An interesting idea but I think you will have several problems with this:-
By parraleling two drains into a single inlet, you will be halving the pull through each drain. This may reduce the effetiveness of the draw through the drains and may result in a less effective debris and waste removal from the pond bottom.
The pipework from each drain forming a pair will need to be carefully plumbed in. The pipes should be identical in length and incorporate the same number of bends and joints to ballance flow through each drain as much as possible. It may be worth valving each drain too so that you can adjust the pull though each drain forming the pair independantly.
I don't think you need to worry about the force of water through this arrangement as long as you use at least two vortex assemblies. Two drains teed to a single inlet to a vortex is under no more or less presure than a single drain, due to the single inlet maximum throughput so this should be ok. Running two pairs of drains to a single chamber will almost certainly flood though and cause excessive turbulance though so I would not recommend this.
Alan.
Posted on Dec 23, 2005, 11:43 AM from IP address 213.120.101.21