Which pressure gauge to use?

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Bill Shields
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Re: Which pressure gauge to use?

Post by Bill Shields »

Or just shove your air hose in the firebox door, pointed toward the fire tubes and give it a blast.
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NP317
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Re: Which pressure gauge to use?

Post by NP317 »

That idea sucks...
RN
RET
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Re: Which pressure gauge to use?

Post by RET »

Hi Glenn,

Vacuums inside the smokebox will be quite low and likely would need an inclined manometer to measure. Using one of these while running the locomotive would be interesting, to say the least.

I had a similar problem with the Boston & Albany locomotive about 20 years ago, but I went at it a different way. I had been told by other club members that with any wide firebox locomotive, you had to really work them hard to get them to steam well and when I first ran it, it performed that way. I didn't think it should have to be that way so I started trying different things to make it better.

I had read Koopman's book, "The Fire Burns Much Brighter" and I learned quite a bit from that, especially where he talks about multiple blast nozzles and how the flow from them impinges on the stack. For a round stack, it seems that the optimum is four. So with this in mind, I took the blast nozzle and filed a cross in the orifice, then put a plug in the middle so I had four slightly rectangular nozzles. This seemed to help a little. I also decided to combine the blast nozzle with the blower, so I used a triangular file to file four grooves on the outside of the blast nozzle and then slid a hollow sleeve over the outside to form an annular chamber. Then I connected the blower to this chamber, giving me four little blower nozzles spaced around the blast pipe. This design is simple to make, effective and easy to install and remove.
Smokebox showing secondary petticoat in place.
Smokebox showing secondary petticoat in place.
It still didn't perform as well as I thought it should, so I remembered Joe Nelson's book where he talks about a "secondary petticoat." I raised the locomotive petticoat to give the room I needed and then made a secondary petticoaat that slips over the blast nozzle. With the secondary petticoat in place the difference is like night and day. The locomotive is a "pussycat" and anyone can run it. Take it away and it runs just the way I was told that any wide firebox locomotive would run.
Without secondary petticoat. You can see the petticoat lying horizontally at the bottom of the picture
Without secondary petticoat. You can see the petticoat lying horizontally at the bottom of the picture
The basic idea is that there is a lot of energy in the blast pipe exhaust, but to make effective use of it, you need to entrain the gasses in the smokebox, mixing them thoroughly and transferring the blast momentum to the larger volume that results from the mixing, then get it pointed out the stack.

In the pictures you can also see the superheater flues and tubes. I spent a lot of time figuring out how to put things in place so they were relatively easy to remove but still allowing access to the tubes for cleaning. The superheaters are stainless and they extend into the firebox, but only by 1 1/2 inches. On my "to do list" is extending them another 3 inches, but it hasn't happened yet.

I hope this helps a bit.

Richard Trounce.
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NP317
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Re: Which pressure gauge to use?

Post by NP317 »

That extra petticoat makes sense. On full-sized logging locomotives I have worked on, some had "annular venetian blind" petticoats:
Several tapered rings stacked together. An interesting setup for oil burners.
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Re: Which pressure gauge to use?

Post by Soot n' Cinders »

NP317 wrote: Thu Nov 28, 2019 11:37 am That extra petticoat makes sense. On full-sized logging locomotives I have worked on, some had "annular venetian blind" petticoats:
Several tapered rings stacked together. An interesting setup for oil burners.
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NP317
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Re: Which pressure gauge to use?

Post by NP317 »

Similar.
Picture 3 or 4 such rings stacked together.
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Glenn Brooks
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Re: Which pressure gauge to use?

Post by Glenn Brooks »

Richard and Tristan, very interesting! Fascinating that your design works so well in pratice. Coincidentally, just finished reading the part of Koopmans book discussing double petticoats - and four nozzles- first implemented by Chapelon(?) on the French railways around 1928. Seems like your design can produce up to 100% improvement in smoke box vacuum over single stack nozzles; meaning more draft across the fire and less backpressure in the cylinders. Exactly what I am looking for :o

Good stuff!

Glenn.
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RET
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Re: Which pressure gauge to use?

Post by RET »

Hi,

With the four small rectangular blast nozzles at the top of the blast pipe, there is space for the smokebox gasses from the lower part of the smokebox to come in between the jets and mix with them, then the combined mixture goes through the secondary petticoat at a lower velocity (conservation of momentum). After this mixing, the combined flow through the secondary petticoat entrains more gasses from the upper part of the smokebox and then the whole mass is directed out through the main petticoat pipe into the stack. This is in 3 1/2" gauge, for the other gauges you simply have to scale up the parts, just keep the proportions the same as you see in the pictures.

One thing you have to remember is that if the blast pipe is set too high in the stack, the blast won't "make a seal" inside the smokestack and the reduced pressure inside the smokebox can pull outside air down along the inside wall of the smokestack and into the smokebox. That is part of the reasoning behind the 1 in 6 and the 1 in 3 triangular cones that many people talk about when they are describing the proper positioning of the blast pipe in relation to the petticoat.

You can learn a lot from Josh Koopman's book "The Fire Burns Much Better."

