Constant Fill / Fixed Speed Type fluid Coupling Or hydraulic coupling

This type of fluid coupling or hydraulic coupling consists of following parts:

Fusible plug, copper washer, helicoil, impelller, snap ring, oil seal, star ring, bearing, conical baffle plate, flat baffle plate, runner shaft, runner, casing, chamber.

Fixed Speed Hydraulic Coupling Or Fluid Coupling Assembly


Related Link

Basic Working Principle Of Fluid Coupling

Fixed Speed Type Hydraulic Coupling Or Fluid Coupling Oil filling

The Fluid coupling oil filling will be determined by :

  1. The power actually transmitted to the machine.
  2. The required starting torque.

The maximum allowable oil fill amounts to approximately 80% of the total capacity of the Fluid Coupling. This level should never be exceeded since overfilling may cause over pressure inside the coupling and damage to the seals.

Checking Of Oil Fillhydraulic coupling oil filling angle

1 ) Place filling plug in vertical position and remove it.

2 ) Rotate the coupling slowly until the oil just comes up to the filling hole. This position must match the angle.

3 ) If necessary, remove or add some oil.

4 ) Replace filling plug or tighten.

Work Involved During Preventive Maintenance Of Fixed Speed Fluid Coupling / Hydraulic Coupling

  1. Checking oil level and oil quality
  2. Checking alignment
  3. Checking for any leakages
  4. Checking fusible plug


1 Driven shaft fails to reach speed.

Probable Causes :

  • Insufficient oil – Check oi level.
  • Coupling seals not fully oil tight – Check tightness of seals.
  • Faulty motor or motor coupling .

2 The fusible plug melts

Probable Causes :

  •  Insufficient oil – Check the oil level.
  •  Coupling seals not fully oil tight – Check tightness of seals.
  •  The driven machine stalls or jams – Check machine and remove cause of stall.
  •  Excessive power consumption of the driven machine – Verify power consumption by means of a double watt meter.

3 Abnormal vibrations/noise levels

Probable Causes :

  • Incorrect alignment – Check alignment.
  • Damage to bearings – Check the coupling. Locate noise and vibration sources by ear or by means of sound measurement instruments.
  • Nut and bolt loose assemblies Check that holding-down bolts on motor, bed-plate and driven machine are correctly tightened.
  • Undue vibration of the assembly.

Related Questions

  1. At what temperature Fusible plug melts.

For industrial applications, the maximum temperature is 140 degree centigrade . At that temperature, the fusible plug melts, allowing the oil in the coupling to drain off and removing the load from the motor.


Working of fluid coupling