Glossary Terms
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Angle Valve - 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.
Babbitt - 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 an engine.
Balanced Valve - 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.
Blowing down - 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.
Blowdown Valve - 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.
Cab - 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.
Cannon bearing - Large casting that contains either the drive countershaft or the rear axle.
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.
Check Valve - 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.
Compression Cup - Lubricator that continually feeds grease by means of a spring-loaded device.
Conduction - A method of heat transfer, in which heat energy is passed directly from one object to another, adjacent object.
Connecting Rod - Part of the reciprocating engine. Connects the crosshead to the crank disc.
Convection - A method of heat transfer, in which heat energy is carried by the flow of gases or fluids.
Counterflow - A type of engine that uses the same ports for both inlet and exhaust, causing the steam to flow first one direction, then reverse.
Countershaft - 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 connecting rod.
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.
Crankshaft - Main shaft of the engine. Usually has the crank disc on one end, the flywheel on the other, and the valve eccentric, clutch, etc, in between.
Crosshead - Supports the outside end of the piston rod and controls the off-axis motion of the piston end of the connecting rod.
Crosshead Guides - 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.
Crosshead pump - Feedwater pump actuated by a plunger connected to the crosshead. Usually is a simple displacement design.
Crown Sheet - 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.
Cylinder Cock - Drain valve used to allow recondensed steam to be drained from the cylinder.
Cylinder Head - Cast cover for the end of the cylinder.
D Valve - 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.
Dead Center - 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.
Differential - 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.
Displacement - 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 surrounding it.
Eccentric - Round disc casting with an off-center mounting, similar to a cam. Used to provide motion for valve gear.
Eccentric Strap - 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.
Electrolysis - Corrosion process driven by galvanic currents caused by dissimilar metals submerged in a fluid.
Electrolyte - 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.
Exhaust Nozzle - 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.
Expansion, Steam - 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.
Expansion, Thermal - 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.
Extension Rim - Additional section of a driver, used to add width, increasing traction and decreasing soil compaction.
Feedwater - Fresh water added to replace the water lost by the consumption of steam.
Feedwater Heater - 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.
Fire Triangle - Fuel, Heat, and Oxygen. A fire must have all three to successfully burn.
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.
Flue Scraper - Device used to clean soot and other debris from inside boiler tubes.
Flywheel - Heavy cast iron wheel used both to store rotary momentum and as a belt pulley.
Friction clutch - 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.
Fusible Plug - 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.
Galvanic Action
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.
Globe Valve - 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, paste-like lubricant.
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.
Hand Hole - Opening in the boiler shell used for washing and inspection purposes.
Head - Circular, flat end of a tubular pressure vessel.
Heat Transfer - The process of transmitting energy from one item to another, in the form of accelerated molecular motion.
Horsepower - 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.
Indicator - 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.
Indicator card - 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.
Inside Admission - Valve arrangement that places the inlet steam ports towards the middle of the valve, and the exhaust ports to the ends.
Intermediate Gear - Idler gear that transfers power from the crankshaft pinion to the differential gear on most traction engines.
Jacket - 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 prevent loosening.
Lagging - Insulation for a steam boiler. Can be wooden slats, ceramic fiber, or asbestos.
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.
Lubricator, Drip - A device that feeds oil into a bearing via gravity and a needle valve for control.
Lubricator, Hydrostatic - 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.
Lubricator, Mechanical - A device that uses motion from the engine to drive a piston pump that forces steam cylinder oil into the throttle line.
Make - 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 Skid Ring
Oil - Refined petroleum, used to lubricate moving parts other than those within the steam flow.
Outside Admission - Valve arrangement that places the exhaust steam ports towards the middle of the valve, and the inlet ports to the ends.
Overfire Air - Fresh air admitted to the firebox above the grate line, for the purpose of more complete combustion of furnace gases.
Packing - Soft material compacted against a moving part, designed to form a seal between the steam and the atmosphere.
Packing Gland - 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.
Piston Valve - 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.
Pressure Dome - Chamber mounted above a displacement pump that provides an air pocket to regulate output pressure.
Prony Brake - 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.
Quadrant - A semi-circular bracket that provides a place for lever latches to engage, generally on throttle, clutch, and reverse levers.
Radiation - 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 the tractor.
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.
Relief Valve - See Pop Valve
Reverse Gear - 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.
Reverse Lever - 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.
Rocking Grates - 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.
Running Board - Plank attached to the boiler below the cylinder area. Provides a place for the engineer to stand while maintaining the engine.
Safety Valve - 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.
Serial Number - 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.
Sight Glass - 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.
Simpling Lever - Operating lever for a simpling valve.
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.
Slide Valve - 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.
Smokestack -Vertical tube that carries the exhaust steam and fire gases up and out of the boiler.
Soft Plug - See Fusible Plug.
Spark - Small particle of burning material pulled off of the main fire by the draft.
Spark Arrestor - 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.
Speed Control - Portion of the governor used to set the target RPM, generally by adjusting the effective length of the governor valve stem.
Stack - See Smokestack.
Stack cover - 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.
Staybolt Tap - 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.
Steam Chest - 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.
Steam Gauge - Device used to indicate the internal steam pressure in PSI, Pounds per Square Inch.
Steam Ports - Openings in the valve seat face that lead to the cylinder.
Steering Chain - 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.
Superheater - 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.
Tallow - Lubricant made from animal fat. Used in steam cylinder oil because it can withstand the high temperatures without burning inside the engine.
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.
Thermodynamics - The science and study of work, as expressed by heat transfer.
Throat Sheet - Section of a locomotive style boiler shell just in front of the firebox.
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 pressure.
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.
Under Mount - 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.
Valve Gear - 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.
Venturi Effect - The ability of flowing liquids and gases to create a partial vacuum when temporarily speeded up by passing through a briefly narrowed passage.
Vertical Boiler - Steam boiler in which the tubes are oriented up and down, with a circular firebox at the bottom.
Washout Plug - 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.
Waste, Cotton - 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.
Water Column - Cast iron plumbing fitting on which water sight glass and tricocks are mounted.
Water Leg - Area between firebox and outer boiler shell.
Water Tank - Reservoir for water mounted to an engine.
Water Wagon - 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 maintenance.
Whistle - Signal device that operates much like an organ pipe, using steam to produce a fairly clear tone.
Wiredrawing - Steam flowing through too narrow of a passage sometimes briefly condenses to water and rexpands.
Wood - Commonly available fuel.
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 area.