I bought a CSV a few weeks ago for a new build, it's been "hung" in the basement but well pump still not installed yet. The plumber had never heard of a CSV and is installing it because he couldn't convince us it was a bad idea and switch to a standard system. He thinks we'll burn up the pump or blow out the line when the pump runs continuously while water is needed (say taking a shower) because pump is going to be pumping full power but system is using much less. Can someone explain to me so I can explain to him why this is not the case? Also, we bought the material to make a shroud but haven't brought that subject up yet. If my well is 250' deep but water level is 55' and located in southwest Virginia, if a shroud still recommended? Thanks in advance for any info provided.
Cycle Stop Valve (CSV) and shroud question
- Thread starter SueInVA
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I'm sure Valveman will answer this, but here's some info.
Below is a simple pump curve.
As you can see, when the flow rate is low, the power consumption is also low. And the pressure at low flow is higher than at normal flows, but nothing that the pressure tank can't handle. So, as you can see, the pump is not operating at "full power".
Pumps are not what usually fail in a system, but rather it is the pump motor. And the motor failures are caused by heat. When a pump motor starts, there is an inrush of current that is required to get the motor to start turning. As electricity to a motor isn't 100% efficient, some of that inrush current results in heat. On some large motors, there are actually controls that keep a motor from starting too frequently because of that heat. Now one may think because a well pump is surrounded by water, there is no way it can overheat. But that is not the case.
So, running a pump for even a few hours is MUCH better on the pump and motor than having it start and stop a dozen times. And with a CSV, you have constant pressure instead of the cycling of pressure which can be a issue on some components.
I'm sure Valveman will provide a more detailed description of the benefits of a CSV, but that's my quick input.
Below is a simple pump curve.
As you can see, when the flow rate is low, the power consumption is also low. And the pressure at low flow is higher than at normal flows, but nothing that the pressure tank can't handle. So, as you can see, the pump is not operating at "full power".
Pumps are not what usually fail in a system, but rather it is the pump motor. And the motor failures are caused by heat. When a pump motor starts, there is an inrush of current that is required to get the motor to start turning. As electricity to a motor isn't 100% efficient, some of that inrush current results in heat. On some large motors, there are actually controls that keep a motor from starting too frequently because of that heat. Now one may think because a well pump is surrounded by water, there is no way it can overheat. But that is not the case.
So, running a pump for even a few hours is MUCH better on the pump and motor than having it start and stop a dozen times. And with a CSV, you have constant pressure instead of the cycling of pressure which can be a issue on some components.
I'm sure Valveman will provide a more detailed description of the benefits of a CSV, but that's my quick input.
I never really understood how this works either. It would seem logically that a pump moter turns at whatever speed it's set for, turning the pump mechanism at its prescribed flow rate.
So if your choking the flow down say from 10gpm to 2gpm, it would seem it would generate a lot of back pressure. Which would logically to me , make the motor work harder to maintain its speed. The pump mechanism may have a bypass that would reduce this (but I am unaware or ignorant of how the pump mechanisms work)
I know valveman has produced charts but they just don't make sense to me.
I'm aware it does work as advertised, just don't really understand how.
So if your choking the flow down say from 10gpm to 2gpm, it would seem it would generate a lot of back pressure. Which would logically to me , make the motor work harder to maintain its speed. The pump mechanism may have a bypass that would reduce this (but I am unaware or ignorant of how the pump mechanisms work)
I know valveman has produced charts but they just don't make sense to me.
I'm aware it does work as advertised, just don't really understand how.
constant pressure valves do cause back pressure and your pipe must be in good enough shape to take that pressure. New systems shouldn’t have any problem.
Unless there is a variable speed drive in the system, the motor turns the pump at the speed of which the motor is designed, like 1750 RPM or 3600 RPM. The pump then develops a flow rate based on the system head it sees at that flow rate. The more head the pump has to generate, the less flow it can develop. So, throttling the discharge through a CSV increases the system head which in turn reduces the ability of the pump to develop flow.
The primary "work" the pump is doing is moving a volume of water. The less water the pump moves, the less work it is doing. The less work it is doing the less energy it takes. The less energy it takes means the motor is actually "working" less at lower flow rates.
Look at it this way. You're lying down and decide you are going to jump up and run 300 yards. You jump up and run hard for 100 yards which takes a lot of energy. You slow down to a jog for the next 100 yards which takes less energy. Then you slow down and walk the last 100 yards which takes less energy yet. You do have to stand up for all of those activities, but the primary "work" you are doing is moving your body 300 yards.
