To all Ladegaard builders

[ThorstenL]

Konnichiwa,

Originally posted by J Epstein
Would I get more PSI if I added a second aquarium pump feeding my surge tank? Or would the pressure just be limited by whichever pump created the least pressure?

If you connect the pumps in parallel you are limited by how much pressure the weaker one generates, but if you where to feed a pump with air that is already at a higher pressure than that the surrounding air, in other words connect the pumps in series.....

Sayonara

[Paul Ebert]

Originally posted by J Epstein
While we're asking questions . . . .

Would I get more PSI if I added a second aquarium pump feeding my surge tank? Or would the pressure just be limited by whichever pump created the least pressure?

-j

I think the extra pump would act as if it was in parallel - increase the airflow, but not the pressure. You'd have to figure out how to do the equivalent of putting them in series.

Maybe it could be done this way: start with two pumps (A and B) and a box. Route the output of pump A into the box. Enclose pump B inside of the box (except for the power cord, of course). Have the output of pump B exit the box and supply the pressure to the tank. The box, of course, needs to be airtight.

If you wanted to double the pressure, that might be worth trying. But I don't think I'd bother as an approach to get 20 or more psi. I think an airbrush or dental compressor would be better. But those aren't exactly cheap, though you could find an airbrush compressor used.

What we need is a pneumatics engineer. There must be a way to convert high airflow/low pressure into high pressure/low airflow. Such a person could probably solve my problem of the side forces as well.

Paul

[livemusic]

we need is a pneumatics engineer

OK, I'm just plain mechanical engineer, but I'll try to help here.
Paul, there is nothing complicated about your side force origin.
From the picture below, you'll see the slider is looking for equilibrum at some angle relatively to the bearing axle, while moving away from the bearig center, just beacause of the distance between its center of gravity (CG) and center of pressure applied by the bearing. So, projecting the slider weight vector on its axle, you have the side componet of the slider weight, which is driving crazy your arm. This is unstable system: the further slider moves away from the bearing center, the more side force is. Of cource, the angular deviation is rather small, but because you slider is so heavy, the side force becomes substantial enough, to bother you.
From my experience, air tracking arm reacts histerically on any side force, and shall be perfectly levelled and balanced.
That's why I'm saying the only way to build good high pressure/stiffness air arm is to make lightweight symmetrical slider/bearing/arm assembly and leave heavy shaft fixed firmly on its place.
As for air pump performance, typical pressure vs. flow chart shows, the more airflow you need, the less pressue you get. Any air pump is designed for specific pressure/flow characteristics. Looking through those currently proposed on ebay, I got an impression, the good air brush compressor performance suits well air tracker needs, providing typically 30-60 psi pressure and sufficient air flow. I now nothing about how loud are they, but some claimed to be very silent...

[garbage]

according to this stereophile review, kuzma uses the sil air technology compressors.

a google on the web revealed that Silent Aire produces these compressors.

they have a supersilent model... comparisons of noise levels shown below:

[livemusic]

There is one currently on eBay:
http://cgi.ebay.com/Air-Brush-Compre...QQcmdZViewItem

[Paul Ebert]

Originally posted by livemusic

...projecting the slider weight vector on its axle, you have the side componet of the slider weight, which is driving crazy your arm. This is unstable system: the further slider moves away from the bearing center, the more side force is.

This makes sense. I wonder how the ET2 pulled it off.

Originally posted by livemusic

That's why I'm saying the only way to build good high pressure/stiffness air arm is to make lightweight symmetrical slider/bearing/arm assembly and leave heavy shaft fixed firmly on its place.

Your probably right about this. If I go back to the design, I'll most likely try this approach; looking for a very small, torsionally flexible air line with some sort of set-up that allows it to pivot. In that case, the 1/4" bearing might be preferable.

My compressor is rated at 43 dB. It is OK when I put it in the basement except for when it reaches its maximum pressure setting. It then has some sort of release that causes a loud hissing that must be much higher than 43 dB. If the pump ran continuously it would probably be acceptable. I wonder if the airbrush pumps have such a release valve.

[peterr]

I wonder how the ET2 pulled it off.

the biggest difference is weight. As far as I know ET use a hollow tube.

Would I get more PSI if I added a second aquarium pump feeding my surge tank? Or would the pressure just be limited by whichever pump created the least pressure?

In my experience presure and airflow are strongly related. Even the smallest aquariumpump is capable off quite high presure as long as the airflow is kept sufficiently low. In other words the amount of airflow needed restricts the pressure a certain pump is able to deliver. Therefore putting two pumps in parallel means you can double the airflow at a certain pressure, but at the same time if the airflow through the airbearing exceeds what one pump can deliver at a given pressure, two pumps might be able to keep the pressure at the desired level.
(Kuzma state in the manual their the arm needs about 4 bar at 4 liters of air per minute).

does anyone know how to calculate airflow for a given presure and airgap (and whatever else you need to know)

Really nobody that knows the answer to this one?

[livemusic]

does anyone know how to calculate airflow for a given presure and airgap (and whatever else you need to know)

Look here:
http://www.efunda.com/formulae/fluid..._flowmeter.cfm
Just calculate your air gap area and put the equivalent circular hole diameter into calculation - this shall give you reasonably good approximation (fluid density and flow coefficient are already set for air).

[peterr]

Look here: http://www.efunda.com/formulae/fluid..._flowmeter.cfm

Thanks Livemusic!
It seems to be what I was looking for. (too bad you can only use it a few times before it shuts you out, but I found it will work again next day)