These are well-known devices for so controlling the draught of the
chimney that the steam pressure in the boiler will be increased or
decreased automatically, that is, without the aid of a person. The
regulator shown in Fig. 92, which is one of many excellent forms on the
market, has the power to move the damper in both directions by water
pressure, exerting a force on the end of the lever of nearly 200 lbs.,
thus compelling a certain and positive motion of the damper when a
variation in the boiler pressure takes place. It will open or close the
damper upon the variation of less than one pound of pressure. The close
regulation affords a test for the correctness of the steam gauge.
[Illustration: Fig. 92.]
This regulator, by using the water pressure from the boiler as a motive
power, becomes a complete engine without the connecting rod and crank,
having a balanced piston valve, the valve stem of which is enlarged
where it passes through the upper end of the chest into a piston of
small area, working in a small open ended cylinder cast on the chest.
The pressure forcing this piston outward is counterbalanced by weights
as shown in illustration.
The differential motion is accomplished by the device shown at the top
of small cylinder.