Absolute Pressure: is zero-referenced against a perfect vacuum,
and is equal to gauge pressure plus atmospheric pressure, and labeled
Babbitt bearing: Babbitt, also called Babbitt metal or
bearing metal, is any of several alloys used for the bearing surface in
a plain bearing.
original Babbitt metal was invented in 1839 by Isaac Babbitt in Taunton,
Massachusetts, USA. Other formulations were later developed but Isaac
Babbitt's exact formulation is not known with certainty.
Babbitt metal is most commonly used as a thin surface layer in a
complex, multi-metal structure, but its original use was as a
cast-in-place bulk bearing material. Babbitt metal is characterized by
its resistance to galling. Babbitt metal is soft and easily damaged,
which suggests that it might be unsuitable for a bearing surface.
However, its structure is made up of small hard crystals dispersed in a
softer metal, which makes it a metal matrix composite. As the bearing
wears, the softer metal erodes somewhat, which creates paths for
lubricant between the hard high spots that provide the actual bearing
surface. When tin is used as the softer metal, friction causes the tin
to melt and function as a lubricant, which protects the bearing from
wear when other lubricants are absent.
There are many Babbitt alloys in addition to Babbitt's original. Some
common compositions are:
90% tin, 10% copper, or
89% tin, 7% antimony, 4% copper, or
80% lead, 15% antimony, 5% tin, or
76% copper, 24% lead, or
75% lead, 10% tin, or67% copper, 28% tin, 5% lead
Boiler charging car: A narrow gauge coal dumping rail car moving
of coal from a storage pocket hopper to the coal shoveler for a boiler stoker hopper.
Balanced Poppet Valve: was invented and patented by H. F. Frisbie,
July 23,1884, then owner of the
Engine and Machine Company, Cincinnati, Ohio. A similar
valve called the double-beat valve, the drop valve or
equilibrium valve was invented by Jonathan Hornblower from the UK in
The valve is arranged to allow opening against a high pressure with a minimum of force. The valve has
two valve plugs that ride on a common stem, with the pressure on one
plug largely balancing the pressure on the other. The
force needed to open the valve is determined by the
difference between the areas of the two valve openings. The valve is
balanced when pressure pushes the valve in both directions, both open
and closed, but slightly more in the closed position.
engines the double balance poppet valve was a favorite choice
because it maintained it's ability to handle a large volume steam flow
yet required little force to operate.
Centrifugal "fly ball" Governor: a servomechanism that
adjust the speed of the engine by regulating the amount of process steam
admitted to the cylinder.
As the speed of the engine increases, the central spindle of the
governor rotates at a faster rate and the kinetic energy of the balls
increases. This allows the two masses on lever arms to move outwards and
upwards against gravity.
If the motion goes far enough, this motion causes the lever arms to pull
down on a thrust bearing, which moves a beam linkage connected to the
governor hook rod attached to the knock-off cam on the Corliss valve.
The knock-off cam controls the position when the valve closes
early in the piston travel cycle.
Condensing Steam Engine: for a stationary
steam engine a condensing engine refers to the recovery of the water
from the exhaust steam using a surface condenser to produce condensate,
which allows the engine to operate on absolute pressure as compared to
atmospheric pressure, and increases the thermal operating efficiency.
A steam locomotive condensing apparatus differs in purpose from the
closed cycle steam engine condenser, where its function is primarily
either to recover water, or to avoid excessive emissions to the
atmosphere (important for tunnel operations), rather than maintaining a
vacuum to improve both efficiency and power. It usually takes the form
of a series of pipes, valves and other ancillary equipment usually
attached to an otherwise conventional steam locomotive. The apparatus
takes the exhaust steam that would normally be lost up the funnel and
routes it through a heat exchanger, into the normal water tanks.
Coal passer, brings coal from the coal storage building to the
stokers for the boiler furnace.
Coal dump car:
A two ton capacity narrow gauge coal dumping rail car.
Corliss Valve: Invented by and named after an American engineer
George Henry Corliss in Providence, Rhode Island, the semi rotary
Corliss valve requires very little power to operate and can be opened
and closed very quickly. The valve allows steam into the cylinder
without significant pressure drop which leads to the steam cooling and a
consequential loss of power and thermal efficiency. Another advantage is
that cold exhaust steam does not exit through the inlet valve which
would cool the valve and further reduce thermal efficiency.
Condensate pump / hot well pump
removes water from the hot well and returns it to the boiler pre-heater.
Deaerating: Deaeration is the mechanical process of removing
scale and dissolved gasses such as oxygen, carbon dioxide and other
harmful chemicals from the boiler feed water caused in part by the
boiler tubes. Tap water at standard atmospheric pressure and temperature
contains about 3% air, and process steam contains some of this air along
with other chemicals absorbed from the metal tubing and piping
Dissolved oxygen in boiler feed water will cause serious corrosion damage in steam systems by
attaching to the walls of metal piping and other metallic equipment and
forming oxides (rust). Water also combines with any dissolved carbon
dioxide to form carbonic acid that causes further corrosion.
