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Well tailpieces for well pump protection:
Well Tailpipes or Tailpieces serve as Low Water Protection Devices.
This article describes the use of a tailpipe or tail piece, or other low water cutoff controls to protect a well pump from damage in a low-recovery rate well, thus extending the life expectancy of water pumps and pump controls.
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How do we protect the well pump from damage if the well is subject to seasonal or permanent low flow rates or has a poor recovery rate? Here we explain the function & role of a tailpiece installed at the bottom of well piping in order to protect the pump and other water supply equipment controls from damage.
When the well pump's capacity is known to exceed the flow rate of the well, a tail pipe, tail piece, or low water cutoff control is installed to protect the pump from damage such as that caused by well pump cavitation or motor overheating.
Details: some wells that are known to have intermittent low water problems may be equipped with a special tailpiece on the water pick-up end of the well pipe precisely to prevent the well pump from becoming damaged when water level in the well drops too low. The red component in our sketch (left) is the ejector used by a two-line jet pump to bring water from the bottom of the well. This red component shows where a well flow protection tailpiece may be added - as an extension below.
A longer taipiece (blue in our sketch) extending into well water (30 inches recommended by the Alberta Canadia DOA) may help avoid air intrusion, but in addition, a special fitting at the in-water end of the tailpiece can cause water to recirculate through a well pump if well water level becomes too low. If the well pump is a submersible model (recommended for well depths over 80 feet), a similar low well water protection device may be installed in the well. In our sketch at left the foot valve is shown in yellow.
The well piping tailpiece (also shown in this sketch) permits the in-well water pump to continue to run by recirculating well water within the pump but by halting delivery of water or slowing delivery of water to the building.
Many sources, including the Penn State School of Forest Resources recommend installing a low water cutoff device to protect a well pump that has to operate in an inadequate or low-yield well. That resource describes an electrical low-water cutoff switch:
Normally, a low-water cut-off switch controlled by water-level sensors in the well should be connected to a relay at the pump switch box. A low-water signal relayed to the main switch should override other pump controls and stop the pump if the water level drops to a critically low point where air or sediment would be pulled into the system.
A low water sensing device to protect a well pump may be installed in an intermediate water storage tank, for example.
A different approach to water pump protection where the well yield is poor is a tailpiece that is installed in the well itself. When the water level inside a well drops too low, the tailpiece re circulates water through the well pump (keeping the pump cool and protecting it from damage) until the well has recovered and the water level has risen.
Watch out: the low water cutoff devices that we discuss here are intended for building water supply piping to prevent well pump damage. These low water cutoff devices or switches are distinct from and have nothing to do with the heating or steam boiler low water cutoff safety devices discussed at LOW WATER CUTOFF VALVES
A still different approach that may provide some water pump protection by reducing the well pump cycling rate is the installation of a Smart Tank that regulates water flow in the building. According to the manufacturer, Flexcon Industries,
Every Smart Tank system includes a relief valve and a manifold that provides ports for the system’s pressure switch, pressure gauge, drain valve and relief valve.The Smart Tank pressure system works just like a standard pressure tank system but with one major difference - consistent water pressure delivery!
1.On demand, water is drawn from the Online pressure tank until the cut-in pressure of the switch turns the pump on.
2.System water now flows through the regulating body of the Smart Tee valve. The valve will maintain constant water pressure at each given flow rate, and consistent water pressure over a broad range of flows.
3.When system demand ends, the Smart Tee’s calibrated bypass port keeps the pump running just long enough to fill the tank and satisfy the cut-out setting of the pressure switch. The pump shuts off, and the system is now ready for the next demand.
The Smart Tank pressure system will reduce pump cycles by as much as 75%, and give the homeowner the benefit of constant water pressure. Fewer pump starts and longer run times means longer pump and tank life.
Well pump cavitation describes the entry of air or gases into the mechanical parts that are trying to move water through a water pump. The presence of air or other gases in the actual pump chambers or around the water pump impellers leads to overheating of these parts and mechanical damage to the pump moving parts.
Cavitation can also cause the pump to have to work longer to satisfy the water demand and thus its electric motor to overheat, also reducing motor life.
Cavitation inside of a water pump can be caused by several problems including:
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(May 23, 2011) Sage Hill said:
Our local pump installer is recommending a 7 GPM pump for our 5-6 GPM well (which will likely be less in the summer). He says that 7 GPM is the minimum needed to keep a pump cool and that when it runs out of water it will turn itself off. Is this true? I thought it was best not to let the well run dry.
You are quite correct that a water pump pump should not be allowed to run dry, it's likely to damage its bearings and lead to a need for pump replacement.
There may be a switch that actually turns off the well pump under low well water conditions but more common is a tailpiece that cycles water through the pump to keep it from overheating and simultaneously reduces or stops sending water up into the building.
Unless such a pump protector is installed, no the pump is not protected. That protection can be electrical or by a tailpiece.
(Oct 22, 2012) Ted Platt said:
40 year old ejector on this deep (100 ft.), system, with a foot valve. Rebuilt pump, changed sediment filter but suspect that the jet in the ejector may be the problem. Pump unable to reach the 45 lb shut off pressure even when running for an hour or more. I reduced the shut off pressure to 35 lbs. now to temporally resove this problem. The pump holds the prime, the slight taste of sand in the water is also a concern. perhaps a now submerged parts in sediment?
I would look for dirt or debris in the pump impeller assembly first. If the well screen were partly clogged you'd slow the input into the piping and pump system but you'd not limit the pressure achievable by the pump.
(June 13, 2014) Anonymous said:
A jet pump tailpipe question. How does the tailpipe prevent the ejector from drawing down the water level in the well casing far enough to admit air into the foot valve? Is the suction efficiency of the ejector venturi low enough that it can pull up from below itself only a small height of water column into the tailpipe so that the foot valve is always submerged? If so how would one evaluate the suction capability of a given ejector assembly to determine the minimum length of the tailpipe needed to balance the suction? I have a fairly shallow (40 ft) well with a low recharge rate (1 ½ - 2 gpm) that I can easily overpump with the smallest available jet pump. I don’t want to sacrifice too much of the depth and capacity of the casing so that I can avoid short cycling - a minimum length of tailpipe would be desired.
The tailpiece is designed to recirculate water through the submersible pump rather than letting all of the water volume pushed by the pump flow up the pipe and into the building it serves. By recirculating water through the pump we prevent damage from pump cavitation (circulating air or air and water).
Yes a foot valve is normally always submerged, well below the top of water in a properly-functioning well.
The tailpiece is installed above the foot valve - see our sketches above.
Should water level fall abnormally low for any reason air or a mix of air and water can enter the well piping through the foot valve. But the introduction of that air should cause the tailpiece to recycle water rather than sending air up the well piping system.
In the case you describe, you might want to check out the wide range of well pump short cycling protection devices now on the market. These devices, typically electrical controls, take a different approach to well pump protection, monitoring current draw to detect when air is entering the well pump.
Those devices are discussed separately at WATER PUMP PROTECTION SWITCH
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