Engineering solutions provider BMG’s extensive portfolio of Transfluid couplings comprises constant fill fluid couplings that have been designed to withstand operation in difficult conditions, including hazardous environments.

The K series comprises three main elements – the driving impeller (pump) that is mounted on the input shaft, the driven impeller (turbine) mounted on the output shaft and the cover, which is flanged to the output impeller, with an oil-tight seal. An advantage of this system is that the driving and driven impellers can work both as a pump and/or turbine.

“Transfluid’s constant fill fluid couplings have been designed for hydrodynamic transmission, to improve the overall performance of internal combustion engines and electric motors used in diverse industries,” says BMG power transmission product manager Brandon Bouillon.

“The impellers perform like a centrifugal pump and a hydraulic turbine. With an input drive to the pump – such as an electric motor or diesel engine – kinetic energy is transferred to the oil in the coupling. The oil is forced, by centrifugal force, across the blades of the pump towards the outside of the coupling. The turbine absorbs kinetic energy and generates a torque always equal to input torque, thus causing rotation of the output shaft. Since there are no mechanical connections, the wear is practically zero. The efficiency is influenced only by the speed difference (slip) between pump and turbine.”

He explains that the slip is essential for the correct operation of the coupling as there would not be torque transmission without slip. The formula for slip, from which the power loss can be deduced is as follows: In normal conditions, standard duty slip can vary from 1.5% in large power applications, to 6% in lower powered applications.

The Transfluid K series constant fill fluid couplings follow the laws of all centrifugal machines, where transmitted torque is proportional to the square of input speed; transmitted power is proportional to the cube of input speed and transmitted power is proportional to the fifth power of the circuit outside diameter.

Advantages of constant fill fluid couplings include smooth start-ups, the reduction of current absorption during the starting phase and protection of the motor and the driven machine from jams and overloads. Drive systems using Transfluid fluid couplings also have the advantage of the motor starting, essentially, without load and enabling the use of asynchronous squirrel cage motors rather than special motors with soft starter devices.

The protection function achieved by fluid couplings results in higher duration and operating convenience of the entire drivetrain and, because fluid is used as a power transmission element, there is torsional vibration absorption for internal combustion engines.

With the use of constant fill fluid couplings, it is possible to achieve a high number of start-ups, with an inversion of the rotation direction and, because there is the same torque at input and output, the motor can supply the maximum torque even when the load is jammed. To ensure load balancing in the case of a double motor drive, fluid couplings automatically adjust the load speed to the motor’s speed.

The K series couplings work using oil and are also available for a mixture of water and glycol operation on request. This range can be supplied with certification according to ATEX directive 94/9/EC, covering all categories.

These constant fill fluid couplings are supplied with delayed fill chambers, typically required for machinery with large inertia values and for belt conveyors. The advantages of the delayed fill chamber are evident when the power to be transmitted increases.

Transfluid offers coupling arrangements which include in-line series for horizontal axis between the motor and the driven machine and allow radial disassembly without moving the motor and the driven machine. A pulley version for belt driven applications is also available.

These constant fill fluid couplings are available in two different mounting options – standard mount, where the least possible inertia is added to the motor and is therefore free to accelerate more quickly and a reverse mounting option for higher inertia connected directly to the motor.

Typical applications for constant fill fluid couplings include bucket wheels, centrifugal and volumetric pumps, conveyors, crushers and debarking drums, as well as wood chippers, dryers, fans and blowers. They enhance operation of blowers, forest machinery, mill mixers, pulpers and shredders and are also used for wind generators and in marine propulsion.