UNDERSTANDING RURAL WATER SYSTEMS
(Page 3 of 4)
September/October 1987
By the Mother Earth News editors
With that done, shut the pump down, disconnect the hose, and close the outlet valve. Then, using a standard tire gauge, check the precharge pressure at the Schrader valve in the top of the tank. It should be between 20 and 30 psi; the exact figure will depend upon the pressure at which the pump cuts in, and to some extent whether the pump is sized to meet peak demand.
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In fact, the optimum setting will be specific to your system, but one rule of thumb — generally applied when the pump can't fully provide for those periods of peak water usage — is to create a supplementalsupply by charging the tank to a level somewhat below the pump cut-in pressure. This works well when that cut-in occurs at 30 psi, but is less efective at lower pressures. Tank manufacturers, in fact, recommend that both the precharge and the cut-in pressures be the same — probably the best choice if supply doesn't seem to be a problem.
Charging the tank, by the way, involves nothing more than adding air to it with a tire pump. But before you do, determine the factory-set cut-in and cut-out pressures of your control switch. The correct settings should be indicated on the switch housing (the switch itself may be at the pump, if it's aboveground, or in the delivery line near the tank).
If no specifications are available, turn the pump back on and note the reading at the water line pressure gauge when the pump switch shuts off with an audible click. (If you don't have a gauge, this too should be on your installation list.) Then run some water and note again what the pressure reading is when the pump clicks on. The standard settings are a cut-in pressure of 20 psi and a cut-out of 40 psi. Recently, because of the prevalence of pressure-sensitive water-using appliances, a higher range — 30 to 50 psi — is becoming the norm.
At any rate, the switch is usually set to cut in at a fixed pressure, but can be adjusted to cut out at any pressure above that. The smaller differential adjusting nut controls the lever spring which sets the upper limit; tightening the nut increases the water pressure. But heed these two warnings: Shut the breaker off before uncovering and adjusting the pressure switch. A 220-volt accident can easily and instantly be fatal. Also, never set the cut-out pressure higher than 25 psi above the cut-in; it could cause the pump to overheat and fail.
It's worthwhile to note that, though this type of pump control is very common, models that use sensors to determine the water level in the well casing (or floats to monitor reservoir levels) are not unheard of. These can be complicated, and should be serviced by someone with experience. Likewise, systems with plain steel pressure tanks may employ air-volume controls that are best fixed by a professional.
Service With a Smile
If your system is fitted with water-conditioning equipment or filters of any kind, you can count on their needing service periodically. Generally, these sophisticated components are fully guaranteed and may even come with a service contract. If this isn't the case, make an effort to find out from the installer how often the units require attention, what warning signs to look for if performance isn't up to par and, of course, whether you can do the maintenance yourself.
