Instruction Manual and
Experiment Guide for
the PASCO scientific
Model SE-8575
THE VISIBLE
STIRLING ENGINE
012-06055A
2/96
© 1995 PASCO scientific $5.00
012-06055A The Visible Stirling Engine
T able of Contents
Section Page
Copyright, Warranty, and Equipment Return .....................................................ii
Introduction ......................................................................................................1
History and Theory of Operation .......................................................................2
Operation
Operating on Ice .........................................................................................3
Power from your Fingertips.........................................................................3
Operating with Hot Water ...........................................................................4
Operating on Maximum Power ...................................................................4
Experiment .......................................................................................................5
Demonstration: An Engine that Runs on Ice ......................................................7
Maintenace .......................................................................................................8
Troubleshooting ................................................................................................9
Credits ............................................................................................................10
Technical Support ...........................................................................inside back cover
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The Visible Stirling Engine 012-06055A
Copyright, Warranty and Equipment Return
Please—Feel free to duplicate this manual
subject to the copyright restrictions below.
Copyright Notice
The PASCO scientific Model SE-8575 The Visible
Stirling Engine manual is copyrighted and all rights
reserved. However, permission is granted to non-profit
educational institutions for reproduction of any part of
this manual providing the reproductions are used only for
their laboratories and are not sold for profit. Reproduction under any other circumstances, without the written
consent of PASCO scientific, is prohibited.
Limited Warranty
PASCO scientific warrants this product to be free from
defects in materials and workmanship for a period of one
year from the date of shipment to the customer. PASCO
will repair or replace, at its option, any part of the product
which is deemed to be defective in material or workmanship. This warranty does not cover damage to the product
caused by abuse or improper use. Determination of
whether a product failure is the result of a manufacturing
defect or improper use by the customer shall be made
solely by PASCO scientific. Responsibility for the return
of equipment for warranty repair belongs to the customer.
Equipment must be properly packed to prevent damage
and shipped postage or freight prepaid. (Damage caused
by improper packing of the equipment for return shipment will not be covered by the warranty.) Shipping
costs for returning the equipment, after repair, will be
paid by PASCO scientific.
Equipment Return
Should the product have to be returned to PASCO
scientific for any reason, notify PASCO scientific by
letter, phone, or fax BEFORE returning the product.
Upon notification, the return authorization and
shipping instructions will be promptly issued.
ä
NOTE: NO EQUIPMENT WILL BE
ACCEPTED FOR RETURN WITHOUT AN
AUTHORIZATION FROM PASCO.
When returning equipment for repair, the units
must be packed properly. Carriers will not accept
responsibility for damage caused by improper
packing. To be certain the unit will not be
damaged in shipment, observe the following rules:
➀ The packing carton must be strong enough for the
item shipped.
➁ Make certain there are at least two inches of
packing material between any point on the
apparatus and the inside walls of the carton.
➂ Make certain that the packing material cannot shift
in the box or become compressed, allowing the
instrument come in contact with the packing
carton.
Credits
This manual authored by: Brent Van Arsdell
This manual edited by: Mary Ellen Niedzielski
Address: PASCO scientific
10101 Foothills Blvd.
Roseville, CA 95747-7100
Phone: (916) 786-3800
FAX: (916) 786-3292
email: techsupp@pasco.com
web: www.pasco.com
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012-06055A The Visible Stirling Engine
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Introduction
The PASCO Visible Stirling Engine is a tool to teach
students how engines work and to excite them about
physics.
Stirling engines have the most efficient cycle in the
world. Does that mean the Model SE-8575 engine is the
most efficient engine in the world? No. It means that
Stirling engines with regenerators have a cycle that
matches the Carnot cycle. The Carnot cycle determines
the maximum theoretical efficiency of a heat engine.
temphot – temp co
temp hot
The temperatures must be measured in absolute degrees
(Kelvin or Rankine) for this formula to work.
No real engine (one that could be built in a machine shop)
can achieve the Carnot theoretical efficiency. But real
Stirling engines come closer to the Carnot cycle than any
other engine! Some research Stirling engines have
attained 50 percent of the theoretical Carnot efficiency!*
The efficiency of the SE-8575 is calculated in the experiments section of this manual.
