Absolute Pressure: is
zero-referenced against a perfect vacuum, and is equal to gauge pressure
plus atmospheric pressure, and labeled as p.s.i.a..
Babbitt bearing: Babbitt,
also called Babbitt metal or bearing metal, is any of several alloys
used for the bearing surface in a plain bearing.
The 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 6 tons 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
Frisbie 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
about 1800.
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.
With steam 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.
^Top^
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.
^Top^
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 steamboats.
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 will stop 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 "Kicking Engine".
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 balance.
Two-cylinder compounds can be arranged as:
-
Cross compounds -The cylinders are
side by side.
-
Tandem compounds -The cylinders are
end to end, driving a common connecting rod
-
Angle compounds - The cylinders are
arranged in a vee (usually at a 90° angle) and drive
a common crank.
Triple 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%.
^Top^
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 the boiler.
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.
Steam:
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.
Wet steam:
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.
Steam tables:
Steam Tables
Surface 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.
^Top^
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
temperature.
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 efficiency.
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.