TheFertilizer
Well-Known Member
I would get one of the 500 gph pump options available and see how that works. It's hard to really judge because the flow-rate always gets reduced by your manifold and the rest of your line, so even if a pump says it's 500 gph, if your manifold is rated at 20 gph that's the max flow you'll see, and then if you have 1/2 gal emitters, then you'll only have 1/2 gal a minute flow regardless of what the flow-rate is on the pump. What is really changing is pressure, but with more pressure you can have more equally distributed flow--so in my 3-emitter ring design, if you have a low pressure system, then water won't come out of the middle ring, but rather the two side rings because there's not enough pressure to drive it to the back ring. The overall flow and amount of water that comes out of that end line will be the same, but it won't be equally distributed through the ring and thus not through the pot. So really the bigger pump will just ensure you have adequate pressure through all that line to drive your water out of the emitters in an equally distributed amount. There's all sorts of pressure-compensating emitters you can get for that reason, but they may clog up if you want to use nutrients, so if you want to use a wide-open emitter type with max flow then you need to produce pressure at the pump end of things.
Anyway, all that blabbing, the riser can be basically any length up to 10 ft for most of these pumps. They will have a "lift" specification, which means they'll maintain the stated flow-rate even when pushing water vertically up to that height. BUT I would try to make the vertical height of the riser as short as I could, because that will end up giving you more pressure down the line.
Did you understand what I meant about needing to keep an extra port on the manifold open to prevent siphoning? Because that's pretty important, otherwise you may find that after you shut your pump off, your pots siphoned the water out of the reservoir anyway. I bring that up because you can compensate for a lack of pressure by elevating your reservoir, but then it becomes even more crucial to have anti-siphoning considerations. Leaving an open port on the manifold will just allow a place for air to enter in once the pump drops pressure in the riser pipe, making sure no siphon effect can form through the riser and pump once it's off.
