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torsionbar
Samba Member
Joined: December 11, 2010
Posts: 2215
Location: earf
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 Posted: Wed Mar 30, 2011 12:53 pm Post subject: |
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| kielbasa wrote: |
| Every nub is not suppose to be welded. Every other one should be, to allow some flexing. And yes air will cavitate |
| Csaba wrote: |
Well that's news...I guess we should inform all of the jet engine design engineers that their calculations are all wrong, and that thrust models are not limited to airspeed through the compressor stage... I am sure they will be knocking on your door to consult. |
you both are wrong. cavitation occurs only in liquids. air is not a liquid. ergo, cavitation cannot occur in a fan.
don't take my word for it though, here's a few definitions for you. but don't let that stop you from flexing your google-muscles. 
http://chemistry.about.com/od/engineeringglossary/g/cavitation-definition.htm
Cavitation is boiling of a liquid that is caused by a decrease in pressure rather than by an increase in temperature.
http://www.thefreedictionary.com/cavitation
The sudden formation and collapse of low-pressure bubbles in liquids by means of mechanical forces, such as those resulting from rotation of a marine propeller.
http://en.wikipedia.org/wiki/Cavitation
Cavitation is the formation of gas bubbles of a flowing liquid in a region where the pressure of the liquid falls below its vapor pressure. Cavitation occurs when a liquid is subjected to rapid changes of pressure causing the formation of gas or vapor bubbles in the lower pressure regions of the liquid. |
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Pink MG
Samba Member
Joined: June 01, 2009
Posts: 226
Location: Lower Slower Delaware
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| Posted: Wed Mar 30, 2011 1:14 pm Post subject: |
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I bought a P.O.S. unit drop shipped from SCAT...it had "PRO MSA" stamped on it. The backspace was so deep that it couldn't be shimmed away from the alternator tin without the fan coming off the flat spots of the hub.
I am sure is was made "offshore". Now it's a $90 paperweight.
I contacted the vendor I bought it from who then forwarded my e-mail to SCAT. They never freaking answered me. |
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77charger
Samba Member
Joined: November 12, 2005
Posts: 1492
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| Posted: Wed Mar 30, 2011 8:32 pm Post subject: |
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| Pink MG wrote: |
I bought a P.O.S. unit drop shipped from SCAT...it had "PRO MSA" stamped on it. The backspace was so deep that it couldn't be shimmed away from the alternator tin without the fan coming off the flat spots of the hub.
I am sure is was made "offshore". Now it's a $90 paperweight.
I contacted the vendor I bought it from who then forwarded my e-mail to SCAT. They never freaking answered me. |
I bought a scat at first fro a local vendor got home the fan was so out of round.The center hole was off center too.Took it back and got my money back.
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jbbugs
Samba Member
Joined: September 16, 2002
Posts: 2152
Location: Behind the wheel
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| Posted: Thu Mar 31, 2011 5:22 am Post subject: |
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Here's a Scat fan that lasted about 1 minute on it's first test drive.
NO, it wasn't using a serpentine belt either.
It took out about $350 bucks worth of parts when it went.. It made one Horrible sound when it went on me. This was on my Buddy's 2332 motor when I was driving it. At first I though it threw a rod. The fan looks like it actually just split at the hub, rather than throwing it's blades.
I'm surprised it didn't crack a cylinder.
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Pink MG
Samba Member
Joined: June 01, 2009
Posts: 226
Location: Lower Slower Delaware
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| Posted: Thu Mar 31, 2011 8:00 am Post subject: |
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Glad I didn't use the thing. Scary looking pics.
This was just another Chinese POS I've encountered in the VW aftermarket. I think people new to the air-cooled VW hobby get turned off by all the Chinese crap the vendors are selling. It is far worse than the Streetrod/American Muscle aftermarket.
The iconic names of VW aftermarlet vendors of decades ago now stand for "Chinese POS"...don't waste your $$. I find almost the only quality stuff is privately made in the USA and sold in the Samba classifieds.
