A
float switch is a device used to detect the level of
liquidLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
within a tank. The switch may be used in a
pumpA pump is a device used to move fluids, such as gases, liquids or slurries. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure; they only displace fluid, causing a flow. ...
, an indicator, an alarm, or other devices.
Float switches range from small to large and may be as simple as a
mercury switchA mercury switch is a switch whose purpose is to allow or interrupt the flow of electric current in an electrical circuit in a manner that is dependent on the switch's physical position or alignment relative to the direction of the "pull" of earth's gravity, or other inertia.Mercury switches...
inside a hinged float or as complex as a series of optical or
conductanceElectrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current...
sensors producing discrete outputs as the liquid reaches many different levels within the tank.
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A
float switch is a device used to detect the level of
liquidLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
within a tank. The switch may be used in a
pumpA pump is a device used to move fluids, such as gases, liquids or slurries. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure; they only displace fluid, causing a flow. ...
, an indicator, an alarm, or other devices.
Float switches range from small to large and may be as simple as a
mercury switchA mercury switch is a switch whose purpose is to allow or interrupt the flow of electric current in an electrical circuit in a manner that is dependent on the switch's physical position or alignment relative to the direction of the "pull" of earth's gravity, or other inertia.Mercury switches...
inside a hinged float or as complex as a series of optical or
conductanceElectrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current...
sensors producing discrete outputs as the liquid reaches many different levels within the tank. Perhaps the most common type of float switch is simply a float raising a rod that actuates a
microswitchA micro switch is a generic term used to refer to an electric switch that is able to be actuated by very little physical force, through the use of a tipping-point mechanism. They are very common due to their low cost and extreme durability, typically greater than 1 million cycles and up to 10...
.
A very common application is in
sump pumpA sump pump is a pump used to remove water that has accumulated in a pit commonly found in the home basement to collect water called a sump pit...
s and
condensate pumpA condensate pump is a specific type of pump used to pump the condensate produced in an HVAC , refrigeration, condensing boiler furnace or steam system...
s where the switch detects the rising level of liquid in the sump or tank and energizes an electrical pump which then pumps liquid out until the level of the liquid has been substantially reduced, at which point the pump is switched off again. Float switches are often adjustable and can include substantial
hysteresisA system with hysteresis has memory. Such a system is said to exhibit path-dependence, or "rate-independent memory". .In a deterministic system with no dynamics or hysteresis, it is possible to predict the system's output at an instant in time, given only its input at that instant in time...
. That is, the switch's "turn on" point may be much higher than the "shut off" point. This minimizes the on-off cycling of the associated pump.
Some float switches contain a two-stage switch. As liquid rises to the trigger point of the first stage, the associated pump is activated. If the liquid continues to rise (perhaps because the pump has failed or its discharge is blocked), the second stage will be triggered. This stage may switch off the source of the liquid being pumped, trigger an alarm, or both.