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HYDRAULIC COUPLING

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Page 1: Hydraulic Coupling

HYDRAULIC COUPLING

Page 2: Hydraulic Coupling

Fluid coupling is a combination of pump and turbine acting and reacting simultaneously to give a new element for torque transmission. As we know that pump is transforming kinetic energy of impeller into pressure head in fluid and turbine in turn absorb the pressure head and produce kinetic energy of runner. So the kinetic energy transfers from one shaft to other one without any mechanical contact in between them.

Now the point comes into play on the selection of working fluid for smooth running of pump and turbine placed in closed vicinity in a common chamber. Like in all cases of transmission and energy transformation, lost energy handle is very big problem in this case. Considering heat generated due to loss and lubricating requirement of the internal components, lub oil of low viscosity and high flash point is selected as working fluid.

Usually mineral oil is used as working fluid for the following reason:- a) Universally available. b) Relatively low in cost. c) Lubricates the fluid coupling internals when running, and protects them from

stationary. d) Non-toxic, requiring only simple precautions in use. e) No erosion or cavitation problems arise within the working chamber. The torque transmitted by the coupling is proportional the difference in moment of

momentum of the fluid as it enters and leaves each member. The speed difference or slip, creates the net difference in opposing centrifugal heads of impeller and runner to circulate the fluid against the friction & shock loss with in the vane space. So speed of the primary shaft is greater than the secondary shaft (i.e. output shaft).

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SLIP is defined as 100 x (primary speed-secondary speed)/primary speed.This slip characteristic is deciding factor for the selection of working fluid and the necessary of cooling circuit of working fluid and provision of heat dissipating fins as change in viscosity at elevated temperature may deteriorate the performance of coupling.

CLASSIFICATION OF FLUID COUPLING

(A). Constant fill fluid coupling &(B) Controllable fill fluid coupling.

FIXED OIL TYPE FLUID COUPLING

This is a PEMBRIL FLUIDRIVE fluid coupling which is a simple power transmitting unit to couple an electric motor to a machine. It consists of two rotating assemblies only, contained in a casing- one is driven by the motor and the other is on the driven machine side. The casing is filled with light oil and it is this oil that passes the power from the motor to the machine it is driving.The fluid coupling greatly improves the performance of motors. Full load is carried with an insignificant loss in speed and no loss in torque.

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CONSTRUCTION

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The main components are: INPUT SIDE- Impeller and casing.OUTPUT SIDE- Runner and shaft.

The impeller, runner and casing are high tensile aluminium alloy castings, and the impeller and runner both have a large number of straight radial vanes. The runner shaft is carried in ball and roller bearings in the casing and the runner. There is no mechanical connection between the runner and the impeller.The amount of oil in the coupling may be varied over a wide range, to give adjustment of acceleration and torques. A gland sealing is fitted between the casing and the runner shaft.How the fluid coupling works:The impeller, driven by the motor, and runner coupled to the driven machine, both have a large no. of straight radial vanes. The impeller behaves like a centrifugal pump, creating an outwardly flowing stream of oil, which crosses the gap to the runner which acts as a turbine. The oil stream gives up power as it flows inwards between the vanes of the runner and, as it returns to the impeller. Again, the cycle is repeated.

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CharacteristicsTypical characteristics of the fluid coupling (when used with direct connection of motor) are shown in the following figures;

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StartingAt the motor switch on, the fluid coupling has no torque capacity. As the motor accelerates , the coupling torque remains low. The motor thus starts under light load and runs up to speed quickly, while the torque of the fluid coupling increases smoothly to start the machine.

RunningTypical coupling torque/output speed characteristics available for bringing the machine up to speed smoothly and rapidly.High torques available for starting and accelerating machine, also accelerating torque can be adjusted by varying coupling oil filling.

Filling the fluid couplingBefore the machine is started up, the fluid coupling has to be filled with the correct quantity of mineral oil of low viscosity. I.O.C make servo system -311 or 314 oil to be used.The exact quantity of oil to be poured in the coupling as per recommendation of manufacturer.Two filling plugs are fitted to the fluid coupling. Turn the fluid coupling until one of the plugs lies at the recommended filling angle from the vertical centre line. Take out the plug and pour in cold oil to fill up to the plug hole. Then screw the plug in again, with its joint washer and tighten securely.In a drive where the coupling shaft is not in level, but is inclined , then the angle to which the plug hole is set for filling must be altered .

