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- Plumbing fitting for controlling flow, and changing direction
90 degrees. General construction is the same as a globe valve.
Ash Hoe - Short
handled tool used to remove ashes from grates and ashpans.
Ash Pan - Area
of firebox under the grates. Collects unburned residue from fire
and acts as an air passage for the flow of oxygen to the underside
of the fire.
Axle - Shaft
supporting a wheel.
- A soft metal alloy with a high lead content used for friction
bearing sufaces. The moving component is suspended within the supporting
component, the edges packed with clay, and then the Babbitt melted
and poured into the cavity. When cool, the edges are smoothed and
the bearing is ready.
Backhead - Rear
flat face of a return flue or locomotive style boiler.
Baker Fan -
A testing device that uses wind resistance to create a load for
- A slide valve that uses a chamber vented to the exhaust port to
relieve pressure on the main valve.
Bell Crank -
A lever that changes the direction of a mechanical movement.
Belt - A loop
of canvas, rubber, or leather used to transmit power between pulleys.
- The act of releasing water from a boiler. Venting boiler water
and replacing it with fresh feedwater can help correct chemical
imbalances in the boiler water, by lowering the average contaminant
load. Also refers to using residual steam pressure in a nearly cool
boiler to dump all the water out quickly.
- Valve located near bottom of boiler, used for blowing down and
draining the boiler.
Blower - Steam
jet directed up the stack. Used to force a draft through the boiler
to speed the raising of steam pressure, or to help eliminate smoke.
Boiler - Pressure
vessel used to heat water to steam.
Bore - Inside
diameter of cylinder
Brace - Support
member joining backhead or front tube sheet to wrapper or barrel.
Used to resist the distorting effects of the pressure of the steam
and to hold the supported sheet flat.
Brass - 1) Copper/tin
alloy known for its free-machining properties 2) bearing section
made of brass. Brasses are often used on connecting rods, and are
sometimes themselves lined with Babbitt.
Brick Arch -
A ceramic structure installed in the fireboxes of straw burning
engines to direct the flames back into the fuel.
Bull Gear -
Large gear attached to driving wheels.
Bunker - Box
mounted on engine platform to carry fuel.
Butt Strap -
Style of boiler construction where the barrel of the boiler is rolled
so that the edges meet, but do not overlap. The joint is made be
sandwiching the edges between two strips of metal, with the rivets
going through all three layers. Butt-strap construction is thought
to be inherently stronger than lap-joint construction.
- Housing used to protect the operator from the elements. Usually
covers only the platform area, and has some sort of sides, and sometimes
windows. Full length cabs are usually called canopies, although
Port Huron built some engines with combination cab/canopies.
- Large casting that contains either the drive countershaft or the
Canopy - Flat
roof structure used to protect the engine and operator from the
elements. Sometimes included a detachable curtain to surround the
engine when not in use.
Cellar - Cavity
in a bearing designed to hold a supply of lubricant. Sometimes filled
with cotton waste to act as a wick or to regulate the flow.
- Globe type valve that allows flow in one direction, but automatically
shuts when flow is reversed. Used primarily on feedwater lines and
mechanical lubricator feeds.
Cinder - Unburned
residue from a coal fire.
Clinker - Unburnable
residue from a coal fire, composed of non-burning impurities that
melt out of the coal and then fuse together on the grates or in
the ashpan. Enough clinker can choke off the air flow, causing the
fire to burn inefficiently and the grates to heat.
Coal - Petrified
vegetable matter used as a fuel. Contains more potential heat energy
than wood for a given volume, but requires some modification of
the firebox to be burned efficiently.
Compound - Engines
that utilize steam more than once by using the exhaust steam from
one cylinder as inlet steam for a second, larger cylinder.
- Lubricator that continually feeds grease by means of a spring-loaded
A method of heat transfer, in which heat energy is passed directly
from one object to another, adjacent object.
- Part of the reciprocating engine. Connects the crosshead to the
A method of heat transfer, in which heat energy is carried by the
flow of gases or fluids.
