Does anyone have tips on choosing a proper pump for an Affnan bell siphon system? In his videos, he mentions pumps around 12 watts, and certainly under 20 watts. This seems smaller than pumps used in timed flood and drain systems. I have a 55 gallon tank and a roughly 67 gallon grow bed. I will also have a sump tank of around 20-25 gallons. I will be using 1" plumbing from the pump to the growbed. The top of the growbed will be about 40" higher than where the pump is. Thoughts, anyone?
20 watt is typical for pond and debris passing pumps. You need to remember that if a pump is rated at 475 gph that is the head rating at the pump. Many garden pumps have a limit of 6.5 - 7 feet but you can check with companies like tetra that have debris passing, pond, garden or statuary pumps can pass a farther distance, but keep in mind you typically loose 30% pressure for every vertical foot (lift) the pump has to work.
When looking for the pump commercial or retail, check the head pressure and check it's lift pressure, no two pumps are equal. I prefer Tetra Pumps. You also need to consider that the pump needs to move all the fish tanks water to the grow bed over an hour, give or take but something close.
What I have is a 20 Gallon fish tank, and a 10 gallon and a 5 gallon beds. With 5 ft. lift. I opted for the Tetra SP425, it has a listed 7 ft lift max @5 gph. It is a 425 gph filterless statuary pump. At 5 ft. It still pumps at 30 gph so I am getting 18min fills and 30 second drains using Affnan's model for the bell siphon, slightly modified. So I have no problem with keeping the water in the FT moving to keep ammonia in check.
I opted to go with the lowest cost pump with the best lift ratio. I installed ball valves on my lines to fine tune the flow. I spent $25 on an open package for my pump and normally sells $49-$60. I would not go with anything less than the SP330 for the size and the distance you need to pump vertically.
Of course you won't be needing 1" plumbing to run these pumps given your system ratios and pump size.
True, you can use 1/2" - 3/4" on all the SP series Tetra pumps for the water feed. It will help keep the the water pressure up.
For a siphon on your intended 67 gallon growbed if you use 1 inch siphon stand pipe I would recommend a pump with 260 gph rating. 475 gph pump should be use for 2 growbed with its individual siphon. Size of growbed recommended for single siphon is about 4x6, not a problem to the siphon to handle bigger growbed. But a bigger growbed will require bigger tank for fish and water circulation is much better if smaller growbed are used.
Water inlet using 1/2 inch pvc is good enough, nothing stopping you from using 3/4 or bigger.. its just not necessary.
Hope this help.