How to Install a Venturi Wrong: Learning to Harness Ozone and Venturi Injection Principles to Clean up Dirty Well Water

 

Computer simulation of Mazzei injector.

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.

Sketch of circulation pump design

 

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.

Completed Working System – note the balance barometer and pressure gauges.

Learning How to Harness the Power of Ozone – The Balance Barometer

A balance barometer is a very simple device that provides fool-proof protection of ozone generating equipment in a venturi injection system.   As someone new to the ozone industry learning how to harness the power of ozone, I was intrigued by the balance barometer I was asked to construct for one of our systems.  How does it work?  Why are they useful?   Is there anything particular about the dimensions that make it work properly?

 

A balance barometer is used to keep water from backing up into the output side of an ozone generator.  Corona discharge ozone generators will reliably generate ozone if, and only if, they stay very dry.  Any moisture coming into the ozone generator will shorten its life.   In a system where a venturi is used to inject and dissolve ozone in water, a catastrophic flood of water into the ozone generator is always only seconds away.  Critical to the success of any such system is that point between the ozone generator and injecting the ozone into the water stream.

 

Under normal operating conditions, the venturi through which water is forced will create suction and prevent any water from flowing back to the ozone generator.  This water will immediately flow to the generator if water flow is reduced or stops in the venturi.  A simple check valve is built into Mazzei venturis to prevent this backflow.  An additional series of stainless steel and Kynar check valves will stop or slow this water most of the time.   But even “slowing the water” or “most of the time” is a risk that can be eliminated with a simple balance barometer.

 

A balance barometer is a U shaped tube with one side about twice as high as the other.  The top of the high side is capped off, and two holes are drilled into the cap: one straight down from the top, and one in the side at the bottom edge of the cap for ozone tube fittings. One inch clear PVC works well for visual monitoring, and the diameter allows bubbles and water to pass by one another without hindering its performance.

 

So let’s hook it up to see how it works.  The very top fitting goes to the ozone generator, and the side fitting just below the top fitting goes to the venturi suction port in our system.  If sufficient water flows through the venturi, it will begin to draw air through the check valves, ozone generator, and balance barometer.  If we put some water in the balance barometer, it will block off air flow through it and force all the flow to pull through the ozone generator.  This would be the normal operation.

 

Now if the particular water system has some water pressure when water isn’t flowing through the venturi, as in a well water system, water will be forced back out the injection port.  The check valve should prevent water back flow, but if ozone has deteriorated the seal or a tiny speck of something prevents a tight seal, water will begin to flow past it and toward the ozone generator.  When it reaches the balance barometer, it will simply add water to it until the short end overflows.  Once water flow is restored to the venturi, the suction will return.  Any water in the line or extra water in the barometer will be sucked into the venturi and normal operation resumes.

 

The balance barometer works well with ozone generators that operate under very low pressure or a slight vacuum.  Only 1 psi of pressure or vacuum will balance with 27 inches of water making the minimum size short side of the tube for such a system 27 inches.  Systems that simply use the venturi to pull air through the ozone generator work well with a balance barometer.  If a balance barometer is not practical for a particular application, our stainless steel backflow preventer will provide the same type of protection using a built-in float.