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# Letter Re: Backup Generators and Well Pumps

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JWR,
The following is probably more than you want to know about pumps!!

There is a finite limit to how far one can “lift” water with a pump.  It is based on the fact a pump does not really “suck” a fluid but rather creates a vacuum and atmospheric pressure forces the water up the pipe.  On a standard day at sea level that pressure is equal to just under 34 feet of water column.  Therefore a PERFECT vacuum (which does not exist) could “lift” water a shade less than 34 feet.  At higher altitudes, or low atmospheric pressure the distance would be less.  The rule of thumb at 1000 feet elevation is a little less than 25 feet of “lift” with a good pump.

A sump pump is designed as a “flooded suction” or high Net Positive Suction Head (NPSH) pump which has almost no practical suction capability.  It will “push” water to it’s head limit (which isn’t all that great either) but that is all.  A submersible pump is also a flooded suction type pump that “pushes” water to it’s head limit.  The distance from the surface of the water to a line equal in elevation to the point of use is the head distance.  Pressure seen on the gauge is in addition to this.  As an example, a well with a water level while being pumped of 100 feet (3 atmospheres) and a pressure gauge reading of 59psi (4 atmospheres) at the tank has a pump that is producing about 230 feet of head (7 atmospheres).  The pump will produce maximum pressure (and minimum power requirement) at zero flow.  As flow increases, pressure decreases and amps go up, as with any centrifugal pump.   Pressure drop in the pipe comes into effect when water is actually flowing and will reduce the available pressure.

A jet pump is an above ground pump that uses TWO pipes down the well.  The pressure pipe (smaller one) pumps water DOWN the well to a JET.  The water from the JET is forced through a venturie where it creates a vacuum, draws in water from the well and forces the total of the new water + what was pumped DOWN the well back toward the above ground pump via the larger pipe.  In order to work, these have to be primed and ALL air eliminated.  (Some times that can be a challenge!)  Because far more water is recirculated DOWN the well than is delivered for use, the energy consumption of a JET pump is far higher, per gallon delivered, than a submersible pump.  HINT:  I often make use of the fact you can only “draft” or “lift” water about 25 feet with most pumps.  I place the foot valve 30 feet below the jet.  That way, if the water level in the well drops, the pump keeps it’s prime as it can not lower the water level more than 25 feet below the JET and therefore won’t draw air into the system.  The pump will just deliver exactly the amount of water the well can produce up to the maximum capacity of the pump.

With a submersible pump a low capacity well should have a flow restrictor installed that limits delivery to a bit less than well capacity.  That prevents drawing the water below the pump and allowing air into the system.  Far MORE important is the fact submersible pumps are water cooled and will burn up rather quickly if the water level is reduced to pump level.

Ever wonder why most pumps are 240 volt rather than the 120 volt many survivalists might prefer?  Well pumps run from 1/3 to several horsepower in size depending on depth to the water and pressure and flow desired.  Higher horsepower means higher amperage required.  Submersible pumps are often a long way down, particularly out west, so have a LOT of wire.  For best motor performance voltage drop in that long run of wire needs to be minimized and that is most cheaply accomplished by doubling the voltage to 240 volt and cutting the amps in half.  Retrofitting a well to the less desirable 120 volt pump will require twice the breaker size, maybe a change of pressure switch and almost certainly increased wire size.  While the difference is not large, the 120 volt motor WILL use more energy due to I squared R losses. In all of the electrical devices involved.  (Amps X Amps X Ohms)

For those wells where one can pull the pump by hand, a homemade “baler” consisting on 3” PVC pipe, a foot valve and long rope will get you enough water to drink if TSHTF.  More water requires a more complex solution.  A generator has many uses and is my preference but DOES require fuel.  Wind power has been used for the purpose for eons.  Human powered pumps require a fair amount of effort but have certain obvious advantages.  Hand pumps for deep wells are not cheap but they are available from places that cater to the Amish, among others (Lehman’s [5] comes to mind.) Hope some find this useful! – Mike G