our-cylinder
tandem has four cylinders, the high pressure being ahead of the low
pressure on each side, and both pistons connected to one piston rod and
one cross-head. A balanced compound has four cylinders, the two
high-pressure cylinders being between the frames, each having a main rod
connected to a crank axle. The two low-pressure cylinders are located
outside the frame, each having a main rod and crank pin connected to
the driving wheel center. A Mallet compound consists of two separate and
independent engines, one fixed to the boiler, the other swinging from a
center and sliding back and forth under the front end of the boiler. The
rear engine works steam at high pressure; steam from this engine
exhausts through a receiver pipe having flexible joints to the forward
engine which works the steam at low pressure, then exhausts it to the
front end and stack.

27. Q. How many main steam valves has each type?

A. The Vauclain has one valve on each side, distributing steam to the
high and low-pressure cylinder on that side. The four-cylinder tandem
has two valves on each side, one for each of the two cylinders. A
Baldwin balanced compound has two valves the same as the Vauclain. The
American balanced compound has four valves, one for each cylinder, the
two valves for one side of the engine being connected to one valve rod.
A Mallet compound has a separate valve for each cylinder the same as a
simple locomotive.

28. Q. How do you test for blow in high and low-pressure cylinder
packing for each type of compound engine?

A. Simple the engine if a cross compound, then make test the same as for
a simple engine. For Vauclain four-cylinder compounds, test low pressure
first. A blow past the low-pressure piston will show the same as on a
simple engine; a blow past the high-pressure piston will make the engine
stronger on that side when working a full throttle and the exhaust from
the low-pressure cylinder will be heavier. To test the valve on either
side, cover the ports. Broken packing rings in the steam valve will show
a blow in one position and be tight in another. For tandem compound, to
test high-pressure piston packing, stand engine on the top quarter,
lever in back gear, drivers blocked and starting valve closed; remove
back indicator plug or open back cylinder cock of high-pressure
cylinder. Steam coming from the back cylinder cock must get by the
piston packing or by-pass or starting valve. Now put reverse lever a