The FLS (Flygt Leakage Sensor) is a miniature float switch for detection of liquid in the stator housing or junction box. Due to its design it is best suited for pumps/mixers in vertical position.

The FLS consists of a rigid aluminium frame. Inside the frame, a mobile float element can move up and down guided by a shaft. Two resistors and a reed contact are built into the frame surrounded by a polyurethane filler. On top of the float element there are two permanent magnets. In case of leakage, the element raises to the upper position and the proximity of two magnets makes the reed contact close. The resistance changes from the non-alarm value of 1530 ohms to the alarm value of 330 ohms (see figure below).

Electrical properties
The FLS is provided with two leads for external connection. The supply voltage is 12 V DC. Both leads are blue indicating that the polarity is irrelevant.

The most common application is in 3000 series C/D pumps, at the bottom of the stator housing, on the top of bearing holder, bonded to it with an epoxy-based adhesive. For use in mixers, the sensor is located in the lowest position of the stator housing. For correct function the angle of the mixer should not exceed 30°. The FLS can also be used to check for water intrusion in the junction box for big pumps and hydroturbine generators.

When used with the MiniCAS II supervision relay, the FLS is connected in series with pump motor thermocontacts, so only two wires are required to connect both leakage and thermal sensors. If a CLS sensor is also used, the FLS and CLS are connected in parallel.

For installations in the big pump junction box, the FLS can be connected to the A- or B-channel of the CAS supervision relay.
Technical data
Supply Voltage:  12 V DC 
Signal:  7,8 mA non-alarm current  
  36 mA alarm current 
Max. continuous duty temperature:  90ºC  
Material:  Aluminium 
Physical size    
-Length:   25 mm ( .98 in.) 
-Width:   17 mm ( .67 in.) 
-Height:  20 mm ( .79 in.) 

The FLS can be tested with a regular ohm-meter.
The FLS resistance should be:
Non-alarm value: about 1530 ohms
Alarm value: about 330 ohms.

An alternative is to connect the sensor to MiniCAS II or CAS (or any 12 V DC source) and measure the current.
Non-alarm value: about 7,8 mA
Alarm value: about 36 mA

Refer to the CLS/FLS/MiniCAS II Installation and application guide for additional information, part no: 89 24 72

CAUTION: Never apply more than 14 V DC to the FLS - a higher voltage can destroy the sensor.