Steam water feed injectors

[sbwhart]

I've just completed making some steam injectors for my 5" gauge locomotive.

Injectors are a very cleaver little device that uses the flow of steam through a series of cones to pick up water and to feed it into the boiler against the boiler pressure, it's all to do with changes of velocity and pressure I won't even start to explain the physics of it as its way beyond me it enough just to know they work.

This is what they look like.



They are notoriously difficult to make to work as they have critical features that are difficult to actually measure, you have to get to these features in a round about way, and as I found out there are other pit falls just waiting to catch you. I did have a great deal of help from a friend and very talented model engineer (Pete) who gave me a great deal of advice as to the best way to go about making them, he also has a injector boiler test rig, that greatly help.

The first part to make is the body:- this is fabricated from some 3/8" thick brass bar.

First thing is to square the bar up and centre for the 5.5mm through hole postion



Then in the four jaw set up on this centre with a wobble bar.



Turn up and thread 5/16" * 32 ME and ream through 5.5mm



Then drill through for the overflow chamber and clack valve and tap again 5/16" * 32 ME.



Drill through for the water feed and the overflow and make some 5/16" * 32 ME. connectors



Silver solder the connectors and overflow to the body and drill through.



Make and fit a cap for the clack valve



And that's the body made.

Next up I'll show you how to make the taper D bits and how to make and fit the cones.

Cheers

Stew

[awemawson]

Derek Brown (DAG Brown) was always the acknowledged expert on injectors - don't know if he is still around.

I've never needed an injector in my life, and likely never will, but I remember attending a lecture by Derek at SM&EE HQ - Marshall House in London where he described the process and the pitfalls. It is always fascinating to listen to someone who is master of his subject, even if that particular branch of knowledge isn't initially something you are seeking 


http://www.teepublishing.co.uk/books/operation-valve-gears-injectors/miniature-injectors-inside-and-out/

[chipenter]

That looks like L B S C work . D H Lawrence did a series in ME from round bar that worked better for me .

[awemawson]

D H Lawrence did a series in ME from round bar that worked better for me .

I think that D H Lawrence was too busy writing books and poetry, not to be confused with T E Lawrence who was busy riding camels in the desert,  so try D E Lawrence 

[DavidA]

 It seems they are quite fussy devices. Even a change in feed water temperature can cause them to stop working.

Dave.

[DMIOM]

OT:

I think that D H Lawrence was too busy writing books and poetry, not to be confused with T E Lawrence who was busy riding camels in the desert,  so try D E Lawrence 

Not to forget his Brough Superior SS80s & SS100s

[chipenter]

OK I got it wrong it was D E Lawrence and shifted more water .

[awemawson]

Those came out nicely 

[chipenter]

Those came out nicely 

Thaks Andrew and they both work which was a suprise for a first time effot .

[awemawson]

  I love the apparent impossibility of an injector working - how can you possibly inject water into a pressurised vessel using that very pressure to do it 

.... but they do 

[mattinker]

A hydraulic lever!

Regards, Matthew

[vtsteam]

Stew, thank you for starting this thread and showing how you made yours with detailed photos. Looking forward to the reading the rest of this project!

[sbwhart]

Wow I didn't think this would have so much interest.

I'm afraid I'm going to have to keep you all in suspenders until next week as I'm  a little tied up on domestic duties at the moment , and I didn't photographs making the D bits or the cones at the time so I'll make some spare and walk you guys through the procedure.

As 

It seems they are quite fussy devices. Even a change in feed water temperature can cause them to stop working.

Dave.

My loco is a tank engine as a result the feed water is warm to the touch, but my injectors work with it, I put this down to my friend Pete advice to have a slightly larger annulus (0.002"/0.05mm) between the steam cone and the combining cone, the theory being is that you need a greater volume of warm water to condense the steam and form the vacuum. I suppose those of you who studied the drawing are wondering how the hell doe's he control the annulus to that level well I'm afraid you'll just have to wait until next week to find out. 

