So a customer puts up a new house in the country. Water is supplied by well from old house that had been on site. Unfortunately, the well is pushing up some sediment and bacterial contamination. One possible solution is to put in a new deeper well in the hopes of finding cleaner water. Another, much less expensive solution is to use filtration and harness the power of ozone to purify the water.
The simplest setup includes a Mazzei venturi which uses the existing water flow to pull ozone into the water stream. A small mixing tank would increase contact time for disinfection before use in the home.
This would be a perfect project for me, the apprentice. I put the system together and brought it out for the install. Having worked in our shop putting together a number of industrial systems, I was confident it would work well. Plumbing was complete. I flipped the pump breaker switch and water began flowing. My balance barometer indicated some suction and the ozone generator light kicked on …. and then it turned off again as the water pressure increased. What was wrong?
A Mazzei venturi injector is at the heart of this system. The small plastic venturis we often use are very simple, but the careful and precise design makes them very reliable and effective. Essentially they use some of the energy from the water flow to create a suction that will pull a gas into the water stream. Two pressure gauges, one before the venturi and one after the venturi will demonstrate this loss of energy in the water flow. The lost energy is being used to pull gas into the water stream. Injectors need to be built to fit specific water flows and pressure. Your water flow in gpm and pressure requirements will help determine which injector will work. Mazzei has a chart for each type of injector that will tell how much gas flow is created for a range of pressures.
So, back to my system install and what was wrong. When I referenced my pressures before and after the injector to the Mazzei chart, I could see that my water flow was insufficient. I tried a smaller injector which improved the range at which suction was created, but it still was not enough to get the ozone I needed in the water. The Mazzei performance chart indicated that the well pump moved about 5 gallons per minute. When the pressure switch on the well pump sensed low water pressure, it turns the pump on. The venturi worked at first, but as the pressure in the system increased to the point when the pressure switch turned the pump off, the venturi quit working. So how can I increase the time ozone is injected?
I had an idea. If the venturi was working better at low pressures, then adjust the pressure switch so that it allowed the water pressure to get lower before it turned on. I adjusted the switch to turn on at 35 psi instead of 45 and the venturi was able to pull in ozone until it reached 47 psi. The pump continued to pump till the switch turned it off at 75 psi. This water mixed with the ozonated water in the tank. Dissolved ozone measurements indicated adequate concentrations under ideal conditions. But sometimes water use keeps the pump running at a pressure where no ozone is being injected. That simply was not going to work. I left for the day, and got a call the next morning from the customer. The water pressure in the house was not going to work for three teenage girls getting ready for school in the morning.
The well pump was not creating enough flow to make the system work. I needed to add a pump to increase flow. Flow from the well cannot be increased, so the pump would circulate 15 gpm through a loop. I turned the pressure switch back up and installed a pump wired to turn on when the well pump turned on. I plumbed to pull water at a T from the bottom of the tank where the pressure switch and bladder tank were hooked up and push it through a T where the well water was coming in.
Again I turned on the pump breaker switch. My new pump began to circulate water, balance barometer indicated some suction, ozone generator turned on, …. but only for a while. The system was not working any better than before! And a new problem surfaced: the well pump took longer to turn off because the new pump inlet reduced the pressure at the pressure switch.
After pondering this problem and looking at other system diagrams, it seemed to me that the venturi should come before the water inlet from the well pump. More plumbing changes. Multiple venturi size tests. But I still not able to get the flow and pressure differential I needed when the well pump was running. I noticed that if I turned the breaker off for the well pump, I was able to get good suction with just the circulation pump running.
A venturi will work only if you can maintain a pressure differential between the inlet and the outlet. Even with the well pump adding into the circulation pump outlet, the system configuration was not creating the flow needed through the venturi. If I understand it correctly, the well pump seemed to be fighting against the circulation pump.
It would be better if the well pump was feeding water into the system just before the circulation pump. This would level the pressure "playing field" across the loop before the circulation pump pulled well water and some water from the mixing tank through the venturi. Again I flipped the well pump breaker switch. This time the balance barometer showed a healthy level of suction. The ozone generator kicked on. As the pressure increased, the suction reduced but it stayed on until the well pump turned off. This is what I was looking for! Now it was working.