gasometer, alternately starting and stopping the motor as the bell falls
and rises again. Medium pressure generators are provided with a diaphragm
to control the feed motor.

This diaphragm is carried so that the pressure within the generator acts
on one side while a spring, whose tension is under the control of the
operator, acts on the other side. The diaphragm is connected to the brake
and locking device on the motor in such a way that increasing the tension
on the spring presses the diaphragm and moves a rod that releases the brake
and starts the feed. The gas pressure, increasing with the continuation of
carbide feed, acts on the other side and finally overcomes the pressure of
the spring tension, moving the control rod the other way and stopping the
motor and carbide feed. This spring tension is adjusted and checked with
the help of a pressure gauge attached to the generating chamber.

_Gravity Feed._--This type of feed differs from the foregoing in that
the carbide is simply released and is allowed to fall into the water
without being forced to do so. Any form of valve that is sufficiently
powerful in action to close with the carbide passing through is used and is
operated by the power secured from the rise and fall of the gas holder
bell. When this valve is first opened the carbide runs into the water until
sufficient pressure and volume of gas is generated to raise the bell. This
movement operates the arm attached to the carbide shut off valve and slowly
closes it. A fall of the bell occasioned by gas being withdrawn again opens
the valve and more gas is generated.

_Mechanical Feed._--The previously described methods of feeding
carbide to the water have all been automatic in action and do not depend
on the operator for their proper action.