double acting vs single acting float switch

Dear,

my question is what is the difference between single acting and double acting float switch, is it only the counterweight? or it should have 2 separate contacts for example DPDT

thank you!

Double acting for a float switch just refers to its ability to perform two separate control functions. Filling and emptying, or filling and stopping for instance.

With a single acting float switch, it only has the ability to perform one control function. Either fill or empty, for instance. A single acting float switch will have a Single Pole Single Throw (SPST) contact.

A double acting float switch does not have to have a Double Pole Double Throw (DPDT) contact. They will more often have a Single Pole Double Throw (SPDT) contact with a common and two signals for each function.

Example: single acting - filling

A tethered single acting float switch hangs at the empty level in a tank. Its SPST contact is closed. The system is started and the fill pump starts. When the float switch floats up to the tethered full level, it's SPST contact opens and the fill pump stops. Some other function must control the empty pump and stop it. When the tank is emptying, the float switch will drop and reach the empty level again. It's SPST contact will close again, enabling the fill pump. Because the single acting float switch's contact will close again while emptying, the fill pump is usually interlocked off if the empty pump is running.

Example: double acting - filling and emptying

A tethered double acting float switch hangs low in a tank. The fill contact is closed. The system is started and the fill pump starts. As the level rises the fill contact remains closed. When the float switch floats up to the tethered full level, the SPDT contact switches over. The fill pump is stopped and the empty pump is started. As long as the system is running this cycle will repeat. One float switch is performing both functions.

There are many possible applications, but a double acting float switch does provide a way to kill two birds with one stone. Especially when you might be trying to reduce the number of control elements used with a tricky medium.

Regards,
George