Two types of drip systems are used in hydroponic growing - the recovery drip system and the non-recovery drip system.
The recovery drip system is controlled by a pump and timer. Nutrient solution is dripped onto the plant roots and the excess nutrients are collected in a reservoir tank and recycled during the next feeding cycle. Non-recovery drip systems operate the exact same way, except that they don't collect and reuse the nutrient run-off.
Both recovery and non-recovery drip systems operate via a timer and pump that feeds nutrient solution through the tubing. The drip solution is dribbled from the tubing through nozzles and onto the plant. Nutrients trickle through the grow medium and collect in the reservoir beneath. The solution is only recycled if the drip system is set up as a recovery drip system. The drip timer is then shut off and the system is flushed of solution, allowing a rush of oxygen to the plant roots.
Drip systems are typically set to emit nutrient solution every 5 to 10 minutes. Drip systems are vulnerable to power, pump and timer failures. If a power failure should occur, plants can die very quickly, without immediate attention.