Question
The backflow system I have is dripping very fast.
It's a Wilkins Zurn 950XL. Please help me solving this problem. Thanks a lot in advance.  

Answer
Good question.
Your backflow preventor is probably dirty (fouled) internally. It doesn't take much to make them leak.
It has a number of test port on it's side. They are the small valves. While the system is running turn them on. One at a time, then all, then 2. No set order just open them. This isn't the "official" service for a backflow but sometimes it works. By doing so, the internal valves open all the way and may flush the debris out.
If this doesn't cure the problem the backflow needs to be opened and cleaned. You may want professional service for this. It has a few very strong springs inside and can be a bit dangerous and difficult to reinstall. The springs are under the 2 large caps which screw off.
Good luck.

Matt