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OperationThe torque /speed and the stalling characteristics of the fluid coupling can be adjusted by increasing or decreasing the quantity of oil initially filled into the coupling.

FUSIBLE PLUGA fusible plug incorporated in the impeller. The purpose of the plug is to provide additional safeguard to the motor and prevent overheating in the rare event of a stall or failure of the motor overload trip. The plug contains a fusible alloy that melts at a set figure and allows the oil in the fluid coupling to escape, thus removing the load from the motor and allowing it to run free.After removing the cause for the failure of the motor overload trip, it is necessary to fit a new fusible plug and to refill with clean oil to the recommended filling, before restarting.

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CONTROLLABLE FILL FLUID COUPLING:-i)PEMBRILvariable speed control fluid coupling & ii) Variable speed turbo coupling (make VOITH)

PEMBRILL FLUIDRIVE FLUID COUPLING:-The fluidrive fluid coupling is an adjustable speed fluid coupling designed for mounting between an electric motor and a driven machine( such as a pump or a fan), to enable the speed of the driven machine to be varied over a wide and step less range while the motor runs at a constant speed. The power of the motor is transmitted smoothly and without shock by the kinetic energy in the oil flowing between the input and output elements of the oil. This type of fluid coupling provides the ability to control continuously, while the set is running, the quantity of oil circulating between the input and output elements, thus enabling the torque transmitted and the output speed to be controlled. With a constant speed electric motor, therefore the speed of the driven machine can be varied infinitely over a speed range of as much as 5 to 1 by the operation of the control lever SCR.24R fluid coupling. With constant torque drives, the speed range available upto 3 to 1.The efficiency of the drive is high, full load is carried with a very small speed loss.

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CONSTRUCTIONThe construction of this type fluid coupling is shown in the sectional arrangement; The main components are : INPUT SIDE: Driving plate, back casing, reservoir casing and impeller.OUTPUT SIDE: Runner, runner shaft and multidisc semi flexible coupling.The impeller and the runner both have a large number of radial vanes.The bracket carrying the scoop housing and adjustable scoop tube is stationary and is mounted independently on the foundation.MOUNTING The weight of the rotating parts of the type SCR. 24R fluid coupling is shared between the shafts of the driving and driven machines.The input side of the fluid coupling is centered in the driving boss mounted on the motor shaft. The drive is taken from the motor to the casing by means of resilient driving plate which has a small degree of angular flexibility.The output side i.e, runner side is supported by the multitask semi-flexible coupling, which has a small degree of angular flexibility, is rigid radially and part of the weight of the rotating parts is therefore transferred to the bearings of the driven machines. If mis-alignment is there during installation loads on all bearings will be increased and life of the machine will be shorter.

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OPERATIONPower is transmitted from the impeller (driven by the motor) to the runner (coupled to the driven machine) through a rotating vortex of oil.The speed of the output shaft can be controlled by varying the amount of oil in the working circuit contained between the impeller and the runner. Therefore with electric motors giving a constant input speed, the speed of the output side is infinitely variable. The range of variation of the output speed depends upon the application. In the case of fans of similar drives with centrifugal characteristics this range is from maximum speed down to about 1/5th speed. Where a constant torque throughout the speed range is demanded, regulation down to about one-half or one-third speed is obtained. The volume of oil in the working circuit is controlled by changing the position of the scoop tube which can slide radially in the stationary scoop housing.When the fluid coupling is at rest, the oil level is below the opening in the casing through the scoop tube housing pass. Therefore no oil retaining seal is needed. On starting up the set, with the scoop tube retracted radially inwards, the oil in the fluid coupling will form a rotating annulus in the reservoir casing due to centrifugal force. The casing is of sufficient capacity to contain all the oil clear of the tip of the scoop tube, so that the working circuit will remain empty under this condition , with the drive dis-engaged.By sliding the scoop tube radially outwards, its tip enters the rotating annulus of oil and a quantity of oil is picked up by the scoop tube and transferred to the working circuit( through the external oil cooler, if fitted). The amount of oil transferred depends upon the radial position of the scoop tube, which determines the depth of oil remaining in the reservoir casing.

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A continuous circulation of oil is maintained, as oil escapes from the working circuit through small leak-off holes into the reservoir casing all the time that the coupling is running. This allows circulation of oil through an external cooler, if required, and also allows the volume of oil in the working circuit to be reduced progressively as the scoop tube is retracted radially inwards. It will be seen, therefore, that the amount of oil in the working circuit and thereby the speed of the output shaft, is maintained at any desired value by the setting of the scoop tube, controlled by the external lever.The position of the scoop lever may be adjusted by local hand or remote electric control or the lever may be coupled to an automatic control.