- A type of engine that uses the same ports for both inlet and exhaust,
causing the steam to flow first one direction, then reverse.
- Any shaft that crosses the boiler centerline to transmit rotary
force to the other side of the machine.
Course - A length
of the boiler's main barrel. Most steam tractor boiler barrels were
built from a single sheet of iron, but some were built up of two
or more shorter sections.
Crank Disc -
The disc on the end of the crankshaft that holds the crank pin.
Often is shaped to provide a counterbalance to the weight of the
Crank Pin -
Pin in the crank disc that holds one end of the connecting rod,
and is used to convert the reciprocating motion of the connecting
rod to rotary motion.
Main shaft of the engine. Usually has the crank disc on one end,
the flywheel on the other, and the valve eccentric, clutch, etc,
Supports the outside end of the piston rod and controls the off-axis
motion of the piston end of the connecting rod.
- Rigid frame that contains the cross head and controls its travel.
Can be cast integral to the cylinder, be bolted on as a separate
casting, or be built up of four ground bars.
- Feedwater pump actuated by a plunger connected to the crosshead.
Usually is a simple displacement design.
- Top side of the firebox. Tends to be the hottest part of the boiler,
and a significant proportion of the steam is generated here, compared
to its relative surface area.
Crown Stay -
Staybolt that runs between the crown sheet and the top curve of
the wrapper. Supports the crown sheet against the internal pressure
of the boiler.
Cylinder - Hollow
casting that contains the piston.
- Drain valve used to allow recondensed steam to be drained from
- Cast cover for the end of the cylinder.
- Most common type of slide valve, named for its cross sectional
form. The center portion stays in communication with exhaust port,
with the cylinder ports being alternatingly opened to the exhaust,
or opened to the steam chest.
- Term used to describe the two points is the engine's cycle where
the center of the crankshaft and the center of the crank pin are
in line with the center of the crosshead. The dead centers are purposely
used as reference points when setting valve gears, and accidently
encountered when operating single cylinder machines. The engine
can't start running without assistance if it happens to stop at
or near one of the dead centers.
Dead Plate -
Flat plate of steel used to cover one end of the grates, blocking
off the flow of air through that area. It is intended to protect
the lower tubes from being cooled by holes in the end of the fire.
- Device used to compensate for the different rates of travel of
the rear wheels as the engine negotiates a turn. Power is transmitted
to the ring gear, which then uses small bevel gears to pass power
to the two large bevel gears connected to the drivers. When making
a turn, the small gears rotate, and allow the drivers to travel
at whatever speed is required to maintain a balance of power.
- Measurement of the volumetric space within a cylinder occupied
or vacated by a piston or a plunger. Figured by multiplying the
area of the piston by the length of travel.
Dome Valve -
Valve on steam dome used to shut off steam to the throttle or engine.
Draft - The
flow of fresh air through a fire or boiler. Can refer to natural
draft or forced draft.
Draft Door -
Usually located at the rear of the ashpan, the flow of fresh air
to the fire can be adjusted by opening or closing the draft door,
thus regulating the fire.
Drain Cock -
A small valve used to empty plumbing fittings of collected water.
Drawbar - Main
attachment point for pulled implements.
Driver - Powered
wheel on traction units.
Dry Bottom -
Boiler design that has only a sheet of metal as the floor of the
ashpan, as opposed to a water space. Main benefit is ease of retubing,
as you can remove the ashpan for easy access to the firebox ends.
Main drawback is it's harder to wash sediment out of the corners
of the waterlegs.
Dry Pipe - Pipe
running from inside the steam dome to another point on the boiler
shell, and then out to the throttle. So called since the steam within
the pipe is thought to be dryer (less saturated) then the steam
- Round disc casting with an off-center mounting, similar to a cam.
Used to provide motion for valve gear.
- Circular casting that surrounds an eccentric.
Ejector - Steam
jet device that uses the venturi effect to lift water and send it
into a tank at atmospheric pressure.
