Verifying Blast nozzle height

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Glenn Brooks
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Re: Verifying Blast nozzle height

Post by Glenn Brooks »

Steve Goodbody wrote: Tue Nov 19, 2019 1:57 pm Hi Glenn - have forwarded the spreadsheet by Email.
Hope things work out and let us know how you get on.
Best regards
Steve
Steve, this is great.
Thank you!
Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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Soot n' Cinders
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Re: Verifying Blast nozzle height

Post by Soot n' Cinders »

Glenn Brooks wrote: Tue Nov 19, 2019 2:02 pm Hello All, thanks for your comments on this.

In answer to your questions, here are a couple of data points:
- my working pressure is 143 PSI.
- existing oriface size is .238” for each nozzle, .476” total; (1/7th Cylinder dia rule should be .358” )
- nozzles are offset to the rear and left of stack center - by a significant amount

Re: fire tubes. I think my cellphone camera has foreshortened the front end boiler view a bit. The boiler has 4 rows of fire tubes, around 22 flues 1” diameter for all. They could have put 2 more on each side, I think. But overall it seems to be a standard code boiler design...

Definitely the blast nozzles are misaligned with the center of stack. - both are offset to the rear and left side of the stack.
I plan to correct the nozzle placement this winter. I would like to machine a single blast plenum connecting to the two exhaust ports, then put a four hole “pepper box “ design nozzle in the plenum. I tried to nudge the existing nozzles back into alignment, but no movement. The blast tubes are likely 65 year old black iron pipe, so Iam hesitant to try a bend the pipe as an interim measure. (Committed to one last steam up in December]

Also, in the photo, the elbows are part of the throttle plumbing. Behind them, two straight blast pipes come out of the saddle and head up into the stack. Iam thinking about replacing these old iron throttle fittings with stainless or copper pipe, curved around the outside of the firebox to each steam chest inlet. This would free up access to the flues for cleaning. Any recommendations on type of tubing to use? And does it matter the run to the left side is longer than the run to the right steam chest??


Thanks much for your recommendations!

Glenn
All sound stuff here Glenn. If the blast nozzle is only going to be ~3/8" in diameter, I think you'll find a single hole will work just as well as a multihole design. I've seen several multiple hole nozzles tried and they didnt perform any better than a single hole, my guess being the web between the holes is too small on the miniatures for any meaningful amount of gas to be entrained. Centering the nozzle should help although being exactly in the center isnt too critical, just needs to be close. My guess would be Ottoway used a pretty decent design at the time as far as stack height, so Id say start with just the blast nozzle opening and then can fiddle with adjusting it up and down from there, though I imagine closing down the nozzle will make an improvement. It did on my shay, 1/32in too big made the locomotive a little lazy to fire and gave trouble keeping steam.
You might be able to make a reducing bushing to attach to the existing blast nozzles if you want to try a smaller orifice without too much fuss.

As for replumbing the smokbox, copper tube should be just fine. Get some braided stainless sheath from McMaster-Carr though, this will help protect the copper from being eroded by cinders. The two pipes being different lengths shouldnt matter.
-Tristan

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Bill Shields
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Re: Verifying Blast nozzle height

Post by Bill Shields »

in spite of (maybe because of) the spreadsheet calculations, i have a box full of different diameter nozzles and different height blast pipes that I made for each and every one of my locos.

Current model design allows for pipes that can be simply screwed up and down and and quickly interchangeable nozzles.

slow learner....
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Glenn Brooks
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Re: Verifying Blast nozzle height

Post by Glenn Brooks »

Hmmm, One more question has come up regarding round blower nozzles with multiple holes drilled in the ring.

What advantage do they offer over the traditional one nozzle blower?

Also, with multiple blower oriface, does this type use more steam than single nozzles? Hence perhaps be less efficient in terms, of steam generation?

Thanks
Glenn
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Soot n' Cinders
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Re: Verifying Blast nozzle height

Post by Soot n' Cinders »

Glenn Brooks wrote: Tue Nov 19, 2019 10:05 pm Hmmm, One more question has come up regarding round blower nozzles with multiple holes drilled in the ring.

What advantage do they offer over the traditional one nozzle blower?

Also, with multiple blower oriface, does this type use more steam than single nozzles? Hence perhaps be less efficient in terms, of steam generation?

Thanks
Glenn
I found the opposite to be true. I started with a single orifice blower made from a piece of 1/4in copper tube in the shay. It was loud and used a lot of steam compared to what it generated. I switched to a blower ring with 3 1/16in or 3/32in holes drilled equally spaced and found it to be much more efficient and quieter. More smaller jets spaced far enough apart will entrain more gases before they combine in the petticoat.
-Tristan

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apm
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Re: Verifying Blast nozzle height

Post by apm »

A simple trick here one live steamer taught me when I had issues with my blast nozzle, couldn't keep the fire going when I first stared my engine and had to push it around the track. I was pretty discouraged till a fellow live steamer taught me a trick. Rig up the thing to compressed air and hold a scrap of paper say 1"wide by 4"long to the open firedoor with it running. When the paper starts pulling into the firebox you have a good draft. This proved to be a nice trick that allowed for much more experimentation both on the blower and blast pipe arrangement that was a lot better than firing up/down on the boiler each time you needed to make an adjustment. As others have done I made my blast nozzle from pipe nipples so I got adjustment and could experiment, and also temporarily rigged up an air line up the blast nozzle to really simulate things well.

