The Thompson Improved Steam Indicator comes in a dark stained wooden box 285mm wide, 207mm deep, and 240mm tall. It opens about halfway up its height to reveal a number of objects. The box, as well as various components, are serial numbered 4994. Inside the box there are pockets as well as mounts for the various objects to go into which can be seen in the images provided.
In the center is the steam indicator, which resembles two off-center attached cylinders screwed onto a mount. The cylinders are both 90mm in height and 50mm in diameter. The top cylinder has a slot to affix a cardstock, a stylus arm and pull string. The bottom cylinder has the arm holding the stylus and a spring inside to control the stylus arm. The bottom of the bottom cylinder has threads and ties to the mount on the bottom of the box, as well as thumb bars on the bottom to attach or unattach it by hand.
The steam indicator comes with 6 springs numbered 10, 20, 30, 40, 60, and 80, which range in length from 53-63mm long. These springs are threaded onto mounts on the upper half of the box and can replace the spring inside the bottom cylinder of the steam indicator. This allows the system to make more precise graphs depending on the pressure that the engine is putting out.
In addition to the above, there are also two globe shut-off valves with thread sizes of 20 and 25mm. The valves come with caps for one side to prevent damage to the threads that could result in inadequate attachment . There is also a torque wrench used to tighten the lower cylinder onto the engine that the indicator will be attached to. There is also a small vial of oil, for the joints of the stylus arm or the springs. There was also a specialized wrench designed to tighten the components in order to prevent gas leaks. The final component was a ruler with a screw driver end that allowed for the dismantling of the indicator as well as measuring the height of the graphs drawn by the arm allowing the user to find the pressure in the system.
Functional Description:
In order to use the Thompson steam indicator, the user fastened the stainless-steel ball valve to the steam engine being analyzed. The indicator was then be fastened to the open end of the ball valve via a threaded connection. With the ball valve opened, the steam within the engine’s piston exerts pressure on a spring enclosed within a 100 mm tall, 30 mm diam. cylinder of the indicator. A plunger connected to the spring is forced upward depending upon the force received by the spring. The motion of the plunger moves the 80 mm long arm vertically, which determines the markings made by the attached pencil. The pencil marks a piece of paper, which is wrapped around the upper cylinder (90 mm tall and 51 mm dia) of the indicator. Wrapped around this upper cylinder is a string whose function is to rotate the cylinder about its center. If the string were left free to hang, the steam pressure pushes the pencil upward, making a straight vertical line on the paper. However, the string was fastened to a component of the engine to allow for the engine piston and the cylinder to move in unison. The string moves the cylinder of the steam indicator in unison with the piston throughout the entire stroke, and a continuous marking is made to illustrate the pressure at each point of the stroke as the pencil is moved upward and downward while the cylinder pivots throughout the process. Thus, the vertical motion of the pencil graphs changes in pressure, while the rotation of the cylinder indicates the phase of the piston cycle, and so in unison the pencil plots a diagram of the pressure cycle in the engine.
The indicator was designed to record the stroke of a steam engine, particularly locomotives. At the start of the stroke, the inlet valve opens completely, allowing the maximum force to be applied to the spring by the steam. The pencil marks a horizontal line at its highest point in the cycle from left to right. At cut-off, the inlet valve closes and expansion of the steam occurs, during which the force gradually decreases. This phase is indicated by a pencil mark resembling an exponential decay curve. At release, the exhaust valve opens, releasing the steam and the force is at its minimum, resulting in a straight horizontal pencil mark at the lowest point of the curve—this time from right to left. When the exhaust valve closes, compression occurs, causing a gradual rise in pressure. When the inlet valve opens again, the gradual increase in pressure becomes a sharp increase, causing the pencil to mark a straight vertical line returning to the first point of the cycle when the steam pressure exerts its greatest force on the spring. The end product of this device is a card illustrating the change in pressure throughout the continuous cycle of the steam engine. For an engine operating at 250 RPM, the device could generate one cycle plot (or card) per minute.