Dash Pot: is a generic name for a mechanical motion controller or
damper which resists motion via viscous friction. The resulting force is
proportional to the velocity, but acts in the opposite direction,
slowing the motion and absorbing energy. The shock absorber on a vehicle
is a good example.
A steam engine with Corliss valve gearing often used a
specially designed dual cylinder vacuum dashpot to accelerate the closure of the inlet steam
valve rather than slow the motion. Rapid closure was required to
accurately cut-off steam early in the piston cycle to improve thermal
efficiency. A second cylinder compressed air at the end of the stroke to
cushion the stopping forces.
Doctor Pump: aka "boiler feed water pump",
introduced in 1840 and significantly reduced the risk of explosions on
Economizer - used to preheat oiler feed water through a series of
tubes located in the path of effluent gases from a boiler to absorb
waste heat. Patented by Edward Green in 1845, and since then has been
known as a Green's economizer. It consisted of an array of
vertical cast iron tubes connected to a tank of water above and below,
between which the boiler's exhaust gases passed. This is the reverse
arrangement to that usually but not always seen in the fire tubes of a
boiler; there the hot gases usually pass through tubes immersed in
water, whereas in an economizer the water passes through tubes
surrounded by hot gases.
Gauge Pressure: is zero-referenced against ambient air pressure
and is equal to absolute pressure minus atmospheric pressure, and
labeled as psig. Negative signs are often omitted. When steam engines
use a condenser, pressure is often labeled as psig to eliminate
confusion to absolute pressure, p.s.i.a.. The condenser will generally
operate at a very low psia pressure. Since pressure gauges are
referenced to ambient atmospheric pressure, a gauge on a condenser will
often read around -14 psig, but the engine operates on psia.
Governor Rod: connects the fly ball governor to the knock-off cam
on the Corliss valve
Heat of Saturated Liquid: This is the amount of heat required to
raise the temperature of a pound of water from 32°F to the boiling point
at the pressure and temperature shown in the steam table. It is expressed in British
thermal units (Btu).
Hook Rod: connects the eccentric bearing to the steam valve
used on a steam engine.
Knock-Off Cam: a cam attached to the Corliss valve gearing
used to actuate rapid closure of the valve.
Hot well: is the bottom section of a steam condenser
where condensate water settles from the condensing tubes.
Jacking Engine: Also called a "Kicking Engine or a Barring
Engine" is used to rotate an idle reciprocating engine or turbine to
facilitate starting, inspection, or repairs. On occasion a steam engine
at crank-end or head-end dead center and require nudging off dead
center for staring. Often a large metal bar or crowbar was used for this
task thus the phrase "Jacking" or "Barring." On some engines
it is possible to use a person's foot for this task thus the phrase
Latent Heat or Heat of Vaporization: The amount of heat
(expressed in Btu) required to change a pound of boiling water to a
pound of steam. This same amount of heat is released when a pound of
steam is condensed back into a pound of water. This heat quantity is
different for every pressure/temperature combination,
Multiple expansion steam engine.
A single expansion steam engine has one cylinder and can have an
efficiency between 1% and 10%, typically around 8% with enhancements.
Double expansion (usually known as compound) engines expanded the
steam in two stages and increase the operating efficiency over the
single expansion engine. The cylinder pairs may be duplicated or the work of the
large LP cylinder can be split with one HP cylinder exhausting into one
or the other, giving a 3-cylinder layout where cylinder and piston
diameter are about the same making the reciprocating masses easier to
Two-cylinder compounds can be arranged as:
cylinders are side by side.
Tandem compounds -The cylinders are end to end, driving a common
Angle compounds - The cylinders are arranged in a vee (usually at a 90°
angle) and drive a common crank.
expansion extends the double expansion concept into three cylinders,
the HP, the IP and the LP cylinders. When the diameter of the LP
cylinder becomes excessive it was often divided into dual LP cylinders.
On occasion the dual LP cylinder engine would be referred to as a quad
expansion but it was not a four times expansion and remained a triple
expansion engine. The coal to water efficiency of an enhanced triple
expansion engine could reach 25%.
Pocket Hopper: a coal storage bin equipped with a tapered floor
terminating in an adjustable coal spout.
Pre-heater: process steam or exhaust steam is used to preheat the
boiler feed water arriving from the condensate pump prior to re-entering
Re-heater: process steam passing through coils in a receiver to
add additional heat to the expanded steam.
Receiver: temporary storage container for expanded steam
located between stages in an multi expansion engine.
Dry Steam: In early 1900s dry steam was considered to be <5%
liquid however today, 1/2% liquid or less is considered dry.