× 100 = % efficiency
If Stirling engines are so efficient, why don’t we have
them in automobiles? The best answer to this question is
an easy demonstration. Start the SE-8575 on nearly
boiling water and wait for it to get up to full speed. Then
remove the engine from the heat source and notice that it
keeps running for a few minutes.
It is very easy to do an engineering trick to make the
engine stop instantly, but there is nothing in the world that
can be done to make a Stirling engine start instantly.
Today’s drivers want to be able to start their cars instantly
(if not sooner) and some of them want to burn rubber
across the parking lot. Stirling engines can’t do that.
Research automobile Stirling engines generally take
about 30 seconds before the car can be driven away.
Modern drivers do not want to wait.
Computer Compatibility
Photogates may be used to measure the engine rpm.
Additional Equipment Recommended
You may also find it convenient to use:
• A coffee cup.
*
“Stirling Machines: An Emerging Technology Paradigm”
by B. Ross and L.B. Penswick, page 8.
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• A clear water glass
• A Styrofoam dinner plate or a Styrofoam bowl.
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The Visible Stirling Engine 012-06055A
History and Theory of Operation
Why STIRLING Engines are important
Every practical engine ever built compresses a gas then
expands it and moves it through a cycle.
The Reverend Robert Stirling, a minister of the Church of
Scotland, was troubled by some of the dangerous engines
that were used at the beginning of the industrial revolution. Steam engines would often explode with tragic
effects to anyone unfortunate enough to be standing
nearby. So in 1816 he invented and patented “A New
Type of Air Engine With Economizer.”
Hot air engines, as they were initially called, couldn’t
explode and often put out more power than the steam
engines of their day. The only trouble was that the readily
available metal of the early 1800’s was cast iron, and cast
iron oxidizes rapidly when you leave it in a very hot flame.
In spite of these difficulties, Stirling engines were widely
used as water pumping engines at the turn of the century.
They required little service, never exploded, were fairly
quiet and the water provided a good cooling source for
the cold side of the engine. Thousands of these engines
were sold .
In the mid 1800’s a bright Frenchman named Sadi Carnot
figured out the maximum limits on efficiency. His
formula is an accepted standard for determining the
maximum possible efficiency of an engine. No engine
can exceed the Carnot efficiency. [The first law of
Thermodynamics says you can’t get out more than you
put in. You can only break even.] In fact no real engine
can achieve carnot efficiency. [The second law of thermodynamics says you can’t break even.]
It takes good engineering and complex machines to
achieve a significant fraction of the Carnot efficiency.
On the simplest level, a Stirling engine operates as
follows. When a gas in a closed cylinder is heated it
expands and pushes up on a piston. When the same gas is
cooled, it contracts and pulls down on the piston.
The next level of understanding is to realize how regeneration works. Robert Stirling realized that the engines he
built would be much more efficient if some of the heat
that was used to heat the air for one cycle was saved and
used again in the next cycle. Robert Stirling called the
device that saved heat in his engines an economizer.
Today, these are usually called regenerators and probably
are Robert Stirling’s most important invention.
In the model SE-8575, regeneration works as follows.
When the yellow foam inside the engine is near the top of
the cylinder (and the engine is running on a cup of hot
water) most of the air is on the bottom side (the hot side)
where it is heated. When the air gets hot it expands and
pushes up on the piston. When the foam moves to the
bottom of the engine it moves most of the air (it displaces
the air) to the top of the engine. The top of the engine is
cool, allowing the air inside the engine to cool off (reject
heat to the environment) and the piston receives a downward push. This engine would run even if the “displacer”
(the yellow foam) was made of solid Styrofoam. It runs
much better because it is made of a special air filter foam.
When the air is flowing from the hot side of the engine to
the cold side it flows through and around the yellow foam
(the displacer). Since the air is hotter than the foam, some
of the heat from the air will flow into the foam. The air
cools off and the foam heats up. This is called regeneration and is very important in many industrial processes.
When the air makes the return trip to the hot side of the
engine it once again flows through and around the foam.
This time the air heats up and the foam cools off. The
heat that would have been wasted in an engine without
regeneration is saved and a much more efficient engine is
the result.
A Stirling engine with a regenerator has a cycle that
matches the Carnot cycle. It has the same theoretical
maximums and the same theoretical efficiencies.
