Pressure switches are for use with elastic pressure cells or pressure tanks (see storage). With either gravity tanks or reservoirs, a float switch or drawdown control switch should be used.
When tank pressure decreases, the diaphragm is forced down by the range spring. The cam that operates the switch mechanism rides over the top of the operating cam lever and closes the circuit. The motor starts.
Most pressure switches are set by the factory to operate on a 20 to 40
pound pressure range, but pressure switches can be set higher or lower.
Float Switches (2)
A float switch is used to control the pump motor in systems
using gravity tanks or reservoirs. The switch mechanism is similar to that
of the pressure switch, but instead of being activated by water pressure, it
is controlled by the float that follows the water level up and down in the
tank or reservoir.
When the water level in the tank lowers, the float automatically trips
the switch and starts the pump. When the water level rises, the float
moves with it and turns off the pump motor when the desired level is
reached.
Drawdown Control Switches (2)
The drawdown control switch can also be used in gravity tanks and
reservoirs. It consists of electric sensors which can be adjusted to the
desired positions in a water storage so as to start the pump motor when the
water level gets low, and stop it when the water reaches the desired height.
These switches may also be used when there is limited yield from a well.
The two sensors are lowered into the well. One sensor is placed at the
lowest drawdown level desired, while the other is placed at the static
water level. As the well is pumped the water level drops. When the level
reaches the height of the lower sensor, the pump is turned off. The pump
motor will not start up again until the water level has risen to the level of
the upper sensor.
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