The spring within the indicator can be replaced with a larger spring to record higher steam engine pressures. The set of springs are marked according to their compressive strength: the spring marked #100 converts the force from 100 psi gauge-pressuresteam into a pencil movement of one inch, a #80 spring converts 80 psig steam into a movement of one inch, and so on.
Though the steam indicator was primarily used on locomotives, it could also be applied to traction engines and artillery. Due to the high cost of the indicator, it was seldom used on traction engines beyond the confines of the factory in which it was produced. When applied to heavy artillery, the oil in the recoil chamber would replace the steam as the working fluid and exert a pressure on the spring. The string would be fastened to the barrel to allow for the recoil movement to pull on the string.
]]>The Thompson Improved Steam Indicator comes in a dark stained wooden box 285mm wide, 207mm deep, and 240mm tall. It opens about halfway up its height to reveal a number of objects. The box, as well as various components, are serial numbered 4994. Inside the box there are pockets as well as mounts for the various objects to go into which can be seen in the images provided.
In the center is the steam indicator, which resembles two off-center attached cylinders screwed onto a mount. The cylinders are both 90mm in height and 50mm in diameter. The top cylinder has a slot to affix a cardstock, a stylus arm and pull string. The bottom cylinder has the arm holding the stylus and a spring inside to control the stylus arm. The bottom of the bottom cylinder has threads and ties to the mount on the bottom of the box, as well as thumb bars on the bottom to attach or unattach it by hand.
The steam indicator comes with 6 springs numbered 10, 20, 30, 40, 60, and 80, which range in length from 53-63mm long. These springs are threaded onto mounts on the upper half of the box and can replace the spring inside the bottom cylinder of the steam indicator. This allows the system to make more precise graphs depending on the pressure that the engine is putting out.
In addition to the above, there are also two globe shut-off valves with thread sizes of 20 and 25mm. The valves come with caps for one side to prevent damage to the threads that could result in inadequate attachment . There is also a torque wrench used to tighten the lower cylinder onto the engine that the indicator will be attached to. There is also a small vial of oil, for the joints of the stylus arm or the springs. There was also a specialized wrench designed to tighten the components in order to prevent gas leaks. The final component was a ruler with a screw driver end that allowed for the dismantling of the indicator as well as measuring the height of the graphs drawn by the arm allowing the user to find the pressure in the system.
Functional Description:
In order to use the Thompson steam indicator, the user fastened the stainless-steel ball valve to the steam engine being analyzed. The indicator was then be fastened to the open end of the ball valve via a threaded connection. With the ball valve opened, the steam within the engine’s piston exerts pressure on a spring enclosed within a 100 mm tall, 30 mm diam. cylinder of the indicator. A plunger connected to the spring is forced upward depending upon the force received by the spring. The motion of the plunger moves the 80 mm long arm vertically, which determines the markings made by the attached pencil. The pencil marks a piece of paper, which is wrapped around the upper cylinder (90 mm tall and 51 mm dia) of the indicator. Wrapped around this upper cylinder is a string whose function is to rotate the cylinder about its center. If the string were left free to hang, the steam pressure pushes the pencil upward, making a straight vertical line on the paper. However, the string was fastened to a component of the engine to allow for the engine piston and the cylinder to move in unison. The string moves the cylinder of the steam indicator in unison with the piston throughout the entire stroke, and a continuous marking is made to illustrate the pressure at each point of the stroke as the pencil is moved upward and downward while the cylinder pivots throughout the process. Thus, the vertical motion of the pencil graphs changes in pressure, while the rotation of the cylinder indicates the phase of the piston cycle, and so in unison the pencil plots a diagram of the pressure cycle in the engine.
