Author Topic: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine  (Read 15073 times)

Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #120 on: December 13, 2019, 09:29:02 PM »
Have you seen my other Stirling engines run JB  ::)

 <a href="https://www.youtube.com/watch?v=IyDsfIYnyRw" target="_blank">http://www.youtube.com/watch?v=IyDsfIYnyRw</a>

 I am expecting the same out of this one the problem is that the displacer piston is thicker than the displacer cylinder so that while the outer one warms up the inner one does not at the same rate and, as I have learnt, trying to heat it up faster with these high efficient surfaces is not a good idea  :hellno:

Any way I was trying a quick run without any plumbing: The plumbing is there to cool the power cylinder not warm the displacer piston which is what is required. One of the next jobs is the water pump but I am thinking about modifications to it so it might take longer than just bashing it out..

Jo
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Online Jasonb

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #121 on: December 14, 2019, 07:18:27 AM »
I have Jo. I did not say the tea light would not work, you made that decision by using another heat source.  I said that if you were getting the end red hot in a "couple of seconds" that your burner was too hot.

I have also noticed that there are far more linkages and pivots on this engine together with a light aluminium flywheel. The tea light may well work when all is run in but a LITTLE more heat may be needed to get things started initially.

As for the preheating suggestion. Heat travels from coldest to hottest, by preheating the alloy castings will be warm so rather than acting as a heat sink and drawing all your initial heat away from where you want it the heat will go to the cooler parts of the engine which is where you want it. Bringing the engine inside for a few hours and standing near the woodburner will also do a similar thing.
« Last Edit: December 14, 2019, 07:27:59 AM by Jasonb »

Offline Alyn Foundry

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #122 on: December 14, 2019, 01:49:45 PM »
Good afternoon folks.

There seems to be a little confusion about the role played by the " Displacer " piston in a Sterling engine. I'll try to explain.

Any gas, air in our case, expands in volume when heated. If we confine this volume in a sealed system then the expansion becomes a pressure increase acting upon the container. If we allow part of this container to move ( power piston ) then that pressure will move the piston outwardly. Conversely, when we cool the container the gas reduces in volume and the power piston will naturally return to its starting position.

Putting aside the role of " Regeneration " for a moment, let's consider the " displacer " piston. Ideally this piston needs to remain " temperature neutral " as its single task is to move the working fluid, air, between the two temperature differentials, the hot and cold ends. In practice, although air is a poor conductor of heat the bottom of the displacer piston will heat up, partially due to radiation from the heat being applied from the outside.

By phasing the two pistons movements by 90 degrees we can now get the air to either heat up
( expansion ) or cool down ( contraction ) to act upon the power piston. This reciprocating action is then converted, by the crank into a rotary motion. During its development many different ways of providing this phasing were tried, by far having the cylinders placed at the 90 degree angle was the simplest and least energy sapping of them all.

The Robinson model has a crude form of " regenerative " displacer piston. The housing contains a large volume of densely packed wire wool that try's to " grab " some of the heated air as it is passed towards the cold end. Conversely as the air is being moved back towards the " hot end " some of the captured heat is given back, slightly aiding the efficiency.

The Ericsson model has a totally sealed displacer piston so the air has to travel around it rather than through it. Not that it matters it's the displacement part that really counts. The transfer of the working fluid between the two differentials, hot and cold.

The only reason a hot air ( Stirling cycle ) engine works is because we have the two different temperature zones
( extremes ) if you will. Once those differences near equilibrium nothing is going to happen.

Cheers Graham.



Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #123 on: December 17, 2019, 04:03:26 PM »
Thanks Graham  :)

I have not yet returned to trying to run the engine as I have been allowed another set of castings  :D on condition I take my cold away with me to the Workshop and work on the water pump for this engine.

The original design is based around the use of a piece of 19mm square brass. I have a piece of this Thank you Dave   :ThumbsUp: About this point I will be deviating from the published design: I will be making the main body in two parts with a flange joining the two bits more like the original... I already have the rear mounting plate so the next bit is the upper part of the pump body. This should be a simple turning and reaming job but the reamed hole is of course a deep hole and longer than your standard reamer  :Doh: This just means I had to be really careful reaming with a standard length reamer. The end is then tapped for the gland nut.

The lower part of the main body is also taken from a piece of 19mm square brass, this time 25mm long which is held offset to enable the plumbing hole boss to be turned and the thread tapped.

Next up I need those two flanges  :thinking: But it is getting late and I have a new set of castings to fondle :naughty:

Jo
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Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #124 on: December 20, 2019, 03:26:31 PM »
The two flanges were cut from a piece of 3mm thick brass 19mm wide. first the holes were drilled and the two centred bored to fit the end of the main body of the pump before filing to shape. The bottom of the pump then needed to have a register turned on to it before drilling the water hole that doubles up as the seat for the bronze ball that is going to act as the clack valve.

The two sides have been cut out of a bit of scrap-bin-ium. Originally I was going to waste use a piece of 25mm wide by 1.6mm brass and have to cut it down to the required 19mm wide. Instead I found a piece of 19mm angle the right thickness that someone had taken a chunk out of for something which still had one side of the angle intact so I used that instead.

Finally I was ready to solder everything up... The instructions in the book say use soft solder but I should have used hard solder as the brass retains its heat for a long time and things can still move  :facepalm2: Once soft soldered up the bottom of the pump was filed to shape and I have an almost acceptable pump body  :)

Jo
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Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #125 on: January 26, 2020, 03:03:47 PM »
The pump piston/valve is a tricky little bit. The temptation would be to turn it up to size and then cut the three slots but that just makes it difficult to hold the thing to cut the slots  :Doh: .

