Injector Calculator

[chris vine]

Hi All,

Does anyone know of a good site with a calculator (or downloadable spreadsheet) for working out the dimensions and jet sizes for injectors?

I know I have come across one in the past but now I cannot find it.

My problem is that the injectors on my locomotive which runs at 120psi are a bit shy at the full working pressure, especially when the weather is warm. This is a nuisance because just when you want them to calm the safety valves there is nothing doing.

I read recently that it was possible to make the steam jet slightly small diameter to push the working range up a bit. Does any one know by how much etc??

Many thanks
Chris.

[steam4ian]

G'day Chris.
I have just opened "Model steam Locomotive Construction" by Martin Evans. It has a five page article on injectors including formulae for calculating nozzle sizes. Email me and I will forward you some extracts of those passages.

One good turn deserves another.
Regards,
Ian

[chameleonrob]

have a look in ME about a month ago at Kieth Wilson's lillian article, it goes into injectors, including temperature and pressure range, in some detail.

rob

[Steve M. W]

We had a presentation by Derek A.G. Brown on injectorson both the history and making them I am sure he would have the relivant information you need. He did an article in ME but I don't know when.

Steve

[baggo]

He did a series of articles on injectors in Vol. 184 issues 4111,4113,4115, and 4117. I'm hoping to make a couple to his design in the near future.

John

[chris vine]

Thanks all,

Ian, I have Martin Evans' book, not 2 feet from the confuser. I have looked at it and he confirms my understanding that I should reduce the size of the steam cone, but he does not say by how much.

Thanks Rob Steve and John, I will look up the articles and see if I am any the wiser......

Chris.

[baggo]

Chris,

just found a letter in Postbag by D A G B (issue 4252). To quote:

" the correct way to increase the steam pressure rating is by reducing the bore of the steam cone - usually 0.002" or 0.003" does the trick and takes the steam pressure up from say 90 to 150psig maximum"

John

[albertsell]

Hello Chris,
I have had this problem on my locos and traction engines,the cure, draw out the steam cone about 10thou by putting a ring of ferrous (electric)wire around the cone body next to the flange.This has the same effect as reducing the cone bore.
Good injecting Albert.

[chris vine]

Thanks John, 2 or 3 thou is not much but I could try it.

Albert, I have tried pulling the cone out a bit already, but I think it was only around 5 thou. I will try again only this time perhaps 10 or 15 thou. I suspect that the reduction in size of the jet is the more sure fire way of getting it right....

Will let you know what I find.

Chris.

[chris vine]

Hi All,

I have now done some experiments and have found the rather surprising result: That in order to raise the good operating pressure for a 7.25" gauge injector I have had to shim the steam cone out by 40 thou. This is much more than I expected.

After trying about 30 thou and finding no success, I tried 40 and it seems to work a treat. I also tried both shims, IE 70 thou and that seemed to be too much.

I am not sure what the capacity of the injector is, I have a larger one with a 6 stamped on it, would this be 6 pints per minute? If so I would guess that the others are around 4 ppm.

The temperature today was around 18 C and the modified injector picked up easily and unfussily at full boiler pressure with the safeties tearing away. However the acid test will be on a really hot day. I am just waiting for one......!!

Chris.

[ewal]

Hello Chris, I think you will find a No.6 injector supplies 4pints per min.
I always use No.6 on my 7 1/4 engines, but I've found the latest
injectors won't work above 60lbs which is no use.
I have found the recent correspondence useful & I will copy your experiments when it stops raining.

ewal.

[chris vine]

Hi Ewal,

Don't forget to test your results on a nice warm day or you may get a nasty surprise later!

C

[Myford Matt]

I picked up an interesting reprint of an 1894 book from Camden Publishing yesterday at the Guildford show - 'Practice and theory of the injector' (only £7.15).

ISBN1-55918-306-3

Useful if you want to get into injectors in more detail and see how they used to design them.

MM

[baggo]

Hi all,

I'm in the process of making some injectors for my Helen Longish based on the articles by D A G Brown in ME Vol.184. In the article he gives the method for calculating the water consumption of any loco at any speed and cut-off based on the number of cylinders etc.
To make this easier I've designed an Excel spreadsheet to do all the necessary calculations. If anyone is interested you can download a copy from:

www.baggo.copperstream.co.uk/me/injectors/Injector%20size%20calculator.xls

Might be of use if you want to know what size injectors to fit. Mr Brown suggests fitting an injector of twice the capacity as the actual water consumption i.e. fit a 10oz injector if the water consumption is 5oz.

John

[chris vine]

Hi John,

Thanks for that, it will be useful!!

A few years ago I was lucky enough to spend a day with a couple of friends, driving on the Romney Hythe and Dymchurch. Our loco was Green Goddess, one of Capt Howey's originals. One of the many charming features of driving was that once on the move we were told to set the injector running and leave it. It was just about perfectly sized.

I can highly recommend this as a day of sublime pleasure!! Of course it is not too cheap, but then it is unique and you get real long distance running at scale high speed.

One day some b----y bureaucrat will ban this sort of thing.
Chris.

[ewal]

Hello Chris,

Yesterday I steamed No. 7 & did as you did, withdrawing the steam cone 40 thou, it worked successfully at 100 psi & down to 50. The water dribbled at times but I could control it by regulating the flow. I was rather pleased.

ewal.

[chris vine]

Hi Ewal,

Glad it worked for you. I notice that the high operating pressure seems to have been moved up more than the low end. So very satisfactory!!

Yes it does dribble a bit at low pressure but as you say the water flow control stops it....

Chris.

[AndrewP]

Strewth John, how small are your injectors going to be!
I've just put Rob Roy's data into that spreadsheet - excellent btw and get a calculated consumption of 2.77 oz/min so maybe fit a 5 oz injector?
Smallest commercially available that I can find is a No.2 (why do we use cryptic meaningless numbers) which is 11 oz/min.

I guess that's one reason to make one! Looking forward to the write up!

Cheers, Andy

[baggo]

Hi Andy,

I have been told that Gordon Chiverton can make smaller injectors to order but I haven't made enquiries in that direction as I want to try and make my own. I'm hoping to build the test setup in the next week or so with a gas fired boiler and the Bill Carter test rig. I managed to get an 8oz working until I messed about with it trying to get it to run dry but with a proper test rig I hope to get the 4oz working as well. The biggest problem with the very small injectors is the small diameter of the cones and the minute annular gaps. You need very fine filters on the water feed to remove any particles. All good fun though!

John