My father-in-law was a pipe fitter in a steel mill and had to argue with several other pipe fitters when they were installing an inlet pipe into a 1,000,000-gallon water tank. It was to be installed near the bottom of the tank wall with a check valve. His co-workers were saying that this was a stupid design because the weight of all that water would be reducing the flow from the pump, and they should be running the pipe up the side of the tank so the inlet water would not have all that pressure working against it. They had no concept as to system head.
A constant pressure valve is a pressure regulator with a bypass to allow a reduced flow of water around the regulator ( the valve )
When the well pump turns on it pressurizes the piping between the pump and the constant pressure valve.
When the well pump turns on it pressurizes the piping between the pump and the constant pressure valve.
Thanks guys. Even having been raised in the well business and having worked in it for 25 years, I still thought the same thing 30 years ago. I understand why this not being true it is a hard concept to understand. It does make sense that choking a pump back with a valve should make it work harder. This is one of the only things I know of which works just the opposite of what our minds tell us is true. It is certainly counter intuitive. This would be true with a piston type pump, but not a centrifugal. When there is no water moving through the pump for one of many possible reasons, like a closed valve or dry well, the centrifugal impellers are basically just flat disc spinning feely in the perfect lubricant and coolant. Only when they start grabbing water and trying to throw it in an upwards direction do they start becoming a load to the motor. When running against a closed valve and making max back pressure, the pump is easy to spin and basically drawing zero load. The only load is what it takes to spin the motor. But it is a hard concept to understand.
I don't blame pump guys for thinking that way, just for not knowing how to read a pump curve to see restricting the pumps flow makes the amps drop and the motor run cooler. I don't produce those charts, I just post actual pump curves and try to point out the important parts like MicEd did.
So, just to ask, when the well pump turns on at 30 psi, and not using a prv, and slowly increases the pressure up to 60 psi, it seems like your saying the load should decrease, and the pump not draw as much electricity ?
Or is the increasing pressure nit like restricting the flow... maybe not.
I'll have to watch my pump and how much electric it draws as the pressure increases.
Checking a run on my pump. A 10 gpm.. started at 1150 watts and slowly reduced to 1125 . So as the pressure increased the load decreased. Maybe not exactly the same thing but I believe it does show a type of example.
If there was no significant flow, only that required to increase the volume of water in the pressure tank to bring the pressure up to 60 psi, that is pretty much what we are talking about. Again, the "work" the pump is doing is MUCH MORE associated with moving water rather than increasing pressure.
Oh, I'm not arguing about if it works, just trying to get this 68 year old head to understand it and how it works.
But just to make it clear, pump kicks on at low point.. runs like normal 10gpm until cycle stop set point (50 psi) then throttles back to the demand usage (maybe 3 gpm) to keep pressure at 50, until demand stops, then proceeds up to the 60 psi set point and turns off.
What happens between 50 and 60 if the demand returns ? (Another 3gpm) Does it return to a normal type function, where it continues ip to 60, falls to 38, back to 50 and stay there till demand stops again then back to 60?
The piping between the pump and the constant pressure valve is what sees the most pressure. You have to make sure that piping is in good enough shape to handle it. In a new system it will not have a problem.
As you noticed there will be a little drop in amps as the pressure increases from 40 to 60 PSI. But that is in what is call the flat spot of the curve where there is very little difference in flow. At 40 PSI and 1150 watts it maybe doing 12 GPM. At 60 PSI it is still doing 10 GPM and only drops to 1125 watts, but there is still a drop in amperage as back pressure increases. With a ball valve or a CSV on the well head that could restrict the flow to 1 GPM, the back pressure before the CSV will be like 100 PSI, but the amps should drop to as low as maybe 800 watts. So yes, that is a good example.
However, some pumps drop in amps more than others, depending on the impeller design. Plus, there is not much drop in flow on a 10 GPM pump to 1 GPM like there would be on a 20-25 GPM pump down to 1 GPM. You should also realize that that drop in amps, similar to a VFD, is not linear with the drop in the flow rate. So, even though the amps drop by 50% or so, it is costing more per gallon to pump a gallon of water. To be efficient with a CSV or a VFD, the flow rate being used must still be close to BEP or the pumps best efficiency point (WHICH IS AT RATED SPEED AND MAX FLOW).
However, the amps do not have to drop very much, only like 10% to de-rate the motor load enough that it could safely pump hot water if needed. Therefore, it takes very little flow, like only 1 GPM to keep the motor cool. It may not be most efficient to use a 10 or 25 GPM pump at 1 GPM, but it certainly will not hurt anything. It is actually keeping the pump from cycling on and off, which is making the pump last longer.
A VFD "creates" a smaller motor from a larger one, it does not "de-rate" the motor load like a CSV does. That means the VFD controlled motor still needs as much cooling flow as a fully loaded smaller horsepower motor, which is still the 0.5 fps and much more than the 1 GPM you can do with a CSV. For efficiency, it is still required to run sprinkler zones and high use loads at close to max flow of the pump, regardless of VFD or CSV.