The indicator was designed to record the stroke of a steam engine, particularly locomotives. At the start of the stroke, the inlet valve opens completely, allowing the maximum force to be applied to the spring by the steam. The pencil marks a horizontal line at its highest point in the cycle from left to right. At cut-off, the inlet valve closes and expansion of the steam occurs, during which the force gradually decreases. This phase is indicated by a pencil mark resembling an exponential decay curve. At release, the exhaust valve opens, releasing the steam and the force is at its minimum, resulting in a straight horizontal pencil mark at the lowest point of the curve—this time from right to left. When the exhaust valve closes, compression occurs, causing a gradual rise in pressure. When the inlet valve opens again, the gradual increase in pressure becomes a sharp increase, causing the pencil to mark a straight vertical line returning to the first point of the cycle when the steam pressure exerts its greatest force on the spring. The end product of this device is a card illustrating the change in pressure throughout the continuous cycle of the steam engine. For an engine operating at 250 RPM, the device could generate one cycle plot (or card) per minute.
The spring within the indicator can be replaced with a larger spring to record higher steam engine pressures. The set of springs are marked according to their compressive strength: the spring marked #100 converts the force from 100 psi gauge-pressuresteam into a pencil movement of one inch, a #80 spring converts 80 psig steam into a movement of one inch, and so on.
Though the steam indicator was primarily used on locomotives, it could also be applied to traction engines and artillery. Due to the high cost of the indicator, it was seldom used on traction engines beyond the confines of the factory in which it was produced. When applied to heavy artillery, the oil in the recoil chamber would replace the steam as the working fluid and exert a pressure on the spring. The string would be fastened to the barrel to allow for the recoil movement to pull on the string.
The object was made by the firm the American Steam Gauge Company of Boston, MA. The indicator was initially invented by James Watt, who also is credited with the invention of the steam engine. Joseph Thompson is the creator of this steam engine indicator with his patent being granted on Aug 31, 1875. The instrument was manufactured by The American Steam Gauge Company, which was founded in 1851. The instrument was sold as the “American Thompson Improved Indicator”, and was considered to be high end among steam indicators of the time. The improvements of the Thompson indicator over previous models were that the writing component followed an elliptical pattern to maintain a straight line on the recording barrel. This resulted in less inertia and increased the engine speeds, and pressures that the indicator could be used at. The patent granted in 1904 to Earl Vaughn had the benefits of making the indicator easier to disassemble for adaptability of the indicator. For this reason it is believed that this indicator was manufactured sometime after 1904.
"The Story of the Steam Engine Indicator." last modified July/August 2001 http://www.farmcollector.com/steam-traction/story-steam-engine-indicator
Engineer: with which is incorporated steam engineering, volume 35 .. Vol. 42. (Chicago: The Engineer Publishing Company, 1905).
Dorn, Harold. Dictionary of Scientific Biography. Vol. 14. (New York: Charles Scribner's Sons, 1976), 196-99.
Scales
A: 1-20 logarithmic scale
B: 1-20 logarithmic scale
T: logarithmic scale from 0-90
ST: logarithmic scale 0.56-5.73
S: logarithmic scale from 0-90
K: 1-30 logarithmic scale
D: 1-10 logarithmic scale with notation at pi
DF: folded scale ranging from pi-10 and then 1-pi
CF: folded scale ranging from pi-10 and then 1-pi
CIF: descending logarithmic scale pi-1 followed by 10-pi
CI: descending logarithmic scale 10-1
C: 1-10 logarithmic scale with notation for pi
L: 1-10 linear scaleThe calculator generally comprises three main parts: the main housing, the keypad, and the output carriage.
