Hi Marcus
That is a beautiful pump station. Thanks for the pictures. I can’t see where the pressure switch is located but, it doesn’t look like there is enough room at the bottom of the pressure tank to connect the pressure switch. The larger the pumps, the more important it is to have the connection to the pressure switch or switches located as close to the tank as possible. It may even have something to do with the run time.
Run time is not nearly as important with the CSV. I know run time has always been a very important part of properly setting up a pump system. With the CSV, the pump continues to run as long as there is a small demand for water so, run time is really not that important. As long as you have 30 or 45 seconds of run time, you can be sure that the setting of the CSV is lower than the off setting of the pressure switch, and that is really what is important.
Minimum flow through the CSV is actually determined by the differential pressure between the dead head of the pump and the pressure setting of the CSV. When the CSV closes, the little notch in the CSV makes a certain size opening. A little extra or less powder coat, and the stiffness of the diaphragm can change the opening size slightly from one valve to another. This can cause slight differences in the size of the notch opening, which can make run time from one pump to another slightly different.
We like to say that the minimum flow through that size CSV is 5 GPM. However, that is basically an average. The minimum flow can be as little as 1 GPM with a differential pressure of only 10 PSI, or it can be as much as 7 GPM for a pump that delivers 125 PSI differential pressure. I have a chart for this that I can send you on Monday. This will basically automatically adjust the minimum flow to the cooling requirements for the pump. A multistage pump that builds high back pressure needs more cooling than a single stage pump that puts out very little back pressure. So the different minimum flows at different differential pressure works out great.
Depending on the minimum flow created by the differential pressure and the draw down of the tank, run times can vary from system to system. The only thing that is really important is the run and off times when the flow rate is less than the minimum flow. You can use our tank sizing calculator on the web page to give you an idea of the maximum number of cycles per day. With the worst case scenario being a flow rate of about half the minimum flow, you can determine the tank size required to keep the cycles per day less than what is required by the motor and pump manufacturer. Maximum cycles per day is what is important, not so much just run time.
The slightest difference in the pressure setting of the two valves, and a little difference in the thickness of the powder cost over the notch, could easily cause a 40 second difference in run time with such a small tank but, it is not that important.
Normally we set up two pump systems to lead and lag instead of alternating. Alternating wears out both pumps at the same time so you basically do not have a spare pump. Lead lag only runs pump #2 when pump #1 cannot keep up with demand, or if pump #1 stops working. You can use an exercise clock to make sure pump #2 gets used a few minutes once or twice a weak just for exercise, then when a backup or spare pump is needed, it will still be like new instead of being just as worn out as pump #1. In a lead lag set up, pump #2 really does not have ANY run time. This is because the pressure setting of the CSV on pump #1 is what shuts off pump #2. With the CSV, run time is not important because the pump never comes on unless there is enough demand to keep the pump running for a while. Then the pump never goes off unless there is very little or basically no demand. So run time as we used to know it is no more important than the off time. Now run and off time can be figured by using half the minimum flow through the CSV, to determine the required tank draw down. Then again, with the lead lag set up, run and off time is only important for pump #1, as there is really no way to make pump #2 cycle at all.
Also, alternators only switch to the other pump when pump #1 shuts off. When you have a system that is large enough to always have a demand or leaks as much as the minimum flow through the CSV, pump #1 will NEVER shut off, so pump #2 may not ever get the exercise it needs.
The more you use CSV’s, the more ways you will find you can use them, and the less you will worry about run times and other things that used to be so critical.
I hope this helps. Let me know if you have further questions.
Thanks
Cary
