a spring operated check valve
Not sure what you mean. I can put a check valve in the line to prevent backflow to the pump. But I can't figure out how to prevent the pump from pumping into the drain.
If there was a spring loaded check valve that would only close with pressure, I could put that in the drain. Then the pumped (pressurized) water would close it but the draining (depressurized water) would allow it to open.
hmmm... i'm not quite sure what made you decide to plumb somthing like this, from the looks of it.. your "standpipe" would also act as supply and drain, with the drain under the media? do you already have 2 holes in your bed?
you could probably rig something up with a bunch of pvc fittings and a ping pong ball.. but..
instead of doing this, plumb a different supply or drain line, in the long run, it'll be a little easier/cheaper
We designed a bed that fills and drains using a reverse siphon system . The bed is filled from centre of the bottom of the bed with a 1-1/2" pipe fill line from the pump inside a 3" dispersal pipe. Pump is on a timer and a over flow system to control water level in beds. There are no check valves in the fill line, keep the fill line on a lower level of delivery to the bed. when many pumps are turned off that reverse flow is created. there are some advantages and some disadvantages.but they work well with proper care.