On hydroponic systems, the growing medium has the only function to secure the plant roots in place so it doesn't have any means to nourish the plants as the soil does. Therefore, the water caring a nutrient solution is the sole source of nutrients to the plant.
Conventional hydroponic systems consist in a reservoir for the nutrient solution and a pump that delivers this solution to the growing trays as required. For rotary systems, the solution normally doesn't need to be pumped as the growing bed will be partly submerged into the reservoir so every complete turn will deliver nutrient to all plants inside the drum.
In our case, we have a limited volume of water we can store on the bottom of the washing machine drum so we have to combine the 2 methods. We will have the drum partially submerged so the growing medium can absorb the nutrient when dipping into it but due to its low volume it wouldn't last long without refilling it. So we need an auxiliary reservoir to store the nutrient and pump it into the drum when the drum level is low. The drum and the auxiliary tank will have a level switch. The one on the drum will trigger the pump to refill it and the one on the auxiliary reservoir will set an alarm to be manually filled.
Below is the nutrient solution system schematic.
Details of the items
Reservoir - Made using a plastic container. I drilled a hole and installed a threaded fitting with 2 "O" rings to seal the water. I also made a frame on the bottom of the washing machine using 20x20 mm aluminium equal angle so the plastic container is secured in place.
Water Pump - Original water pump connected to the reservoir
Water Level Adjustment - Made of 25 mm PVC Pipe, 2 x 90º Elbows and 1 x "T". Connected to the original flex joint that originally was connected to the water pump. I secured the pipe using a wingnut so we can change the water level adjusting the pipe height. Note that the top part of the pipe assembly is open; otherwise, it would become a siphon draining all drum water.
Water Level Sensor - The original drum water level switch is an interesting piece of equipment, it is a mechanical device that uses air pressure, created by the water weight on the bottom of the drum, to actuate a contact switch. I couldn't imagine but this mechanical sensor can be adjusted to the level we want turning the plastic screws on the back. It took a while to adjust it but I managed to have it switching off when the water inside the drum lowers below the accepted level. This sensor will be used to give a signal to turn the water pump on.
Besides the pump being started once the level inside the tumbler is low. it will also turn on in cycles for 10 seconds every hour to ensure the nutrient solution is refreshed.
Below is a short video of the water pump cycle testing.
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