- Corrosion process driven by galvanic currents caused by dissimilar
metals submerged in a fluid.
- Fluid involved in an electrolytic process.
Engine - Power
producing components on a steam tractor or portable unit. Also can
refer to the tractor or portable as a whole.
- End of the exhaust steam pipe, directed up the stack with a final
restriction in diameter to provide sufficient backpressure to create
forced draft. Different diameters are used for different fuels.
- One cubic foot of water will create 1700 cubic feet of steam at
atmospheric pressure. Containing the steam within a smaller volume
will cause it to pressurize the container. The difference between
the pressure within the container and the atmospheric pressure outside
the container can then be converted into useful work.
- When heated, metals expand slightly, and contract when cooled.
Different metals expand at different rates. The expansion of the
metals must be taken into account when designing an engine (i.e.:
railroad locomotive boilers are built so that one end can slide
on the frame), or can be used, such as the use of brass fittings
- brass expands at a greater percentage than iron, so a brass-within-iron
joint is tighter when hot than when cold.
- Additional section of a driver, used to add width, increasing
traction and decreasing soil compaction.
- Fresh water added to replace the water lost by the consumption
- Device used to transmit residual heat energy in exhaust steam
to incoming feedwater.
Fire - Actively
burning fuel, used to heat the boiler water into steam.
- Fuel, Heat, and Oxygen. A fire must have all three to successfully
Firebox - Section
of the boiler that contains the fire.
Flanging - Metalworking
process for folding the edges of a sheet of steel, including smooth
folds around curved edges.
Flue - Boiler
tube. Term is often used to refer to all boiler tubes, but is more
correctly used to refer to tubes of 3" diameter and larger.
Smaller boiler tubes are just tubes.
- Device used to clean soot and other debris from inside boiler
Flywheel - Heavy
cast iron wheel used both to store rotary momentum and as a belt
- Device that pushes wooden shoes against the inside of the flywheel,
so that they will grip and turn a pinion, thus sending power to
the traction gearing.
Fuel - The type
of combustible used by an engine.
- A brass plug with a tin center mounted in the crown sheet as a
safety device. If the crown sheet is exposed above water level for
too long, the plug will heat up, melting the tin and releasing steam
into the firebox, theoretically extinguishing the fire before the
crown sheet sustains heat damage.
Gasket - A flat
cutout of some soft material used to create a tight joint between
two flat objects.
Gate Valve -
A plumbing fitting that controls flow by sliding a disc across the
flow. Used when uninterrupted flow is desired, and throttling flow
is not common.
- A plumbing fitting that controls flow by means of a tapered cover
over a tapered seat. Used when throttling is frequent or in situations
where debris in the flow is common.
Governor - Device
used to control the RPM of an engine. Typically uses the centrifugal
force generated by spinning balls to push a valve closed.
Grates - Cast
iron frames that support the fire.
Grease - Viscous,
Grease Cup -
Lubricator consisting of a threaded cup and funnel. The cup holds
a supply of grease, and by manually turning it on the funnel the
grease is forced through the funnel and into the bearing.
Grouter - Cast
steel lug bolted or riveted to a driver.
- Opening in the boiler shell used for washing and inspection purposes.
Head - Circular,
flat end of a tubular pressure vessel.
- The process of transmitting energy from one item to another, in
the form of accelerated molecular motion.
A unit of measurement designed to indicate the power of a machine,
using a theoretical animal as a baseline. Generally described as
equaling 33,000 foot/pounds per minute, meaning that a one hp engine
should be able to reliably lift a 33,000 pound weight one foot over
the course of a minute. See a discussion of steam tractor horsepower
ratings here [horsepower page].
Hub - Center
of a wheel, gear, or pulley.
- A device used to plot a graph measuring cylinder pressure and
piston travel. Can be used to detect internal troubles, or to ascertain
the most economical valve settings.
- The paper chart produced by an indicator.
Injector - A
device that uses a steam jet and the venturi effect to lift fresh
feedwater from a tank and into a boiler.