One other thing that is interesting here. I never rigged up the proper baffeling of the master mechanics locomotive smoke box as illustrated in some of the old texts on the subject but I did follow all the other proportions that they recommended for petiticoat pipe extension, blast nozzle distance etc... and all of that got me nowhere in terms of draft. However it didn't take more than 15mins or so of paper strip diagnostics to get the blower and blast nozzle in the right spot.
Glenn Brooks
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Re: Verifying Blast nozzle height

Post by Glenn Brooks »

Tristan,
Thanks for the heads up. Entraining more combustion gasses with small multiple jets seems like an excellent way to go.

Amp- that is one terrific idea! I’ve got an air hook up plumbed into my blower line. I’ll try it tomorrow. Without waiting for the fire to build for two hours!!!

Now that’s efficiency!

BTW, here’s the front end on my 1904 Campbell 4-4-0. 14” dia boiler. Mr. Campbell installed a baffle, as you describe. It’s partially visible in the background. Mounted couple of inches in front of the front flue sheet. You need clear access to the fire tubes in the fire box end to make these work. Can’t do much flue cleaning thru the smoke box :shock: with the baffle in place.
19E3C6AE-AEE4-4535-87BF-61881356E501.jpeg
He also installed a blower ring with several holes in the tubing. I’ll have to go look closer in the morning... might be a good model to copy.

Thanks
Glenn
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Bill Shields
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Re: Verifying Blast nozzle height

Post by Bill Shields »

another way to experiment with this is with a differential pressure gauge and a hollow bolt onto which you can push the hose.

the one I use is a http://www.dwyer-inst.com/Product/Press ... Series2000

yes, they can be a bit pricey but nothing better than actual numbers to work from during operation.

when not on my loco, it monitors the draught on my coal furnace at home.
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Glenn Brooks
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Re: Verifying Blast nozzle height

Post by Glenn Brooks »

Bill, assume you mount the intake on the side of the smokebox somewhere? Does it matter where in the smokebox?

Also what pressure differential range is appropriate for miniature boilers?

Thanks
Glenn
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rkcarguy
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Re: Verifying Blast nozzle height

Post by rkcarguy »

Glenn, the location of the blast nozzle within the stack vertically is quite critical in my opinion(based on non-steam, yet similar industrial and mechanical work). Think about an airbrush or paint sprayer where the air pressure creates a vacuum and how picky that adjustment is of the needle to get good vacuum to suck up the paint. Likewise, the nozzle size is also important. The smaller the nozzle the higher the velocity exiting it and the more draft it will create, but too small and it will obviously be restrictive. If the nozzle is quite off center, you'll have a fast side and slow side, which could result in "tumble" in the stack and very poor draft.
I like Bill's idea of having it pipe threaded with a handful of different lengths and diameter nozzles to try until you find the sweet spot.
Glenn Brooks
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Re: Verifying Blast nozzle height

Post by Glenn Brooks »

Ryan, yes, agreed. I’ve decided to move the blast nozzle down to calculated height above the extension, when I rebuild the front end.

Oriface diameter is critical, as many have said. Iam still learning about multiple oriface nozzles. Several people have mentioned they tried multiple ports with no gain in draft because the oriface size was to small, or where to closely spaced together, thus saw no improved in exhaust gas entrainment/draft. So now started doing some research on minimum spacing between holes in multi oriface nozzles. I

BTW, I’ve just remembered one new, possibly super relevant fact. My best steam production so far were on summer days with temps in the high 80*s. Always saw the pop off value working well in those conditions. My worst performance is always with winter temps of 40-45* F, such as this week. A 40* F drop in ambient air temperature. Keeping with the KISS principle, thinking I will add another layer of insulating blanket under my boiler jacket. :shock: :shock:

Glenn
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rkcarguy
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Re: Verifying Blast nozzle height

Post by rkcarguy »

Insulation always helps. I built an outdoor wood stove that had an exchanger in it for a hot tub...think I've spoke of that before. Originally it just had fire brick on the bottom, then I added some on the sides and then finally the back once I could cut those to fit. The difference in the fire was noticeable each time I added more brick, in that it was easier to get started, burned hotter, and really dropped the time to temperature down.
Multiple small nozzles should work, arranged almost like a propane burner such that each one has the same area of smoke stack to work with and if you can assure that each one gets even flow.
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