There are various types of mechanical float switches like mercury switches that a switched on when a liquid metal binds the circuit. Then there are simpler switches that are linked to the micro switch in order to activate the device. These simpler forms of switches are usually seen in sump pumps and various other household appliances. The float switch installed in the sump pump is used to identify the flooding in the sump. When the pump is done emptying the sump, the float comes down and the switch turns off. Similarly, in a dishwasher the switch is used for activating the valve so that the water can be filled in the appliance. After the amount of water has been filled in the dishwasher, the switch prevents flooding.
Similarly, in septic systems where gravity flow is impossible, the pump system is used. The pump system consists of three mercury float switches. One of three switches, which is the lowest is used for stopping the pump. The middle one is used for activating the pump. The fluid should remain between the middle and the lower switch in normal circumstances so that the pump is inside the water in order to protect it from the corrosive sewer gas. Third switch is activated if the tank crosses a said point and alarm rings.
When you are considering buying the float switches, there are various types for different purposes. It becomes very important to select the one which fulfills your requirement. There are various types of Mechanical float switches.
Tethered or NonTethered switches
A tethered switch is attached to the wire or cable towards its end and a non-tethered one is attached on either the top or the bottom of the tank. Tethered and nontethered switch can further be divided into two classes.
Switches required to switch the pumps directly and can be used in other electrical devices as well
Switches that give the control signals to the control panels
Now, before buying the mechanical float switch there are few factors to be considered. Let us discuss each in details to make it easier for you to buy the float switch next time.
Voltage and current – The popular belief is that for low voltage and low current, any type of float switch can be used. If you use the wrong switch, it can cause failure at some point of time. Reason why certain type of float switch can fail is the design. Arching load is the current or the voltage that will create a small spark when the switch contact is switched on or off. When someone switches to the low voltage, there will be no arching and eventually high resistance deposit collection the contact. Therefore for the low voltage applications, a float switch that has been manufactured for that particular application should be used. You will notice that the switches which are of high quality have the gold plated contact. You can see various names of these switches such as pilot duty switches, control switches and so on. Those control switches which are of high quality will usually be plated with the gold.
In case of high voltage and high current, a float switch that can handle the higher voltage and current should be opted for. Before selecting the float switch in order to control the pump, make sure that it can handle the startup current at first. There are many switches that can handle a higher voltage and current but cannot handle a startup current and therefore look for the better startup current handler.
Pump up or down
Before zeroing in on the switch, you will have to decide how it will be used. For this, you will need to understand the pump up and pump down concept. In case your pump should start when that tank is full and halt once the tank is empty, then go for the float switch that is pumped down. This means that you would like the pump to stop at a point when the level of fluid is going down. In case the tank is low and you are looking for the pump to start as well as stop when the tank is full then a Pump up switch will be needed.
There are usually two wires in the float switches that are pumped up or down. SPDT which stands for Single Pole, Double Throw is another type of float switch that has 3 wires instead of two and can be used for both pumps down and up according to what you want. There is one common contact for both the wire.
There are various other factors that you will need to keep in mind such as angle of the switches, mounted or weighed switches and so on to arrive at the best decision.