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012-06055A The Visible Stirling Engine
Operation
Operating On Ice
Running the engine on ice is a quick and interesting way
to start the engine. Pick up the engine and rub an ice cube
vigorously around the bottom (the blue part) of the
engine. Then place the engine on a pile of ice cubes (ice
chips work best) and flip the prop in the direction indicated on the label.
Ice cream or frozen yogurt also work well as ice substitutes. Ice cream provides a good heat sink, (when compared to ice cubes) because it makes such good thermal
contact with the bottom of the engine. Ice cubes tend to
provide only limited points of contact on the top edges of
the cubes.
If you run the engine on ice cream or frozen yogurt, take
extra care to clean it after you are done. Carefully run the
bottom of the engine under some warm water to clean it.
Stirling Engine on a Bowl Filled with Ice
Stirling Engine on an Ice Cream Cone
Power From Your Fingertips!
When running the engine on ice in a room that is 72° to
75°F the temperature of the top of the engine will drop to
about 68°F. When this occurs an interesting demonstration can be performed.
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Palm over LCD Thermometer
Place a warm hand (as many fingers as fit) over the LCD
thermometer and the surrounding area. Within 20 seconds
you will observe a significant increase in the operating
speed of the engine. Engines run on heat, and in this case
body heat can be used to increase the output power of the
SE-8575.
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The Visible Stirling Engine 012-06055A
Operating with Hot Water
Water is a very good thermal transfer medium. The
visible Stirling engine will run well on a cup of hot water.
Does the water have to be in contact with the bottom of
the engine? No. Steam rising off the water and then
condensing on the bottom of the engine moves the heat
to the hot side of the engine. Here’s how to start the
engine in a hurry.
Fill a coffee mug about 1/3 full of hot tap water then
microwave it until the water is boiling vigorously. Place
the engine on the top of the coffee mug, wait 20 seconds,
and flip the prop in the direction indicated on the label.
This also works well with a clear water glass. Using a
clear glass has the added benefit of letting students see the
steam rise and the water condense on the bottom of the
engine. Make sure to use a glass that is safe for the
temperature of water you will be putting in it.
The engine should start immediately and run at a high
rate of speed.
Operating On Maximum Power
The way to get the most power out of the model SE-8575
is to increase the temperature difference between the top
and bottom plates. The maximum operating temperature
is 212°F and the minimum operating temperature is -40°F.
➤ NOTE: Do not apply direct flame to the unit!
The best way to achieve maximum power is to put boiling
water on the bottom (do not use a Bunsen burner) and ice
cubes on the top. Be careful not to get water down inside the
engine or on top of the piston. Water on the top of the LCD
thermometer is okay.
Air Displacer
(90° out of phase from
the piston)
Propeller
Piston
Yellow Foam
Air Displacer
Stirling Engine on a Cup of Hot Water
Liquid Crystal Thermometer
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012-06055A The Visible Stirling Engine
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Experiment
Equipment needed
– Model SE-8575 Visible Stirling Engine
– (2) Styrofoam cups
– Thermometer
– Hot water (boiling is preferred )
– Paper towels to wipe up water
– Optional: Basic Calorimetry Set (TD-8557)
Purpose
The purpose of this experiment is to get a physical feel for the loss mechanisms in any engine.
Theory
Engines are made to do something. They take in energy from a source, they reject waste heat to a
reservoir, and they do useful work. Every engine has losses. The purpose of this experiment is to
identify the loss mechanisms and determine what could be done to reduce those losses.
Setup
➀ Nest one Styrofoam cup inside the other to make a two cup calorimeter. Weigh the cups.
➤ NOTE: The TD-8557 styrofoam Calorimeter works well to replace the cups.
➁ Fill the cups half full with very hot water. Put a lid over the assembly and weigh it again.
➂ Measure the temperature of the water. Convert the temperature to Kelvin or Rankine.
➃ Measure the temperature of the air in the room. Convert this temperature to Kelvin or Rankine.
➄ Place the engine on top of the hot water and start it. After it gets up to speed stop the engine and
turn it slowly by hand. Watch what happens to the piston when the air shifts from the hot side to
the cold side.
Calculation
Calculate the theoretical efficiency of the engine operating between these two temperatures using
temphot – temp co
the following formula.