- Valve arrangement that places the inlet steam ports towards the
middle of the valve, and the exhaust ports to the ends.
- Idler gear that transfers power from the crankshaft pinion to
the differential gear on most traction engines.
- Sheet metal shroud that covers a majority of the boiler. Intended
mostly to protect the lagging, but also often improves the look
of an engine, and makes cleaning the boiler easier.
Jam Nut - A
second nut on a bolt, designed to wedge against the first nut and
- Insulation for a steam boiler. Can be wooden slats, ceramic fiber,
Lap Seam - Type
of boiler construction in which the barrel is rolled so that the
edges pass each other, and are then riveted together. This method
was simpler and cheaper than butt-strap construction, but is thought
to produce an inherently weaker joint.
Locomotive Style Boiler
- Type of steam boiler that features a round topped square firebox,
a cylindrical horizontal barrel, and a cylindrical smokebox.
- A device that feeds oil into a bearing via gravity and a needle
valve for control.
- A device that feeds steam cylinder oil into the throttle piping.
The oil is displaced from the reservoir by condensed steam and passes
through a needle valve and sight glass for regulation.
- A device that uses motion from the engine to drive a piston pump
that forces steam cylinder oil into the throttle line.
- Term used to refer to the manufacturer of a group of items.
Mud Drum - A
cylindrical extension of the boiler, similar to a steam dome, located
underneath the barrel. The purpose was to provide a gathering place
for sediments to simplify boiler washing, although it worked better
in theory than in practice.
Mud Ring - see
- Refined petroleum, used to lubricate moving parts other than those
within the steam flow.
- Valve arrangement that places the exhaust steam ports towards
the middle of the valve, and the inlet ports to the ends.
- Fresh air admitted to the firebox above the grate line, for the
purpose of more complete combustion of furnace gases.
- Soft material compacted against a moving part, designed to form
a seal between the steam and the atmosphere.
- Chamber that contains the packing material. Includes the nut or
cover, and the follower.
Pedestal - Name used to refer to the front axle/boiler support.
Usually is an inverted pyramid terminating in a ball joint that
forms the pivot for the steering axle.
Peephole - Small
port on the side of the firebox used to inspect the forward part
of the fire, or to see above the brick arch if installed.
Pinion - A small
gear used to drive a larger, slower turning gear.
Piston - Disc
within the cylinder that is driven back and forth by the steam.
Piston Rod -
Shaft that connects the piston to the crosshead.
- Valve that is shaped somewhat like a spool, with ports being located
in the side of a cylinder wall, rather than the flat faces of a
D-shaped slide valve. Main benefit is that since the valve is not
being forced against its seat by the incoming steam pressure, there
is less power lost to friction, and higher boiler pressures are
possible without causing excessive wear on the valve.
Platform - Operating
floor for the engineer.
Poker - Hooked
probe used to rearrange wood fuel for more efficient burning.
Pop Valve - Spring
loaded plumbing device that vents steam to the atmosphere when the
boiler pressure exceeds a preset limit. Automatically shuts off
after the boiler pressure drops a certain amount.
Portable - Boiler
and engine unit mounted on skids or wheels, for use in more or less
temporary locations. Not able to propel itself.
- Chamber mounted above a displacement pump that provides an air
pocket to regulate output pressure.
- Device used to measure horsepower produced by an engine. Consists
of a belt-driven drum with a band brake that pushes against a scale.
A formula involving the RPM of the drum vs. the resistance of the
brake as measured by the weight shown on the scale yields the horsepower.
- A semi-circular bracket that provides a place for lever latches
to engage, generally on throttle, clutch, and reverse levers.
- A method of heat transfer in which heat energy travels directly
from the fire to the firebox or tubes by infrared waves.
Rear Mount -
Refers to tractors in which the rear axle is mounted behind the
boiler, and is generally a solid shaft running the full width of
Receiver - Chamber
in a cross-compound engine that accepts the exhaust steam from the
high pressure cylinder, and holds it until the inlet valve opens
for the low pressure cylinder.
