a division of Gustavo Preston Company

Tech Talk -Elevator Pumps & Float Switches

Is an Elevator Pump an Ejector?

      Elevator sump pumps are an ejector, but without the need for a large reservoir, as they are only used in emergencies.  Daily service is not required. Many elevator pump systems are simplex systems defined as a single pump in the sump which starts when the sump is filled with fluid. 

    Simplex systems are often controlled by inputs from three separate float switches defined as Stop, Start and High-Water Alarm (indicating pump failure). The simplex pump is directed to start pumping by its control panel.  An Analog or Programmable Logic Control (PLC) panel receives a signal from float switches hung in the sump pit from a wall bracket or discharge piping. The challenge when installing these systems is limited sump space.  Very often elevator sumps are 24 Inches by 24 Inches by 24 Inches deep, preventing three float switches from fitting inside the sump volume and activating while not becoming entangled. (Figure 1)

    Float switches hung in the sump pit will either open or close when elevated from horizontal or vertical.

Two Float Switches are Best

Manufacturers have overcome this problem by configuring their analog circuits to allow the bottom float to act as a stop and start signal within the circuit of the panel.  Both analog and PLC simplex control panels can and should be used with two floats in elevator pits. PLC control panels use a jumper placed between the stop terminal and the start terminal to indicate the float switches were activated in order, otherwise an error message and alarm will occur.  Manufacturers layout documentation will indicate the jumper if no start float is present. (See Figure 3)

    Two float switches can be mounted to avoid entanglement in a 24 Inches by 24 Inches by 24 Inches deep sump.  This is the most desirable configuration for elevator pumping systems and has been embraced across the industry.

     Today’s modern electromechanical float switches allow Simplex Two Float arrangements for smaller sump pits.


Figure 1 – Elevator Sump Pump Pit

Figure 2 Elevator Pump Installation

Figure 3 – PLC Panel Tow Float Layout