Steam Injector for my Black 5

[Ron HancockParticipant @ronhancock63652]

Hi well i get my Boiler from GB Boilers on wed so now need to buy a new Injector.

Not sure what size i need as i have an axle pump but only want one injector.

Also what are the ones to avoid and witch can you buy now that are fairly reliable.

I have noticed so many have problems not working and as soon as hot water they definitely often not work.

Hope you can offer some good advice please

Ron

[Ron HancockParticipant @ronhancock63652]

[julian atkinsParticipant @julianatkins58923]

hi ron,

an ordinary miniature injector wont work if the water supply is above 46 degrees celcius. this would only be a problem if a tender loco is being run for a long time on a very hot sunny day, and the water is coming from a static tank as opposed from a standpipe connected to the mains.

so long as all the pipework is ok, and the steam valves dont leak and the clack valve doesnt leak then there should be no reason why a miniature injector should not be 100% reliable. there must be large in area filters of fine mesh on the water supply to the injector.

my locos have 2 injectors fitted on each, and no axlepumps or handpumps.

ive sent you a PM re best make to buy.

cheers,

julian

Edited By julian atkins on 14/09/2015 08:52:17

[Anonymous]

Posted by julian atkins on 14/09/2015 08:46:34:

an ordinary miniature injector wont work if the water supply is above 46 degrees celcius. this would only be a problem if a tender loco is being run for a long time on a very hot sunny day, and the water is coming from a static tank as opposed from a standpipe connected to the mains

I'm afraid I don't understand why the 'magic' number for warm feedwater should be exactly 46ºC?

I thought that the issue was that the high velocity steam jet from the steam cone does not have time to condense properly during its transit of the combining cones when the feedwater is warm. The heat flow is proportional to the temperature differential, so the warmer the feedwater the slower the heat transfer and thus the longer the condensation takes. Of course the temperature and velocity of the steam also has an effect, and will depend on the incoming steam pressure and temperature.

I think there were experiments done with full size injectors adding a cab control that moved the relative position of the combining cones to account for feedwater temperature. I don't know whether the system was ever used in production.

Andrew

[julian atkinsParticipant @julianatkins58923]

hi andrew,

it is quite simple and basic physics. if the feed water is above 46 degrees celcius it cannot condense in the steam and instead of a jet of emulsified water coming out of the combining cone you have boiling 'water'.

the position of the combining cones has nothing to do with this, nor will altering them.

to make a miniature injector work to feed hot water (hotter than 46 degrees celcius) requires a great deal of added complication and isnt worth the trouble. it is far easier to leave the water valve open and re-fill the tanks more often.

cheers,

julian

[Ron HancockParticipant @ronhancock63652]

Hi Julian thank you for explaining in simple terms it really does help us Newbie.

So many i have seen just can't get them to work and several experienced model engineers.

I have taken your advice and ordered an injector from where you said.

Its almost double the price of some i have seen but trouble free is what i want and need.

Does any one use ice cubes in the tenders to keep water from getting hot on hot days.

Just a thought being new to all this but will definatly keep it feeding boiler at a trickle to help keep cool.

Thank you again Julian

Ron

[Anonymous]

Surely the water condenses the steam not the other way round? Hot water will take longer to condense the steam, but it will do so eventually. However, we can do a thought experiment. Let's say we have a pan of water at, say, 20ºC. Let us now introduce steam from a boiler into the pan. under water, through a narrow nozzle. Since the water is below 46ºC then the steam will condense. Correct? Now as we raise the temperature of the water in the pan the steam continues to condense until we hit 46ºC. At this point the steam will not condense and will leave the pan still as steam?

It is interesting to note that Kneass discusses experimental results for a standard injector where, at typical ME operating pressures, the maximum operating feedwater temperature is about 140ºF, or 60ºC. For a special version of the same injector the maximum operating feedwater temperature is about 150ºF, or 65ºC.

Still, as you say, the physics is basic, so I assume it will be simple for you to derive the value of 46ºC, as it would be interesting to see it. I hope it will increase my understanding of injectors.

Andrew

[julian atkinsParticipant @julianatkins58923]

hi andrew,

please dont take my word for it but read D.A.G. (Derek) Brown's bible on Injectors published by TEE. my own empirical observations and making injectors for over 30 years backs up exactly what Derek states in his excellent book. Derek explains the physics and maths far better than i could do.

the 46 degrees celcius is backed up in fullsize and a notable example 2 years back with one of the A4 Gresley Pacifics.

cheers,

julian

Edited By julian atkins on 14/09/2015 22:53:22

Edited By julian atkins on 14/09/2015 23:19:39

[julian atkinsParticipant @julianatkins58923]

as a slight aside,

in fullsize the 'hot water' injectors ive studied in fullsize require the water to not be under vacuum or the first part of the combining cone to be under vacuum. this is usually achieved by a separate steam cone to provide the lift function, in conjunction with the injector water feed sometimes being placed so as not to require lifting. in many fullsize injectors of this type there is in effect half an injector with steam cone and first half of the combining cone below the main injector. in other examples it is before the main injector. if the water is not below atmospheric pressure (as in a normal injector) in the first half, it's boiling point will be higher. there are a few other complications, but this is the nub of the matter.

