Metal packing vs. stuffing box

[Steam Captain]

I've found an interesting online article about the "Paxman-Lentz steam engine".
https://www.paxmanhistory.org.uk/paxlentz.htm

It explains in detail the working principle of the metal ring packing you can find in big steam engines. They are like piston rings around the piston rod and held in place by the "stuffing box" and I thought they work like piston rings. But it seems they work under a completely different working principle. In short, they are complicated labyrinth seals. At least this Paxman-Lentz type. Maybe other metal ring packings do work like piston rings. I don't know. It's just what I gather from the technical drawings.

So now I am wondering does anyone of you use one of these metal ring packings instead of a stuffing box in their launch engines? They seem to be designed for high-pressure apllications, where a stuffing box would have a harder time to work. On the other hand steam cars use stuffing boxes and they run a hell lotta pressure.

Does anyone use metal ring packings?

[RNoe]

I have machined and installed KING type Babbitt packing rings on a full-sized 2-6-6-2 steam locomotive.
Challenging to machine, they worked well for a long time. The spiral closing surfaces were the serious challenge.

Now I use regular packing collars on all my steam machines...
RussN

KingSeal.jpg (13.01 KiB) Viewed 7052 times

[fredrosse]

The main piston rod packing on my steamboat has been in service ten years now, it does not leak, and I have slightly tightened the gland nuts once, about 4 years ago.

The Margaret S engine is made with a piston rod from a high quality pneumatic cylinder piston rod, 5/8 inch diameter, very smooth and chrome plated. Far more precise than anything I could make, and plenty are available on ebay. The stuffing box uses 5 turns of graphite packing, 1/8 inch square. The stuffing gland used to compress the packing is a little over 5/8 bore, and a little under 7/8 OD, and held down with a spherical seated two bolt flange. The spherical seat assures better seating force in the axial direction, with less chance for side loads that might contact the bronze gland from scraping against the chrome plated rod.

I think that good alignment between the piston cylinder travel and the crosshead travel has much to do with this good long term performance.

[TahoeSteam]

Wayward Belle has u-cup seals and polished stainless steel piston rods. Zero leaks at 700 rpm and many miles with 175psi and 500° superheat. Pain to replace though as you have to pull the piston rod from the crosshead to slide the old one off and put a new one on, then get the depth of the piston just right again.

[Steam Captain]

So, I gather metal packing is more fore the non-private-sized engines. Well for sure some designs look very complex and consist of quite some pieces.

Good to know stuffing glands do the trick. But I guess they do swallow a lot of energy due to the friction, or?

[ccdewitt]

I have put mechanical packings in several engines with very good results. I used a bronze filled teflon product. It is spendy but works well. For longevity it is imperitive that the piston rods be very smooth and very straight like hydraulic piston chrome plated rod. I recommend it for superheat steam.

[DetroiTug]

I've been using general purpose square graphite packing from McMaster Carr for years. Cut it into rings and stagger the cuts when stacking the rings in the gland.

For piston rods I just use 303 mild stainless rod.

Never any issues with either.

The little Mason car engines use 3/8" brass piston rods.

Ron

[RNoe]

Steam Captain:
Mt steam locomotives use "regular" soft material packing glands.
Instead of using square graphite packing (which works perfectly fine) I used 1/8" diameter Teflon cord.
Several wraps around the shaft, and application of pressure from the packing gland presses the Teflon into a coherent shape that does not leak, wear, or ever seem to require adjustment. In 15 years of steaming my Ten Wheeler I have adjusted the packing only twice!
And even when cold it exhibits very little friction.

The attached picture shows my new Mikado with the same type of packing gland as my well-run Ten Wheeler.
You might need to enlarge your view to better see the packing gland setup.
And I cannot get this photo to post upright, regardless of how I choose its orientation. Sorry..
RussN

[DetroiTug]

Quote ''Several wraps around the shaft, and application of pressure from the packing gland ''

I've done it that way and it does work, but cut in to rings with staggered cuts evens out the force around the circumference of the rod. Prevents the rod from being pushed to one side.

The 120 year old steam car I'm restoring still had the old original oil soaked cotton or linen string packing in place, we ran it and adjusted the glands and they didn't leak. On the valve rods of those engine, there is no room for eighth inch packing, so I use the cotton string packing from McMaster Carr. Steam cylinder oil soaks into it and it lasts just fine.

Ron

[Steam Captain]

So, Many use teflon now, but "both" variants are used after all - chord and machined rings. I have experience with both from gasoline blowlamps (They either have what seems to be cotton chord packings or (I suspect) asbestos rings.

Are the machined rings squeezed like the chord stuffings or are they just held in place to be able to swim?

I don't always comment on it, but I really like the engines y'all are showing. They're radiating with the dedication and love put into them. Not that it's necessary at all (steam is in my blood), but it's really infecting to see. Link gears have a special magic.