Glands---

[Brian Rupnow]

No, not swollen glands.---The other kind, like you see on the end of a steam cylinder or valve chest, where the piston or valve rod exit. I have built about a dozen double acting steam (air) engines now, and up untill the Popcorn engine, I never used glands. Just a reamed exit hole that was a "good sliding fit" on the rod, to prevent air loss around the rod. I didn't use them, because I deemed then as being extra work, and unnecessary for the small models I was building. And there was a third reason, that up untill now I never had actually proven, but had theorized. I openly admit that I am a total Putz at single point threading. Consequently, I create all of my threads using taps and dies. I have noticed several times while threading different sizes of rod, using die holders in the tailstock of the lathe, that the threads I cut were never quite concentric with the rod they were on. I know my tailstock is "centered" properly. I know my die holders that fit in the tailstock are a good fit on the outer diameter of the die, and are concentric. My dies are new and sharp------But still, the threads are always a bit "off".---Do you see where this is going?---I concluded that any gland nut I machined with a reamed hole in the center for the rod and threads on the outside where it screwed into the cylinder or valve body would give me fits, because of non concentricity issues. And I was right!!! My Popcorn engine runs like a charm on about 15 PSI unless I snug down the gland nuts. IF I snug them down, it takes 60 PSI to run the engine------and its all because of my theorized non concentricity issues. Perhaps I'm going about this wrong. I don't have any packing in the glands right now, so maybe if I can figure out what to use for packing, the gland nuts don't have to be tight enough to cause me a problem. I would like to hear some input and advise from other model engine builders on how they handle this issue, please.----Brian

 

[Catminer]

Hi Brian;

Use Teflon tape twisted into a string , works well on on my fuel pumps and fittings as a rope packing, low friction and wears well.
Peter

 

[kvom]

You can drill/ream the gland nuts after screwing them into the cylinder head or chest as long as you can accurately hold the assembly in a milling vise or lathe chuck. However, you will get a better seal if the packing nut bore is a bit larger than the rod and some packing material is compressed by the nut.

On my loco build the gland is a bronze bushing that retains an o-ring. The ring provides the seal. Both the cylinder head and bushing bores are a few thou larger than the rod. That's another option.

 

[steamer]

I've used the graphite packing and orings and I like viton orings better
Dave

 

[mklotz]

I'm surely no expert but I don't see the concentricity of the threads with the valve stem hole as a major problem. Any minor concentricity issue can be corrected by making the hole in the gland nut slightly larger, not so? The hole in the gland nut provides no sealing. The gland nut serves only to compress the sealing material (graphite yarn, teflon string, etc.) around the valve stem and the hole through which it passes into the valve chamber.

I've never single-pointed the threads on the glands on my small models and they seem to seal quite nicely.

 

[Brian Rupnow]

Marv, those were my thoughts as well. I couldn't see why the gland nuts had to be the same size as the rods that slid thru them, but not having built them before, I wasn't sure. I am certain that a couple of thou clearance wouldn't hurt, and it would certainly get away from the concentricity bind.

 

[SBWHART]

My Popcorn engine runs like a charm on about 15 PSI unless I snug down the gland nuts. IF I snug them down, it takes 60 PSI to run the engine------and its all because of my theorized non concentricity issues. Perhaps I'm going about this wrong. I don't have any packing in the glands right now, so maybe if I can figure out what to use for packing, the gland nuts don't have to be tight enough to cause me a problem. I would like to hear some input and advise from other model engine builders on how they handle this issue, please.----Brian

I'd go along with Marv on this it doesn't have to be perfectly concentric, I just drill and ream the bore and cut the thread with a die on the tail stop, before parting off. You have to take care not to over stuff the gland just a couple of turns then snug them down until you feal the load on the valve stem then just back off a tad. I also tuch the face of the nut with a drill so that you get a slight concave an the face this closes down on the packing pushing it onto the stem, well that my theory. :-\

When you tightened down on the nut with no packing the nut probably rode up the helix and pulled things off centre making the stem tight putting a drag on it.

Stew

 

[Jasonb]

Why thread them at all? do as full size and use plain shanks & hole and retain the gland with a pair of studs fitted with nuts & locknuts just like this, they can be made very small.

Cant see the point of reaming when in place as suggested by Kvom, as soon as you turn the gland to adjust the packing its likely to loose any concentricity.

I usually use the graphite impregnated yarn, you shoul dbe able to get this from a plumbing merchant as it sused to pack taps. Or as suggested PTFE tape folded into about 4 plys then twist it to make a string.

You don't need to wind the glands up tight when there is packing, just enough to close the packing around the rod.

J

 

[tel]

Wot Jason said! The 'proper' way to do 'em is plain, carried on studs - but they can be a real pig to adjust while running, which is why most builders opt for the simpler, screwed ones. No need for ultra precision tho - the packing takes care of the sealing, the gland itself is only a guide.

 

[Brian Rupnow]

Stew and Tel---a question for both of you.----When running these engines on air, do you actually notice any difference in their performance with or without packing?

 

[tel]

The short answer is yes, Brian - but you need to adjust the gland 'just so' - so that it is sealing but not putting undue pressure on the rod

 

[SBWHART]

The short answer is yes, Brian - but you need to adjust the gland 'just so' - so that it is sealing but not putting undue pressure on the rod

As Tel said and you have less air wastage so you get a longer run on a full tank of air, the motor doesn't kick in as often.

If you can get onto the gland I tend to tune as it runs, get a bit of oil around the gland nut so you can see the leak buble then just slowly tighten up until it stops at the same time watching for the engine to slow down your aiming for the sweet spot :- no leak with no slowing of the engine.

Stew