INSTALLATION OF OIL COOLERS

If the cooler are not attached to the coupling guard, they must be installed at a level below that of the flanges on the scoop housing, so that the oil will not drain or siphon back into the coupling when the set is shut down.The successful working of this fluid coupling depends on the oil being clean and free from foreign matter. The ends of all pipes and the flanges of coolers are given temporary covers to exclude dirt during transport, and provided these are intact, no further cleaning should be required before installation.

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If, however, during installation, any of the pipes have to be heated to set them, scale may be formed inside the pipes and this has to be removed by wire brushing or even by shot blasting before the pipe is fitted in place.It is very important that all temporary seals and plugs in the ends of the pipes and cooler connections are removed at the last moment during erection, so that oil circulation is not impeded.All flanged joints should be made with a good quality jointing material 0.4 mm thick. Apply a thin coat of jointing compound, such as a Hermetite, to one side of each join and stick it to one of the flanges. Then lightly smear the exposed side of the joint with grease. This will assist when subsequently dismantling the flanges leaving the joints undamaged.Take particular care not to put any strain on the scoop bracket when tightening up the pipe joints. To ensure this, it is recommended that the whole system is assembled with all the bolts screwed up finger-tight, so that a check can be made the flanges face up to each other squarely without straining the pipes. Finally, tighten up the bolts firmly.

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FILLING THE FLUID COUPLING

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Before running, the fluid coupling has to be filled with thin mineral oil of low viscosity and Servo System-100 (maKe IOC oil is recommended.The following table indicates the quantity of oil required in reservoir casing for the various sizes of SCR.24R fluid coupling.

size Overall dia of reservoir casing in mm.

Approx.QuantityOf oil forcoupling

18 630 16

20 692 21.5

23 789 32

26 891 46.5

29 1018 64

32 1108 86

36 1254 123

41 1413 184

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To fill the coupling, remove the tundish cover and pour or pump into the tundish

about 9/10th of the required quantity of oil. Replace the cover and tighten the nut securely.

Move the scoop operating lever to its minimum position. Check the output shaft is free to rotate.

Now start up the motor. Move the scoop operating lever slowly to its maximum speed position, to circulate the oil through the pipes and coolers and to oil-wet the system.

After the coupling has run for a short while, return the scoop lever to its minimum position and cautiously remove the cover of the tundish.

Most likely at this stage the coupling will be underfilled and there will be no oil appearing in the tundish. It will therefore be necessary to pour in more oil until a definite welling up of oil is seen in the tundish.

When the coupling is correctly filled, oil will be seen to well up in a small steady flow in the tundish. The tundish lid should then be replaced and the nut tightened securely.

If there is too much oil in the coupling, the oil flo in the tundish will be excessive. In this case, replace the tundish lid and put a suitable container underneath the drain plug on the filling valve. Take out the drain plug to allow the excess oil to be pumped out of the coupling, the scoop lever remaining in the minimum speed position.

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Notes: a) Checking the correct filling of the coupling should always be carried out when the

coupling is cold.b) When checking the level or running with the tundish cover off, do not let the scoop

operating lever move away from the minimum speed position , as oil will be violently ejected from the tundish.

c) When checking the oil level, it is important that the filling valve is pushed right down, after removing the tundish lid. Otherwise if the coupling is fully filled, the internal pressure may prevent the valve being pushed down by its spring.

OPERATING ADVICEa) The output shaft will not come up to speed: it may occur (a) if no oil circulation is

there due to blockage of pipe connection , blanks left in cooler flanges. So checking is required. (b) If coupling is underfilled with oil. After scoop tube fully out, check filling carefully.

b) The output shaft will not come down in speed : it may happen if (a) blockage is there in leak off nozzles, remove & clean.(b) coupling is overfilled, check filling.

c) Oil leaks: from joints in cooler pipework, from plugs in reservoir casing or from around output shaft,due to: coupling overfilled ( check filling) or joint between scoop housing and bracket( remake joint).

d) Coupling overheats( oil temp. above 88 degree centigrade).: It may occur (a) if cooling water not circulating due to cooler chocked or water boxes on coolers are incorrectly fitted. Checking required.(b) if coupling is underfilled (c) if oil is not circulating, necessary checking is required.

