I hate when that article is brought up again, because it is confusing. But you have to consider the source. It was written by the man who invented the diaphragm style tank, and produced by a company who makes and sells only tanks. But even though it was set up to make anything except a large pressure tank look good, it has quite a bit of information that contradicts that conclusion if you know how to read it.
But let me clear up your first misconception, as it is the most common misconception when discussing how a CSV works. THE PUMP DOES NOT RUN AT 100% AMP DRAW WHEN BEING THROTTLED WITH A VALVE. The amp draw of a pump will be reduced by 30% to 50% when being restricted with a valve. This is almost exactly the same reduction in amp draw you get by slowing the RPM of pump with a VFD. This is completely counter intuitive, so it is hard to understand. But again, throttling a pump with a CSV will cause the amps to be reduced almost exactly the same amount as when a pump is slowed down with a VFD.
So the pump may run longer periods of time with a CSV, but it is loping along at reduced amperage instead of running at full load as most people think it does.
This one misunderstanding about the counter intuitive properties of a pump makes it easy for consumers to be duped into thinking a VFD will save energy. It also helps dupe people into thinking a large pressure tank is still the best solution. Neither one of these things are true. But pumps are so confusing anyway, that all that is needed is another confusing article like this Amtrol “study”, and people don’t know what to think.
Yes the Amtrol “test” of the CSV was done with a 20 gallons size tank (5 gallon draw). A 20 gallon tank is still a small tank compared to a so called “properly sized” pressure tank. But even with the smaller tank, the “Cycle Control Valve” system still cycled less than either the “properly sized” tank or the VFD. 10 years after this “test” we have concluded through decades of testing, that a 4.5 gallon size tank (1 gallon draw) works just as well with a CSV.
The Amtrol “study” used 31 water demands per day, with a 2 minute lull between each use. So even if the CSV and small tank caused a cycle for each water demand, which it won’t, it would still only cycle 31 times per day. 31 cycles per day is inconsequential for a pump that can supposedly cycle as much as 300 times per day safely.
This is exactly why the VFD shows to have cycled 31 times per day, as it has no pressure bandwidth between on and off. No pressure bandwidth means a VFD is not able to use any water stored in a pressure tank, no matter the size of the tank. So a VFD pump will cycle for every water use.
Even though the amps are reduced by 30% to 50% when using a CSV or a VFD, the drop in amperage is not linear with the reduction in flow. So a CSV or VFD will use a little more energy than a pump that runs at maximum amps until a tank is full, then shuts off. The Amtrol “test” makes a big deal about the “Cycle Control Valve” and the VFD “consuming almost twice as much energy as a properly sized pressure tank”. However, put into proper context, going from .5 KW to 1 KW use per day, is only about a nickel per day or $18 per year difference.
Also notice that the Amtrol “test” was set up to try and make a CSV look bad, by not having any uses for water that last longer than 7 minutes. While this maybe typical for homes in the northeast that rarely use water outside of the house, it is not typical of the rest of the world. In the real world people have irrigation, use heat pumps, or at the very least occasionally use a garden hose for more than 7 minutes.
If this test had been set up for more real world conditions, water uses for longer than 7 minutes would turn the results of the test completely around. Longer run times would make the “properly sized pressure tank” method show numerous cycles per day, while it would further decrease the number of cycles with a CSV or VFD. Longer run times would also make the electric consumption fairly equal between all three methods.
And there is no way a tank manufacturer would ever do a test for a system that uses a small amount of water for long periods of time. A continuous demand of 7 GPM using a 15 GPM pump and a “properly sized tank” would cause more than 360 cycles per day or 131,000 cycles per year. This would then have to be compared to only 1 cycle when using a CSV or VFD, and Amtorl would not want you to see that comparison.
Whether or not the 4.5 gallon tank with a CSV causes 9 or 31 cycles per day is not important. The CSV will only let the pump cycle once for each intermittent use of water. The CSV will not let a pump “rapid cycle” or cycle WHILE you are using water. These are the destructive cycles for a pump/motor. The fact that the pump has to start each time you open a faucet is no where near as destructive for a pump, than continuing to cycle WHILE you are using water.
The initial cost of a CSV and small tank maybe close to that of a large pressure tank, but the life time cost of the CSV system will be considerably less. Eliminating destructive cycling, de-rating the motor load, (making the motor run cooler), preventing water hammer, along with all the other benefits of the CSV, the pump/motor/tank and other components will last many times longer than when a pump continually cycles into a big pressure tank.
Pumps are confusing. The so called “studies” are confusing. My detailed explanation is confusing, even to those who work with pumps everyday. The industry uses this confusion to keep you buying big pressure tanks and cycling all your pump system equipment to death, so you will have to replace pump/motor/tank on an average of every 7 years.
I have to make new customers everyday. I don’t get to sell them a new pump/motor/tank every 7 years on average. Even with a small tank, many CSV customers have not had to work on their pump system in 20 years so far. I don’t know how much longer these CSV systems will last, but they have already tripled the average life of the pump/motor/tank. THIS is exactly why you see “studies” like the one from Amtrol. THIS is exactly why they try to keep you confused. THIS is exactly why many people in the pump industry will try to dissuade you from using a CSV. And THAT is exactly WHY every pump system should have a CSV.