The main housing for the calculator is rectangular as seen from the top, with one pale green slanted face on the front where the keypad is located, similar to a typewriter or cash register. The main housing is a shiny dark green in color with the appearance of a scale-like texture. On the bottom of the main housing are four feet which are steel with a rubber boot. On the front of the main housing, just below the slanted face, a "T" shaped knob protrudes. The knob has a small polished aluminum shaft (15mm long, 6mm diameter) with small black enamel handles (12mm long). Then, on the face to the right of the slanted face (when viewed straight on as if operating) is a knurled aluminum knob about 25mm in diameter. On the back of the calculator (opposite the slanted face) is an electrical connector that is on the right side of the calculator. Lastly, there are "MONROE" logos with yellow letters outlined in red on the front face below the slanted face and centered on the back, under both of which there are the words "HIGH SPEED ADDING CALCULATOR" in yellow. The logo on the back is much larger, while the logo on the front is about half the size and positioned towards the right. Additionally, on the bottom of the calculator in the center is a yellow tag that has the same logo in black letters with additional product information writtten below it.
Housed on the slanted face is the keypad. This pale green panel contains a 10x8 array of white buttons (6mm diam.) with black numerals, 0 through 9. Each column starts with a zeroing key at the bottom and increases to nine at the topmost row. To the right of the number pad is another column of various buttons. Starting at the top is the subtraction button (with an inscribed - symbol) which is long, rectangular (35mm long, 13mm wide), and black in color. Directly below that is the addition button (with an inscribed + symbol) with the same shape, orientation, and color. Under that is a 6mm diameter red button that has no symbol. Then under that is another 6mm diameter red button with a darker red "R" on it. Last below that button is a larger red button (14mm diameter) with a pale green zero. The final component on the front panel is a small aluminum lever directly to the left of the left-most "1" button that stands 10mm tall.
At the top rear is the output carriage. The carriage is primarily the same dark shiny green as the main body. The carriage is a triangular prism in shape with one of the long flat faces facing the operator, which is at the same angle as the input panel. On this primary face are two rows of small windows (5mm tall and 4mm wide). The bottom row closest to the number pad consists of 16 windows, while the top row consists of 8 windows that are directly above the eight rightmost widows of the bottom rows. Inside each of the windows are black numbers (on the top row, there is also a set of red numbers for subtraction) on a white roller much like a slot machine. Directly above the lower set of windows is a rail with yellow numbers above each window, starting with one on the left and ending with 16 on the right. Along this rail is a set of 5 brass sliders with very small knobs (3mm diameter) that are attached to red arrows that point down towards the lower set of windows. Directly above this rail and below the upper set of windows is another shorter rail that matches the shorter number of windows. This rail has eight numbers and one slider that points upwards. A large steel knob (15mm in diameter) is to the right of these rails. Lastly, on the right face of the carriage is a crank with a dark wooden knob about 10mm in diameter with a polished aluminum arm (20mm long).
The calculator generally comprises three main parts: the main housing, the keypad, and the output carriage.
The main housing for the calculator is rectangular as seen from the top, with one pale green slanted face on the front where the keypad is located, similar to a typewriter or cash register. The main housing is a shiny dark green in color with the appearance of a scale-like texture. On the bottom of the main housing are four feet which are steel with a rubber boot. On the front of the main housing, just below the slanted face, a "T" shaped knob protrudes. The knob has a small polished aluminum shaft (15mm long, 6mm diameter) with small black enamel handles (12mm long). Then, on the face to the right of the slanted face (when viewed straight on as if operating) is a knurled aluminum knob about 25mm in diameter. On the back of the calculator (opposite the slanted face) is an electrical connector that is on the right side of the calculator. Lastly, there are "MONROE" logos with yellow letters outlined in red on the front face below the slanted face and centered on the back, under both of which there are the words "HIGH SPEED ADDING CALCULATOR" in yellow. The logo on the back is much larger, while the logo on the front is about half the size and positioned towards the right. Additionally, on the bottom of the calculator in the center is a yellow tag that has the same logo in black letters with additional product information writtten below it.
Housed on the slanted face is the keypad. This pale green panel contains a 10x8 array of white buttons (6mm diam.) with black numerals, 0 through 9. Each column starts with a zeroing key at the bottom and increases to nine at the topmost row. To the right of the number pad is another column of various buttons. Starting at the top is the subtraction button (with an inscribed - symbol) which is long, rectangular (35mm long, 13mm wide), and black in color. Directly below that is the addition button (with an inscribed + symbol) with the same shape, orientation, and color. Under that is a 6mm diameter red button that has no symbol. Then under that is another 6mm diameter red button with a darker red "R" on it. Last below that button is a larger red button (14mm diameter) with a pale green zero. The final component on the front panel is a small aluminum lever directly to the left of the left-most "1" button that stands 10mm tall.