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THE FOLLOWING SHOULD NEVER HAPPEN, BUT ARE SET DOWN AS A WARNING:-

a) Noise from fluid coupling, check alignment of scoop housing bracket.b) Breakage of resilient driving plate, due to incorrect alignment between

coupling and motor. Check alignment.c) Breakage of multidisc assembly, due to incorrect alignment between

coupling and driven machine. Check alignment.

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VARIABLE SPEED TURBO COUPLING (FOR ID FAN), MAKE VOITH TURBO POWER TRANSMISSIONMACHINE DATA:

Power requirements in driven machine 1105 KW

Motor speed 740 rpm

Min. slip 2.9%

Max. output speed 718 rpm

Regulating range 5:1 downwards

Oil tank filling capacity 780L(approx)

Weight without oil 3500 Kg (approx)

Scoop tube stroke length 305 mm

Rotation seen in the direction of power flow.

Clock Wise

Pump 1 filling pump for working Oil & lube oil circuit

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HOUSINGThe VARIABLE SPEED TURBO COUPLING is designed with a split in horizontal direction on the centre level. This housing forms the oil tank at the same time.

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COUPLING The coupling consists of 1) Primary shaft and primary wheel,2) Secondary shaft and secondary wheel,3) Shell (flanged on primary wheel, enclosing the secondary Wheel) 4) and scoop tube housing with actuator.

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Primary shaft and primary wheel are rigidly connected with each other; the same applies to secondary wheel and secondary shaft. The primary shaft is connected with the driving machine and the secondary shaft with the driven machine.Primary wheel, secondary wheel and shell form the working chamber. The working oil circulates in the working chamber.The scoop tube, with scoop tube housing, is integrated in the VARIABLE SPEED TURBO COUPLING housing. The secondary shaft is supported in the scoop tube housing.BEARINGSThe primary and secondary shaft of VARIABLE SPEED TURBO COUPLING is supported by ball and roller bearings. The primary shaft is guided axially via a relative bearing (between primary and secondary shaft).OIL PUMPSA filling pump in the oil tank delivers the operating oil for the working oil and lube oil circuit. The filling pump is mechanically driven by the primary shaft of VARIABLE SPEED TURBO COUPLING. An electrically driven lub oil pump (which is optional) is installed to supply lub oil to external units during start up & shut down.

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POWER TRANSMISSIONThe VARIABLE SPEED TURBO COUPLING transmits power wear free from a driving machine to a driven machine. Power transmitted as follows:Between driving machine and VARIABLE SPEED TURBO COUPLING through a connecting coupling.Hydro dynamically between primary wheel and secondary wheel through the working oil.Between VARIABLE SPEED TURBO COUPLING and driven machine through a connecting coupling.Infinitely variable speed control of driven machine is possible by means of the scoop tube control.The power of driving machine is transmitted through the primary wheel (as a pump) on to the working oil; the working oil is accelerated in the primary wheel, and the mechanical energy is converted in to kinetic energy. The secondary wheel (turbine) absorbs the kinetic energy and converts it back into mechanical energy. This energy is transmitted to the driven machine.The same torque applies to primary and secondary wheel.SLIP On power transmission, the speed of secondary wheel is smaller than that of the primary wheel. This speed difference is called slip. The power loss due to the speed difference heats up the working oil. It is necessary to cool down the oil to dissipate this heat.

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WORKING OIL CIRCUITThrough the working oil orifice plate the oil flows into the coupling working chamber and, due to centrifugal force , forms a rotating oil ring in the scoop chamber. The scoop tube position determines the thickness of oil ring in the scoop chamber and thus also the filling in the working chamber. The scoop tube scoops up the warmed up working oil in the working chamber and directs it back into the oil tank from where the filling pump supplies the working oil to the cooler. Then the cooled down working oil returns into the coupling working chamber through the working oil orifice plate. If it is necessary to enlarge the working oil filling in the coupling, adjust the scoop tube. WORKING OIL TEMPERATUREThe working oil temperature depends on the power losses (slip) and the working oil flow rate and is monitored by temperature measuring instruments.FUSIBLE PLUG If the oil temperature rises to 160 degree C due to a failure, the solder of fusible plugs in the coupling melts and oil is thrown into the housing of VARIABLE SPEED TURBO COUPLING. The coupling drains its oil, thus reducing torque transmission.

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Speed control by means of scoop tubeThe speed of driven machine may be controlled steplessly. For this purpose, the coupling oil filling is changed during operation by means of the movable scoop tube:Scoop tube inserted as far as possible in the scoop chamber of coupling (0%) position: minimum oil ring, minimum output speed.Scoop tube moved as far as possible out of the scoop chamber of coupling (100%) position: maximum oil ring, maximum output speed.

