FREQUENTLY ASKED QUESTIONS
Fluidomat fluid couplings work on the hydrodynamic principle. It consists of a pump generally known as impeller and a turbine generally known as rotor, both enclosed suitably in a casing. The impeller and rotor is bowl shaped and have large number of radial vanes. They face each other with an air gap. The impeller is suitably connected to the prime mover while the rotor has a shaft bolted to it. This shaft is further connected to the driven machine through the suitable arrangement.
Oil is filled in the fluid coupling from the filling plug provided on its body. A fusible plug is provided on the fluid coupling which blows off and drains out oil from the coupling in case of sustained overloading.
There is no mechanical internal connection between the impeller and the rotor (i.e. driving and driven units) and the power is transmitted by virtue of the fluid filled in the fluid coupling. The impeller when rotated by the prime mover imparts the velocity and energy to the fluid which is converted into mechanical energy in the rotor thus rotating it. The fluid follows a closed circuit of flow from the impeller to rotor through the air gap at the outer periphery and from the rotor to impeller again through the air gap at the inner periphery. To enable the fluid to flow from the impeller to rotor it is essential that there is a difference in "Head" between the two and thus it is essential that there is a difference in RPM known as Slip, between the two.
Slip is an important and inherent characteristic of a fluid coupling resulting in several desired advantage. As the slip increases, more and more fluid can be transferred from the impeller to the rotor and more torque can be transmitted. However when the rotor is at standstill, maximum fluids is transmitted from the impeller to rotor and maximum torque is transmitted from the coupling. This maximum torque is limiting torque. The fluid coupling also acts a torque limiter.
Fluidomat fluid couplings has centrifugal characteristics during starting, thus enabling no-load start-up of prime mover which is of great importance.
The slipping characteristic of fluid coupling provides a wide range if choice of power transmission characteristics which also results in speed variation, smooth & controlled acceleration, clutching and declutching operations and other characteristics of load limiting, shock loads & peak load absorption and dampening etc.
Fluidomat fluid coupling has centrifugal characteristics during starting, thus enabling no load start-up of prime mover, which is of great importance.
The slipping characteristics of fluid coupling provides a wide range of choice of power transmission characteristics which also result in speed variation, smooth & controlled acceleration, clutching and declutching operations and other characteristics of load limiting shock & peak load absorption and dampening etc. By varying the quantity of oil filled in the fluid coupling, the normal torque transmitting capacity can be varied. The maximum torque of the fluid coupling can also be set to a pre-determined safe value by adjusting the oil filling.
The fluid coupling has the same characteristics in both directions of rotation.
Scoop Control Variable Speed Couplings :
These coupling have a sliding scoop tube which enters the coupling rotating casing through central clearance. The oil quantity level in the coupling can be varied which in operation by changing the position of the scoop tube which determines the oil level in the coupling. This change of oil level shifts the torque characteristic of the coupling thus enabling step less speed control .See the characteristic curve shown below.
- Wear-free power transmission because of absence of mechanical connection between the input and output elements.
- No-load start-up of motor, irrespective of machine load and motor peak torque utilized for machine acceleration.
- Motor selection to operating HP rather than starting loads. Saving on energy cost and capital cost.
- Simple control of maximum or limiting torque by easy variation of oil filling.
- Added protection for motor and driven machine by limiting torque to a predetermined safe value
- Automatic unloading of prime mover in case of any sustained overload, by blowing-off of fusible plug on coupling, thus draining out oil.
- Automatic synchronization and load sharing in case of multi-motor drives.
- Effective dampening of shocks, load fluctuations and torsional vibrations. Helpful in improving the drive duty conditions in machines subjected to shock loads, frequent load changes, startups and reversals. Reduced fatigue on transmission components / elements.
- Smooth and controlled acceleration of driven machines. Important for machines such as conveyors, wire drawing and textile machines.
- Steeples speed variation in wide range obtained in scoop type fluid couplings.
- Economy on machine and drive designs.
- ENERGY SAVING.
