When the Horsepower is plainly posted on the curve you no longer need to know the head or pressure to figure that out. Everything needed is already on the curve. Now we need to post some curves to show you that not having back pressure when using a VFD doesn't make any difference on the energy use compared to restricting and having back pressure. But I am thinking you are not really wanting any help? If efficiency is your only concern, make sure your pump operates at BEP or it is off, and deal with all the consequences of cycling the pump on and off repeatedly. It is hard to convey all the benefits and convenience of having a CSV in writing, especially when the conversation gets as complicated as this, but those who have one greatly appreciate it.
"The follow on question, where is that 0.3hp going? It has to be dissipated in the CSV."
These quotes and this entire thread are similar to discussions I have had with pressure tank manufacturers trying to justify the expense, space needed, and all the problems that go with cycling a pump on and off. Systems with multiple pressure tanks require frequent tank replacements as the continual cycling causes the diaphragms to fail regularly. Frequent and continual tank replacements are the goal of any tank manufacturer.
The CSV is just as efficient as a large pressure tank when operating at BEP flow and just as efficient as a VFD when operating at minimum flows. A VFD and a CSV both reduce the pump efficiency at low flow rates, but the benefits of not cycling on and off while at low flow can easily outweigh the loss of efficiency. In most cases the loss of efficiency will never equal the cost of all those tanks and the other failures that cycling causes.
To anyone who has followed this thread to this point, I apologize. It got really complicated and I am sorry for your headache. Someone signing in with a number instead of a name and going on and on about 0.3HP efficiency loss most likely has an agenda. This is because after 1993, pump and tank manufacturers labeled the CSV a “disruptive product”. The quote from one pump manufacturer said, “Cycle Stop Valves make pumps last longer and use smaller pressure tanks. Anyone working for this company who mentions a CSV will be terminated immediately”.
Since then, pump and tank manufacturers have had an agenda to make Cycle Stop Valves look flawed any way they can. This is because the truth is that Cycle Stop Valves work so well, they could put pump and tank manufacturers out of business.
A 25 GPM, 5HP is one of the hardest size pumps to make a CSV work with. For one thing it is just a 25 GPM pump. A person could put enough pressure tanks on to make it last quite a while, and it would be efficient. However, it becomes hard to justify enough pressure tanks to properly control a 50 GPM or larger pump. Even though it is only a 25 GPM pump, it requires a 5HP motor because the well is so deep. It is hard to make a 5HP that only pumps 25 GPM be efficient, as 5 Horses for only 25 GPM is not efficient to start with.
Even so, I think I accomplished showing how even a 5HP, 25 GPM pump can benefit from a Cycle Stop Valve. Being as it is the worst-case scenario, if it can be proven that a CSV is the best way to control a 5HP, 25 GPM pump, then a Cycle Stop Valve has even more benefits for almost any other size pump, large or small.
Pump and tank manufacturers labeled the Cycle Stop Valve as “disruptive” for a reason. The CSV makes pumps last longer, use smaller tanks, and are as efficient as a VFD, all while delivering the strongest constant pressure to the system possible. The Cycle Stop Valve is “disruptive” to the pump and tank industry because it saves homeowners and end users lots of money. You won’t find a single pump or tank manufacturer that will even mention a Cycle Stop Valve, which is exactly why every pump should have one.