I've only gotten back into VW's in the last 2.5 years after a 40 year hiatus. I am at the point where I am serioulsy considering selling off all my VW stuff and just sticking with my '40 Ford and other pre-WWII streetrods. I can't keep taking a loss on the junk new parts and I refuse to resell it to another hobbyist...it's junk. |
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jbbugs
Samba Member
Joined: September 16, 2002
Posts: 2152
Location: Behind the wheel
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| Posted: Thu Mar 31, 2011 8:26 am Post subject: |
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I don't think the Scat fan was Chinese. It was probably a cheaper Mexican one. I've purchased original VW of Mexico fans from my suppliers, and they've always been great quality. There are some other Mexican ones that come in a plastic bag w/a Blue and white lable....They ARE junk, and are so out of balance that they vibrate so badly you would swear your flywheel is coming loose. I've not seen any from China as of yet.
Paul
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bugnut68
Samba Member
Joined: June 10, 2003
Posts: 4180
Location: Eugene, OR
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| Posted: Thu Mar 31, 2011 9:27 am Post subject: |
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| kielbasa wrote: |
| Every nub is not suppose to be welded. Every other one should be, to allow some flexing. And yes air will cavitate |
Why would you want flexing in the fan? |
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Pink MG
Samba Member
Joined: June 01, 2009
Posts: 226
Location: Lower Slower Delaware
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| Posted: Thu Mar 31, 2011 10:58 am Post subject: |
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jbbugs...then who is "PRO MSA"???
This is stamped into the fan. |
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torsionbar
Samba Member
Joined: December 11, 2010
Posts: 2215
Location: earf
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| Posted: Thu Mar 31, 2011 2:12 pm Post subject: |
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| Pink MG wrote: |
| I think people new to the air-cooled VW hobby get turned off by all the Chinese crap the vendors are selling. |
the problem imo is that those who are new to air-cooled vw's don't know the difference, and end up spending a lot of money on these garbage parts, because they're advertised all over the place. they then spend a lot of time and effort installing them, trying to get them to work. and finally, they become frustrated and discouraged because their "pos vw" doesn't run right or is constantly having problems.
it's an epidemic, but as long as there are cheap-skates and broke teenagers buying vw's, there will always be a market for this china garbage. |
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jbbugs
Samba Member
Joined: September 16, 2002
Posts: 2152
Location: Behind the wheel
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| Posted: Fri Apr 01, 2011 5:26 am Post subject: |
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| Pink MG wrote: |
jbbugs...then who is "PRO MSA"???
This is stamped into the fan. |
I've not seen a fan like that.
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Pink MG
Samba Member
Joined: June 01, 2009
Posts: 226
Location: Lower Slower Delaware
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| Posted: Fri Apr 01, 2011 6:55 am Post subject: |
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I agree 100% with your observation torsionbar. It's a shame it has to be this way though.  |
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Bruce
Samba Member
Joined: May 16, 2003
Posts: 17290
Location: Left coast, Canada
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| Posted: Fri Apr 01, 2011 4:12 pm Post subject: |
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| kielbasa wrote: |
| And yes air will cavitate |
No it can't. Read this:
http://en.wikipedia.org/wiki/Cavitation
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bugnut68
Samba Member
Joined: June 10, 2003
Posts: 4180
Location: Eugene, OR
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| Posted: Fri Apr 01, 2011 4:19 pm Post subject: |
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| Kielbasa, never heard back on your comments regarding fan flex? Why would you want the fan to flex at all, let alone a little bit? |
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bugnut68
Samba Member
Joined: June 10, 2003
Posts: 4180
Location: Eugene, OR
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| Posted: Mon Apr 04, 2011 11:58 am Post subject: |
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| bugnut68 wrote: |
| Kielbasa, never heard back on your comments regarding fan flex? Why would you want the fan to flex at all, let alone a little bit? |
Nothing but crickets... case closed. |
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bugninva
Samba Member
Joined: December 14, 2004
Posts: 8858
Location: sound it out.
