Heat Engines, Prime Movers & The Simple Steam Engine

Front 1

What are Energy Transfer Systems designed to do?

Back 1

These systems are designed to take a natural, and available, source of energy at one location and deliver it to another location as useful energy. If the distance is large, the energy may have to be transformed into intermediate forms along the way.

Front 2

Define Engine

Back 2

A machine designed to convert some form of energy into mechanical work.

Front 3

Define Heat Engine

Back 3

An engine that uses heat energy from a fuel, in a thermodynamic process, to produce mechanical work.

Front 4

To what scopes can the term Heat Engine apply?

Back 4

- Single Devices

- Systems

Front 5

How do Heat Engine Single Devices work?

Back 5

In each of these a fuel is burned to produce heat in a working fluid (combustion gases and air). This heat, combined with the internal design of the engine, initiates a thermodynamic process in the working fluid, which produces mechanical work at the engine shaft.

Front 6

Describe Heat Engine Systems

Back 6

The system may contain several, seperate devices, which together have the same result as a single heat engine, e.g. typical power plant system. Fuel is burned in a boiler to produce heat, which is used to produce steam; the steam passes through a steam turbine, which produces mechanical work (to turn a generator).

Front 7

Define Prime Movers

Back 7

A single device that converts any source of energy into mechanical motion. The energy source might be electrical, pressure, heat, etc. Often referred to as the driver.

Front 8

What energy sources are used for large-scale production of power?

Back 8

- Solids

- Liquid and gaseous carbon-based fuels

- Water power

- Nuclear energy

Front 9

Why are steam plants so widely used eventhough they are large and complex?

Back 9

They are able to burn solid fuels such as coal, wood and biomass. In addition, their cycle of operations has the highest overall efficiency.

Front 10

What is currently used instead of Steam Engines?

Back 10

Steam turbines, combustion engines, and electric motors.

Front 11

What are the specialized applications of Steam Engines?

Back 11

a. When slow rotational speed, without the use of reduction gearing, is required. Motors, turbines and combustion engines are essentially highspeed devices.
b. When reversal of rotational direction, without the use of gearing, is required.
c. For driving reciprocating pumps. The piston and cylinder design of steam engines has been well suited to the simple and rugged construction of these pumps.

d. In vintage museums

Front 12

Through which valve does steam enter from the main steam pipe into the steam chest of a steam engine?

Back 12

Throttle Valve

Front 13

What is the function of the Slide Valve?

Back 13

The slide valve controls the steam admission and exhaust to and from the engine cylinder.

Front 14

Describe the motion of the slide valve with regard to the piston.

Back 14

The slide valve has a reciprocating motion timed to match the motion of the piston and imparted by the valve gear.

Front 15

What does the valve gear consist of?

Back 15

1. Eccentric

2. Eccentric Rod

3. Valve Rod

Front 16

How is steam admitted to the piston by the slide valve?

Back 16

The steam is admitted above the piston to give a downward thrust and then below the piston to give an upward thrust. In each case the steam supply is cut off when the piston has made only part of its stroke, this may be 1/4 to 1/3 depending upon the engine load. The steam then in the cylinder maintains a thrust on the piston by expanding throughout the remainder of the stroke. Finally the slide valve opens a passage to the exhaust and allows the steam on this side of the piston to escape in preparation for the return stroke under the action of live steam on the other side of the piston.

Front 17

What does the term "expansive" use of steam mean?

Back 17

The principle of cutting off the steam supply and allowing that in the cylinder to expand is termed “expansive” use of the steam and results in economical operation.

Front 18

When is expansive use of steam not implemented?

Back 18

Very few steam engines continue steam admission throughout the whole stroke. This will only be the case where reliability of operation is most important and economy is not a consideration.

Front 19

What is the eccentric?

Back 19

The eccentric is a disc fixed on the crankshaft in such a way that the center of the disc is “eccentric” or “out of center” with the center of the shaft.

Front 20

Which part of the eccentric is called the sheave?

Back 20

The disc which is made into two halves secured by bolts and split cotter pins.

Front 21

What part of the eccentric is called the strap?

Back 21

The band surrounding the sheave.

Front 22

Describe the motion of the sheave.

