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Steam water feed injectors

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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  :thumbup:


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:

--- Quote from: chipenter on June 16, 2015, 05:06:45 AM --- D H Lawrence did a series in ME from round bar that worked better for me .

--- End quote ---

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  :lol:

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

Dave.

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