How Dual Float Switches Control a Pump Between Two Water Tanks

In many buildings, water is stored in two tanks: a ground tank (Tank A) that collects water from the utility supply, and an overhead tank (Tank B) that supplies water to the building by gravity. A pump is installed near Tank A to move water from the ground tank to the overhead tank.

However, float switches are used for the system to operate safely and automatically. In this setup, two float switches—one in each tank—are connected in series to control the pump. Let’s see how it works.

System Setup

• Tank A (Ground Tank): Receives water directly from the utility supply.

• Tank B (Overhead Tank): Supplies water to the building through gravity.

• Pump: Installed near Tank A, pumps water up to Tank B.

• Float Switches:

  • Float Switch in Tank B (Overhead Tank): Controls the operation of the pump based on the water level.

  • Float Switch in Tank A (Ground Tank): Protects the pump from running dry when the water in the ground tank is too low.

How the Float Switches Work

1. Float Switch in Tank B (Overhead Tank)

• Purpose: To start and stop the pump based on the water demand in the building.

• Operation:

  • When the water level in Tank B drops below a set low point, the float switch closes the circuit, allowing the pump to run.

  • As the pump fills Tank B, the water level rises.

  • When Tank B reaches the full level, the float switch opens the circuit and stops the pump.

• Result: Tank B is always kept filled, and the building receives water by gravity without interruptions.

2. Float Switch in Tank A (Ground Tank)

• Purpose: To protect the pump from running dry when the water supply is insufficient.

• Operation:

  • When the water level in Tank A is above the low-level mark, the float switch remains closed, allowing the pump to run when Tank B calls for water.

  • If the water level in Tank A drops too low, the float switch opens, cutting power to the pump.

• Result: The pump never runs without water, preventing damage from dry running.

Float Switch Configuration (Series Connection)

The two float switches are wired in series with the pump’s control circuit.

• Tank B float switch acts as the demand controller (decides when to pump).

• Tank A float switch acts as the safety controller (decides if pumping is possible).

This means:

• The pump runs only if Tank B needs water and Tank A has enough water.

• If Tank B is full, the pump remains off, even if Tank A has water.

• If Tank A is empty, the pump remains off, even if Tank B needs water.

Advantages of This Setup

1. Automatic water transfer without manual switching.

2. Continuous water supply to the building.

3. Pump protection from dry running.

4. Simple, reliable, and cost-effective system.
   

By using two float switches—one in the overhead tank to control filling, and another in the ground tank to protect the pump—you create a safe, reliable, and fully automatic water supply system. This series configuration ensures that the pump runs only when needed and never runs dry.