What is the theoretical efficiency of a Carnot engine operating between these temperatures?
temp hot
× 100 = % efficienc
Questions
➀ Which would do more for efficiency of the engine, raising the temperature hot by 50°, or
lowering the temperature cold by 50°?
➁ The hot water in the cups is a form of stored energy available to do work. Would it be possible
to run a car on very hot water?
➂ How much energy is stored in the hot water?
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The Visible Stirling Engine 012-06055A
➃ When you buy gasoline to run your car, what is it that you are really buying?
➄ If hot water could be used to run a car, why do we buy gasoline instead of hot water? Hot water
would be a zero pollution engine.
➆ How much stored energy is there in a gallon of gasoline?
➇Some of the air makes the piston bulge up around the edges when the air moves to the hot side.
Does this air do any useful work?
➈ Would the engine put out more power if this flexible piston was replaced with a very tight fitting
light weight graphite piston?
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012-06055A The Visible Stirling Engine
DEMONSTRATION:
An Engine That Runs On Ice
Setup
Set the SE-8575 up to run on ice chips, ice cream, or frozen yogurt. Detailed instructions are in
the Operation section of this manual. Start it running and ask the following questions.
Questions
➀ What is the source of energy to run this engine?
➁ Since there is no such thing as a free lunch, who paid for the energy to make this engine run and
what company did they pay it to?
➂ After the SE-8575 has been running for some time, do the Power From Your Fingertips demo as
explained in the operations section. Who paid for this energy to make the engine run faster and
who did they pay it to?
➃ Would it be possible to have a full power engine that had zero pollution and used the heat from
the room as a hot source.
➄ Calculate the Carnot efficiency of an engine running with liquid nitrogen as a cold sink and a
72°F (23°C) ambient hot source.
➅ Liquid nitrogen is readily available. What determines whether it would be a good idea to build
an engine like this?
➆ Since the air is roughly 80% nitrogen, would an engine like this cause any pollution?
➇ When an engine is running on a heat source the Carnot formula determines how much of the
heat can become useful work. In this engine as in most engines the majority of the heat that
could become useful work doesn’t become useful work. What happens to this heat? Identify the
specific loss mechanisms.
➈ Internal combustion four stroke engines have one power pulse every other trip of the piston.
Stirling engines have two power pulses per trip of the piston (one going up, and one going
down). All other things being equal (which they never are) how much smoother should a
Stirling engine be than an Otto cycle engine?
➉ Are you likely to see a Stirling engine offered for sale in a car? Why or why not?
Would Stirling engines be good candidates for powering submarines? Stirling engines are quiet
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and submarines like quiet.
Would Stirling engines be a good source of auxiliary power generation for yachts? Good
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cooling water is available, and people on yachts like it quiet too.
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Maintenance
The PASCO Visible Stirling Engine SE-8575 is a delicate
apparatus. Treat it like a fine piece of laboratory equipment and it will last a very long time.
Maximum Operating Temperature
The engine is made for intermittent use with a maximum
operating temperature of 100°C (212°F).
For Intermittent Use Only
➤ IMPORTANT: The PASCO SE-8575 Stirling
Engine is not made for continuous use.
It may be tempting to find a source of waste heat and let
the engine run continuously. Do NOT do this!
• The piston has a limited life time. While it should
last for years with occasional use, it will only last
for about 6 weeks running 24 hours a day.
• To extend the life of the engine, do not exceed its
maximum operating temperature. Do not run the
engine on heat sources other than hot water.
Non-Acceptable Heat Sources
➤ IMPORTANT: Do NOT heat the engine using
any type of flame!
The SE-8575 will indeed run very fast on the heat from a
candle flame, but you will exceed the maximum temperatures of the materials in the engine and ruin it.
If you use a burner to heat the water, put the engine on
top of the water after the burner is shut off.
Running the engine on top of a lamp or a similar heat
source is likely to raise the temperature of the acrylic
above its yield temperature and ruin the engine.
DO NOT USE LIQUID NITROGEN!
➤ IMPORTANT: Liquid nitrogen is far too cold
for this engine and very likely will break it. Dry ice
would probably be okay but has not been tested.