OT:

I think that D H Lawrence was too busy writing books and poetry, not to be confused with T E Lawrence who was busy riding camels in the desert,  so try D E Lawrence 

Not to forget his Brough Superior SS80s & SS100s

I was admiring a model of a Brough Motor Bike at the Midlands show last year, and I said to my wife who was with me that Lawrence of Arabia was killed riding a Brough:- a military sounding voice interrupted and said "he wasn't you know, he was killed by the British secret service", in a tone that wouldn't take any other view:- you meet all sorts in this game

 



Stew

[Pete W.]

An uncle of mine had two Brough Superiors, one after the other.

He told me that they were made to measure and if Mr. Brough didn't take a shine to you, then you never got to the top of the waiting list! 

[vtsteam]

D.H. Lawrence did write about injectors......

[awemawson]

Would that be Lady Chatterley by any chance Steve ????

[lordedmond]

That said gentleman was a teacher at the school I attended a bit before i was there


Stuart

[DavidA]

 ...D.H. Lawrence did write about injectors.....


..Would that be Lady Chatterley by any chance Steve ????...


Has to be Mellors..

Dave.

[vtsteam]

Don't make me ban myself, Andrew! 

[awemawson]

The book was banned in the UK by the censors until (guessing) early 1960's when eventually the unexpurgated version was printed. Never forget the day when I was an early teen and not very 'aware' the Mooseman twin girls came round with a copy and calmly told me that they'd marked up the saucy bits for me - clearly going to enjoy my embarrassment - clearly girls developed earlier than boys even then. Oh where are they now 

[philf]

The book was banned in the UK by the censors until (guessing) early 1960's when eventually the unexpurgated version was printed. Never forget the day when I was an early teen and not very 'aware' the Mooseman twin girls came round with a copy and calmly told me that they'd marked up the saucy bits for me - clearly going to enjoy my embarrassment - clearly girls developed earlier than boys even then. Oh where are they now 

You've rekindled some happy memories Andrew. My mate Brian's elder sister, Beryl, read it to us in a 'den' we made in a wheatfield. I was probably only 10!

Phil.

[sbwhart]

You lot need to take an ICE COLD SHOWER

 



I'll now try to explain the method I used, I must admit that I had a lot of coaching from friend Pete on this which I would like to thank him for.

So making the cones:-

I'll post this in instalments as the method is rather long winded.

First Job is to make some tooling.

D Bits you will need two tapered D bit whilst you set up make a few spares to allow for breakages.



9 deg and 13 deg made from 3/16" dia silver steel (drill rod) to turn the taper you will need a razor sharp tool set perfectly on centre, to set you compound at the exact angle turn up a test length and run a DTI over a set length and not the deflection of the pointer for the 13 deg over a 10mm length the deflection will be 1.132mm




With the compound set gently turn the bar down until you have a sharp point, and give it a polish.

Part it off and centre drill the back and whilst your at it put a groove into it.



Then on the milling machine using a sharp milling cutter to reduce deflection of the point setion the D bit so that it is 0.003" 0.1mm above the centre line.



Use the groove to hang the D bit from a bit of wire , this is so you have something to hold onto, heat to cherry red and quench vertically into water, so that it stays straight.



When you make the 9 deg bit with the compound set make the assembly tool for the combination cones, this has to be made as accurately as you can.



To get the 0.101"(2.565) run out correct first turn a parallel diameter to this size, then with the compound gently turn the point down until it just runs out at the shoulder this shoule give you the correct size. then accurately turn the 0.431" (10.95mm) length.

You will also need to make a 0.037" (0.94mm) thick washer and a setting ring drilled with a No 38 drill, and some stop sleeves for the D bits

The cones have to be made in the correct sequence as you use one to make the other.

