=Safety Valves=, or pop valves, as they are sometimes termed, are made
in many different kinds and styles, but the one most commonly used on
a farm engine is constructed with a coil spring, which is adjustable,
to allow the valve to pop off at a certain pressure. When the pressure
exceeds this amount, it raises the valve from its seat and allows the
surplus steam to escape. It should be set with the steam gauge, to
allow a little margin of steam pressure over that which is necessary to
drive the load, and should be compared with the steam gauge frequently
to see that it works accurately. It is furnished with a lever for
raising the valve, which should be raised occasionally to see that it
operates freely.
[Illustration: Kunkle Safety Valve.]
[Illustration: Kunkle Safety Valve, Sectional.]
The safety valve being set with steam gauge, the gauge should be
watched when safety valve blows off. If it indicates more or less than
the gauge something is wrong, the valve marked incorrectly or the
steam gauge is out of order. In case the safety valve and steam gauge
do not register alike, the valve should be examined to see that the
valve is not stuck in its seat, and should be thoroughly cleaned of
all sediment; then put back in place again and compared with the steam
gauge as before. If they do not register alike, the gauge should be
examined.
Q. Is not a safety valve attached to a boiler to prevent explosion and
loss of life?
A. The Safety Valve is only intended to prevent an explosion from
excessive steam pressure, and should never be set to hold more than
the required pressure to give the rated power for which the engine is
designed.