Part 2 – The Design

How the system was designed and built was influenced by a few more factors:

Our household sometimes needs to run from a generator – being in a rural area, we lose utility power a few times a year (in December 2006, we lost commercial power for eight consecutive days after a particularly bad windstorm).  The existing circuit for running the well (220v, 30 amps), already wired to the generator panel, would also need to run the additional pump without increasing the peak load on the well circuit.  This meant that only one of the pumps (well pump or water tank pump) would run at the same time, requiring a lock-out circuit.

For testing and cleaning purposes, we needed the ability to ‘run from the well’ directly by switching the controller and water valves to that mode.  With such a mode, it’s also possible run-down the water storage tank in preparation for tank maintenance.

Ease of repair was considered, and unions placed between components that are system ‘wear items’.

The ‘standard’ layout for a pressurized water system is shown here.

There is a pressure tank, consisting of a metal tank containing a rubber bladder and an air pocket above the bladder. Water is not compressible, but the air is. A pressure switch measures the pressure in the water line, and if the pressure in the water drops below a certain point (for example, 30 PSI), the switch snaps closed, causing the well pump to run. As the well pump pumps water into the system, the bladder inside the pressure tank is compressed, and the pressure sensed by the switch increases. At the switches upper limit (for example, 50 PSI), it snaps OPEN, turning off the pump.  The difference between the ‘turn on’ and ‘turn off’ pressure is the differential pressure. It is typically set to a value that allows the pump to run for a reasonable length of time to charge the system with water without causing too noticeable a pressure drop in the house system. If the differential is too small, the pump will ‘short cycle’, turn on and off rapidly. For a conventional well water pump, that’s not a good thing, and can lead to early failure. ‘New Technology’ water pumps have entered the market in the last few years that are built to short-cycle, and keep the pressure within a much narrower range.  These pumps are build differently, and have more intelligence in their controllers.  The system that I’m describing here is applicable to the conventional well and water pumps.

The cistern-enhanced system is shown here.

Note that the ‘water to house’ output goes to the original pressure tank and pressure switch, which have been reconfigured in a way detailed below.

Here's a picture of the completed plumbing:

In the diagram, there are multiple valves to redirect the output from pump either directly to the house, or through the tank and tank pump. With the valves in the “A” position, water from the well is directed through a check valve to the top of the water tank. Water to the house is pumped from the bottom of the tank by the tank pump.  To fill the water tank, the controller monitors the ‘tank full’ switch to determine when to turn on the well pump.

If the valves are placed in the “B” position, water from the well pump flows directly to the house pressure tank.

Part 3 - The Controller