Start first with the combination cones:- turn the dia down to be a push fit into the body and part off two slugs one 0.162" (4.11mm) long the other 0.213" (5.4mm) long.



These little slugs are not easy to hold true, I solved this by using soft jaws bored out to a step to grip the slugs



You will also have to set depth a stop on the 9 deg D bit using the setting ring.



Start with the shorter of the two slugs 0.162" check that it is running true, and centre drill and drill through No 56 then its best that use use the D bit floating so with ut held in a carrier and pushing with the tail stop cut the taper , position the d Bit flat side is underneath or on its side if you have it on top the swarf will build up and probably break it.





Then using a triangular scraper radius the mouth of the cone.



Remove the cone from the chuck, now your going to use it along with the washer to cut the next cone



Put the thicker slug in the chuck checj that its running true centre drill and drill No56 and using the D bit with the first cone and washer to cut the taper to the correct depth, with the triangular scraper radius the mouth of the cone, its important you do this things won't work without it.



With the tapers correctly cut in the cones all that required now is to finish off the stepped diameters





To assembly the cones into the body you know use the assembly tool to get them to the correct depth check that you have a gap between the two cones of 0.037" (0.94mm) by using a No 63 drill as a gauge through the over flow chamber. As a belt and brasses action secure with a tiny drop of High temp loctite 640.



 

Phew

That took some explaining.

Stew

[sbwhart]

OK on with the Steam Cone



This cone and its location is the most critical part of the injector so its worth taking your time and if you have any doubts start again.

First job is to turn up the blank make it a nice slide fit in the body for a length of 1/2" (13mm) there are a number of pits falls her, so slightly undercut the shoulder so that it will but up flat against the body and won't be held off by any radius in the corner, also with a a radius tool just skim a short shoulder this is to avoid a false assembly from any residue of adhesive from the combining cone.



Face the length down so that the gap between the body is 0.094" measured with a No 63 drill, and set the saddle dial at zero, this is important.





Set the 9 deg D bit depth with a setting ring drilled with a No 40 drill, and centre drill, drill No 56  and cut the cone.
This D bit operation will swell the diameter so its best to do this before the next operation, I fell into this trap.



Now I will say this only once this is important. taking small cuts .001" reduce the diameter of the end for a short length with the radius tool until the body just buts up flat with the cone, then face off by a further 0.0015" (0.38) if you set you're dial at zero this is quite easy. This gives the steam cone the correct insertion into the combination cone with the correct annulus.





You should have a cone with an end that looks like this.



Part off

Set back up in the collet face the head off to length  centre drill.



13 deg D bit  depth set with a 1/8" diameter setting ring.



And finally radius the mouth with a triangular scraper.



Only one part left now.

Stew

[sbwhart]

Delivery Cone

Turn up the blank again making it a nice slide fit in the body, and face the length off so that it just buts up against the body, zero the dial and reduce the length by 0.024" (0.61mm) this forms the gap for the over flow.



With the radius tool turn the end down for a short length 3.5mm to a diameter of 3.2mm, just touch the face with the centre drill to give the No 68 drill a start and drill about 8mm deep, keep drawing the drill back and clean away any build up of swarf from the flutes or you'll end up breaking it.





And radius the mouth with the triangular scraper this is important.



Part off

Face the collar off to length centre drill and 13 deg D bit and radius the edge with the scraper



That's it with a bit of luck you should have a Injector that works.



These are the tools.



Injectors are a bit of a challenge to make you have to follow the procedure carefully and there are lots of little pitfalls that can catch you out, so you have to work very methodically, I got paranoid about getting the drills mixed up so I threaded them through a bit of paper.



And I found it paid to keep the D bits sharp on an oil stone.



But its a great sence of achievement when you get them working, and it gives you the bragging right at the track to say of course I make my own.

 

Stew

I'll try and take a Video of the injector working the next time I steam my loco.

[awemawson]

  Nicely done and shown Sir !