LUBRICATIONSelf-lubricationBearings and gears of VARIABLE SPEED TURBO COUPLING need to be lubricated prior to and operation.Lub oil circuitDuring operation the filling pump delivers oil out of the oil tank from which the tube oil is branched off to the lube oil circuit through the tube oil orifice. ThroughHeat exchanger,Double oil filter andLub oil orifice The filtered and cooled oil gets to the lubrication points.

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VOITH GEARED VARIABLE SPEED TURBO COUPLING FOR B.F.P

VARIABLE SPEED GEARED COUPLING AS BOILER FEED PUMP DRIVEPower requirements of driven machine: 3000 kwMotor speed: 1483 rpmGear ratio: 139/39 (=3.56)Primary speed: 5285 rpmFull load slip: 2.0%Max. output speed of the variable speed geared Turbo coupling: 5178 rpmRegulating range: 4: 1 downwardsOil tank filling: 700 litres (approx)Filling pump & lub oil pump: together driven as gear tooth System drive via the pump shaft.

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DESIGN & OPERATION The geared variable speed turbo coupling is used for infinitely variable speed control of high speed machines. The variable speed turbo coupling and step up gear are incorporated in a mutual housing, while the lower section op the housing serves as an oil tank.Flexible connecting couplings are applied for power transmission from the motor the to the geared variable speed turbo coupling and from there to the machine. The speed is reduced between input and primary shaft by means of a gear stage. Torque is transmitted hydrodynamically from the primary wheel to the secondary wheel by the working oil.The torque generated by the driving machine is provided to accelerate the fluid in the primary wheel (impeller). This is delayed in the secondary wheel (turbine) to produce an equal torque. The fluid can only circulate by a pressure drop between the primary and secondary wheel. This requires that the secondary wheel speed is lower than that of the primary wheel. Thus a slip is required for power transmission.The coupling size is selected so that the full power can be transmitted with a low slip, the “full load slip” (at max. filling). The output speed can be regulated infinitely by changing the oil filling in the working chamber between the primary and secondary wheel. This is accomplished by positioning the scoop tube accordingly, which will determine the oil filling of the working chamber.The power loss caused by slip will heat up the working oil. Cool the oil to dissipate this heat.

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Operating Oil CircuitAs the type of regulation supplied is a slip regulation, hydraulic losses unavoidably occur in the variable speed turbo coupling. These losses manifest themselves in heating up of the coupling oil which is then cooled in a heat exchanger in order to dissipate the heat. The amount of output losses depends on the load characteristics and the slip required for attaining the desired output speed.

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StartingThe centrifugal pump 1 delivers through a restrictor 63 into the circulation control valve casing 57. The coupling is filled according to the resistances via the cooler II and the scoop tube 41 as well as via valve III. The pressure holding valve IV is closed.

Normal Operation (without regulation)The amount of circulating oil required for dissipation of heat is a product of the pressure (1.2-2.4 bars) preset in the circulation Control valve housing 57 by means of the pressure holding valve IV and the cross sectional area uncovered by the valve III control piston. The amount of oil approaching the coupling is collected at the scooping edge of the scoop tube after flowing through the impeller parts and pumped back from the scoop tube 41 via the cooler II into the circulation control valve casing 57 against the pressure prevailing in this valve casing. The filling pump I delivers a differential amount into the circulating control valve casing via the restrictor 63 against the pressure prevailing. With the same position of valve III, the additional amount would mean a pressure rise in the circulating control valve casing, unless the same amount would be able to flow back to the sump via the slightly opened pressure holding valve IV and the pipe V.

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Step-up speed regulation.The scoop tube moves away from the coupling oil level, the delivery decreases, the pressure inside the circulating control valve casing 57 drops, the pressure holding valve IV closes, the filling pump delivery is used for filling the impeller parts.Step-down speed regulation.The scoop tube moves into the oil level, the scoop tube delivery increases, the pressure inside the circulating control valve casing 57 rises. The pressure holding valve IV opens again and discharges the oil scooped up plus filling pump differential volume into the sump.The circulating operating oil is controlled via the cam disc 72 as a function of the heat generated. The maximum oil flow rate is computed from the output and preset in the works. The ratio between maximum oil flow rate and scoop tube position is preset according to the coupling rating and the expected traction by turning the cam disc on the control shaft 45.The cross section of the scooping edge of the scoop tube is so dimensioned that additional volume accumulating is safely scooped up is safely scooped up even with a large circulating oil volume and short scoop tube setting period.

