DIY syphon nozzle

[Tony]

So I built this out of bits for a little over a tenner:







It atomises a stream of bio very finely and my modest little compressor can easily keep up with it - bonus.

Problem is that I need a new regulator, it produces way too much air and blows the flame front right away.  It resonates that tube like a good'un when it does burn though - must've woken up the whole neighbourhood

[julianf]

Looking good Tony,

Have you tried a simple valve to cut down the air flow?

Also, have you managed to get the tube hot?  Im thinking then it should self sustain, even with too much air.

[Tony]

Construction:





Parts:

1x crappy airgun duster off eBay for the nozzle http://www.ebay.co.uk/itm/300886071240 £1.64
1/4" BSP stainless equal tee £2.08
1/4" BSP stainless street elbow £0.99
1/4" -> 1/8" BSP reducer £0.99
1/4" BSP To 4mm Compression Stud £2.29
10ml syringe and 10cm long needles blunt x 2 £2.25
Some 4mm nylon pipe (already had, it's about £1 a meter)

Total cost £11.24 (excluding airline PCL adapter - I plan to add a regulator here instead).

The airgun nozzle isn't BSP but it's close enough to grip a few threads with PTFE.  The syringe needles I melted the original plastic end fitting off over the stove and melted into the end of the 4mm nylon pipe such that the distance was set to have the tip just protruding from the end of the nozzle.  (Actually in the photos at the top of the thread it was perfectly flush, I'm tweaking to see what happens)!

Edit after measuring:
Airgun nozzle outlet is 2.1mm
Blunt needles are 1.6mm OD with 0.2mm wall - this makes them approximately needle gauge 16

[Julian]

Looking good.

I was surprised to see the tube protruding through the nozzle ... does that work better than being within the nozzle?

Have you thought of using an 'O' ring in place of the brass olive?  It would let you adjust the position of the tube easily.

[Tony]

Looking good Tony,

Have you tried a simple valve to cut down the air flow?

Also, have you managed to get the tube hot?  Im thinking then it should self sustain, even with too much air.

Not played long enough to get the tube glowing just hot enough to make a ridiculous amount of smoke when the flame goes out.

I don't have a 1/4" valve to hand, and the reg I picked up on eBay for a few quid has 1/8" ports.  Grr!

[Tony]

I was surprised to see the tube protruding through the nozzle ... does that work better than being within the nozzle?

Don't know, when I tried it the tube was flush and that worked fine.  Not tried it protruding yet.

Have you thought of using an 'O' ring in place of the brass olive?  It would let you adjust the position of the tube easily.

Hadn't thought of that, good idea.  I'll see if I have a suitable sized one.

Edit: Nope, they're either slightly too small or slightly too big.  No worries, the nylon melts easily enough to adjust the position.

[Julian]

I've probably got a small control system regulator, not sure on the port sizes.  I'll check in the morning.  PM me your address and if it's ¼" I'll pop it in the post.

[Julian]

Just thinking about it.  Is it a regulator you need?  If it's working against and open ended tube, it can't regulate pressure effectively.

You may be better off regulating the flow than the pressure as I think has already been suggested.  A needle valve will do it most accurately if you don't need a massive volume. 

[oakwoodtv]

Have some 1.5mm x 100mm blunt needles if any one wants to play
let me know and I will post them of foc.

[Tony]

Just thinking about it.  Is it a regulator you need?  If it's working against and open ended tube, it can't regulate pressure effectively.

Ah, I didn't know that.  I was planning on running it with somewhere around 7 psi of back pressure?

You may be better off regulating the flow than the pressure as I think has already been suggested.  A needle valve will do it most accurately if you don't need a massive volume.

So pressure reg then needle valve?

I assume this would do the job then: http://www.ebay.co.uk/itm/231262703823

[Julian]

All my pneumatic control experience was dealing with systems that were effectively closed ie pressure transmitters etc, and I'm not sure that a combination of the two would be viable unless the regulator was of sufficient flow to build pressure against the needle valve orifice.

However if you want to try, I've got a small regulator with ¼" ports and a ⅛" tapping to take a pressure gauge ... the only suitable gauge I can find has the "glass" attacked by bio.  You could take the glass off and use it without if you wish.

Got a couple of ¼" - 4mm push-in fittings too.

Yours if you want it for the cost of the postage.

[julianf]

I used one of these when i was messing with turk burners off the compressor -



It was £4.50, which seems quite a bit now!

All it is is a valve, not a regulator (although that's what it was sold as) - i would have thought that any valve would do you well, just so long as you can fit the air line to it.

[knighty]

does it use much air ?

I'm guessing if your little compressor can keep up with it, it can't use loads ?


without a regulator the air flow will increase/decrease as the compressor kicks in/out ?


even if you set the regulator pressure high (the min your compressor will fall too) it'll mean there's constant pressure to your needle valve so air flow should be constant ?

[Julian]

What you're saying can't be strictly true.

I've nicked this diagram from wikipedia ...




If the outlet on the left is an open pipe, the mechanism will open up fully trying to regulate pressure against nothing.  Block the outlet pipe and it will balance to whatever pressure it's been set at.

I guess in this situation the regulator should be considered as a pressure limiting devise for when it sees sufficient resistance against which a pressure can be created.  The rest of the time it will just run full bore.

Tony's suggestion of using both is probably the best solution in retrospect ... needle valve to control the flow and a regulator to control the pressure against the needle valve.

[knighty]

but... if the needle valve after the regulator slows the air flow to less than the max the compressor can supply

then ther should be enough back pressure for the pressure regulator to work as normal ?



(I've never done it before, so just guessing)


EDIT: I think the important bit is that Tony said his modest little compressor can keep up with it, so it can't be using shed loads of air ? - trying to start the turbo jet engine at the BBB my little compressor ran out of air pretty quick... after about 60sec it was starting to run low...