Flow rates must be equal and are adjustable either by cutting the discharge microtube or with suitable taps. Control Equipment A range of controllers is available for automatic dosing and control of pH. Some work on 12 volt solenoids, while others use 240 volt systems. When purchasing the solenoids, ensure that the correct wattage and voltage for AC or DC are obtained. Control of units exceeding the rating of the control equipment is possible through a relay. Operating the NFT System Nutrient from the A and B tanks is added in equal amounts to the catchment tank, to maintain the correct concentration measured by conductivity.
Water enters the tank to replace that lost by transpiration.
The solution in the catchment tank is circulated through the NFT system and returns, dropping some distance into the tank to assist aeration. The solution is dumped and replaced as unwanted ions, such as sodium, reach unacceptable levels. The temperatures of the solution should normally be run between 15 degrees C and 24 degrees C. Stainless steel electric immersion heaters or heat exchange units may be used. While few growers use alarms, the following are systems where it is desirable to have alarms or safeguards fitted. A flow restrictor may be required on the mains side of the pressure switch.