I started by mounting a longer piece of 9.5mm brass in a chuck on the BCA, the table on the BCA is also a rotary table which makes it easy to rotate the required 60 degrees for each of the holes. With the 2mm holes drilled I could then swop over to a 2mm slot drill and, using the rotary table, mill between pairs of holes to form the three required slots to a depth of 4mm. This piston is only 3mm thick but the extra depth of the slots means the face can be cleaned up on the lathe, the centre drilled 2.2mm and then parted off and the slots will still be intact.

The other item needed for the pump is a little plastic plate which fits above the piston which is a simple turning task. With this part finished all that was needed was to open out the central hole in the valve to provide a tight push fit onto the pump piston rod.

There is not much of this engine left now  :)

Jo
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Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #126 on: April 03, 2020, 03:28:04 PM »
Negotiations for another set of castings has failed because I have been told like the rest of us they are in lockdown  :wallbang: So  I have returned to the Rider-Ericsson now that the "o"rings have finally turned up from China for the top of the power piston. After all the waiting for them I have decided they are a waste of time and will not be using them: the fit of the piston to the bore is bouncy and the O ring comes out of the top of the cylinder and makes it harder to get the piston back into the cylinder.


I have started painting the bits. She is going to be a lady in Red like the original engines, this makes a change for me as this is my first engine I have painted red  ::).


While the various layers of paint go off I have started looking at the plumbing. On the original engines there seems to be air traps both in the water in and water out to the engine  :headscratch: I can see the need for the one on the way in because it is there to try to prevent air getting into the pump (which also has an air bleed valve I have not yet done  :facepalm: ) but why on the way out  :thinking: unless that was used to pump into the house the engine provided water for.

Both the cylinder and the pump have been tapped 3/8 26tpi, logically this implies the use of 9.53mm copper pipe but I have decided it looks out of scale so will be using 8mm which is lucky as I have some of that. To begin I have cut two pieces of thick wall brass tube and threaded them 3/8" 26tpi to fit the cylinder and the pump, next up I need to make a couple of tee pieces, these will take the threads down to 5/16" 26tpi for the 8mm copper pipe.

Jo
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Online Jasonb

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #127 on: April 03, 2020, 04:10:40 PM »
Jo by " air traps" do you mean the air chambers that are there to damp the changes in pipe pressure and give a more constant flow?

Be careful with that red paint, once you have done an engine in red it's hard to use anything else :-[

Offline Alyn Foundry

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #128 on: April 03, 2020, 04:11:39 PM »
Hi Jo.

The one on the outlet is to reduce the pulsing effect that would be seen at the delivery, the air being compressed helps even the water flow.

Cheers Graham.

I see Jason beat me to it   :)   I've just come in for a cuppa, pleased to report that there'll be a bonanza of line boring of engines later as I now have two strapping lads to aid me.
« Last Edit: April 03, 2020, 08:45:26 PM by Alyn Foundry »

Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #129 on: April 08, 2020, 03:48:47 PM »
The engine is slowly coming back together.

I have put a nut under the top fitting on the displacer rod to lower the displacer in the cylinder and for use as a lock nut.

I have made two tee unions for the water feed and outlet out of brass bar silver soldered together.   These each have two threads 3/8 by 26  for where the piping goes into the engine and for the air chambers and the third is threaded 5/16 by 26 for the 8mm copper pipe. Once mounted on the engine you can see how close the rear one is to the flywheel.

Next job is to make the firebox and sort out a chimney, there are variations on the design of these  :thinking:

Jo
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Online Jasonb

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #130 on: April 08, 2020, 04:52:09 PM »
Looking smart and I like the beads on the pipe fittings :)

Offline Chipmaster

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #131 on: April 08, 2020, 06:44:02 PM »
Should be running very soon :ThumbsUp:

Andy

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #132 on: April 08, 2020, 09:00:29 PM »
Looks sharp, Jo.  Can't wait to see it ticking over... :popcorn:

Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #133 on: April 11, 2020, 03:30:31 PM »
Thanks Guys but things are going slowly  :(

The mounting bracket round the firebox took me a while to get right. I started with two pieces of 3.2mm square steel and bent them into two U shapes to go around the firebox.

I then needed the four lugs which were cut out of a piece of scrapbin-ium. The dance to join the pieces was over come by drilling holes and putting a rivet through, having not forgotten to flux the joint first  :)

It could then be silver soldered up and the fit checked. I am pleased to say it is a nice tight, tap down with a hammer fit  :wine1:


Why is it you can explain something that takes days to do in very few words   :noidea: It must be time to think about the other firebox fittings

Jo
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Offline Jo

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Re: Camden 3" scale Rider-Ericsson Hot Air Pumping Engine
« Reply #134 on: April 12, 2020, 04:41:50 PM »
The chimney was also fun  ::)

There are two styles of chimney on these engines one comes out with an elbow up to the chimney: The drawings use a copper bend fitting to do this but I couldn't get hold of one to fit. So I was stuck with the second design that has a flattened oval coming out of the back of the box and the chimney fits on the top.

Having found a piece of 1.2mm plate I punched the hole for the chimney then bent the metal round to form the flattened oval shape. To this I added a brass fitting which allows the chimney to be a sliding fit over it and makes the silver soldering job easier. I chose to fill both the inside and the outside using a flat plate. This I regretted as they are on opposite sides and it made silver soldering difficult  :ShakeHead:

Having soldered it together a bit of filing then it was time to check the fit  :thinking: it seems to clear everything.

Jo
« Last Edit: April 12, 2020, 05:05:02 PM by Jo »
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