OK almost all said above but because you have different options it might not be as clear.
First you need to decide what do you want to do.
If you just want to keep your reservoir full the simplest installation will be:
a) Install a float valve in the reservoir and the ASOV (Auto Shut Off Valve) valve in the RO/DI unit.
When the reservoir is full the float will close thus increasing the pressure in the product line. The ASOV detects the increase in pressure in the product line and closes the waste line. Without the ASOV the waste will continue being produced.
Now this is the simplest form but your RO/DI water produced will be somehow crappy. When the RO/DI unit is turned off, impurities pass across the membrane so on initial start up the first product water produced contains contaminants, after a couple of minutes of production (2 to 5) the produced water purity increases.
Because of the mode of operation, evey time the float lowers a bit say 1/4 to 1/2", the RO/DI unit opens to produce water to replace the little bit used thus you will have that initial crappy water many times in small batches.
To prevent this you need a system that turns on production when there are large changes in the level of the reservoir tank. In other words you do not want to produce water until the reservoir is almost empty or at least 3/4 empty. This way you will produce crappy water only once for an almost full volume of the reservoir thus diluting the effect of the start up impurities over the almost full volume of the reservoir.
b)For this improved purity sytem you need:
- The ASOV valve
- The float valve
- Two float switches (or a two level auto top off system)
- one electrically actuated solenoid valve
The operation is rather simple. You install the two float switches one slightly below the float valve and the other one close to the bottom of the reservoir. Install the solenoid in the RO/DI unit product output.
The lower switch close to the bottom will energize the solenoid that will open to start production of water. When the water level reaches the upper switch it will turn off the solenoid which will not turn on until the lower switch is reached again.
If the upper switch fails to turn off the solenoid the float switch located a bit higher than the upper switch will close the water product line which will prevent a flood.
If you are good at a DIY I can post a diagram or if not I can post sources for the parts you need to install this if you are interested in automateing the reservoir.
By the way, there are systems that allow you to purge the bad product water during initial production and flush the membrane after production is completed but are a bit pricey.