as previously stated, it would require quite extreme conditions for a miniature tender loco to be subject to a temperature of water in the tender to be above 46 degrees celcius. a side tank or saddle or pannier tank loco however might not be so fortunate in miniature.

the only successful miniature 'hot water' injector ive come across is by Basil Palmer in South Africa described in ME some years ago. it would be quite a chunky affair on our UK prototypes.

cheers,

julian

Edited By julian atkins on 14/09/2015 23:37:39

[Anonymous]

I bought my copy of the book on injectors by D. A. G. Brown as soon as it was first printed. For those who haven't seen it the book contains detailed notes and designs for making injectors in a variety of sizes, backed up by experimental data. It also contains very useful chapters on fault finding, servicing and testing injectors as well as notes on ancillaries such as pipework and fittings. It also has a succinct description of the internal workings of an injector and some basic maths to illustrate the principles.

For those interested in injectors a complementary publication is 'The Model Injector' by Ted Crawford. This has some generic notes on the manufacture of injectors, but over half the book is concerned with the theory and it contains a fairly significant amount of mathematics, albeit not at a difficult level. The various design parameters are discussed in detail, and in Appendices, as well as the basic calculations for throat sizes and angles, there are discussions of how to calculate things like minimum and maximum operating pressures and maximum feedwater temperature for operation with a given steam pressure.

For me the study of injectors is a precursor to designing an injector with a maximum flowrate of 3 pints/min and capable of working into a boiler pressure of 170psig.

Andrew

[John BaguleyParticipant @johnbaguley78655]

+1 for the Ted Crawford book. I got a copy some time ago and if you want to delve into the theoretical side of injectors then I think it is the better book. However, by following Derek's original articles in ME I did manage to make some 4oz and 8oz injectors that actually worked

It's always surprised me that so far as I know no one has supplied the necessary reamers commercially. Must be a market there for someone

John

[julian atkinsParticipant @julianatkins58923]

Kennions used to market tapered 'D' bit type reamers of LBSC sizes.

i have been sent yesterday a batch of miniature loco injectors to sort out. one is a brand new commercial injector marketed and sold by a well known model engineering supplier. it is quite appalling, and no way will it work. i am quite shocked that such an inferior and defective product should be sold. virtually every detail was incorrect and wrong and also badly made.

no wonder injectors sometimes get a bad reputation if this is what gets peddled by the trade.

cheers,

julian

[Ron HancockParticipant @ronhancock63652]

Hi Julian you can see why i have been against injectors nearly all the ones at our club give problems most bought from Reeves 2000 or Polly.

At least half the time they do not work i think most are now made in China that why they are a lot cheaper.

Polly sell them £33 from the guy you suggested £60 plus delivery but still ordered from him as i want a decent one as i think it would be to much for me to set up just to make one.

All th best

Ron

[nigel jones 5Participant @nigeljones5]

Hi Julian. I have never had an injector work for more than a very short time, so if there is someone out there making/selling ones that actually work I think you would be doing us a big favour by letting us know. You wont be plugging a company, but merely passing on your experience.

[julian atkinsParticipant @julianatkins58923]

hi nigel,

i make my own and have done so for 30 odd years for my own locos and for friends.

so far as commercial injectors are concerned the only ones i would recommend were those made by the late Gordon Chiverton. Gordon's injectors were taken over by Len Steel and are marketed by Pavier Steam

**LINK**

i havent tested any of Len's products but if they are up to Gordon's standards (which i have no reason to doubt they are) they are IMHO the best currently available. order well in advance, as Pavier are currently out of stock due to high demand.

cheers,

julian

Edited By julian atkins on 20/09/2015 00:11:21

[Ron HancockParticipant @ronhancock63652]

Posted by julian atkins on 19/09/2015 23:53:25:

hi nigel,

i make my own and have done so for 30 odd years for my own locos and for friends.

so far as commercial injectors are concerned the only ones i would recommend were those made by the late Gordon Chiverton. Gordon's injectors were taken over by Len Steel and are marketed by Pavier Steam

**LINK**

i havent tested any of Len's products but if they are up to Gordon's standards (which i have no reason to doubt they are) they are IMHO the best currently available. order well in advance, as Pavier are currently out of stock due to high demand.

cheers,

julian

Edited By julian atkins on 20/09/2015 00:11:21

I have ordered mine Christmas delivery seen to many that don't work so as i trust Julian i ordered mine from them not cheap almost double the price of some others but did not want to be having problems not being able to steam as not working as i have often seen.

It was tempting to buy a cheaper one as at £33 again £60 plus delivery but only had to see a video with a good Model engineer struggling to get tt to work and packing up in defeat made me determined to get a good one.

Ron

[Author]

Posts