At the top rear is the output carriage. The carriage is primarily the same dark shiny green as the main body. The carriage is a triangular prism in shape with one of the long flat faces facing the operator, which is at the same angle as the input panel. On this primary face are two rows of small windows (5mm tall and 4mm wide). The bottom row closest to the number pad consists of 16 windows, while the top row consists of 8 windows that are directly above the eight rightmost widows of the bottom rows. Inside each of the windows are black numbers (on the top row, there is also a set of red numbers for subtraction) on a white roller much like a slot machine. Directly above the lower set of windows is a rail with yellow numbers above each window, starting with one on the left and ending with 16 on the right. Along this rail is a set of 5 brass sliders with very small knobs (3mm diameter) that are attached to red arrows that point down towards the lower set of windows. Directly above this rail and below the upper set of windows is another shorter rail that matches the shorter number of windows. This rail has eight numbers and one slider that points upwards. A large steel knob (15mm in diameter) is to the right of these rails. Lastly, on the right face of the carriage is a crank with a dark wooden knob about 10mm in diameter with a polished aluminum arm (20mm long).
The purpose of this calculator is complete simple arithmetic such as adding, subtracting, multiplying, and dividing.
Before doing any calculations, users will need to reset the registers (number windows on the carriage). Operators can do this by rotating the crank attached to the carriage until the register reads zero.
For adding, users type in the first number into the keypad by depressing the corresponding buttons, where the number furthest to the right is the smallest digit (which could represent a decimal). Then, the user shall click the plus button causing an electric motor to spin and load the number into the lower register (the longest set of windows). After that, users type the next number to which they would like to add in the same manner. Then, after selecting the add button, the value in the lower register will be the sum that the user is looking for.
For subtracting, the user should perform a similar process where they type in the larger of the two numbers and then press the add button to add the larger value to the register. After that, operators should input the subtracting value into the keypad. Then the user shall select the subtraction key, causing the motor to spin in the opposite direction. This will yield the desired difference in the lower register.
For multiplication, the user must input the larger value into the number pad. The operators shall select the red key with an R. This locks the number so that after the addition key is selected, the number pad will not reset. If the small number of the multiplication is less than ten, the user shall select the addition key as many times as the smaller number. The upper register will count the number of times the user has selected the addition key, and the lower register will display the product.
If the smaller number happens to be larger than ten, the user can select the add key for the smallest digit of the smaller number, and then they can shift the entire carriage with the T-shaped knob so that they add to the power of ten more. Operators should repeat this process until the upper register shows the smaller number of the multiplication, and the resultant in the lower register will be the product.
Operators can perform division in the same manner as a multiplication; however, they shall input the larger number into the lower register. Then, they can use the subtraction key instead of the addition key until the lower register reads as close to zero as possible (remainders may exist). The operator can then read the result of the division in the upper register in red numbers.
In addition, the calculator has some extra useful functions. One is at the bottom of each column is a zeroing button which can be used to clear a column if the incorrect value is selected. Similarly, there is a larger read zeroing buttons that clear the whole number pad. Another feature is a small lever that users can move to hold down the leftmost one on the number pad. This will cause the leftmost digit in the register to count the number of additions or subtractions performed. Another functional feature is the set of sliders on the registers. Ultimately, these sliders are used for the reference of the user and are often used for dealing with decimal numbers where the digits furthest to the right are the smallest decimal value or unit of precision. Lastly, there is a knob on the right side of the calculator that can be used to spin the motor and perform calculations without electricity. In this case, the knob shall be rotated clockwise to add and counterclockwise to subtract.