Re: Water Well Problems

Posted by T_Bone on December 20, 2005 at 07:09:38 from (4.240.42.161):

In Reply to: Water Well Problems posted by john in la on December 19, 2005 at 18:05:30:

Morn'n John,

Lets build a simple well system to understand why your is not pumpimg water 100% of the time.

The well Shaft/Bore:
Here we sink a hollow hole into the ground at underground water depth that contains water in the sand and gravel. This hole void allows water from the sand and gravel to collect in the bore hole to be pumped to the surface.

To keep the bore hole from filling with sand and gravel as the water runs into the shaft we add perferated bore casing. This "screens" out the sand and gravel only allowing water to run into the shaft and called the static water head.

Static water head is amount of the available water to be able to be pumped the surface.

Next The Pump:
When we add a pump to the bore, we have to size the pump to the demand of the available water static head inside the bore plus how much free water runs into the bore as we pump it out.

To size the pump needed, we pump the water out of the shaft until the bore runs dry and measure how long this process takes. This determines how many gpm our well can produce at maximum available water.

The system pump is then sized slightly smaller so we don't pump the well dry when in use and is typicaly loacated 20ft to 40ft off the bottom of the shaft. This is to keep the pump from pumping sand.

Next Add the Foot Valve:
When we first install a new pump, we have to prime the pump and related piping with water to start the water flowing. Once we stop the pump then water will drain back into the well shaft.

The foot valve is nothing more than a check valve on the suction side of the pump and keeps water available to the pump at all times.

We also add check valves on the pump discharge piping at every vertical joint until the surface. The vertical check valves keeps the vertical pipes full of water.

At this point if you have to wait for the pump to pump water then you could have a bad (leaking) foot valve, or you don't have the water available to pump.

Next We Add Pump Control:
When we want the water to stop we shut the pump off. We can do this manualy or automaticly. A pressure switch(PS) is the most common way to automaticly control the off/on of the pump.

A the same time the PS also controls the pump discharge pressure. This allows us to add a PS sensing tube to the PS bellows and the bellows orperate the electrical switch.

As the pump builds pressure to 40psi, then the pressure is applied to the switch bellows and open the PS contacts and shuts off the pump. As the pressure drops from the bellows to 20psi, then this turns on the pump hence the term 40/20psi PS. Another common PS setting is 30/50psi.

So at this point if the pump is on and pumping a steady stream of water then the system is working just fine. If you shut off the water flow, close a main line discharge valve, and the pump shuts off, then this confirms that the PS is working just fine and the PS turns the pump on/off when it should.

If the PS doesn't turn off/on at the listed PS pressure setting then the PS is bad or the sensing tube is plugged. The PS is non-repairable.

Also note at this point that the pump will turn off/on almost in direct relationship to the depening/closing of a facuet and it's almost impossible to read pump pressure kick on/off pressures as this happens very quickly, called short cycling.

Next We Add A Pressure Tank:
If don't want our pump coming on and shutting off every time we open a facuet then we need to add a pressure tank in the main water line.

The most common pressure tank has a bladder bag. A bladder is nothing more than a rubber "type" bag inside a steel cylinder. The bladder is filled with water every time the pump runs. The bladder tank is installed from a "T" in the main water line.

Water is not compressable but air is. So we add a air charge above the bladder bag of 2psi less than pump cut on pressure. In the case of a 20/40psi PS, then our precharge air would be 18psi when the bladder is empty. The precharge of air sits between the bladder bag and the tank walls and is never in contact with the water.

Our pump now pumps water into the main line as well as the bladder tank to 40psi thus storing water inside the bladder and shuts off the PS that turns off the pump.

As a water facuet is turned on, then water will flow from the bladder bag into the main line until there's no water left inside the bag. This is called the bladder tank draw down rating. A common draw down rating is 11gal. So you have to use 11gal of water before the pump will kick on. Different size pressure tanks have different draw down ratings. The larger the draw down rating the less your pump will run. The less a pumps runs, the longer the pump will last.

After the draw down rating is met, then that will drop pressure to the PS, in this case 20psi, thus turns on the pump to refill the bladder tank while at the same time suppling water to the system main line. When the water pressure hits 40psi the pump will shut off.

So if a bladder tank looses it's precharge pressure, then the system will cycle just like a bladder pressure tank was not installed and once again short cycle the pump.

If the precharge air pressure is less than the the correct amount then most likely you have a hole in the bladder bag but also could have a leaking schrader valve core/fitting.

*****************************************

Check your pressure tank. Leave the pump off and turn on the facuet until the water quits running. Take a precharge air pressure reading.Correct the precharge air pressure if required.

If your system once again doesn't work after a short time and the precharge air is again low then you have a bad bladder tank.

Next check your PS for correct orperation. Pump turns on at 20psi and off at 40psi. If not then replace gauge. If the pump doesn't turn on/off then check to see if the sensing tube is plugged. Sensing tube ok then replace switch.

Next you will need to turn on a facuet then turn on the pump.

If you loosing water pressure or volume during this test, then your pump or the amount of available water in your well has a problem.

If you have a steady stream of water to the facuet then your pump and well system are in normal running condition. Do not leave your pump running with the facuet shut off and without the orperation of a working pressure switch.

This is just one type of water well system but very common.

T_Bone

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