Nova 3 water rocket

Hi to everyone! Since study reasons I have not made a lot of progress on my water rockets. Fortunately, now I got free time in order to spend it on my projects. The first I want to do is make a new launcher, this will be portable, light and it will launch rockets of diferent sizes. I am working on a new rocket called Nova 3, its volume is about 6.7 l and its structure is a combination of two 3.35 l sections joined by a tornado coupling. I have made the pressure test today but, one section exploded breaking the torando coupling. I will redisign the rocket and I will buy metal adaptors in order to avoid tornado coupling from breaking.