- See Pop Valve
- System of eccentrics, levers, and cranks used to actuate the engine's
valve that can be altered to make the engine run in either direction.
- Lever used to control the reverse gear.
Rivet - Pin
used to join sheet metal together. A hole is drilled or punched
in both pieces, the pin is pushed through the holes, and then the
protruding end is hammered or swedged over, locking the pin in place.
- Grates mounted on pivots and joined to a lever so that they may
be rotated back and forth somewhat. Used on coal burning boilers
to help break up and clear clinker.
RPM - Revolutions
Per Minute, a measurement of rotative speed.
- Plank attached to the boiler below the cylinder area. Provides
a place for the engineer to stand while maintaining the engine.
- See Pop Valve
Schedule 40/Schedule 80
- ASME specifications for pipe pressure ratings and wall thicknesses.
Schedule 40 is commonly used for household plumbing and its cast
iron fittings are good for 125 PSI or so. Schedule 80 has a greater
wall thickness, and thus is more able to withstand internal pressure
and retains more wall thickness after threads are cut. Schedule
80 cast iron fittings are rated for up to 300 PSI, and thus are
a better choice for boiler work.
- Unique number given to the engine by its maker for record purposes.
Shim - Thin,
flat piece of metal used to take up lost motion or removed to allow
for wear. Often is cut to conform to the outline of the piece it
is used with.
Side Mount -
Refers to tractors in which the rear axle is mounted on brackets
studded to the sides of the boiler, and is generally two short shafts,
one on either side.
- Glass tube used to visually check the water level in a boiler.
Simple - Engine
in which the steam is expanded once before being vented to the atmosphere.
- Operating lever for a simpling valve.
- Special valve on a compound engine that sends boiler pressure
steam to both the high and low pressure cylinders, turning it into
a double cylinder engine. This is done during startup to warm the
engine, or when circumstances require extra power, albeit at the
risk of a snapped crankshaft.
Siphon - 1)
Plumbing fitting that uses water to insulate the steam gauge from
the heat of the steam. 2) See Ejector.
Skid Ring -
Rib on the steering wheel intended to help prevent sliding sideways
when driving through mud, improving handling.
- Valve in which the valve and its seat have matching flat faces,
with the pressure of the steam within the steam chest holding the
valve tight against the seat.
Smokebox - Chamber
of the boiler in which the tubes end, and the fire gases turn and
go up the stack.
tube that carries the exhaust steam and fire gases up and out of
Soft Plug -
See Fusible Plug.
Spark - Small
particle of burning material pulled off of the main fire by the
- Screen-like device within the smokestack intended to prevent the
sparks from escaping the stack. Often includes some sort of hopper
to contain the trapped solids.
- Portion of the governor used to set the target RPM, generally
by adjusting the effective length of the governor valve stem.
Stack - See
- Cap placed over the smokestack when boiler is not being fired.
Prevents rainwater from entering the smokebox and causing corrosion.
Staybolt - Rod
threaded through firebox and boiler shell, used to support the boiler
plating against the internal steam pressure.
- A extra long thread cutting tool used to thread both inner and
outer sheets in one operation, thus ensuring that the threads will
be in time from one hole to the other.
Steam - Gas
phase of Dihydrous Oxide.
- Boxlike formation on the side of the cylinder containing the valve
and boiler pressure steam.
Steam Cylinder Oil
- Mixture of mineral oil and beef tallow used to lubricate moving
parts within the high temperature environment of the steam flow.
Steam Dome -
Raised section of the boiler. Designed to vertically separate the
output valves for the steam from the water level, to reduce the
possibility of drawing solid water into the engine.
- Device used to indicate the internal steam pressure in PSI, Pounds
per Square Inch.
- Openings in the valve seat face that lead to the cylinder.
- Chain connecting the ends of the front axle to the winch used
to steer the engine.
Straw - Dried
stems of grain bearing grasses, part of the waste product after
threshing wheat, oats, etc. Can be baled for use elsewhere, or burned
in boilers equipped for the purpose.
