Sources for steam engine packing material

[toad281]

I am working on a 2-cylinder steam engine build. both cylinders are double acting. Stationary cylinders with crossheads. The bore of the cylinders is 1.250 inch, and the stroke is 2 inches. I am looking for a source to get some packing for the connecting rod fitting and to use on the valve mechanism. The connecting rods are 0.25 diameter and will pass-through a brass packing fitting that has a 0.028 hole necked to .5 inches. I need advice on the packing material to use and where to get some. I see the graphite packing on granger, but I really do not need the lengths that they sell. Does anyone know place that sells short, [12 inch] pieces? I also thought perhaps a better option would be to get some vitron o-rings to fit, instead of the graphite. I bought and have installed them on the pistons, but don't know if they would work for sealing the connecting rods.I can not see a reason they would not work, but I thought it better to post a question here. I will post some pictures soon of my progress. Thanks in advance, and thanks again for all the help so far.

 

[raveney]

Hi Toad,
A hardware store will sell a small quantity in the plumbing aisle. Ace Hardware sells 2 ft for $3 for valve packing.

ace hardware graphite

I believe graphite packing is superior to Viton o-rings because it conforms to any non-concentricity of the packing and stem. It also swells a bit once steam hits the yarn and lubricates too. We have cases of it at work for the 1000s of steam valves.
Only valves that have o-ring packing are the small air solenoids and low temperature ball valves.

I am in the midst of a similar steam engine build as you described. Check it out: Muncaster Joy Valve 1/2 scale

link

 

[toad281]

I believe I bought that very package [although a different size] from a local ACE hardware store. I tried using it on a previous build but had some issues with it. After cutting the material, and stuffing the gland, I applied a drop of 3+1 oil to the shaft. [figuring it would be exposed to the oil in the live steam anyway] before installing the packing nut. The stuff I have turned into a gooey sticky mess that needed acetone to clean up. I will dig out the package of packing I bought and look it over again. Maybe I bought something other than what I thought it was. Thank you for the reply.

 

[plipoma]

Yes, O'Rings have too much friction.
There is a product called Grafoil! It's in the form of a tape and has no fiber base. I have used it very successfully. Make a 2 piece mold the size of the gland you need, pack the mold with Grafoil then pressing it. It makes a perfect gland that seals with very low friction the size you need. See URL below!

https://www.aspseal.com/grafoil.html

 

[Richard Hed]

I am working on a 2-cylinder steam engine build. both cylinders are double acting. Stationary cylinders with crossheads. The bore of the cylinders is 1.250 inch, and the stroke is 2 inches. I am looking for a source to get some packing for the connecting rod fitting and to use on the valve mechanism. The connecting rods are 0.25 diameter and will pass-through a brass packing fitting that has a 0.028 hole necked to .5 inches. I need advice on the packing material to use and where to get some. I see the graphite packing on granger, but I really do not need the lengths that they sell. Does anyone know place that sells short, [12 inch] pieces? I also thought perhaps a better option would be to get some vitron o-rings to fit, instead of the graphite. I bought and have installed them on the pistons, but don't know if they would work for sealing the connecting rods.I can not see a reason they would not work, but I thought it better to post a question here. I will post some pictures soon of my progress. Thanks in advance, and thanks again for all the help so far.

May I ask just which engine your are making? I intend to build a 2 cyl some time and am looking for ideas.

 

[Chiptosser]

Has anyone tried using Teflon thread sealing tape to make rod packing??
I use the rope in my Stirling hotair engine.

 

[packrat]

McMaster-Carr will sell you what you need, go to there catalog page..

 

[toad281]

May I ask just which engine your are making? I intend to build a 2 cyl some time and am looking for ideas.

This build is almost completely scratch built. The cylinders are repurposed from parts of a vintage backhoe that I own. Hardwar will be store bought for the most part. It is to be used in a radio-controlled sternwheeler approximately 7feet in length. This is not my first scratch build motor nor radio-controlled boat, although it will be my first sternwheeler. The other steam engines I have built I used graphite washers designed for carburetors. However, I have none of those left. I was researching and came across the idea of using ones made for Colman type pressure gas camping applications. I have to do a bit more research on them. I am sure, when this is done, she will not win any beauty contests. Just a project to putter about the lake.

 

[toad281]

Yes, O'Rings have too much friction.
There is a product called Grafoil! It's in the form of a tape and has no fiber base. I have used it very successfully. Make a 2 piece mold the size of the gland you need, pack the mold with Grafoil then pressing it. It makes a perfect gland that seals with very low friction the size you need. See URL below!

https://www.aspseal.com/grafoil.html

I visited the website provided [thank you] It seems the smallest amount they sell is 170 feet. I need just a few inches. It is also out of my budget

 

[plipoma]

McMaster Carr has 1/4" wide by 50 ft long graphite tape for $8.40 along with other sealing materials.

 

[Steamchick]

I have some graphited string for gland packing. I have also used twisted plumbers PTFE tape to make a fine string for gland packing as well. Works about as well as the graphited string, but can be fiddly to get right. No good for pistons.
O rings - with ZERO interference - if Viton or Polyurethane (very special ones!), can be useful for piston rings, but are designed for ZERO interference for axial motion and low speed. So only good in model engines if well lubricated and on very finely polished bores... (like the hydraulic finish on a brake cylinder!). In the average steam engine they wear quickly, especially on regular cross-hatched cast iron bores.
Some steam engines are quite successful without piston rings, but using labyrinth seals. (4 to 6 grooves of the narrowest cut you can make - say 16th inch - and the same depth as width).
Labyrinth seals as piston seals work by pressure drop at each change of leakage passage cross-sectional area. Sharp corners are needed. A piston seeing 100psi and with 5 grooves will have 10 "changes" of leakage CSA - so 5psi drop at each, thus restricting the leakage to "not a lot" due to aerodynamic turbulence at each groove corner... I use a hacksaw blade to make a tool that is only as thick as the blade. Grooves the same depth as blade thickness, and spaced the same as blade thickness.
Just not good enough for infernal combustion engine pistons though.
K2

 

[Steamchick]

On a factory job we had custom made (Solid) PTFE rings for gas-seals of pistons and (ground and polished) shafts. Low friction, but poor durability. Can work well on steam engine pistons in well polished bores. Just DO NOT BREATH THE DUST when machining. If it gets hot the fumes are DEADLY Flourine products. (invisible).
K2

 

[toad281]

McMaster Carr has 1/4" wide by 50 ft long graphite tape for $8.40 along with other sealing materials.

