DAMPING

303

and blowing it on the web. This is very difficult to regulate, as microscopic
differences in the orifices of the air jets, and their immersion in the water, make
it necessary for each jet to be separately controlled, and the results of adjust-
ments are not fully known until the paper is being super-calendered. Direct
sprays have the same disadvantage.

Filtered water is necessary and a high pressure, but under the best conditions

[Watford Engineering Works
FIG. 131. — WATFORD PATENT AQUAMIST DAMPER WITH ADJUSTABIE NOZZLES

a small particle of any foreign substance may stop a spray or reduce its volume,
causing streaky and irregular finish.
Jets of water impinging on a glass or metal plate, so as to rebound in the
form of spray, form a very good damping arrangement, give good results and
little trouble.
A form of damper which is now falling into disuse is in the form of a brass
or copper cylinder cooled by an internal flow of water. Steam jets are made
to play on the outside surface, and the condensed steam in a fine film is trans-
ferred to the paper. This form of damper does not give much variation in
volume of applied water, and is expensive owing to the use of steam. A felt-
covered roll, partly immersed in water, is sometimes used to wet a damping
cylinder.