In a top feed hydroponic garden, the nutrient solution is dripped through the growth media, mimicking the natural effects of rainwater. Most commercial hydroponic farms use some version of a top feed system, but a homemade system does not have to be large or complicated. A good working system can be created using basic materials available at any home improvement warehouse.
The most crucial part of a top feed hydroponic system is the pump. If it is too weak, it will not be able to pump the nutrient solution from the reservoir to the drip system. How big a pump you need depends upon how far (both vertically and horizontally) your nutrient reservoir is from the grow tray and how big your garden is.
Pumps are rated by three factors: gallons per hour (GPH), PSI (pounds per square inch---a measure of the force put out by the pump) and head. Head is the maximum distance over which the pump will produce the rated GPH. To decide whether a pump will meet your needs, first calculate the cubic feet of your growth tray, then factor in the density of the growth medium to find out how many gallons of nutrient solution the growth tray can hold. Then, double the PSI to determine the maximum distance at which the pump will work.
The Drip System
If you have a growth tray filled with perlite or another soillike growth media and your plants live directly in the growth tray, a length of soaker hose is the simplest drip system. Connect one end of the soaker hose to the tubing that runs from the pump to the growth tray. Lay the soaker hose around the base of your plants, and connect the loose end of the hose to the drainage tube so that any extra nutrient solution is returned to the reservoir. Be sure to seal the connections with waterproof sealant to avoid leaks.
If your hydroponic system relies on individual plants in net pots, you will need to use drip nozzles connected to a web of plastic tubing. The pump pushes nutrient solution into the main tubing, which feeds into smaller tubes that run to each plant. The smaller tubes feed the nozzles, which slowly drip nutrient solution onto the base of the plant. Be careful that the nozzles fit securely into the tubing or you could end up with leaks.