Answer - To enable the fluid to flow from impeller to rotor it is essential that there is a difference in 'Head' between the two and thus it is essential that there is a difference in speed known as slip, between the two. Slip is an important and inherent characteristic of a fluid coupling resulting in several desired advantages. As the slip increases, more and more fluid can be transferred from the impeller to the rotor and more torque is transmitted.
Answer By varying the quantity of the oil filled in the fluid coupling, the normal torque transmitting capacity can be varied. The maximum torque o limiting torque of the fluid coupling can also be set to a predetermined safe value by adjusting the oil filling. The fluid coupling has the same characteristics in both the directions of rotation.
Answer Characteristics of operating fluid affects the transmission behavior of fluid coupling by its viscosity & density .The higher the density of the operating fluid, the better the transmission capacity. The higher the viscosity of the operating fluid, the more unfavorable the transmission behavior. The viscosity Index and flash points of operating fluid are important. It must be ensured that the operating fluid is compatible with coupling components & their materials & operating conditions.
Answer - Fluidomat bagged prestigious order from Elecon Engineering for manufacture and supply of its Scoop controlled fluid coupling for Crusher Application at POSCO KOREA.
Answer - They are suitable for operation with
- Water (aqua)
- Water oil emulsion as per HFB classification of European Mines Safety Commission.
- Mineral Oil
Answer - fluid coupling has operating slip, therefore loss is converted into heat. The temperature rise is normal. If temperature rises above specified values then the cause must be established and rectified.
Answer - Thermal protection on a fluid coupling provides safety to a fluid coupling and directly to the driver and driven machine.
Fusible plug is most common thermal protection. If the temperature of fluid in the coupling increases due to any reason (which includes overloads) than the fusible metal in plug melts & all the fluid in the coupling drains out thus stopping power transmission & reloading the prime mover.
The other types optional Thermal tripping systems include:
- Type MTP with a ejector pin & limit switch to stop the motor in case of temperature rise over preset limit.
- Non Contact Type IRNC & ENC sense coupling body temperature & provide trip signal if temperature rises above preset limit.
There is no loss of fluid in case of MTP, IRNC & ENC type of protection and they must be set to operate at a temperature lower than the set temperature lower than they must be set to operate at a temperature lower than the set temperature of fusible plug.
The fusible plug must be provided along with type MTP, IRNC & ENC systems.
Answer - The outer wheel drive means prime mover connected to outer wheel (impeller) and inner wheel drive means prime mover connected to inner wheel (rotor).
The difference is in starting torque characteristics which can be adjusted by due changes in design/construction.
Answer - The load sharing between motors can be adjusted and balanced by adjustment of oil filling.
Answer - Certain quantity of oil is stored in delayfil chamber during coupling at stand still. Thus a motor starting run up the oil quantity in working circuit is low which results into quick motor acceleration and low starting torque achieving smooth acceleration of driven machine. After some period the oil in delayfil chamber drains into working circuit resulting into better efficiency during operation.
Answer - Fluidomat fluid couplings are bi-directional in design and can be used in any direction.
Answer - Yes, the torque transmitted changes as square value with the input speed Torque N12/N22 & Power transmitted changes as cube of input speed N13/N23
Answer - All exposed rotating parts must be suitably guarded against contact and spray hot oil incase of fusible plug blow off. The guard must be so designed that they do not impair the ventilation of the fluid coupling.
Answer - The first fill of Oil should be drained after first 400 working hours. This oil can be filtered and refilled or fresh oil may be filled. After 1st fill change, oil can be used for next 15000 working hours. Oil level should be checked periodically & if needed should be topped up.
Answer - The serial number of a fluid coupling is very important for all queries and spare parts orders. It helps us to clearly identify the coupling. Normally, the operating manual for your coupling contains a note about the location of the serial number. For constant-fill fluid couplings, the serial number and the coupling type are punched in the outer wheel, either at the outer periphery or close to it.
For variable controlled fluid couplings, the serial number is shown on the identification name plate & also punched on top side of housing in variable speed coupling.