Well this does depend on how old your Bezzera BZ10 is. Seen you have 2 model versions. There is a pre- 26-06-2010 and a post 27-05-2010 version. The older type is in it’s original configuration isn’t available anymore, for this is a relay rebuild kit available which is the same as the new model.
They are both operated with a Ma-ter  pressure  switch with is fitted with a safety valve and with a relay. The older ones had a build on relay, but the latest ones have a separate relay.