Raspy
Veteran Member
- Joined
- Dec 16, 2006
- Messages
- 1,636
- Location
- Smith Valley, Nevada
- Tractor
- NH TC29DA, F250 Tremor, Jeep Rubicon
Harry,
I'll try again.
I'm not advocating the use of check valves. This is just an explanation as to why they are used when they are used, as far as I understand it.
Obviously, the pump is immersedand there is no suction on it's intake side. Let's get beyond that.
Now, imagine a system with the pump down in the water. The stand pipe to the surface is open and the distance to the surface from the standing water line is much farther than 30 feet, say 300 feet. We turn on the pump and water gushes out at the surface. Then we close a valve on the pipe at the surface and block the flow. Then we turn off the pump and what happens?
The atmospheric pressure down in the well is not sufficent to hold the column of water at 300' elevation. The water level in the pipe drops to about 30' above the water level and holds there.
The void in the pipe above the water is not air or a "cushion", as you mentioned. It's an empty vacuum.
Now we have about 270' of empty pipe. The key is "empty". No air. Not a cushion. This where the word suction was used in my previous blurb. A high vacuum area, if you will.
Now we turn on the pump and the water rushes up the pipe. Remember, no cushion, and slams into the closed valve. This caused an instataneous pressure rise that can break the pipe or just jar the whole system.
However, if there were check valves at every 25', there would not have been a void at all.
Again, I'm not saying they are needed in yours or any system. Each one is different and can be arranged in many ways.
The pressure tank is not necessarily useful in this case because the closed valves could be beyond or before it and the configuration can still cause a hammer. When there is this kind of vacuum, the diaphragm tank has zero volume because the bladder is pressed agains the connetion port. Sometimes the tank port is quite small and the tremendous pressure hit is more than it can handle to prevent a hammer.
Some systems can sit for months, unused, and this condition can gradually develop.
Do you see the difference between this scenario and the initial startup when the system is full of air? An air cushion vs an empty pipe? Not the same thing at all.
I'll try again.
I'm not advocating the use of check valves. This is just an explanation as to why they are used when they are used, as far as I understand it.
Obviously, the pump is immersedand there is no suction on it's intake side. Let's get beyond that.
Now, imagine a system with the pump down in the water. The stand pipe to the surface is open and the distance to the surface from the standing water line is much farther than 30 feet, say 300 feet. We turn on the pump and water gushes out at the surface. Then we close a valve on the pipe at the surface and block the flow. Then we turn off the pump and what happens?
The atmospheric pressure down in the well is not sufficent to hold the column of water at 300' elevation. The water level in the pipe drops to about 30' above the water level and holds there.
The void in the pipe above the water is not air or a "cushion", as you mentioned. It's an empty vacuum.
Now we have about 270' of empty pipe. The key is "empty". No air. Not a cushion. This where the word suction was used in my previous blurb. A high vacuum area, if you will.
Now we turn on the pump and the water rushes up the pipe. Remember, no cushion, and slams into the closed valve. This caused an instataneous pressure rise that can break the pipe or just jar the whole system.
However, if there were check valves at every 25', there would not have been a void at all.
Again, I'm not saying they are needed in yours or any system. Each one is different and can be arranged in many ways.
The pressure tank is not necessarily useful in this case because the closed valves could be beyond or before it and the configuration can still cause a hammer. When there is this kind of vacuum, the diaphragm tank has zero volume because the bladder is pressed agains the connetion port. Sometimes the tank port is quite small and the tremendous pressure hit is more than it can handle to prevent a hammer.
Some systems can sit for months, unused, and this condition can gradually develop.
Do you see the difference between this scenario and the initial startup when the system is full of air? An air cushion vs an empty pipe? Not the same thing at all.