Paddlewheeler trunk steam engine - help me id and restore it

[Eddy Matthews]

To clarify a little, (or confuse a lot?), here's a typical trunk engine...

The trunk engine, a type of direct-acting engine, was developed largely as a result of the demand for warships to have a powerplant with a profile low enough to fit entirely below a ship's waterline, where it would be as safe as possible from enemy fire. The type was generally produced for military service by John Penn.

This type of engine had a horizontal cylinder, through the centre of which passed a cylindrical "trunk" or passage containing the connecting rod. The walls of the trunk were either bolted to or cast as one piece with the piston, and moved back and forth with it. The working portion of the cylinder was annular or ring-shaped, with the trunk passing through the centre of the cylinder itself.

Eddy

[kno3]

Hello,

I have started disassembling the engine for clean-up and also because I was very curious about the pistons. As you can see, it didn't have any gaskets and also no traces of liquid sealant. I guess whoever cleaned this engine up in the past and painted it, didn't run it, just kept it for display. YOU CAN CLICK ON THE PICTURES FOR A LARGER VIEW.

2010-11-27 003 by -kno3-2, on Flickr

Here is what I have found inside, the piston is as i had expected, wider than the trunk.

2010-11-27 004 by -kno3-2, on Flickr

And a close-up of the piston + trunk assembly.

2010-11-27 005a by -kno3-2, on Flickr

Well, given this piston configuration, it means that one side of the cylinder (upper) has much less volume than the other (bottom).
I'm wondering if or how this would affect the way the engine runs. However, since the larger cylinder volume is on the upper stroke, perhaps things get somehow balanced, because it requires more power to lift such a heavy cylinder + trunk assembly than to lower it. Seems reasonable - does it make sense to any of you?

Here are some more views of both pistons out of the cylinders.

2010-11-27 014 by -kno3-2, on Flickr


2010-11-27 017 by -kno3-2, on Flickr

The upper cylinder covers have yarn for insulating the trunk.

2010-11-27 018 by -kno3-2, on Flickr

Well, I am still considering how to proceed with getting this engine back to running condition. The option I'm thinking about are:
1. Re-assemble using liquid gasket (Hylomar), which seems the easiest solution.
2. Make some Teflon gaskets for the cylinder covers (and bottom covers as well?), as I have some Teflon sheet.
3. Since the pistons are plain, I am also considering cutting a small groove into them, to hold either an O-ring or some rolled Teflon tape. This should greatly improve the running of the engine, especially at low pressure.

What do you think?

[derekwarner_decoy]

Hi PD's....&  .....what a great project kno3 & 

1) lets call the extension side of the piston the BLIND side & the retraction side of the piston the ROD side
2) it would be interesting to understand the ratio of diameters ie., the blind side diameter & the rod diameter
3) we must remember that all simple double acting steam engines have this 'blind side to rod side ratio'
4) In photograph 2010.11.27.017...in the left hand cylinder base we see counterbores @ 10.0, 7.0 & 3.0 o-clock
5) we also see three equally spaced similar diameter pegs on the piston blind face
6) I assume these are to limit the piston stroke & hence not block the steam admission ports & get a full face for liftoff ?...however the crankshaft 'throw' limits piston stroke & so shouldn't bottom out anyway.....
7) In photograph 2010.11.27.004 & 005a..... ...is the rod side gland upside down
the rod side gland has very little parent material on the ID of the PCD of the bolt holes to 90 degree face for Hylomar to seal ...teflon sheet would have the same issue & be difficiult to cut  with such a thin surface between diameters
9) you could use the same setup in the lathe when you make the rod side gland o-ring cavities...& also machine o-ring cavities for the spigot diameters ....that would solve those two issues
10) this then leaves the piston sealing........this page is near full limit.........  ...I will post another page .....Derek

[kno3]

Hi PD's....&  .....what a great project kno3 & 

1) lets call the extension side of the piston the BLIND side & the retraction side of the piston the ROD side
2) it would be interesting to understand the ratio of diameters ie., the blind side diameter & the rod diameter
3) we must remember that all simple double acting steam engines have this 'blind side to rod side ratio'

I didn't get to measure things up yet, but it is on my to do list.

4) In photograph 2010.11.27.017...in the left hand cylinder base we see counterbores @ 10.0, 7.0 & 3.0 o-clock
5) we also see three equally spaced similar diameter pegs on the piston blind face
6) I assume these are to limit the piston stroke & hence not block the steam admission ports & get a full face for liftoff ?...however the crankshaft 'throw' limits piston stroke & so shouldn't bottom out anyway.....

No they are not there to limit anything. They are 3 screws that hold the piston together, and the 3 counter-bores are there so that these screws don't hit the cylinder bottom. I'll post some more pictures with the piston disassembled.

