JG plumbing
Well-Known Member
Does the motor on your ceiling fan, in your living room, get bogged down when you close the doors to your house?
Air in Water Lines Only first thing in the Morning
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It would bog down If I grabbed a hold of it to try preventing it from turning.
JG plumbing
Well-Known Member
There's nothing preventing it from turning. That's the point. It's grabbing air from behind it and throwing it in front of it. So you can open the door and let some go into your bedroom or keep the door closed and leave it in the living room.
Right. That one I do understand. That type of controller electrically varies the current to the pump motor to actively control its speed.
I get that too. The CSV is an automatic mechanical valve inserted into the pipe in order to progressively restrict the flow. No electrics involved.
You lost me there.
The electric motor drives the pump. If you restrict the output flow of the pump, doesn't the electric motor "feel" that? If it gets harder for the pump to work against the increased back pressure, doesn't the electric motor need to work harder to keep driving the pump?
Obviously not.
If it WAS a piston pump used to drive water out of my garden hose, I flip the electric switch on, the electric motor drives the pump, water sprays out the end of the garden hose. Now, instead of shutting the pump motor off, if I slowly close the valve on the end of the garden hose, but the pump is still running, either the garden hose eventually explodes or the piston pump becomes fluid locked and forced to a stop, with the electric motor still powered and humming straining to drive the pump. So obviously that cannot be how the CSV system works.
I realize the CSV valve never actually closes fully. It varies the restriction on flow rate to maintain a constant pressure in the lines downstream of the valve. But by choking down the flow rate it raises the back pressure in the line between the pump and the CSV.
Even if it's not a positive displacement piston pump, it's still a pump working against an increased back-pressure. The pump is still being driven by an electric motor that only has a simple on/off switch. Where is the excess water pressure going? Is it leaking back through the pump itself? If the elevated water pressure from the pump isn't escaping anywhere, then it must mean the increased back pressure is forcing the pump to run slower. If the pump is being forced to run slower, that means the electric motor is also being forced to run slower than it wants and it will be straining more and more trying to drive the pump onward. That motor would be drawing more amperage when forced to run slower, not less.
That's the part I'm not understanding.
JG plumbing
Well-Known Member
Since water isn't air it's not a prefect analogy. But it's similar. The motor is affected some but not like what your thinking.
JG plumbing
Well-Known Member
It creates differential pressure. Negative behind and positive infront. So when it just spins it just spins.
JG plumbing
Well-Known Member
It does draw more. Just not enough to offset the vfd cost of breaking all the time.
So in your example, the bedroom door is the CSV valve, and the water pump is just circulating water around in the living room.
But is the water actually circulating between the pump in the well and the CSV valve? Isn't the pump trying to stack water up the pipe with nowhere for it to go? The pump is running but the water isn't going anywhere. How does that work? That's what I'm missing.
Air can do that, but not water. If the pump is thrashing paddles through the water without moving any of it, doesn't that create destructive cavitation?
JG plumbing
Well-Known Member
It doesn't stack. Just like if you sealed your living room. The fan isn't the size of the living room scoopin every bit of air, but since it's moving if you own the bedroom door it'll come spilling into the bedroom where the air has less movement.
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JG plumbing
Well-Known Member
It could cause cavitation if there was no water one one side.
JG plumbing
Well-Known Member
The analogies aren't perfect you said your brain was hurting and I'm trying to explain.
I'll just have to admit I really don't understand how a water pump works. I can't picture it as being a tiny propeller suspended in a living room sized pipe. That seems way too inefficient and leaky to me. I would have thought the impeller would be sealed tighter than that.
I gotta go to bed. Think more tomorrow... Cheers.
I gotta go to bed. Think more tomorrow... Cheers.
JG plumbing
Well-Known Member
When you choke a centrifugal pumps output the amp draw decreases.
The RPM of a centrifugal pump doesn’t have to be reduced for the pump to use less power, it’s using less power because it’s doing less work.
Counterintuitive isn’t it.
The RPM of a centrifugal pump doesn’t have to be reduced for the pump to use less power, it’s using less power because it’s doing less work.
Counterintuitive isn’t it.
The motor is not running slower. It’s just not having to move as much water being restricted so the load is actually decreased on the motor even though it’s spinning at the same RPM.
