FLS 10

The FLS is a miniature float switch for detection of liquid in the inspection chamber of a pump. It has been designed for the new series of midrange pumps 3153 up to 3301. It has also replaced FLS20 in all large pumps.

The sensor is mounted in a 45 degree angle, which makes it suitable both for vertical and horisontal position of the pump.
The sensor consists of a guide bar that runs through a hole of a cylindrical float element. This body, made of nitrile rubber, is mobile along the bar and raises to its upper position in case of leakage.
Two resistors and a reed contact are built into the hollow bar. The float element contains is a permanent magnet and its proximity makes the reed contact close in case the body floats up. The resistance then changes from the non-alarm value of 1200 ohms to the alarm value of 430 ohms (see figure below).


Electrical properties
The FLS 10 is provided with two leads for external connection. The supply voltage is 12 V DC. Both leads are brown indicating that the polatity is irrelevant.
FLS10 is specially developed for the new midrange pumps, which are designed with an inspection chamber. The sensor is mounted in the bearing holder with its sensing part located in the inspection chamber and the wire entry in the stator housing. The sensor can be used with Flygt pumps aimed for explosion hazardous locations.

The purpose with the sensor is to give a leakage indication if the buffer volume of the inspection chamber is filled. The chamber should then be drained and if necessary coolant to the cooling system should be provided. In the event repeated alarms occur in a short period of time, the mechanical seal unit and coolant should be changed.

FLS10 is connected in series with the thermal switches in the pump motor to the Flygt MiniCAS II monitoring relay, so only two wires are required for leakage and thermal sensors. The recommended wiring of MiniCAS II is to provide a warning in case of a leakage alarm and not to stop the pump (see documentation related to MiniCAS II).
Technical data
Supply voltage:  12 V DC 
Signal:   10 mA non-alarm current 
  28 mA alarm current 
Max. duty temperature:  90ºC 
Material:  Brass and nitrile rubber 
Compliance:  Approved for EX-applications 
Physical size:
-Length:  44 mm 
-Diameter:  22 mm 
-Thread:  M12 x 1, length 9 mm 
Part number:   663 0400  



The FLS can be tested with a regular ohmmeter. The FLS10 resistance should be:
Non-alarm value:   about 1200 ohms 
Alarm value:   about 430 ohms.  
An alternative is to connect the sensor to MiniCAS II (or any 12 V DC source) and measure the current.
Non-alarm value:  about 10 mA 
Alarm value:   about 28 mA  
Refer to the MiniCAS II information or to the guide "Installation and application, Leakage detectors, CLS/FLS/FLS10/FLS30" for additional information.
Never apply more than 14 V DC to the FLS10 - a higher voltage can destroy the sensor.