7) In photograph 2010.11.27.004 & 005a..... ...is the rod side gland upside down
the rod side gland has very little parent material on the ID of the PCD of the bolt holes to 90 degree face for Hylomar to seal ...teflon sheet would have the same issue & be difficiult to cut  with such a thin surface between diameters
9) you could use the same setup in the lathe when you make the rod side gland o-ring cavities...& also machine o-ring cavities for the spigot diameters ....that would solve those two issues

You've lost me with all the abbreviations. But if you look at this pic closer

2010-11-27 018 by -kno3-2, on Flickr
you'll see how the trunk (rod, whatever) is sealed: the smaller ring compresses a spiral of (cotton?) thread, which you can see in there. That thread is kind of short on one cylinder, so I'll replace both with Teflon tape which I will twirl first, to make a thread out of it. Done this before, it is quite easy and very effective.

10) this then leaves the piston sealing........this page is near full limit.........  ...I will post another page .....Derek

Shoot! 

[kno3]

Now back to business: I have managed to disassemble the piston+trunk and this is what it looked like. Lot's of dirt accumulated in there. The connecting rod is not bent, just thinned on one side to clear the trunk.

2010-11-27 023 by -kno3-2, on Flickr

After some cleaning up:

2010-11-27 024 by -kno3-2, on Flickr

During disassembly, a steel screw decided to shear off...

2010-11-27 025 by -kno3-2, on Flickr

I have spent an hour filing the stub flat, and then carefully boring it out with 1 and 1,5 mm drills. Then I was able to remove it and luckily I didn't damage the thread in the brass part!

2010-11-27 026 by -kno3-2, on Flickr

[derekwarner_decoy]

mmmmmmmmmmm 

11) you certainly have sufficient room for piston o-rings & gland spigot o-rings
12) we have previously discussed the advantages & disadvantage of both VITON & Silicone o-rings as they both have a very low abrasion resistance...but are suitable for our ~~~~~150 degrees C steam temperature when coupled with steam oil, however we must also remember that o-ring manufacturers nominate 1.6 umRa as the required surface roughness
13) we also must remember that TEFLON has ZERO memory & will not pressure energise in our low pressure dynamic applications ....this is totally different to high pressure static steam gland spindle application where if we get a bypass, the gland is mechanically tightened to compress the TEFLON packing

It will also be interesting to learn the diametrical clearances between the piston & the barrel ....& also the rod & the gland.......as Viton & Silicone also must have minimal exrusion gaps  ....Derek

[Eddy Matthews]

Just to clarify, the abreviations Derek has used:

ID = Inner diameter (or Inside Diameter)
PCD = Pitch Circle Diameter

Regards
Eddy

[derekwarner_decoy]

Thanks Eddy......please see that attachment as ......

the rod side gland has very little parent material on the ID of the bolt holes to 90 degree face for the Hylomar to seal ...teflon sheet would have the same issue & be difficiult to cut  with such a thin surface between diameters

Sorry all ....PCD was a silly term to use .....Derek

[kno3]

OK now I think I know where the misunderstanding is: I won't put any Hylomar there. The Hylomar was meant for sealing the larger ring to the cylinder (but I'll try to make a gasket first).
To make things clear - the ring with 4 screw holes compresses the gland packing and fits into the ring with 6 holes (which is the cylinder cover):

2010-11-27 017 by -kno3-2, on Flickr

[derekwarner_decoy]

Hi PD's....just thinking again kno3
14) the cylinder barrels are probably bolted in the same manner to the lower engine plate....so will require re-gasketing
15) the steam chests will also have inner & outer faces that will also require gasketing
16) JMC uses 0.02 mm thick TEFLON sheet for his engine gaskets...although I suspect he has purpose built dies to stamp out his gaskets
17) TEFLON sheet material is rather unforgiving & if used would require far higher bolt torque levels to achieve steam tightness...over the Hylomar steam sealant
17) one of the better methods of cleaning up horizontal engine component surfaces is a 12"square pane of glass + a sheet of 1200 W&D paper...then hand rotation lap or <<<< ....>>> lap with water...you will see evidence of bronze/brass dust in the water ...but essentially the amount of material removal is near non measurable for our purposes
18) you also mentioned in your very first post here that you thought the steam valve gear rod thread was imperial.....is this the case? & are all the engine dimensions imperial?

Keep us posted........Derek .......

[kno3]

Hi PD's....just thinking again kno3
14) the cylinder barrels are probably bolted in the same manner to the lower engine plate....so will require re-gasketing
15) the steam chests will also have inner & outer faces that will also require gasketing

You are right about both.But the steam chests only require 1 gasket as they have no separate cover.

18) you also mentioned in your very first post here that you thought the steam valve gear rod thread was imperial.....is this the case? & are all the engine dimensions imperial?

Keep us posted........Derek .......

Yes, the screws and threads are BA sizes.

Thanks for the advice re. Teflon and lapping.