I had asked the question as to whether the extension set will also work with the older model WV50. Since I've gotten several answers that this set is not compatible with it I would like to share my experience!
The set is very comfortable fit and is functioning properly. Did it just get used and immediately! The holder is also perfect for the elderly Kärchermodell. In my case, WV50. So you should give comments only if you have it tried it myself!