Another good question. That is the mechanical timer I talk about. When demand stops, the CSV starts filling the tank at 1 GPM from 50 up to 60 PSI where the pressure switch will shut off the pump. Depending on the CSV setting and the size of tank, this time needed to fill the pressure tank can be adjusted from 30 seconds to say 3 minutes, even with a tank that only holds 3 gallons of water, like a 10 gallon size tank. During this 1 to 3 minutes the CSV is filling the tank, if anyone, anywhere, inside or outside the house uses any water, the pump continues to run, the pressure falls back to 50 PSI, and the CSV supplies the demand. When the demand stops, the mechanical timer starts all over again. We find that when people in a house or group of houses start using water, someone will open a faucet every couple minutes or so. The CSV usually just keeps the pump running continuously for an hour or three, until every one is out of the house(s) and headed for school and work. The pump stays off most of the day, and the continuous running happens again in the evening hours until the lights are out and everyone is down for the night. This is much preferable for the pump than cycling on/off dozens of times during those high use times of day. It is also preferable for the occupants as they see strong constant pressure in every faucet, of every house, every time they open one.
The back pressure is always less than most people would think. A 10 GPM, 1/2HP pump can only make about 100 PSI max. You can scale up the HP and flow without increasing back pressure. A 20 GPM, 1HP or a 40 GPM 2HP will also only make about 100 PSI max. It is the small volume, high horsepower pumps that build the most back pressure. A 10 PM, 1HP can build almost 200 PSI. But a pump like that should be installed in a well where the water level is at least 150'-200' deep, which will eat up a 100 PSI of the 200 that pump can build. Which means you still only see about 100 PSI back pressure before the CSV. Only pumps that are way over sized, like when made for a 500' deep well and the water level is only 100' does back pressure become an issue. But no matter how much back pressure it makes, each pump was designed to make that much. So, as you said, the only issue, even with way oversized pumps, is to make sure the pipe before the CSV is rated for enough pressure. After the CSV, any pipe will work as it will only see 40 to 60 PSI max.
When the pump is set above the bottom end of solid casing or above the perforations, water will draw down from above until the static water level drops to the dynamic or pumping level, then water will start coming from below. In a rock well or one with no casing, water will come to the pump from which ever direction it enters the well. If the cracks and fissures are above the pump, the pump will be fed from above. If the cracks and fissures are below the pump, it will be fed from below, but only after the static level has drawn down. What is not known is the percentage coming from above and below at the same time until the well draws down to the dynamic level. Hopefully enough will come from below to adequately cool the motor until the static level draws down, but you can never be sure. Since the motor is on the bottom and the water intake between the pump and motor, only water coming from below will cool the motor. A flow inducer or shroud makes sure the flow always goes past the motor before entering the pump, no matter if the well is top feeding the pump or not. A shroud also works as a centralizer and protector as it keeps the pump/motor from being able to bang against the casing or rock. There are lots of good reasons to use a shroud on every pump installed. The only reason not to use a shroud is if the casing is too small for it to fit, which I consider a well design error.
Sometimes a motor in a well with lots of standing water needs a shroud more than when in a well with only 10' of water above the pump. If the water level pulls down every time the pump is started from 55' to say 200', the motor receives little to zero cooling from below during the first few minutes of running. Only when the water level stabilizes will flow start coming from below and cooling the motor. Shrouds are probably not common in your area, but IMO they always help and never hurt.
Thank you for giving me a better comprehension of how the csv works.
You have a very in depth knowledge of pumps / wells and of course the csv (that I understand you invented) .
My well is 65 feet, the pump is set at 40 feet static is at 24 (16 feet of wet pipe when pulled up) well was rated at 35gpm but that was 40 years ago.
There crude measurement was blowing air down the well and catching the water that came out in a 5 gallon bucket. And just saw how many times it filled in a minute. (At least that is what I remember) over 40 years who knows what the water table has done, but as much water as I pull out of that well (since I'm running a geo heat pump from it) I've been told and read, that my large use would have helped create better channels for the water to flow to my well.
I'd love to have a camera down there to see what that water level does when the pump kicks on.
All the other wells near me are much deeper, 300-600 feet. One neighbor has a well like mine, I think he hit the same vein.
I picked where I put my well by water witching it... that actually works.
But thanks again !
Like I said, the pressure increases between the pump and the constant pressure valve.
Weldy
New Member
This is the first discussion I have read since joining the forum a couple of weeks ago. Just want to say Thank You to all who participated in the above discussion. In my opinion, a very interesting topic and lots of very good information shared by all. Thanks again for sharing your time, thoughts, experience and expertise !!!
