Simon
Group exhaustvalves
The name sound perhaps a bit strange to you but is a very common Royal Navy term in the submarine service, meaning a device collecting several connections, like exhaust outlets from 6 cylinders (manifold). Down below is a photo showing the valvewheels in the engine room for the 3 pairs of relevant exhaust valves.
The arrangement deviates a bit from British and US subs as it is adopted for using exhaust pressure for blowing the ballasttanks in semisurfaced position instead of a lowpressure electric blower as the case of other submarines. The muffler valves were used in a semi open position when blowing the tanks in order to adjust the exhaust backpressure. One disadvantage of the system was that the muffler ( dry muffler) exhaustvalve had a tendency to get carbonizes and deposits could be formed both on the valveseating as well as the gear rim and wormwheel, thus blocking the device. As this was mostly common on the mufflervalve a pneumatic motor was fitted and the valve had to be rotated may be once a watch whereas the group exhaustvalve had a hand turning with handles and ratchets.
As you see the wheels have a bore where you could put a bar giving an extra force to the shutting moment, moreover the group exhaustvalves had a pointer for shut and open 90 degrees.
Tore