Author Topic: Float Needle Valve.  (Read 1287 times)

Offline MotoJouni

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Re: Float Needle Valve.
« Reply #45 on: November 14, 2017, 02:20 »
Just Jouni.
Exactly what you said Cam.

Only purpose to my calculation was an approximation when the tip starts to restrict the hole. I also omitted many other geometrical factors, for example if the carbs are tilted 20 degrees forwards (cos 20 degrees) and the lever turning (cos(arctan (8/27))), these drop the value to about 7mm instead of 8mm. And because of the square root law (for circle area), the metering is very nonlinear and I think the last 3mm has a very small influence. Most of the metering can happen approximately on the first 5mm level drop from the closing position.

I presume you used these formulas: area for a circle, flow on a channel which is a square root from a pressure difference multiplied by some constants and formula for hydrostatic pressure. That 2.65mm sounds what would really happen there on normal conditions and would have reasonably small effect to mixtures.







« Last Edit: November 14, 2017, 03:12 by MotoJouni »
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Offline Paul H

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Re: Float Needle Valve.
« Reply #46 on: November 14, 2017, 13:18 »
All looks like jolly good fun, just a thought about release points and 'tip' travel....

Some valve shuttles are spung, between the [float] input end and the conical tips.

So, some change in float bowl level may be taken by the spring and so not fully present iteself at the sealing tip.

Offline AndyW

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Re: Float Needle Valve.
« Reply #47 on: November 14, 2017, 13:24 »
I believe Dellorto jets are rated by size rather than flow rate, so a #120 jet (near enough to stock size for a Lav triple) has an orifice diameter of 1.2 mm. So presumably a #250 float valve has an orifice of 2.5 mm diameter, which will have more than 4 times....etc
Cheers,
Cam



Best check your belief systems and calcs : pretty sure a 120 jet relates to 120 millitres of fluid (fuel?) passing per minute in a standardised test.
« Last Edit: November 14, 2017, 13:27 by AndyW »
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Offline Gravelroad

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Re: Float Needle Valve.
« Reply #48 on: November 14, 2017, 13:55 »
Cam is right Andy, Dellorto jets are rated by size, so a 120 jet acutally means 1,20mm diameter hole.

Offline MotoJouni

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Re: Float Needle Valve.
« Reply #49 on: November 14, 2017, 16:06 »
According to Dell'Orto manual, the sizes are 0.01mm's.

I was once told those Dell'Orto jets are very accurately made, even much more accurately than many other manufacturers do which actually state the size respect to flow characteristics. I don't know how true this is. It would need a flow bench to test that.
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Offline AndyW

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Re: Float Needle Valve.
« Reply #50 on: November 14, 2017, 18:48 »
Cam is right Andy, Dellorto jets are rated by size, so a 120 jet acutally means 1,20mm diameter hole.
Damn: more egg on my face!!🙄 and yet their pumper jet sizes are calibrated in terms of flowrate or have I been misled there too?

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Online sfcpiet

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Re: Float Needle Valve.
« Reply #51 on: November 14, 2017, 19:43 »
According to Dell'Orto manual, the sizes are 0.01mm's.

I was once told those Dell'Orto jets are very accurately made, even much more accurately than many other manufacturers do which actually state the size respect to flow characteristics. I don't know how true this is. It would need a flow bench to test that.

They're actually rather crap... a jet guage is a good investment if you want to fathom the limits.

piet
180s feel quick, 120s are...      If it ain't broke, fix it till it is.

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Offline Gravelroad

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Re: Float Needle Valve.
« Reply #52 on: November 14, 2017, 20:41 »
I once measured them on a very accurate microscope and have to agree with Piet, not too bad with the original INC logo imprinted stuff, but even those can be 0,05mm (5 digits) or even more off their rating. At least they usually tend to be bigger than rated. ;D

Offline MotoJouni

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Re: Float Needle Valve.
« Reply #53 on: November 14, 2017, 21:48 »
I was once told those Dell'Orto jets are very accurately made, even much more accurately than many other manufacturers do which actually state the size respect to flow characteristics. I don't know how true this is. It would need a flow bench to test that.
I have a gauge and reamer set. The man stated that they flow similarly but the diameters vary, not the opposite way as usual. He said that the original Dell'Ortos are flow bench calibrated and therefore refuse to ream jets for multicylinder engines if a flow bench is not available and use only factory sizes on them. If this is true, Dell'Orto must have a some kind of flow vs. nominal diameter chart when they state the size in diameter.

He also stated this is the reason why they are sold in single units and has relative high price. I know some other brands are mostly sold in sets and most of the sizes end to the trash bin.
I still have no clue did he actually ever worked with them on a flow bench.
« Last Edit: November 14, 2017, 22:19 by MotoJouni »
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Offline Dellortoman

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Re: Float Needle Valve.
« Reply #54 on: November 14, 2017, 23:11 »
Damn: more egg on my face!!

A Gerni should get it off  ;)

I think Mikuni jets are calibrated for flow rate. But without looking it up I'm not sure, or what the units of flow are.
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Offline MotoJouni

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Re: Float Needle Valve.
« Reply #55 on: November 15, 2017, 04:16 »
These two things doesn't necessary have anything to do with each other how accurately the jets actually flow or how the sizes are stated (such as some kind of nominal or flow diameter, flow rate or something else for example). According to many other conversations this may make some confusion.
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