2.3 Cover seals
On large modern HP valve chests, it is difficult to provide an adequate bolted joint between the valve chest and its cover. Current practice on these chests generally is to utilise pressure-assisted seal joints si¬milar to that shown in Fig 2.34.
On reheat steam chests, bolted flanged joints are used. These joints usually have gaskets that are either of the Metaflex type backed up by a metal-to-metal joint face, or they employ an Inconel ring. All such bolted joints are designed not to require retightening for at least 30 000 hours of operation.