Biopowered - vegetable oil and biodiesel forum
General => Wiki and forum discussion => Topic started by: Rotary-Motion on March 02, 2011, 08:54:44 AM
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hi all
is the new GL pic up here with valve v9 on it?
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(http://www.biopowered.co.uk/w/images/6/6b/GL_processor_with_valve_to_allow_use_of_sight_tube.png)
V9 was to do with filling the processor and sight tube at the same time.
I don't have one on my processor as I use an external pump for filling, but I can see why you might want one.
It's not in the original GL design though, which makes me reluctant to suggest that we include it on the GL page.
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Diagram with V9 comes under the heading "Subsequent modifications and additions to Graham's design".
Grahams original design didn't even show a sight tube, it's only mentioned as an addition in the text on his site.
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Fair point.
I think Graham would've added the sight tube subsequently to the diagram if he was as deft with graphics packages as you Julian :)
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Oh Gee, I'm going all shy now!
Big question is ... would he have added valve V9?
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I'm going to be all controversial now and suggest we ask him ;D
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For the sake of adding one valve to make the design far more flexible, I'd guess Yes, but ask away!
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could i mount this way?
(http://img29.imageshack.us/img29/8203/glprocessorwithvalvetoa.png)
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Yes you could. Personally I prefer to see the venturi above the oil level in the tank. That way, if you forget to close valves, oil won't find it's way to places it shouldn't be.
Then there's the old chestnut about vertical vs. horizontal mounting of the venturi, there have been several threads on that subject! With a good venturi, I don't think Grahams original layout will work too well without a jet breaker™.
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My first two builds had a horizontal venturi with drilled spray arm in the tank for back pressure. This worked fine.
Current build has vertical venturi following Jamesrl's advice. It does suck amazingly well, but it also makes loud slurp - slurp - slurp noises out of the vent when demething, which the horizontal ones didn't.
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I get a constant "slurp" from the vent when demething using a horizontal one!
I've offered the theory on the forum a couple of times that it's not so much back pressure as ensuring the pipe down stream of the venturi is "filled" whilst still retaining a good flow.
When I get a chance I want to play around with divergent nozzles in a venturi of preferably and ejector. If I'm right the venturi could be connected immediately adjacent to the tank and could offer a good spray pattern within.
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Now I'm 100% with you there on the filled venturi thing!
The venturi action must only work if the liquid sticks to the sides of the 10 degree cone on the way out. If the throat velocity is too high I guess it can just "jet" past that.
I think we ask a lot of the venturi to both draw in liquid and also air (adding bubbles to break the surface contact with the 10 degree cone).
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I don't think it needs to fill the cone, or at least not all of it. I drilled the throat of my cast venturi on the lathe so it was exactly concentric and it wouldn't always establish a vacuum when the suction valve was opened. By putting a jet breaker™ just down stream of the venturi it establishes every time, but I doubt most of the flow from the throat touched the discharge cone. If it ran all the way down the discharge cone you could speculate that it may "block " the suction port and possibly blow back up the suction line.
I recon that a parallel throat in a venturi is a bad thing (contrary to what has been stated on the forum in the past) and that the transition direct from the 60° inlet to the 10° discharge will offer a diverging nozzle effect. I need to make another venturi, with no parallel section to the throat and see if it will perform without a jet breaker™.
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Certainly the big commercial ones don't have a straight section in the middle, it's cone straight to cone with the side feed at the transition.
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V4 and V7 can be left open after meth has gone in via venturi if! the venturi is on the top horizontal?
vertically vlaves need to be shut?
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That is true, but in practise the valves should be left closed during processing - mixing air into the flow increases backpressure to the pump (on my system from 1.0 bar to 1.3 bar) with consequential reduction in flow and batch turnover rate. Plus there might be some oxidisation considerations to take in (though it would be the same air going around and around so perhaps only limited oxygen available anyway).
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Best practise is to close V4 and V7. If the oil is very thick or you make a complete batch of soap (as I did recently!) the flow will take the easiest path. So if the resistance in the main circuit is high, it will also find it's way into the vapour circuit and Methoxide mixer, regardless of orientation or position.
General rule of thumb should be close everything and only open the valves you need and then double check you've opened the right ones. My system has grown quite complicated over the years. I have two pumps which can run simultaneously in tandem or on separate circuits. The Mono has flying hoses so I can pump just about anything from anywhere to anywhere. My favourite trick is to leave a hose valve open and pump oil or bio all over the place ... shot myself in the back with warm bio once!
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i got 2 questions
1, if the venturi is fitted as in the picture (at the top horizontal) will it still work? as no back pressure creating suck
2, do we really need valve V7 ? as this valve only sucks air, if you need to suck air in reacting just leave valve V4 open as when meths gone it sucks air after!
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My venturi is horizontal, similar layout to GL's drawing, as are several other peoples.
Jim advocates that a venturi should be vertical with one swept bend between it and the processor to create back pressure. Personally I think the requirement is slightly different ... I think the jet from the throat needs to "fill the pipe" for the venturi to function correctly, the two are not quite the same. If a venturi is accurately made (mine are drilled on a lathe), I recon the tendency is for the jet from the throat to travel up the centre of the pipe without touching the sides. It can be encouraged to touch the sides by a bend and gravity can assist, especially if the venturi is vertical.
Given time I'd like to try some experiments with diverging jets which should, by design, fill the pipe.
(http://www.palmergroup.co.uk/Bio/venturigraphics.jpg)
With the last venturi I made I believe it wasn't "filling the pipe" despite having a swept bend down stream, so I fitted a jet breaker™ after the venturi and it works fine. The jet breaker™ is simply a brass rod inserted through opposing holes in the pipe and soldered in place. This, as the name suggests, breaks up the jet forcing the flow to fill the pipe. It seems to work really well. If I'm right it should be possible to only have a short, straight run into the processor, but don't hold me to that as I haven't tried it!
(http://www.palmergroup.co.uk/Bio/jet_breaker.jpg)
Personally I prefer the venturi up high, above the fluid level in the tank, that way, if you forget to close valves the vent pipe work can't fill with oil.
Re valve V7 ... yes, you need it.if you omit it, when you open valve V4 to entrain Methoxide you most likely won't. This is because the flow will take the path of least resistance which will be to suck air from the vapour circuit.
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hmm that is very intersting julian, i still think V4 left open would be fine as when meth carbouy empty it will carry on sucking its air, and as its venturied with keep a circulation of vent vapour ok via processor...
just read a guy on veg site has horizontal and no bends just straight in and gets 20mins for 30ltrs,
Originally posted by mon
Thought venturis worked on the pressure difference across the input/output, mine on the horizontal going into the processor with only about 12" of straight copper after.
Takes about 20 mins for 30l of methanol, although it does lift the methanol around 1.5 metres.
Would I benefit by adding back pressure?
your finding or thoughts on the after pipe in the venturi is interesting! i think if you look at a NigeB due to plumbing fittings used it makes its own back pressure (if its needed at all) so no need for bends and would be quite happy horizontal, begood to know if anyone has a nigeB fitted this way?
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Oh I do like that Jetbraker idea. Personally I prefer horizontal and up high, next build I'll try it out!
Other possibility is horizontal with a 90 elbow into the tank, so the venturi is beside the tank if you see what I mean?
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That's exactly the way mine is, but the bend is very slow. The suction would establish some times but not others. With the jet breaker ™ it establishes every time.