Fill the cylinder with nylon rope as mentioned and then roll it to the top, that will keep the valve in place. Take a 3/4 socket and a hammer and "pop" the retainer before you use the spring compressor, sometimes the retainers stick and this will brake them loose-I have had them come completely off when I do this, so make sure the valve is held in place first. The single spring unit is the cheapest and works well with most set up.