Flexible intermediate drives

There are two types of flexible intermediate drives used to transmit torsional power belt drives and chain drives. Flexible belts are used in industrial power transmission applications primarily when the speeds of the driver and driven shafts must be different or when the shafts must be widely separated. The trend toward higher speed primary drivers and the need to achieve a slower, useful driven speed are additional factors favoring the use of belts. In addition to V-belts, there are round belts and flat belts. Chain drives are typically used in applications where space is limited or obstructions prevent direct coupling of machine-train components. 

Jackshafts Some machine-trains use an extended or spacer shaft, called a jackshaft, to connect the driver and a driven unit. This type of shaft may use any combination of flexible coupling, universal joint, or splined coupling to provide the flexibility required making the connection. Typically, this type of intermediate drive is used either to absorb torsional variations during speed changes or to accommodate misalignment between the two machine-train components. 

The motor shaft is connected to the intermediate drive shaft by means of a flexible coupling. If a squirrel-cage motor is used, a fluid clutch is additionally provided, in order to facilitate motor starting and prevent surges in the supply system. 

Sometimes, conventional techniques do not produce a satisfactory steam balance for all operating modes. Options are available for steam drives for flexibility, such as extraction and induction turbines. Extraction turbines are widely used. In these, an intermediate pressure steam is removed or extracted from an intermediate turbine stage with the extraction flow varying as required over preset limits. Induction turbines are not as widely used as extraction turbines, but are a very satisfactory application... 

A first round of the systematic review of the reactor operating eiqierience has been completed for the absorber rod drive mechanisms, main sodium pumps and intermediate heat exchangers (IHXs) which has revealed sensitive points for EFR. Examples are the importance of succeeding with the EFR features which prevent die sodium aerosol problems on the absorber mechanisms, the need to confirm adequate operational flexibility whilst avoiding the check valve at the primary pump outlet and to ensure full benefit is taken of the piston seal experience for the IHX / pool boundary replacing the gas bell originally selected for EFR. 

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