Stroke - Length
of piston travel.
- Device that routes the steam flow to the engine through pipes
within the boiler flues, thus allowing the steam to pick up additional
heat energy. Superheaters before the throttle are referred to as
"wet", and superheaters after the throttle are known as
"dry". Superheated steam tends to be hotter and more expansive
than saturated steam, and causes less condensation within the cylinder,
thus improving the efficiency of the engine.
- Lubricant made from animal fat. Used in steam cylinder oil because
it can withstand the high temperatures without burning inside the
Tandem - Style
of compound engine that places both high and low pressure cylinders
in line, on a common piston rod. This arrangement takes advantage
of the gains in efficiency that compounding provides, without making
the valve gear more complex. However, counterbalancing the greater
weight of the reciprocating parts is more of an issue, and the probability
of a single cylinder engine to stop at dead center is unaffected.
Tender - Cart
for fuel and water more or less permanently attached to a steam
tractor. These often had some sort of linkage to the front axle
so that the tender was self steering when backing, instead of acting
as a trailer.
- The science and study of work, as expressed by heat transfer.
- Section of a locomotive style boiler shell just in front of the
Throttle - Lever
operated fast acting valve used to control steam supply to the engine.
Through Stay - Staybolt running the entire length of a boiler, generally
with nuts on the exterior side of both ends of the boiler. Supports
the front and back heads of the boiler against the internal steam
Tractor - Steam
engine capable of propelling itself, plus a load.
Tricock - Small
globe valve generally located next to the water sight glass, used
to verify water level inside the boiler. Operated by cracking the
valve open, and judging if it's steam or water coming out.
Tube - Thin
wall pipe running the length of a boiler barrel, from firebox to
smokebox. Hot gases from the fire pass through the tubes, which
conduct the heat to the surrounding water.
Tube Sheet -
In a locomotive style boiler, the front of the firebox and the front
head of the boiler are punched for a number of boiler tubes.
- Refers to tractors in which the rear axle is mounted to a frame
that the boiler sits on.
Uniflow - A
style of cylinder that places the exhaust port at the center of
the piston travel and the inlet ports on either end, so that no
energy is wasted requiring the steam to physically reverse the direction
of its flow.
- System of eccentrics, levers, and cranks used to actuate the engine's
valve. Includes both single direction and reversing types.
Valve Lap -
The amount that a valve overlaps the port edges when centered.
Valve Stem -
The valve's equivalent to a piston rod.
- The ability of flowing liquids and gases to create a partial vacuum
when temporarily speeded up by passing through a briefly narrowed
- Steam boiler in which the tubes are oriented up and down, with
a circular firebox at the bottom.
- Large threaded plug, usually brass, placed in locations on the
boiler that are advantageous for washing sediment from the boiler.
Plugs tend to be easier to remove and replace than hand holes.
- Byproduct of textile industry. Consists of loose, unwoven scrap
thread that can be used as a large, shapeless wick to hold or meter
oil flow in open bearings.
Water - Liquid
phase of Dihydrous Oxide, H20.
- Cast iron plumbing fitting on which water sight glass and tricocks
Water Leg -
Area between firebox and outer boiler shell.
Water Tank -
Reservoir for water mounted to an engine.
- Independent trailer used to carry several hundred gallons of fresh
water, and often fuel storage as well. Usually a four wheeled wagon.
Wet Bottom -
Type of locomotive style boiler that includes a water space under
the ashpan. Benefits include ease of washing sediment out, drawbacks
include a much more confined space inside the firebox during major
Whistle - Signal
device that operates much like an organ pipe, using steam to produce
a fairly clear tone.
- Steam flowing through too narrow of a passage sometimes briefly
condenses to water and rexpands.
Wood - Commonly
Worm Gear -
Cylindrical gear with one spiral tooth traveling the length of the
gear. Used to transmit rotary motion to a shaft that is perpendicular
and not in the same plane.
Wrapper - Section
of a locomotive style boiler that forms the outer shell of the firebox