about two 3rds full with water and tested with an 8g co2bulb, needles to say the air found its way back out as quickly as it went in! I found most of the air was leaking out of the sides of the cap and a bit was coming out through the sides of the valve on the cap, when inspecting the cap I found that the valve wasn't assembled properly as it wasn't tightened properly(you'd think at this price the minimum the manufacturers would do is pressure test them before shipping)
So I disassembled the valve and reassembled it tightly using a wrench, I also put a bit of ptfe tape around the threads of the valve 1st, I then but a lot of ptfe tape around the threads of the keg smeared a bit more Vaseline inside the cap, then screwed the cap back on tightly(not excessively tight, just as tight as I could with 1 hand) I tested again with another co2 bulb an hurray! this time it held pressure, though not for 2 long as the pressure was too high(almost 20psi according to my digital pressure gauge) so after about a minute the pressure release valve started whistling and let out some of the pressure, which then left the pressure in the keg at exactly 10psi(perfect, at least I know that works now!) though most of the pressure in the keg had gone after about 20 mins I don't think iy leaked out,, just dissipated into the water(at least this is what im hoping)
Also I put ptfe tape around the threads of the tap inside the keg before screwing the bolt on,
Just for those that aren't sure, PTFE tape(aka plumbers tape) should be available in all diy type places and is very cheap(usually less than a pound a roll) or I can be bought in bulk very very cheaply(currently 10 rolls for under 4 quid at b&q-
http://www.diy.com/nav/fix/plumbing...al-heating-fittings/ptfe_tape?noCookies=false ) it also comes in handy for other diy jobs around the home and garden.
So... with these kegs you need to have a good look at how they work before using, completely disassemble and reassemble adding ptfe tape on all threads and make sure everything is physically and air tight, a little time consuming(and again, you really shouldn't have to do these things at this price) but they do seem pretty solid and sound once you get them right.