This may be heresy for some, but when you have enough back pressure at the blast nozzle to give the exhaust a "bark," you are wasting power. The Boston & Albany (and our other locomotives) don't "bark," it isn't necessary, but if that's what you want, go for it!

Richard Trounce.
Glenn Brooks
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Re: Which pressure gauge to use?

Post by Glenn Brooks »

As Richard says, you can get draft into the smoke box from the top of the stack! I just tested my exhaust out the stack and found 1/3rd of my stack drawing air INTO the smoke box (blower offset a little) on the port side of my engine. I used a long strip of paper. The exhaust sucked the paper into the smoke box on the one side- yet blasted it out of the nozzle on the other. A real eye opener. Now, I think this was due to nozzle placement. Both blast nozzles and the blower nozzle are catiwampus, offset to the rear and left of center in th stack.

Glenn
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JJG Koopmans
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Re: Which pressure gauge to use?

Post by JJG Koopmans »

About the four nozzles, it does not make sense to position them on the same level as a single orifice. The optimal distance is about 6-7 orifice diameters, so with 4 orifices they are closer to the chimney entrance. As for the petticoats, I wonder why nobody cares to look again at the Goss experiments of about 1902. He condemns them all!
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RET
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Re: Which pressure gauge to use?

Post by RET »

Hi Glenn,

Yes, the axial alignment of stack, blast nozzle and blower nozzle are very important, as well as the vertical positioning of the components. As you found out, misalignment of the components can really affect performance. Using the long paper strip is a simple and effective way to see what is going on. Smart! Often simple things like this can give a better picture of what is happening than measuring pressure, velocity etc at a single point. As I said, adding the secondary petticoat makes a great difference, but the other components are important too.

When I first got "Jubilee," the 3 1/2" gauge 2-6-4 English tank locomotive, it had a simple copper tube loop with 4 holes drilled in it to serve as a blower nozzle and that wasn't really well aligned with the stack. It kinda worked. That is one of the many things I changed. This was also my first locomotive and I learned a lot from it. If I remember right, your locomotive has something similar.

Since what you have is somewhat of a Rube Goldberg setup, I would recommend that you adopt the blast nozzle and blower combination that I use in the Boston & Albany. A close look at the pictures combined with the description should give you the basic idea. As I said, it's easy to make and works well. In addition, concentricity of the blast nozzle and blower is built into the design. If you need more of an explanation, just say so.

Jos, thanks for still looking at the Chaski website. I'm glad you still find it interesting. I'll have to go back and reread parts of your book to refresh my memory. Jos, before I added the secondary petticoat, the main petticoat was quite a bit lower than is shows in the pictures, so the vertical positioning wasn't too bad although probably not optimum. With the addition of the secondary petticoat, I believe the vertical positioning is pretty close to optimum, at least it seems to be because of the greatly improved performance.

Richard Trounce.
Glenn Brooks
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Re: Which pressure gauge to use?

Post by Glenn Brooks »

Joss and Richard, thanks much for your input and suggestions. Looking forward to upgrading the Ottaway’s front end with a “state of the art” multi nozzle Lempor evaculator system. Apparently, Ottaway’s, as a standard class for amusement park locomotives, were originally not considered to be very efficient steamers. So I am hoping this will significantly improve its performance and efficiency.

Dr. Koopman, Nigel Day and Stephen Goodbody, and Michael Guy have each offered valuable interpretations of formula to help determine appropriate orifice diameter, blast nozzle height and some other critical dimensional information for the Ottaway.

Iam still researching how to equalize (and improve) gas flow through each of the fire tubes, and if any components of the Lempor system can be configured to reduce spark emission out the stack. Dr. Koopman’s thesis mentions several possible approaches - slowing the exhaust velocity up the stack looks intriguing. But I didn’t flag them on first reading, so off searching for those references again...

I also appreciate Joss following our discussions and adding his insight; particularity regarding landmark early steam research. Regarding Joss comments about Goss’s work - I’ve found it difficult to locate or consolidate many of the original, benchmark reports on locomotive performance. Perhaps this is why these original findings are not as well known as they could or should be in the live steam community

I just did find Goss’s original 1909 report titled “Locomotive Performance” on line, courtesy of the Google books project.

See: https://babel.hathitrust.org/cgi/pt?id= ... =1up&seq=9

The Hathi trust seems to have assembled a considerable collection of steam age research.

There may be additional publications by Goss, as I searched the above report and found only one reference to petticoat performance ( pg 250) - which stated he couldn’t comment about applicability of petticoat usage as a general rule on other types of engines. (The petticoat in my Ottaway is apparently an historical artifact from the early 1957 rebuild, so I have retained it, as it appears so far, to be a benign influence regarding drafting)

Regardless, Joss raises an important issue. today’s live steam hobbyists don’t seem to have a level of access to best practices that master machinists enjoyed during the age of steam. A contemporary, live steam maintenance and performance reference guide, even a collection of on line links, would certainly be beneficial for making better decisions regarding small boiler performance improvements.

So, on to more front end testing and design, then hopefully: front end plumbing and nozzle machining.

Glenn
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