Back 22

The sheave rotates inside the strap in the same way as the crankpin rotates in the connecting rod head. The eccentric rod is attached to the strap, and the slide valve receives a reciprocating motion from it, similar to that received by the piston from the crank pin, but on a reduced scale.

Front 23

Describe the effect of the steam on the piston.

Back 23

As the valve moves endwise on the valve seat steam is allowed to flow through passages called steam ports into or out of the cylinder. When the piston has steam at boiler pressure on one side it is open to a lower pressure on the other side and the difference between these pressures on its two sides causes it to move along the cylinder transmitting its force through the piston rod, the connecting rod and the crank pin to the crankshaft.

Front 24

Describe the function of the Crank Pin.

Back 24

The reciprocating motion of the piston is changed to a rotary motion at the crankshaft by a crank pin shrunk into a crank disc into which the end of the crankshaft is also shrunk.

Front 25

Describe the function of the Crosshead.

Back 25

The crosshead takes the angular push or pull of the connecting rod against the piston rod during the greater part of the revolution when these rods are not “in line”; the valve rod guide fulfills the same function in the case of the valve spindle and eccentric rod.

Front 26

Describe the function of Lubricators.

Back 26

Whenever motion causes surfaces to slide or rub against each other there is friction and wear. Lubricators are provided at all such places to feed oil between the sliding surfaces and reduce the friction and wear to the lowest possible amount.

Front 27

Describe the function of Packing Boxes.

Back 27

Steam must not be allowed to leak past the piston rod and valve rod where they pass out of the cylinder and valve box. A packing box filled with flexible packing is provided at each of these places. The packing is squeezed tightly into the box around the rod by a gland which is held in place by a covering nut, or studs and nuts in the cylinder body.

Front 28

Describe the function of Drain Cocks (valves).

Back 28

Drain cocks are fitted into the lowest part of the cylinder and valve box for the removal of any water caused by condensation of steam.

Front 29

At what part of a piston's stroke is the greatest pressure applied by the steam?

Back 29

In most engines the admission of steam is stopped before the end of the stroke and allowed to do work by expanding during the latter part. Thus there is a greater force on the piston at the beginning than at the end of the stroke which causes the piston to move faster towards the beginning than towards the end.

Front 30

Describe the function of the Flywheel.

Back 30

While a governor is provided to take care of changes of speed due to changes of load over several revolutions, a flywheel is fitted to dampen or even-out these changes of speed caused by varying steam pressure and also to carry the engine over the dead center when no work is being done by the piston. The flywheel does this because considerable force is necessary to start it in motion or to stop it, also to increase or decrease its speed if it is already in motion.

Front 31

Describe the function of the Frame.

Back 31

The frame of the engines serves to hold the parts together in their relative positions and also provides a means of securing the engine solidly on its foundation.

Front 32

What are the 5 steps to starting a Steam Engine?

Back 32

1. See that no tools have been left around the engine where they may cause damage, and that all is clear around flywheels, pulleys, armatures, or other moving parts.

2. Check the steam chest and cylinder drains to be sure they are open to clear all water from the steam chest and cylinder.

3. Open the separator drain on the steam line to empty it of water, or, if the steam separator drain is fitted with a trap, see that the trap is operating properly.

4. When water ceases to flow through the drain valves, open the stop valve slightly (cracking the valve) until steam blows freely through the drains. Some steam will be condensed in the steam line and cylinder at first and more water will flow through the drains, after the valve is cracked.

5. Never open a steam valve suddenly or any water present in the steam line will be driven violently along the pipes, causing water hammer, which may result in the fracture of pipes or fittings.

Front 33

Describe the procedure for inspecting the running steam engine at regular intervals.

Back 33

At regular intervals make a tour of inspection of all engines, pumps and machines. Examine all lubricators to see that they are filled and feeding properly and feel around all bearings to see if any are heating above the ordinary running temperature. This inspection should be made, say every half hour, or more often if an engine is heavily loaded, or is known to have certain bearings that have a tendency to “heat up” rapidly.

Front 34

What is the importance of knowing how the steam engine sounds?

Back 34

Know the sound of your engine or engines so that any change in the noise made by the engine running will give warning that something is wrong. The ability to detect any change of sound, however slight, will often lead to the detection and remedy of minor troubles that might assume serious proportions if allowed to continue without being adjusted or repaired.