I was given two Corny Kegs a friend had on a scrap pile. These kegs were complete with the exception of having no relief valve, only a rubber plug. The lids are the domed plastic. I searched the keg supply vendors for a valve replacement. What I found was supposed to be a direct replacement for this type lid, but only if one was installed originally. I called the supplier to get some technical assistance and he indicated I needed to drill a 3/4 inch hole in the lid. I drilled the holes and tried to install the valves. What the supplier did not tell be was I also needed to mill the curved top and underside of the lid flat so it will properly seal. This post is for information to those that may run across this problem in the future.