The S30 conversion pack makes it simple to change between S30 and 8g use without buying another valve. Your original S30 valve is all you need.
The Hambleton Bard S30 conversion pack
The S30 conversion pack contains a high grade stainless steel pin for use with 8g CO2 bulbs, plus a small o-ring to fit inside the S30 valve. For conversion of an S30 valve, simply put the pin in and you have a 8g bulb version of the valve (use the S30 bulb holder for injecting the 8g bulbs).
The S30 valve always contains a small o-ring inside. The one in the conversion pack is there only in case you damage the original one when you change over and put the pin in. For inserting or removing the 8g pin, you need to first temporarily remove the small o-ring. That is best done with a small knife or a very small screwdriver.