Help me understand

[N_Jay]

It looks like the CSV trades off number of cycles for longer run time, but under low flow a lot of that time is at fairly high head pressures?

Wouldn't having a decent size tank and putting the pressure switch ahead of the CSV Pressure regulator) be a better overall solution for constant pressure (although a bit more expensive)?

[Cary Austin]

It looks like the CSV trades off number of cycles for longer run time, but under low flow a lot of that time is at fairly high head pressures?

Wouldn't having a decent size tank and putting the pressure switch ahead of the CSV Pressure regulator) be a better overall solution for constant pressure (although a bit more expensive)?

Longer run times at low flow and high back pressure cause the pump to draw lower amps and run cooler which is good for the pump.  Short runs at high flow, low back pressure, and max amps are hard on the pump.

A pressure regulator after the tank does nothing for the short run times, hard starts and stops, water hammer, and other problems caused by cycling.  Plus you still need an expensive and large pressure tank.  You would also need a 50/70 pressure switch to maintain 50 on the discharge.

A Cycle Stop Valve on the inlet side of the tank only requires a 40/60 switch to give 50 PSI constant to the house.  The CSV also allows a small tank and solves all the problems associated with cycling the pump on/off.   

A pressure regulator on the discharge of the tank is exactly what the pump companies want you to do as it doesn't affect the 7 year average planned obsolescence life of the pump.  A Cycle Stop Valve on the inlet side of the pump will make the pump system last 30-40 years instead, which is exactly why the pump manufacturers call it a disruptive product and will say anything to keep you from trying a CSV. 

BACK PRESSRURE IS GOOD FOR A PUMP!!!  CYCLING ON AND OFF IS NOT GOOD!!!!!

[N_Jay]

Thanks for clearing up a few points.
It seems that what you are saying is true as long as the designed maximum head pressure for the pump is not exceeded or the minimum flow is not held too long.
Although I would think that at low flow rates (single small residence) flow may often be well below the desired minimum for the pump.
Additionally, at fairly low flow, the efficiency will go down.

One additional question.

Are the CSV just regulators, or are they specially designed for the application, because many regulators will creep towards the input pressure, in this application you would wan that to happen fairly quickly.

[Cary Austin]

Most pump manufacturers have blacklisted the CSV as a disruptive product, as it is so perfect it makes pumps last longer and uses smaller pressure tanks.  The CSV has been reduced down to the simplest and most perfect pump control available.  There is no flow rate that you could use that would hurt the pump.  If you are using less than the minimum flow designed in the CSV the pump will cycle slowly.  If you are using more than the minimum flow designed in the CSV the pump can run continuously 24/7/365 without hurting a thing.  The minimum flow set in the CSV is designed to keep the pump cool and happy even if it ran this way all the time.  The CSV can never completely close.  It is specially designed for this application and will always "creep" a certain amount through to keep the pump cool.  There is no time limit on how long you can run at minimum flow.  I have several patents at USPTO.GOV is you want to get technical.

54 years of experience has gone into making the CSV is so perfect for pump control that it makes pumps last several times longer than normal, which is why it is hated by pump manufacturers and many pump installers.