66. Q. If it is not necessary to take down the main rod of disabled side
of the engine, how would you arrange to lubricate the cylinders?

A. If cylinder and piston are in good shape and it is possible to block
the valve to admit a small quantity of steam into the back end of the
cylinder, oil from the lubricator will go through this opening and oil
the piston rod and cylinder packing. If not possible to block the valve
properly, cover the ports and oil the cylinder through the indicator
plug openings or relief plug holes. If not possible to do this, slack
off the bolts on the front cylinder head, wedge the head open so oil can
be introduced. In some cases it may be necessary to take the head off;
that however, allows dust and grit to enter the cylinder.

67. Q. What is the by-pass valve, and what is its duty?

A. By-pass valves are connected to the steam port leading to the
cylinder. Its duty is to open when the engine is drifting with steam
shut off, and close when working steam, to allow air to pass back and
forth from opposite sides of the moving piston.

68. Q. What is a vacuum relief valve? What a cylinder relief valve?

A. A vacuum relief valve is usually located on the steam chest or the
live steam passage to the chest and opens when steam is shut off and
engine drifting, allowing atmospheric pressure to pass into the steam
chest, closing when working steam. A cylinder relief valve is a pop
valve screwed into the cylinder head and set at high enough pressure so
it does not open in ordinary service, but will open to allow water to
pass out when the exhaust port is closed by valves; or on compound