I think I do want the pressure tank to act like a plug under ~72psi (my set working pressure of the pump). This was not due to the pump running above its configured pressure. When I first added the pump, I believe the internal check valve must have closed the system from the city main and this is when I saw pressure creeping up toward 100psi during non-use, so I added the pressure tank. Before that, I had no pressure tank, and no cycling. This cycling problem only began when I added the pressure tank. Pressure gauge on the VFD system is at about 40 seconds. The stuff in the drawing I posted earlier can be much less than 800 bucks, will last a long time, and does deliver strong constant pressure without the pump cycling. It is just a matter of how long a person wants to put up with the problems and how many times they can get them to shell out another 800 bucks before they try something different. We replace a lot of those with Cycle Stop Valve systems. I would try reducing the air charge in both tank to like 40 PSI, AND see if the pressure holds when no water is being used. You are not putting a drop in the tank until it gets to 76 PSI. With 75 PSI air in the external tank, it just acts like a plug in the end of the line when there is less than 75 PSI pressure in the system. If you want a tank to work like it is smaller, reduce the tank air charge. If it is not leaking in the house plumbing somewhere, the check valve in the pump is leaking back. It doesn't matter how much air is in what tank or how much elasticity the system has, the pressure will not drop unless water is leaking somewhere. I guess not?Īlso, when you are not using any water the pump should stay off. SCALA2 has integrated speed control which allows maintaining perfect pressure in the taps. I guess that is one way to handle one of many very technical problems with VFD controls, but it doesn't go along with what they say the pump will do. If the pressure drops, the pump knows you are still using water and comes back on. So, they just bump the pressure and turn off the pump every few seconds. Long explanation but it has to do with the pump not knowing how slow it can go and when to shut off. That is also the way the Pentair PID system works. I cannot believe the distributor told you that is the way they are supposed to work. I have a video of this happening and will try to post it. It is also very common for the pressure transducer or VFD itself to malfunction, which will also cause the pressure to spike above 100 PSI. Expansion would also only cause spike pressure sometime after the pump shut off. If expansion was what caused the pressure to spike above 100 PSI, it would show you the tank in the pump is so small it is useless. The little tank built into the pump is after the check valve that is also built into the pump. You are correct that a variable speed pump should slow down to supply the demand and never shut off as long as there is a demand. This video shows what I am experiencing, but I have longer cycles: I went with a larger Amtrol ST-12 thinking it would help maintain a bigger buffer of pressure and smooth out the pump engagement, but maybe it is taking a little too much work off the pump slowing the feedback loop that the pump depends on. I might give a smaller pressure tank a try. I imagine if I had much higher flow, or a lower set pressure, it might stay on longer or continuously. My theory is now that there is more "elasticity" in the system that allows pressure to be maintained within the 10psi target band of the pump for longer so it takes breaks. It seemed to cycle a lot less before I introduced the external pressure tank. I just spoke with their distributor and he told me that this seems normal, but my understanding was that the pump should "slow down" to maintain a constant pressure. It clearly has speeds, as the pressure settings on the pump create audibly different frequencies. I thought the speed was supposed to be variable and expected it to hold a steady pressure at whatever speed was needed. Maybe it's unnecessarily stressing me out, but I don't like the sound of the pump turning on and off. My measured pressure seems to ping-pong from 60-70psi as the pump goes on and off. With 2 taps open wide, the pump clicks on for a mere 5-10 seconds, and then stays off for around 30, before cycling back on. Internal pressure tank, and external pressure tanks set to 70% of that = 50.75psi. Pump outlet pressure set and measured 72.5psi. I had a chance today to drain and triple-check my pre-charges were set to exactly the recommended pressure.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |