Special Weber needle valve -non sequitur

[John Fitzpatrick]

On another thread a member said that some VW guys were using a needle valve with a glass ball in order to run higher fuel pressure in the 48 IDA. I Googled that and came up with a site that sells them, with this explanation:

These Needle Valves Are Special Made With A Lightweight Glass Ball, Eliminating Flooding Caused By The Overweight Steel Ball That Our Competitors Sell. The Glass Is Less Than 1/4 Of The Weight Of The Steel Ball Which Allows You To Raise The Fuel Pressure. We Have Run Up To 9 Pounds In Our Own Cars.
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If the problem with the original seats was that they leak under higher than recommended pressure, how would a lighter ball help that?

 

[Dave Bilyk]

John,
I think that the float has to lift the ball to seal the valve, so you have a balance of upward force of float buoyancy = (downward force of ball weight + fuel pressure force) so if you reduce ball weight you can have higher fuel pressure.
It is a fine balance, for sake of illustration if you used a heavy metal such as uranium, the float could not lift the ball at all, and the chamber wopuld flood.

Dave

 

[John Fitzpatrick]

Hmm. What I was questioning is how much difference the ball's weight makes in keeping the valve open. When you compare the leveraged boyant force (up) of a comparitively huge float against the combined forces (down) of the weight of the ball and the force created by the fuel pressure against the ball, the ball's weight would appear to be a very small factor and could be overcome by increasing the float volume only slightly.
I'm not arguing with success here--something's different if they're running 8 psi-- but I would have thought the quality of the seal between the ball and it's seat would have a larger contribution to it.
John

 

[Dave Bilyk]

I see your point John, can't question it and I think your comment about the strong effect of an increase in float volume and leverage is astute.

I suppose I am making some assumptions, without any personal experience I should add, but;
a) That because there seems to be hard evidence and the effect has been widely reported, it is likely to be true; and if it is true, the ball weight does have a significant effect.

b) The fundamental physics (without doing any calcs) agrees with the effect reported.

c) The quality and design of seat are good.

Now as to what is the calculated balance between the three forces, and whether it agrees with the above would be a final piece in the jigsaw puzzle.
With details of the float arrangement, and knowledge of the float weight and volume, the leverage on the valve, the ball size, ball weight, and seat diameter the relationship could be calculated. I have a Haynes Weber manual, but it does not show a section of the needle valve, is there more than just the ball in there?

One other thing, rough roads might also be more able to momentarily unseat a heavy ball, I wonder if this is a factor too. Its a simple device, but the statics and dynamics could be more complex than first imagined.

Dave

 

[Rick]

John I think it was me that initiated the thread you are refering to. I have been doing a lot of research on the topic of fuel pressure and needle / seat design etc. The 3.3 glass ball valve is designed for hard running VW drag engines that are going to require a lot of fuel. A 3.3 valve in anything other than an all out competition engine will have difficulty controlling fuel level because of the amount of fuel they are capable of flowing. They cannot accurately monitor fuel at a low consumption rate as well as a smaller valve can. Use the smallest opening of valve that will supply the necessary fuel for your application. The design mimics the old D & G valve that was popular (and still is) with the SU carb crowd (SUs need all the help they can get). The originator of the D & G is deceased and therefore copys of the design are what are currently sold (as far as I can determine). There are some that say the current Weber valves are suspect but I have been told if they will hold 14" of Mercury on a Mity Vac hand pump that they are fine. If they leak, replace them untill you find one that will hold 14". As far as fuel pressure 2-3 lbs max, regulated.

 

[John Fitzpatrick]

I've been asked to post the site selling the glass-ball needle valve, and it's Glass Ball Needle And Seat For Weber 48 Ida - VW Parts
Rick- so just what does the number stamped on the valve indicate? I've got both 250 and 300 valves and I've always assumed it was an indication of how much gas they would flow. If the glass-ball units come in different sizes, would that would make them more suitable for our application?

 

[Rick]

It is the diameter in mm of the internal (hole) opening that the needle closes upon. To get a better idea look through the opening (threaded end) of a Needle/Seat assy. The larger hole will definately flow more fuel but cannot be controlled as accurately. From what I have been able to decern, these items are made by Gene Berg Enterprises and are available in 3.0+ sizes only. I have not seen anything smaller as being available. Perhaps a with a group buy they could be convinced to make something smaller available, It would just be a matter of changing a drill or reamer(??) during production.