The check valve discussion.

[speedbump]

I believe testing is a requirement here too. Good racket for someone.

The irrigation back flow preventers I'm familiar with don't have springs. When water flow and pressure stops, the poppet drops breaking the vacuum. When water flow starts the poppet is slammed shut for the duration. The other ones, I have to go with your experience because I have none other than I know they hurt when you hit one with your shin bone.

bob...

[Cass]

I believe testing is a requirement here too. Good racket for someone.

The irrigation back flow preventers I'm familiar with don't have springs. When water flow and pressure stops, the poppet drops breaking the vacuum. When water flow starts the poppet is slammed shut for the duration. The other ones, I have to go with your experience because I have none other than I know they hurt when you hit one with your shin bone.

bob...

Here they get anywhere from $125.00-$175.00 for about 15 min. work. More if something needs to be replaced.

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Where does an old fart get a certification to check and repair these brass wonders????

[hj]

One of the first things to clear up is that when the pump stops the water does not "drop down to the water level in the well", at least not unless you have a leak or vacuum breaker on it that would allow air to enter the pipe and thus permit the water to drop. (If it did that then everytime the pump started you would have to expel the air in the pipe when you opened a faucet.) Otherwise the pipe stays full of water and the pressure increases linearly as the pump spools up to full speed and pressure. Therefore there is no "bang" when the check valve opens. In fact it will not open until the pressure in the pump pipe exceeds the system's pressure and then it will merely swing open, "gently".

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I disagree HJ, if the droppipe has no leaks what so ever, there is no check valve in the pump or anywhere in the droppipe but there is one at the top of the well to hold the pressurized side of the system there. The water level is lets say 100 feet. The pump shuts off, what is going to hold that water up in that column of droppipe. I say there will be a vacuum created from the top of the pipe down to around the theoretical 32 feet. If the water level in the well is say 15 feet, then the water can drop to that depth or somewhere in between depending on the physics that I can not explain.

Make sense?

bob...

[rshackleford]

I think you have to consider that magic 32’. I would say that the column of water would probably fall if it is unchecked for a distance greater than this. A good question would be when does this vacuum become a hazard for the drop pipe.

Also, what about multiple checks in the drop pipe when setting a deep sub. I think they recommend one ever 200’ or 300’.

[Bob NH]

If the droppipe has no leaks what so ever, there is no check valve in the pump or anywhere in the droppipe but there is one at the top of the well to hold the pressurized side of the system there. The water level is lets say 100 feet. The pump shuts off, what is going to hold that water up in that column of droppipe. I say there will be a vacuum created from the top of the pipe down to around the theoretical 32 feet. If the water level in the well is say 15 feet, then the water can drop to that depth or somewhere in between depending on the physics that I can not explain.
bob...

A vacuum is just the absence of pressure. Atmospheric pressure of 14.7 psi in the well will push on the water in the top of the well, forcing it through the pump to an elevation of about 14.7x2.31=34 feet above the level in the well.

Therefore, if the check valve is more than 34 feet above the static water level in the well, then the water will drop down to 34 feet above the static level, creating a vacuum in the upper portion of the droppipe. It works the same was as a mercury barometer. (There is actually a small pressure above the water in the drop pipe equal to the vapor pressure of the water.)

If the check valve is much higher than 34 feet above the static water level, then when the pump shuts off the check valve will stop the reverse flow from the pipe above the valve, but the weight of the water between the pump and the valve will cause a reversal of flow through the pump, actually causing it to rotate in the reverse direction. I saw one installation where the check valve was at the top of a hill and the pump was a turbine pump in a pumphouse. It was possible to both see and hear the effect of the reversal of flow. It is especially bad if the pressure tank/pressure switch causes the pump to restart when the pump is rotating in the reverse direction.

[rshackleford]

The reverse flow thing is a big deal on line shaft turbines since there is no way to put a check on them. However bad this situation is we have never had a customer twist off a shaft, though. We do install some on delay timers when automation makes restarting a risk, but not very often. I guess that must be part of the reasoning behing NRR heads on motors and gear drives.

[hj]

[QUOTE=speedbump]I disagree HJ, if the droppipe has no leaks what so ever, there is no check valve in the pump or anywhere in the droppipe but there is one at the top of the well to hold the pressurized side of the system there. The water level is lets say 100 feet. The pump shuts off, what is going to hold that water up in that column of droppipe. I say there will be a vacuum created from the top of the pipe down to around the theoretical 32 feet. If the water level in the well is say 15 feet, then the water can drop to that depth or somewhere in between depending on the physics that I can not explain.

Make sense?

No, but if it did, then when you stick a straw into a glass of water and hold your finger over the end and then pull it out, according to your "theory" the water would drop down to the level of the water in the glass. But it doesn't. And when I want to start a siphon, I immerse the hose in the water, hold my finger over the end and then pull it up and over the rim of the sink and place it in a bucket. Again, if your "theory" were correct the water would drop back down in the hose and thus not start the siphon. And water heaters would never have to be given an air input source to drain the water out of them because it would always drop down to the level of the drain valve.

[almostdone]

HJ -

I'm just a science teacher, but the theory proposed is correct. The reason that you don't run into the problem of water draining out of your siphon hose is that atmospheric pressure is adequate to hold up a column of water that is 32 ft high. If you filled the hose with water and then climbed up 40 ft, you'd find that the water would drain from the hose down to the 32 foot level, despite the fact that no air was leaking around your finger.

BTW, this is why an old style leather-flapped single piston pump won't work for a deep well. You can't rely on atmospheric pressure to push the water to top of the well, so you have to "throw" the water to the top of the well with an impeller.

DM

[rshackleford]

Almostdone is right about Olson Johnson being right. I wash born here, an I wash raished here, and dad gum it, I am gonna die here, an no sidewindin bushwackin, hornswaglin, cracker croaker is gonna rouin me bishen cutter.

I am quite interested in the comment on the piston style pump. Are we talking about cylinder pumps with leather cups. I was not aware that there was a depth limitation on these pumps.

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This thread gets better all the time. Since I am not edjumicated and only have experience to rely on, I can attest to the fact that a piston pump will only lift water somewhere around 25 feet. I believe they will go a little better than 25 feet depending on elevation etc. But because of the positive pull a cup leather makes over an impeller, the vacuum created is better. They can make some horrendous pressures too. I saw a 42 gallon tank that launched because of a plugged pressure switch. The bottom blew out sending the tank to the ceiling of the basement, which broke two floor joists (2X6's) pushed the kitchen floor up high enough to break the counter top and ruin everything glass in the entire kitchen. I feel much safer standing next to a jet pump now.

I have seen a few unscrewed deep well turbines and have fished a few. But you can put a foot valve under a turbine. Most are installed that way here in these parts. I have also seen shafts twisted off from the back spin of the water going back due to a faulty or missing foot valve; then the motor starting while the pump was counter rotating.

bob...

[rshackleford]

I had never though of putting a check valve on the bottom of a line shaft turbine. We have lots of irrigation wells up here with only checks on the discharge.

Give me an example of one of these piston type pumps, please? I assume this is not a cylinder pump under a windmill.

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These are the best images I could find of a piston pump. Since they are like hens teeth these days.

Forget the attatchments, they don't work. Maybe .bmp files won't work.

I'll try after I convert them to .jpg's.

[speedbump]

Let's try them now!