How Can Leakage Flow Monitoring Extend the Service Life of My Drawbar?

By: Harold Goellner, OTT-JAKOB Drawbar Specialist

Rotary unions function by connecting a stationary input (supply) to a non-rotating housing of the union, preserving the moving connection and permitting the flow of coolant, air, and/or oil. It is natural for the primary seal in the flow to experience operational wear, which could lead to flooding and the risk of fluid entering the motor spindle if preventative maintenance does not occur. Leakage flow monitoring detects the presence of fluid in the leakage tube before it can damage electronic components or even the bearing in the motor spindle.

External Leakage Flow Monitoring

Ott Leakage Flow Monitoring External leakage flow monitoring detects the presence of coolant or oil in the leakage tube. The calorimetric sensor is positioned in a measuring device that is installed in the leakage drain of the rotary union.

If the programmable and predetermined flow limits is exceeded inside the tube, a signal is emitted. The signal appears directly onto the measuring device or is sento to the machine control unit. There are two basic variants available:

  1. Water-based coolants
  2. Oil-based coolants

Advantages of external leakage monitoring include:

  • Easy installation -- As it is installed in the leakage tube, it is not necessary to interfere with the machine spindle. 
  • Various applications -- The external option can be used wherever the leakage or drainage of a medium has to be monitored. 
  • Retrofitted -- Can be installed whenever without having to replace the rotary union.

Internal Leakage Flow Monitoring

Internal leakage flow monitoring OTT-JAKOBInternal leakage flow monitoring a two-tier sensor. It monitors possible fluid leakage in the area of the sealing bushings,and the possible flooding of the bearings inside the rotary union.

Rotary unions integrated with condition monitoring use two calorimetric sensors for measuring leakage flow rates. A blockage in the leakage drainage causes fluid to build up. The rotary union bearings are at risk of being flooded if a certain level of fluid is exceeded. Outgoing switching signals are emitted if:

  1. A certain level of fluid is exceeded and; 
  2. Fluid enters the bearing of the rotary unit.

Both outgoing switching signals are generated separately so that a pre-warning level is possible.

Advantages of internal leakage monitoring include:

  • Trouble-free retrofitting -- Can be installed whenever without further modifications.
  • Built-in temperature sensor -- Provides rotary union temperature monitoring in all operating modes.


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