Cray cray huh ?
JG plumbing
Well-Known Member
JG plumbing
Well-Known Member
As I understand it, the trick of the csv is sensing pressure or volume on both sides of the valve. Not sure which one I'm guessing pressure.
Lol JG! Sorry for the long posts. But as you can see for the CSV to be such a simple valve it has a complicated explanation. "Counter intuitive" is the key word. Pumps work just the opposite of what our brains tell us. This is why people who sell variable speed pumps or VFD's have such and easy time duping people into paying way to much for a VFD controller. They are tricking people into purchasing a VFD to make the pump do what it already does naturally. Unlike a piston or positive displacement pump, the amps of a regular centrifugal pump are proportional to the flow rate. In other words the higher the pressure or backpressure the lower the amps, which is completely counter intuitive. Even with a simple ball valve, the more you "choke" back on a pump the lower the amps, making the motor do less work and run cooler as well. The valve just makes the pump think the well is deeper so it can't pump as much water. All pumps work on a curve. At low pressure they produce a lot of water and pull max amps. At high pressure, like in a deeper well, they produce less water and draw lower amps.
The CSV is a simple valve that just works like a ball valve. However, the spring in the CSV makes it open when pressure is lower than the set point and close when the pressure gets higher than the set point. When set at say 50 PSI, the CSV will open or close as needed to produce exactly the right flow rate to keep the pressure at a constant 50 PSI. When the pressure drops below 50 the CSV opens. When the pressure gets above 50 the CSV closes. It basically varies the flow rate of the pump to exactly match the amount being used, by maintaining 50 PSI constant. When you stop using any water and the CSV closes as much as it can at 51 PSI, it basically leaks 1 GPM though that has no place left to go but the tank. Then at 1 GPM rate the CSV tops off the tank until the pressure reaches 60 where the regular 40/60 pressure switch shuts the pump off. The speed of the pump is never altered, the amps just lower with the flow rate as that is how pumps work.
To make this an even longer post and blow your mind some more, the pump actually speeds up when the flow is "choked" off with a valve. The electric current is spinning through the motor windings at 3600 RPM. However, because of the load the rotor cannot spin as fast as the electric current. The amount of difference between what the windings are trying to make it do and the rotor speed is called "slip". Under load there is about 4% slip. So, a 3600 RPM pump/motor is actually spinning 3450 RPM. However, when the flow rate is restricted with a valve the load and therefore motor amps drop. With less load on the motor there is also less slip. Instead of 4% slip now there is only1-2% slip. This makes a 3450 RPM pump speed up to about 3560 RPM. The counter intuitive part is that even though the motor speeds up it is drawing lower amps and using less energy. The same thing happens if you put your hand over the outlet of a blow dryer or vacuum cleaner. You can hear the motor speed up because there is less load. If you check the amps they will drop when the motor speeds up because it isn't blowing any air, which is how it sees the work or load. I will post a video that explains this in more detail using the pump curves and power charts.
By request, in 1994 I went to several pump manufacturers and answered these questions for their engineers on staff. It blew their minds as well. The head engineer for Goulds pumps even told me, "He had no idea the amps of their pumps would drop so much when simply restricted with a valve". When they finally figured out how the CSV works they were horrified. It took me several years to find it out, but the CSV was blacklisted by several pump manufacturers that day. They said, "The CSV makes pumps run cooler, last longer, and use smaller pressure tanks". "Since their company makes pumps and tanks, any employee who mentions a Cycle Stop Valve would be fired immediately." That is really when they started pushing Variable Speed Pumps or VFD's as they wanted something that could compete with the constant pressure performance of the CSV without shooting their planned obsolescence in the foot. The VFD was perfect for that as it varies the pump flow and amps similar to how a CSV works, but is expensive, short lived, and even shortens the pump/motors life. All they have to do to sell a VFD is not tell the truth about how pumps really work. Anyone who sells VFD's, especially if they claim energy savings, is lying by omission.
Sorry for the long post JG. But I have been trying for almost 30 years now and it is impossible to explain a counter intuitive property in a short post.
JG plumbing
Well-Known Member
I'm fine with it. I was hoping you'd go into it for the guy. Mainly becuse the more times I see you go into it the better I understand it. Thanks.