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To better understand what benefit a fluid coupling provides when connected between an electric motor and gear train, the speed and torque profile of the electric motor must be considered. During start up, an across the line started motor transmits torque to the drive system components. As shown in the graph, these values can range anywhere from 180 % starting torque to 250 % breakdown torque based on full load.Severe damage may result to the connected equipment if less than 180 percent of full-load torque for starting is required because components in the drive train must absorb the additional load. Any number of components, from belts on a conveyor to bearings or rotating shafts and more, could fail as a result of “over-torquing”.If the driven equipment requires more than 180 percent breakaway torque, Motor will fail to start. This is when the benefits of a fluid coupling become evident. The fluid coupling controls the motor’s output characteristics to match load requirements. When the electric motor is started, no load is demanded since fluid has not flowed between the impeller and runner. The only load imposed on the motor is the inertia of the casing and impeller.As the motor accelerates, the impeller begins to pump oil to the runner and gradually builds following the square of the motor speed. Therefore, torque build-up is smooth and gradual. Once the torque build-up has matched the required breakaway value, the runner will begin to rotate and accelerate the driven load. The electric motor is now running at full-load speed and “flow” in the coupling is fixed. The torque developed by the fluid coupling is directly related to the amount of oil circulating between the impeller and runner. Adjustment of the coupling’s fill can provide a wide range of torque values. More oil in a fluid coupling provides higher starting torque and more available torque for acceleration.

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Selection criteria.Due to the operating principle of hydrodynamic couplings, they affect the Power train in several ways. Various selection criteria therefore apply.Hydrodynamic couplings are generally selected according to the requirements on torque transmission and power train characteristics.The following conditions apply to hydrodynamic couplings with constant filling level :1.The drive motor power depends on the coupling rather than The machine being driven startup relief low-cost drives).2.The couplings limits maximum shaft torque as a function of speed (overload and jamming protection).3.Slip-free drive systems (system separation, stepped start-up of multimotor drives).4.For improving dynamic characteristics of the drive train (by damping and for separation of torsional oscillations and shock loading).5For easily adjusting power transmission characteristics by altering the filling (to suit operating requirements, or for load sharing between multimotor drives.The overall effect of hydrodynamic drive characteristics is to protect electrical and mechanical drive elements, above all with high switching frequencies and reversing.

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The following criteria apply to hydrodynamic coupling size and type selection : 1. Characteristics. 2. Low rated slip. 3. Installation conditions. 4. Thermal storage capacity (switching frequencies). 5. Heat transfer and disposal. 6. Temperature limitation (explosion risk). 7. Operating medium. 8. Secondary wear and tear (bearings, seals). 9. noise development. Fluid media. Power is transmitted in hydrodynamic couplings as specific kinetic energy of fluid flow. This depends primarily on the physical properties of the fluid density and viscosity- and also demands the efficient removal of heat due to losses. The fluid characteristics required in practice very widely, dependingOn the kind of coupling and how it is integrated in the drive system. As far as energy transmission is concerned, water is even better than mineral oil or synthetic fluids. With regard to safety and availability, water is excellent. However, river or seawater in particular is unsuitable with regard to abrasion, bearing lubrication, corrosion and cavitation.Although Fottinger carried out tests with seawater, it turned out to be unsuitable in practice. The fluids mainly used comprise mineral oils, which can be modified according to drive system demands. Apart from their good long-term operating characteristics, mineral oils also meet control and lubrication requirements.

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The majority of these oils comprise paraffin-based solvates with excellent ageing resistance and additional properties as required. MineralOils with low viscosity are preferable, since they reduce flow friction losses through the blading channels and thus increase power transmission efficiency. If hydraulic oil is also used for gear lubrication, properties must be carefully balanced. In order to keep oil supply aggregates as compact as possible, good delivery capacity is also important.

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Let us assume w(p) is input speed ,w(s) be secondary speed i.e angular velocity. So power input to the primary wheel & power output in terms of torque (T) and angular velocity (w)P(in) = T(p) . w(p) and P(out) = T(s) . w(s) Therefore efficiency of transmission = T(s) .w(s) /T(p) . w(p) and as there is no parts is in between to provide torque reaction , so the input and output torque is considered to be same ignoring the minor losses. T(p) = T(s). So efficiency = w(s)/w (p). = 1-S S=w (p) –w(s)/w (p)

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