A good cooling source is “freeze spray”. This is sold in
an aerosol can at Radio Shack and other electronics
supply stores. It’s a lot of fun to make the engine appear
to run on “nothing”.
DO NOT OIL THE BEARINGS!
During the development of this engine, many different
lubricants were tried in an effort to improve performance.
None of them improved performance at all, and most of
them made the engine run less well or not at all.
All the bearing surfaces contain Teflon. It is unlikely that
any lubricant you might use would improve performance.
To Remove Oil:
Oiling the engine will probably degrade performance or
cause the engine to quit. Use a TINY drop of WD-40 (a
very light dispersant petroleum based product) to clean
off the oil. Be careful to keep the oil from running over
the red anodized surface as it will stain the anodizing.
KEEP THE ENGINE DRY!
After running the engine, make sure it is completely dry
before putting it away. The metal ring that holds the blue
plate on the bottom of the engine in place is made of a
stainless steel alloy that contains some iron. It can rust if
not put away dry. Towel dry the engine carefully before
you put it away. Blow drying it is also a good idea.
Most Common Reason for Engine Failure
• The most common reason for the engine failing to run
is inadequate thermal transfer. If the engine won’t run
try putting about an inch of water in a coffee mug and
microwaving it until it is boiling vigorously!
• Remove the mug from the oven and place the engine
on top of the boiling water, wait 15 seconds, and turn
the prop the direction indicated on the instruction label
for “hot on the bottom.” The engine should start
quickly and run rapidly.
➤ NOTE: Boiling water is dangerous. Handle
with care!
If the engine still does not work or runs very slowly, refer
to the Troubleshooting section.
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012-06055A The Visible Stirling Engine
Troubleshooting
There are three general reasons why the SE-8575 Stirling
Engine might not run.
➀ Not enough temperature difference between the hot and
cold side of the engine. This Stirling engine needs about a
40°F (23°C) difference in temperature to run. If the room
is at 72°F (23°C) and the ice temperature is 32°F or
cooler the engine should run at 100 rpm or faster.
If ice is used as the “cold” source, it is possible to have
the bottom of the engine rest on only a few high points
on top of the ice cubes. The best solution is to pick up
the engine and rub an ice cube vigorously around its
bottom. Then place the engine on a pile of ice cubes
(ice chips are best). Push down on the LCD thermometer with your warm hand to help establish contact
with the ice. This will simultaneously warm up the top
of the engine and help establish better ice contact with
the cold side of the engine.
➁ The engine may have developed a leak in the system.
The Stirling cycle engine is a sealed system. It can
only tolerate one tiny leak. If there are any obvious
holes in the grey diaphragm (which is the piston) the
engine will not run. Contact the Magic Motor Company 1-800-503-2906 for replacement parts or service.
➂ There might be internal friction in the system. Every
engine ever built has internal friction losses. However
this engine when operating between such small temperature differences does not have room for much
wasted power.
There are two things that have been observed to sometimes cause problems. There must be about slight looseness in the collars where the crankshaft goes through the
aluminum upright near the propeller. In other words, If
the engine is held in one hand and the prop is moved back
and forth along the axis of the crankshaft it should be
possible to hear the collars make a clicking sound, and
see the bushings which hold the crankshaft in place move
back and forth about the distance of 2 to 4 sheets of
notebook paper.
Also, the piston must move freely without binding at the
top or bottom of its travel. This should never need
adjustment, but it can be adjusted if someone accidentally
moves it out of its range. The piston (grey rubber diaphragm) should, at the bottom of its travel, be almost (but
not quite) tight. At the top of its travel it should also be
almost but not quite tight. If the piston is tight at either
end of its travel it can be adjusted slightly by hand.
The black tubing that covers the rod connecting the piston
and the crankshaft is a slip adjustment mechanism. If the
piston is too tight at the bottom of its travel, shorten the
connecting rod by pushing in (ever so slightly) on the
piston end and the crankshaft end. Hold one hand at the
crankshaft end of the connecting rod and the other at the
piston end and push these ends together. If the piston is
too tight at the top end of its travel then lengthen the
connecting rod (very slightly) by pulling down the piston
and pulling up on the crankshaft end of the connecting
rod. In other words, reverse the previous process.
