Cheers Chris.

I did a quick search and found this forum

Burkert 5404 have already caused quite a bit of trouble
I might get one pressure tested just for piece of mind. I'm sure they are fine and have proven themselves anyway but don't want to make anyone relive that thread.

I'm thinking of putting 1 on the inlet and another 1 to vent. I will probably leave scope to add another to the inlet, incase flow is a problem.