Bolt heaters are used to expand the stud bolts around the main steam and condenser chests in a turbine set, in order that the nuts may be slackened or tightened to the high degree of control necessary.

In detail design, the heaters are of extremely robust construction. Tubular sheathed elements are sintered in a stainless steel outer tube of accurate outside diameter to fit into standard bores machined in the full length of the stud bolts. Heater tube diameters range in seven steps from 0.625" to 1.438" with lengths from 12" to 60" and loadings from 500W to 10kW.

Spare heater blades (sintered assemblies) can be readily screwed into the boxes when replacement becomes necessary. Two standard sizes of terminal box are used to cover the range, these having maximum current ratings of 30amps to 100amps.

To meet the safety regulations appropriate to the handling of heater tools of this type, the electrical connection to the terminal box is made via the approved Harvey-Hubble inlet and plug. This system, which incorporates a return pilot lead in the supply cable, provides safety against inadvertent breaking of the supply connection whilst the heater is still energised, an essential requirement where high currents are involved.

Normally, a number of heaters are fed from specially designed 415v/110v supply transformer trolleys fitted with outlet sockets backed up by fuses, earth fault relay, contactor control circuit and voltage indication.

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