Sea is me without the n, whoops.
Since the return is pumped the size isnt so critical, the overall flow rate will just be reduced if the plumbing is constrictive. That said if these will be handling all your return you would be better using as a big size as is possible, I would rule out 1.5".
Have a look at http://www.mdminc.com/Friction_Loss_Chart.htm and divide the flowrates there by 1.2, they are US gallons, that chart will give you an idea of the losses of the various sizes of pipe but will not be exact, it's for US pipe.
I just used std plumbing and sewage pipe by Brett Martin but I have no high pressure applications, check with tha pipe makers to see what their pipes will hold.
Posted on Aug 9, 2005, 2:02 PM from IP address 84.68.168.54