Koi.Comets.Happy -
My pump is rated at 3000gph, but I have a 3' head plus some restriction in the plumbing... I figured 2500 is a good guestimate.
As for your skippy setup - you can run in either configuration, the physical location of the filters is not critical, however keep in mind:
- the higher you place the filters, the harder your pump(s) will have to work to get the water INTO the filters
- If the filter is above your pond's water level, when the pumps stop running, the filters will drain back into the pond (flushing all the waste from the bottom of the filter) and likely overflow the pond.
For the backflow problem, I tapped a 1/8" hose fitting into the pipe running down from the top-center of the filter. This gives me a small stream of water to show how well the pump is working (the flow will drop off if there is a restriction in the line), and if backflow starts to happen, air will be sucked into the pipe and break the siphon.
For the position of the filter, on my setup I buried my filter barrel about half way, so the outlet is about 12 inches above the pond water level. This eliminates any excessive working of the pump and positions the barrel outlet for the waterfall.
And finally, about your purge drain in the filters... Run the drain from the bottom center of each barrel, bring the pipe back up the side, and put a T just above ground level. Attach a short (3") pipe to the side of the T and cap it off. From the top, run a straight pipe up to the height of the barrel...
-- The pressure inside the barrel will push water out of your drain pipe, and back up to at least the height of the water inside the barrel - therefore burying the barrel does not cause any problems with drainage, simply pop off the cap from the side of the T and everything from the bottom of the barrel will be purged in a few seconds.
-- You may be wondering why I include an open pipe up to the top of the barrel? The first Winter I had my pond, my drain pipe froze solid, and cracked my valve and pipe, so the moment it started to thaw, all the water drained out. With the vertical pipe, the freezing water has a place to expand to. The cap can be pushed out nearly an inch by freezing water without coming off, so I just push it back in tight in the Spring. With this setup, I've never had another pipe break.
So place your barrels somewhere between the height of your two images. Even if you don't plan on a waterfall, having the water drop from the barrels back into the pond a short distance will increase the oxygen in the water and ensure that even if your pond freezes, there will always be a hole in the ice. If my descriptions didn't make sense, I'll post some pictures to clarify.
