4 Jaw Work

Strewth , i never realised they were so easy to understand

At sea It's called an eductor and works on the venturi effect

The motive fluid fires into the tapered nozzle at high speed and sooks fluid and anything else from the inlet, gas liquid or other bit

Great for sooking crap out of cargo holds full of bits which would gum up or damage a pump

Edited By Ady1 on 03/10/2014 17:42:28

They make shower heads which use the same principle

You can feel the air being sooked into the hole at the bottom of the handle if you put your thumb on it

A sandblaster which uses high pressure water uses the same principle to sook the sand up the pipe and into the nozzle

Edited By Ady1 on 03/10/2014 17:52:28

If you want the full lowdown on how these 'mysterious' devices work and how to make them, get a copy of Miniature injectors inside and out by D.A.G Brown. Fascinating read.

Edited By CoalBurner on 03/10/2014 19:54:32

To all those people still struggling to understand the scientific principles, I apologise, unreservedly for starting this thread with photos of work which had no connection whatsoever with injectors.
Blame Neil. It's all his fault really.

Jack, no one's to blame, this is just an ordinary conversation as you might have with a few blokes in your workshop, or at the pub, and even if it's not how it started, we all learn something.

Ian S C

Just my implausible attempt at humour, that's all Ian.

I've looked at Gary's link, and examples of injectors - I've made a sketch [I'll apply some rational dimensions to it] I've found a billet of aluminium which will be suitable, and I intend to have a go at making one. It may never work, for no other reason than that I don't have an application for it - but I would like to have a go at it anyway.
I'll post the results, in due course.

The eductor is more like a loco blower and petticoat pipe, or a traction engine water lifter, or a compressed air vacuum cleaner, or a school chemistry lab water powered desicator vacuum exhauster.

If you think the high pressure injector is clever bear in mind that there are also injectors using the low pressure exhaust steam, way below boiler pressure, that still manage to get that water into the boiler against the internal pressure.

I see Jack that you mentioned an "internal depth stop" which you intend to make from one of my books. I think perhaps you are referring to what is normally called a "Back Stop". If so, then you may be interested in the improved version, complete with drawings, etc., which can be found on my web site here. **LINK** The pages also detail the reason for the update to the design.

Harold

Thank you Harold. I shall look at that in a lot more detail tomorrow, and create a link into your website.
A backstop is precisely what I meant when I referred to an internal depth stop.
I am going to be busy during the coming months.
Your advice and **LINK** is much appreciated

Edited By Jack Foreman 1 on 08/10/2014 00:01:20

Bernoulli's principle also applies to subsonic aeroplane wings
**LINK**

They don't break any physical laws. the do radiate heat so they are not 100% efficient. IF they were placed inside teh boiler to prevent this, the feedwater would get too hot and they wouldn't work. Nature has its ways!

Neil

Similar functioning items in aircraft fuel tanks known as jet-pumps or scavenge pumps - slow but non-mechanical method of getting the last drops out of the tanks. Old technology to new technology!

Rgds

Bill

For an explanation of how Monsieur Giffard's injector works, and the pitfalls involved in making them, contact D A G Brown He is often to be seen at UK M.E. Shows on the SMEE stand.

I am sure that he has written a book on the subject.

As said, it is about converting the pressure energy of the steam into kinetic energy and so on. But talk to DAG, he will make it clear, so that even I can almost grasp what happens, not that I could make one so that correct and good operation could be taken for granted.

Howard

I've started on making an injector ~ again, out of a billet of aluminium, for no other reason than this is what I have a stock of, in appropriate sizes. I started by doing a sketch from the *LINK* information which several of you kindly provided; to ensure that I had a steam inlet, a water inlet, an overflow & a safety valve which incorporates the outlet to the boiler. That done I put some dimensions to it, which would enable me to access all of the internal parts to fit the pressure cone. (one cone will do for the purpose of the exercise)
So - the body is machined ~ I don't yet have a mill, so some of the drilling was done in the pillar drill and some done on the lathe in the 4 jaw chuck. All of the openings line up and are where I anticipated they would be [internally] and I have bored out the two ends to take the cover caps which I have also made. These will bolt onto two BA studs each. (I do appreciate that the real injector would have more than two fixings, but two on each end is sufficient for this exercise purpose)
My next task is to machine the four spigots for steam in, water in, overflow and high pressurized steam out. I intend to make the cone and the external connections with brass and use 1/4" copper pipework.

Can you please advise on the thread type and pitch for gland and connection nuts ?

Thanks
Jack

D.A.G.Brown will explain in detail HOW an Injector works for steam, and how to make them.

He has now written a book on Injectors.

The Steam Injector was invented by Henri Giffard

(I say Steam Injector, to differentiate from the Injectors (Sprayers or Atomisers) used in Compression Ignition engines)

Howard