The locomotives had a Winterthur cogwheel drive with one
lower and one upper pair of cylinders. On the level, they ran like normal steam
locomotives using the lower, higher pressure, pair of cylinders driving on the
third coupled axle. Before entering the rack section the upper drive was
started using live steam. At the same time the r.p.m. was matched to the
running speed so that entry into the rack section could be achieved smoothly.
Once the cogwheel had engaged the rack, the exhaust from the lower cylinders
was routed to the upper, lower pressure, ones using a change valve and was
expelled from the chimney. The locomotive now worked as a compound.
The cylinders of the adhesion and cogwheel drives have
the same diameters (Ø 560 mm). The difference in volume (after expulsion from
the adhesion system, the steam doubles its volume) is compensated for because
the cogwheel drive turns twice as fast. The driving cogwheel is housed in a
special frame, that lies above the second and third axle. The higher cogwheel
drive and the lower cogwheel are coupled via an intermediate gear with a
transmission ratio of 1:2.43.
The boilers were given steel fireboxes and the frame was
reinforced, especially in the area of the drive. The outermost axles, which had
side play, were given return springs to minimise hunting.
The DRG organised these tank locomotives (there were 4 of them) into Class 97.5
in their numbering plan. They were employed on the 1-in-10 Honau-Lichtenstein
rack railway, 2.2 km long, which employed a Riggenbach-Klose rack system. Apart
from 97 503, which was destroyed during the Second World War, the other tank
locomotives continued working until their retirement in 1961.
This postcard came from Anika (19 May 2015) Postcrossing.
Source: Wikipedia
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