I have some graphited string for gland packing. I have also used twisted plumbers PTFE tape to make a fine string for gland packing as well. Works about as well as the graphited string, but can be fiddly to get right. No good for pistons.
O rings - with ZERO interference - if Viton or Polyurethane (very special ones!), can be useful for piston rings, but are designed for ZERO interference for axial motion and low speed. So only good in model engines if well lubricated and on very finely polished bores... (like the hydraulic finish on a brake cylinder!). In the average steam engine they wear quickly, especially on regular cross-hatched cast iron bores.
Some steam engines are quite successful without piston rings, but using labyrinth seals. (4 to 6 grooves of the narrowest cut you can make - say 16th inch - and the same depth as width).
Labyrinth seals as piston seals work by pressure drop at each change of leakage passage cross-sectional area. Sharp corners are needed. A piston seeing 100psi and with 5 grooves will have 10 "changes" of leakage CSA - so 5psi drop at each, thus restricting the leakage to "not a lot" due to aerodynamic turbulence at each groove corner... I use a hacksaw blade to make a tool that is only as thick as the blade. Grooves the same depth as blade thickness, and spaced the same as blade thickness.
Just not good enough for infernal combustion engine pistons though.
K2

Thanks for all the information. It just so happens that the cylinders I am utilizing are hydraulic brake cylinders. The last model I made had no rings, cast cylinders and brass pistons. It was a much smaller model and was built just as a learning experience. I will try this with the Vitron o-rings, and if it is unsatisfactory try using the labyrinth type sealing. [By the way it is also used in steam turbines] I found some graphite string used for colman products and ordered some last night. I will have to see how that works. I have used graphite packing in steam valves before but that was in my occupation, and much larger than anything needed for model engines.

 

[Steamchick]

For viton o-rings to work they must be size on size to the bore, "sliding fit" tolerances, and not compressed in any way. The pressure and dynamic forces will provide adequate elastomer distortion to form the seal.
K2

 

[metalmangler]

Some steam engines are quite successful without piston rings, but using labyrinth seals. (4 to 6 grooves of the narrowest cut you can make - say 16th inch - and the same depth as width).
Labyrinth seals as piston seals work by pressure drop at each change of leakage passage cross-sectional area. Sharp corners are needed. A piston seeing 100psi and with 5 grooves will have 10 "changes" of leakage CSA - so 5psi drop at each, thus restricting the leakage to "not a lot" due to aerodynamic turbulence at each groove corner... I use a hacksaw blade to make a tool that is only as thick as the blade. Grooves the same depth as blade thickness, and spaced the same as blade thickness.

Do labyrinth seals work on engines powered by compressed air ? I'm building a Kennions 'Tina'. The piston (about 1" dia) and cylinder are both gunmetal. How much clearance should I allow between cylinder and piston for a labyrinth seal ?

 

[Steamchick]

Metal Mangler: Labyrinth seals are very good for all gases. They rely on gas turbulence at each change from narrow-to-wide and wide-to-narrow leak passage, and need a little leakage to work. Try this for sliding fits. H8 hole, f7 or f8 piston. (roughly size to +0.0005" bore, versus you nearest size to -0.0005" piston). A 0.5mm (0.020") to 1mm (0.040") wide blade cutting a groove of the same dimension depth as the blade width is very good. Keep the groove outer corners sharp and do not chamfer them.
https://in.misumi-ec.com/pdf/fa/2014/p1_2287.pdf I used them on industrial equipment with high speed valves needing "no" friction. Also on Oscillating engine pistons (~1/2"dia and 3/4"dia).
As you are using the same materials there will be no need to accommodate for differential expansion, providing the clearance exists and is suitably lubricated (an air tool oiler may give too much oil?) But air tool oil is good for these engines. - Blow it and see!).
Otherwise 40microns is a good guide. (0.04mm, ~0.0016")
K2

 

[Zeb]

Metal Mangler: Labyrinth seals are very good for all gases. They rely on gas turbulence at each change from narrow-to-wide and wide-to-narrow leak passage, and need a little leakage to work.

I had no clue they were used (with that name) outside of turbine engines. The seals typically work with main bearings with gas piped from the gas producer. One of the reasons propellers get tied down is those will grind down some and start leaking. With enough wear you can hear a harmonic buzz at startup. At 30k+ RPM everything floats happily.

 

[Steamchick]

I didn't know they were used in Turbines, but Labyrinth seals are in lots of things. I used them (at work, in the 1980s) on high speed pneumatic valves.
K2

 

[toad281]

Well, it looks like you have talked me into changing to the labyrinth seals. I will also try the hacksaw blade tooling that was mentioned. Always game to learn something new. [Even at my age]

 

[Steamchick]

Good luck Toad281 - or should we call you Methusalah if you feel so old? We (relatively) young folk still enjoy learning every day from the shared ideas on this site.
But don't be shy, blame me when it goes wrong. (Many have). You'll feel less upset.
K2