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| Posted: Mon Apr 04, 2011 5:56 pm Post subject: |
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| bugnut68 wrote: |
| bugnut68 wrote: |
| Kielbasa, never heard back on your comments regarding fan flex? Why would you want the fan to flex at all, let alone a little bit? |
Nothing but crickets... case closed. |
flexing of the fan is a double edged sword.... a little flexing is good to keep sudden shocks(like quick accelleration or decelleration) from deforming the fan... the other side of that blade is that flex in a welded fan can cause stress fractures to the fusion points, which can lead to failure... pick your poison, for an unwelded fan, flex may be a good thing, but flex may not be the best thing for a welded fan...
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| [email protected] wrote: |
| With a show of hands, who has built over 1000 engines in the last 25 years? Anyone? |
GEX has. Just sayin |
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tezer71
Samba Member
Joined: February 07, 2009
Posts: 126
Location: norway
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| Posted: Tue Apr 12, 2011 2:14 pm Post subject: |
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| i ordered the gene berg fan!only read and hear good thing about that one! |
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kielbasa
Samba Member
Joined: November 28, 2007
Posts: 1443
Location: Garbage Grove, CA
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| Posted: Tue Apr 12, 2011 2:48 pm Post subject: |
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You want some flex because the blades see a great amount of pressure at higher rpm. And the fans aren't really welded, more like tacked. There isn't very much material to fuse together with these fans. And the tacks can only hold so much. If the fan flexes at the non welded points, it gives you a little..... flexibility sort of speak.
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Hotrodvw
Samba Member
Joined: July 06, 2004
Posts: 6327
Location: Orygun
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| Posted: Sat Oct 29, 2011 7:55 pm Post subject: |
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| kielbasa wrote: |
| Every nub is not suppose to be welded. Every other one should be, to allow some flexing. And yes air will cavitate |
Interesting..............every 'welded' fan that I have seen is fully welded, including the 'Almighty BERG' fans.
What say you?
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Hotrodvw
Samba Member
Joined: July 06, 2004
Posts: 6327
Location: Orygun
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| Posted: Sat Oct 29, 2011 7:56 pm Post subject: |
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So, welding them is the easy part. How does one balance one themselves? I know how it's done, but have any of you done it yourself at home?
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 76941
Location: Sneaking up behind you
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| Posted: Sat Oct 29, 2011 7:59 pm Post subject: |
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I got a Berg fan so far so good 
| kielbasa wrote: |
| And yes air will cavitate |
http://en.wikipedia.org/wiki/Cavitation
| Quote: |
Cavitation is the formation and then immediate implosion of cavities in a liquid – i.e. small liquid-free zones ("bubbles") – that are the consequence of forces acting upon the liquid.[1] It usually occurs when a liquid is subjected to rapid changes of pressure that cause the formation of cavities where the pressure is relatively low.
Cavitation is a significant cause of wear in some engineering contexts. When entering high pressure areas, cavitation bubbles that implode on a metal surface cause cyclic stress. This results in surface fatigue of the metal causing a type of wear also called "cavitation". The most common examples of this kind of wear are pump impellers and bends when a sudden change in the direction of liquid occurs. Cavitation is usually divided into two classes of behaviour: inertial (or transient) cavitation and non-inertial cavitation.
Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants. In man-made objects, it can occur in control valves, pumps, propellers and impellers.
Non inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Such cavitation is often employed in ultrasonic cleaning baths and can also be observed in pumps, propellers, etc.
Since the shock waves formed by cavitation are strong enough to significantly damage moving parts, cavitation is usually an undesirable phenomenon. It is specifically avoided in the design of machines such as turbines or propellers, and eliminating cavitation is a major field in the study of fluid dynamics. |
http://www.offroadvw.net/tech/wes/fan.html
| Quote: |
| The fan cavitates - wrong, cavitation is only a liquid phenomena, it is boiling of a liquid due to a localized pressure drop below the vapour pressure of the liquid, you cannot boil a gas. |
Let's see your references.
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