I can’t argue with the few people who say they only use 50 gallons per day and a tank that holds 25 gallons (80 gallon actual size) will only cycle the pump twice a day. But hey, if you only use 50 gallons a day, you probably only touch a faucet or toilet 6 or 8 times a day to use that 50 gallons. So even if a CSV system with a small tank makes the pump come on every time you use water, the pump is only going to cycle 6 or 8 times per day, as compared to 2 times a day with a really large tank.
The benefits of the CSV and smaller tank for houses that use very little water per day, still far outweigh a few extra cycles. An obvious benefit is the much smaller tank. The smaller tank cost less, takes up less space, requires less energy to heat, and is easier to install.
A benefit that will quickly BECOME obvious, is the constant pressure supplied to the system while you are using water. Constant pressure from the CSV with a small tank will fill washing machines and toilets faster, maintain a steady flow to keep instant water heaters from shutting off, and make the pressure in the shower so strong you will no longer need soap to get the dirt off.
The freshness of the water is another benefit of the CSV with a small tank that quickly becomes obvious. An 80 gallon tank holds 25 gallons of water, stored in a rubber bag, and warmed to room temperature. Not only does this waste energy warming water to room temperature, but the warmer water is not as palatable, and even accentuates the taste of the rubber bag it is stored in. If your house only uses 50 gallons per day, you get 2 bags of warm, rubber tasting water.
A 4.5 gallon size tank commonly used with a CSV only holds 1 gallon of water. Only the first gallon that comes out of the faucet has been warmed to room temperature or had any time to take on the taste of the tanks interior liner. So your water is always straight from the well as fresh Mother Nature can supply it.
Other benefits are just as important but harder to notice. The elimination of water hammer on pump start or stop is one such benefit. The mechanical soft start/soft start caused by the CSV being in the 1 GPM position, eliminates water hammer that stresses and shortens the life of faucets, check valves, fittings, pipe, and even the thrust bearing in the motor.
A CSV eliminates destructive cycling by adjusting the flow from the pump, causing the motor to run at reduced amperage. This de-rates the load, making the motor run cooler, and requiring shorter run and off times. Increasing the life of the pump/motor is a benefit you won’t even think about for many years.
The CSV only lets the pump cycle once for each water use, no matter how long that water usage last. The CSV also de-rates the motor, making it run cooler. The 1 gallon of draw down in a 4.5 gallons size tank, being filled by the 1 GPM bypass in the CSV, creates a mechanical timer that guarantees proper run and off times. So even if your pump cycles 20 to 50 times per day, there are still many benefits to the CSV and small tank as compared to supplying your house with a few big bags of warm, rubber tasting water from a large pressure tank.
Many tests have been done comparing a “properly sized pressure tank” to a Cycle Stop Valve with a small tank. Depending on the household conditions the test was set up to simulate, the number of cycles varied.
A company that manufactures tanks said, the CSV “does not significantly reduce the number of cycles compared to a properly sized pressure tank”. In other words, although they hate to admit it, the CSV and small tank cycled fewer times per day than a “properly sized pressure tank”. Another individuals test showed the CSV and small tank caused the pump to cycle 7% more than a “properly sized pressure tank”. Our own tests have shown basically no difference in the number of cycles between a CSV/small tank and a large pressure tank.
The CSV will work with any size tank. Many will argue that a CSV with a large tank offers the best of both worlds. For intermittent uses of water like toilets and ice makers, a larger tank can reduce cycles by delivering more gallons before the pump has to start. Then when water is being used for extended periods of time like for heat pumps, sprinklers, and showers, a CSV will still maintain constant pressure and eliminate cycling.
However, when all things are considered, there is basically no reason to continue wasting money or space on large pressure tanks for home water systems. The year 2014 will make it 21 years since the introduction of the Cycle Stop Valve. The CSV/smaller tank has been proven on hundreds of thousands of systems for longer than two decades. The few cycles a large tank can save for intermittent uses of water, will never outweigh the cycles a CSV can save on long term uses of water.
A large CSV controlled pump system can use an 80 gallon size pressure tank to supply an entire city of 40,000 people. So there is no reason to use a tank any larger than 4.5 gallon size for a single home.
If you think the size of your house or running multiple houses on the same water system will require a larger pressure tank used with a CSV, see "Can I use a Large Pressure Tank with a CSV?" at this link.
http://cyclestopvalves.com/smf/index.php?topic=1952.0 
