[Illustration: Lunkenheimer Water Gauge.]
=The Blow Off Valve= is an angle or globe valve attached to the lower part of a boiler for the purpose of blowing off the sediment accumulated by the use of impure water, and should be used more or less frequently according to the condition of the water used, but never less than once a week. There is also a surface blow off which is attached to the boiler at about the safe water level for the purpose of blowing off the scum which accumulates on top of the water. This scum should be blown off once or twice a day.
=A Gauge Cock= is a stop cock attached to a boiler to ascertain the height of water in the boiler. There are generally two and sometimes three gauge cocks attached to a boiler. The lower one enters the boiler as low down as it is deemed safe to allow the water to get, while the upper one enters the boiler sufficiently high to avoid getting too much water. Where three gauges are used, the middle one enters the boiler at about the proper water level. They should be opened frequently to keep them free from corrosion, being sure to close them tightly to prevent leaking.
=Cylinder Cocks= are used in connection with the cylinder to allow the water accumulated by the condensing of steam in the cylinder to escape, and should be opened every time the engine is started or stopped. This should never be neglected, as great damage may be caused by the breaking of the follower plate or cylinder head. They should also be left open when engine is shut down, and at night in cold weather to prevent freezing and the consequent damage.
[Illustration: Lunkenheimer Cylinder Cock.]
=A Check Valve= is the valve on the feed pipe between pump or injector and the boiler. The check valve is so constructed that the pressure of the feed water from the pump or injector lifts the valve from its seat and the water passes into the boiler. Immediately after the pressure from the pump or injector is released, the pressure from the boiler closes this valve and prevents the water from being forced back into the pump or injector. There are two check valves used in connection with a pump, one on suction, the other on deliver pipe.
Q. How can check valves that get stuck open be closed?