Flash Steam: When hot condensate or boiler water, under pressure,
is released to a lower pressure, part of it is re-evaporated, becoming
what is known as flash steam.
Process steam: the final steam product leaving the boiler plant
ready for work.
Saturated steam: There is a temperature below which steam will start to
condense into water droplets. This is called the saturation temperature,
and it varies with the pressure of the steam. Steam that is exactly at
its saturation temperature is called saturated steam. Saturated
Steam is pure steam at the temperature that corresponds to the boiling
temperature of water at the existing pressure.
Saturated steam has three main disadvantages in a steam engine: It
contains small droplets of water which have to be periodically drained
from the cylinders; being precisely at the boiling point of water for
the boiler pressure in use, it inevitably condenses to some extent in
the steam pipes and cylinders outside the boiler, causing a
disproportionate loss of steam volume as it does so; and it places a
heavy demand on the boiler because a large amount of water has to be
evaporated per unit volume of steam.
Superheated steam : is steam that is above its saturation temperature.
is in equilibrium with heated water at the same
pressure, i.e. it has not been heated past the boiling point for that
pressure. Steam that
is below its saturation temperature contains droplets of moisture and is
called wet steam.
condenser: is a heat exchanger that removes heat from exhaust steam
and returns it to the liquid state, "condensate".
Sub cooling: is the effect of saturated liquid in the condenser removing
additional heat from the steam as it falls to the hot well. Sub cooling is
a desirable effect to help prevent cavitations of the condensate pump.
Steam chest: A compartment in a steam engine through which steam
is delivered from the boiler to a cylinder.
Steam trap: A steam trap is a device used to discharge condensate and non
condensable gases with a negligible consumption or loss of live steam.
Most steam traps are nothing more than automatic valves. They open,
close or modulate automatically. Others, like venturi traps, are based
on turbulent 2-phase flows to obstruct the steam flow.
Stuffing box: an assembly housing a gland seal that is used
to prevent the leakage of fluid, such as water or steam, between sliding
or turning parts of machine elements.
Super heater: is a device installed inside a boiler used to
convert saturated steam into dry steam, which raises its temperature to
a point where condensation is much less likely and increases its volume
significantly. A super heater can be installed as straight or hairpin
tubes in the upper part of the boiler between the first two steam drums.
The baffles direct the gas-flow through this area first, so it may reach
the highest temperature. A Foster Super heater: is a drawn steel tube with cast iron radial fins heat shrunk onto the
tubing and allows better heat transfer from boiler gases to steam than
tubing without fins.
Sump Pump/Bilge Pump: a pump to remove water from the pump pit caused in part by seepage in
the pit floor and from leakage caused by a leaking gland seal.
Super heater is a device installed inside a boiler used to convert saturated steam into
dry steam, which raises its temperature to a point where condensation is
much less likely and increases its volume significantly. A
super heater can be installed as straight or hairpin tubes in the upper
part of the boiler between the first two steam drums. The baffles direct
the gas-flow through this area first, so it may reach the highest
Steam Jacket: a second circular casing on the outside of an
operating steam cylinder for a steam engine. The jacket circulates
process steam to help keep the interior hot in an effort to reduce
condensation inside the cylinder which will increase thermal operating
Turbining: The removal of scale or other foreign material from
the internal surface of a metallic cylinder.
Wet Air Pump: removes elastic vapors such as air and uncondensed
steam from the surface condenser and will typically operate with an
absolute pressure near zero.
Work Duty/Engine Duty: is the technical measure for the
efficiency of the engine determined by the cost of the work done in fuel
consumed.. Pumping engines are commonly rated by the work done by the
consumption of a specified weight of fuel, as one hundred pounds. A duty
of 100,000,000 foot-pounds, on this basis, would correspond to a
consumption of 1.98 pounds of fuel per horse-power per hour.
The "horse-power," taken in British measure as 33,000 foot-pounds per
minute or 1,980,000 per hour, requires the transformation of the
equivalent amount of heat into work each minute or hour.
The duty of a pumping engine per 1,000 Ibs of steam,
and 1,000,000 heat units; is the rate of a thousand pounds of steam, and
the million heat units that result from a hundred pounds of coal, giving
an evaporation in the boilers to 10 Ibs of steam for each pound of coal
burned on the boiler grates. Which is 10 Ibs of water evaporated into
steam per pound of coal burned on the grates, and equal to 100 Ibs of
coal evaporating 1,000 Ibs. of water into steam.
Water works that use steam engines often have multiple definitions for the
phrase Low Duty or High Duty. Generally speaking the
phrase refers to the
efficiency of the engine as high or low. However, the same phrase is used to describe
the volume of water pumped per engine or per station. At GCWW Low Duty is
low volume water pumping and High Duty
is high volume water pumping.