Two pressure tanks at different pressures?

[Valveman]

There is one model of CSV that can be installed in the well casing.

Yeah, sorry I didn't see that. In Indiana the frost line is too deep for a valve box. Installing the CSV125 or CSVS125 in the well would be about the only option.

 

[CountryBoy19]

There should be no delay for 3-4 seconds when you open a tap as Bannerman says. There is not much friction loss when just opening a 2-3 GPM faucet and that is not what causes the delay. The pressure tank should start the water moving down the line when you open a tap at the other end. The pressure tank only has to supply as much as you are using. So, the tank should push 2-3 GPM down the line as soon as a tap is opened. However, if the inlet/outlet of the tank is restricted or too small, it cannot supply the water as fast as needed.

The pressure is like voltage and the pressure tank is like a capacitor. There should be no complete loss of pressure at the far tap as long as the pressure tank is charged enough and can push water into the line without any restriction.

Point of clarification, I never stated there was a delay in flow or total loss of pressure. There was a noticeable pressure drop, which decreased flow. IE, the shower flow would decrease for a few seconds if the toilet was flushed.

I'm a bit shocked I'm getting such pushback on basic stuff. This is freshmen level stuff I learned in 9th grade science class. As soon as you open a valve the pressure drops. The pressure is only equal at both ends when there is zero flow.

 

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[CountryBoy19]

CB19, the issues you describe are common symptoms of an undersized (diameter) supply line. Although you didn't specify the diameter or type of the current supply line between the cistern and house, I anticipate there would have been no need to compensate with a second pressure tank in the home if the supply line had been sized appropriately in consideration of the 1350' length of run and the home's flow requirements.

I suspect the pressure tank at the cistern is larger than the PT in the home. If the PT within the home was larger than the other, then as Valveman mentioned in #13, it is likely the pump will become reactivated each time the pressure falls below the pressure switch cut-in setting when it fills the larger tank after the pump was shutdown initially.

Friction will be greatest for the layers of water nearest the inner surface of a pipe whereas the water nearest the center will have the least friction (water on water) and so will flow more rapidly. Because friction loss is cumulative along the length of a run, increasing the pipe diameter appropriately can compensate for friction loss which is calculated in relation to the flow rate needed.

Another potential source of flow restriction is a restrictive or partially closed isolation valve. Full port ball valves are the preferred choice, but gate valves will also provide full flow, but the gate may become disconnected from the stem, which can result in a flow restriction even as the valve seems to be fully open. Since the flow path through a globe valve results in multiple changes in flow direction, globe valves will be most restrictive and should be avoided if possible.

Your motor analogy is not a true comparison as starting a motor from dead stop will be most similar to a short circuit since that is when the motor will briefly consume a much greater amount of power compared to power draw while up to speed and operating within design load. Opening a faucet to allow 2 GPM flow, will not cause a brief 12 GPM flow through the faucet before reducing down to 2 GPM.


As Valveman stated, water is not compressible and once pressurized, will flow immediately in any direction once there is any opening in which to escape.

Consider the many miles that water will often travel between the water source and each home in many municipal water distribution systems. Opening a faucet that is miles away from the source, does not result in any delay before water will flow from the faucet.

The line is a 1" line. Undersized or not, it's what I have and adding the 2nd pressure tank to buffer the peak demands on it worked very well.

Funny you mention municipal water, because municipal water systems DO, in fact, experience pressure fluctuations. I used to experience them a LOT at my old place in a subdivision. The reason you don't usually perceive them when a faucet is turned on is because a single faucet is a very tiny fraction of the total supply available in that line. If, OTOH, there were a big faucet (or everyone turned their faucets on at the exact same time), so that a significant portion of the total flow capacity of the line was turned on at once you would absolutely experience a noticeable pressure drop for a period of time after the flow started.

This principle is the same thing that causes water hammer. I'm sure you've experienced that before.

 

[CountryBoy19]

There is one model of CSV that can be installed in the well casing.

Can it be put right at the pump? This is a cistern we are talking about, the pump is accessible but the penetration the waterline passes through is not, so the CSV would have to be directly in the ground outside the cistern, or under water, right above the pump, laying at the bottom of the cistern.

 

[Valveman]

Can it be put right at the pump? This is a cistern we are talking about, the pump is accessible but the penetration the waterline passes through is not, so the CSV would have to be directly in the ground outside the cistern, or under water, right above the pump, laying at the bottom of the cistern.

Yes, the CSV125 or CSVS125 can be submerged, vertical or horizontal, and even be attached to the check valve on the
pump in a cistern application.

 

[Valveman]

Point of clarification, I never stated there was a delay in flow or total loss of pressure. There was a noticeable pressure drop, which decreased flow. IE, the shower flow would decrease for a few seconds if the toilet was flushed.

I'm a bit shocked I'm getting such pushback on basic stuff. This is freshmen level stuff I learned in 9th grade science class. As soon as you open a valve the pressure drops. The pressure is only equal at both ends when there is zero flow.

Yes, that is one of the things that causes water hammer. A pressure drop and hesitation is common when opening a large valve at the end of a line. But opening a small valve or two should not cause a noticeable drop in pressure as long as the supply can keep up with demand.

Again, a pressure tank works like a capacitor and should instantly supply flow when a small tap is opened. If the main supply line is large enough, opening a small tap should require almost no velocity or friction loss in the line. The water leaving the tap should be instantly replaced by the pressure tank at the other end of the line. Opening the tap is kind of like pulling the slack out of a tow chain. The water doesn't start coming down the line until water is drawn from the tap, leaving a place for the new water coming down the line to go. But with large enough main lines and a pressure tank that is not restricted to a lesser flow rate, the chain is not even one link long, as water is not compressible and/or will draw a vacuum instantly.

Elevation makes more difference in having delays or high pulses in pressure when a tap is opened or closed than friction loss. Being at the bottom of an elevation can cause a pressure spike when a tap is closed as the water wants to keep going downhill. Being at the top of an elevation can cause a delay in pressure as the water doesn't want to start uphill. In these cases a pressure tank or a stand pipe close to the tap can help with delays or spikes in pressure. But on level ground it should hardly be noticeable.

Once the pump is up and running, having a pump control that can instantly react to changes in line pressure is important. When the line pressure decreases because of an increase in demand, it is important that the pump control instantly increases the flow to match the demand. Any delay in response by the pump control will cause a negative pressure in the line, which is followed by a spike or water hammer when the supply finally catches up with the demand. Likewise, when the demand decreases, any delay from the pump control can cause a water hammer spike in pressure.

Being at the top of a hill has a lot more to do with a delay in pressure than being at the end of a long line.