Adjusting the Regenerator
The regenerator is the yellow piece of foam inside the
engine that moves the air from the hot side to the cold
side. In normal use this should never need adjusting.
However if someone grabs it and pulls on it, the regenerator can be moved out of adjustment. Ideally the displacer
should just barely touch (or not quite touch) the top side
of the engine when it is at the top end of its travel. It also
should not quite touch (or barely touch) the blue plate
when it is at the bottom end of its travel.
Turn the propeller slowly through by hand and watch the
regenerator. If it is adjusted as indicated in the above
paragraph then don’t do anything with it. If it hits the
bottom enough so that the flexible rubber linkage tubing
bows out when the regenerator is at the bottom of its
travel then push the black tubing slightly down onto the
regenerator shaft. The regenerator shaft is the shiny piece
of wire that goes down into the engine and attaches to the
yellow foam.
This looseness is essential to proper operation of the
engine. If one of the bushings has moved slightly and
becomes a tight fit on the aluminum upright, the engine
will run poorly or not at all. The solution to this problem
is to use a knife blade to move one of the collars slightly
away from the aluminum uprights.
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If the LCD Thermometer Turns Black
LCD thermometers of this type have specific operating
ranges. When the temperature is within their range they
display colors. When the temperature is out of their range
they turn black.
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The Visible Stirling Engine 012-06055A
If the LCD thermometer is black it means that the
temperature of the thermometer is out of the range of the
thermometer. Either the temperature is above 86°F
(30°C) or below 61°F (16°C). The thermometer is not
damaged by this at all and will again indicate colors when
the temperature returns to its operating range.
Credits
Acknowledgments
This type of Stirling engine is relatively new. The first
Stirling engine ever built to run on small temperature
differences was built in 1983 by Ivo Colin of the University of Zagreb in what was then Yugoslavia.
Jim Senft, a mathematics professor at the University of
Wisconsin River Falls, built engines that substantially
improved on those built by Ivo Colin. This engine is a
follow up design to those built by Jim Senft. The concept
for this engine was created by Darryl Phillips of the
Airsport Corporation, Sallisaw Oklahoma. The detail
design and engineering was done by Brent H. Van
Arsdell of the Magic Motor Company.
The Thermometer Shows 86° But the
Engine Still Does Not Run
Operation of Stirling engines is dependent on a temperature difference. If the engine was running on hot water
and the thermometer now shows a temperature of 86° it is
likely that there is no longer a temperature difference of
40°F or more. This is a normal condition. Reheat the
water (boiling is acceptable) and start the engine again.
How to Get A FREE Book
If you have any experiments that you feel should be
included in the next edition of this manual, we would love
to hear from you. If we use your experiment in the next
edition of the manual we will give you a Free copy of
“Introduction to Stirling Engines” by Jim Senft. Write up
your experiment and mail it to
Magic Motor Company
1945 N. Rock Rd. Suite
1012 Wichita, KS 67206
More STIRLING Information
Additional information on Stirling engines is available
from:
Stirling Machine World [ Brad Ross, Editor]
1823 Hummingbird Court
West Richland, WA 99353 9542
(509)-967-5032
Stirling Machine World publishes a quarterly newsletter.
Additional books and video tapes on Stirling engines are
also available.
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012-06055A The Visible Stirling Engine
T echnical Support
Feed-Back
If you have any comments about this product or this
manual please let us know. If you have any suggestions
on alternate experiments or find a problem in the manual
please tell us. PASCO appreciates any customer feedback. Your input helps us evaluate and improve our
product.
To Reach PASCO
For Technical Support call us at 1-800-772-8700 (tollfree within the U.S.) or (916) 786-3800.
email: techsupp@PASCO.com
Tech support fax: (916) 786-3292
Contacting Technical Support
Before you call the PASCO Technical Support staff it
would be helpful to prepare the following information:
• If your problem is with the PASCO apparatus, note:
Title and Model number (usually listed on the label).
Approximate age of apparatus.
A detailed description of the problem/sequence of
events. (In case you can't call PASCO right away, you
won't lose valuable data.)
If possible, have the apparatus within reach when calling. This makes descriptions of individual parts much
easier.
• If your problem relates to the instruction manual, note:
Part number and Revision (listed by month and year on
the front cover).
Have the manual at hand to discuss your questions.
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