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Unread 04-16-2005, 05:07 PM   #184
Cooling Savant
Join Date: Oct 2004
Location: Canada
Posts: 260

^ you are very clear and 100% correct.
You can not state one type of blade is better then another without considering velocities.

I remember about a year ago, when I designed a real nice impeller based on what I knew from pump theory in school. Dan made a straight 6 bladed piece about as simple as you can get, and it out performed my design by 20% (flow and pressure)

Bob search the net, you will find all the pump theory you need. Just remember 99% of it apply's to larger pumps, and most of it is based on proven designs.

What I am saying is someone designed a good pump, then they based the theory on it, not the reverse as some people think.

Your best beat these days, if you do not have experience, is CFD software, for which AVT has had some success with.

The equation that describes the pressure is U^2/g and U=(N2pi/60)(D/2)
Where D is diameter and N is rpm. This is then reduced by the final angle of the blade tip below 90 deg. D is the final diameter.

In the real world of large pumps, you can not use 90 deg and most pumps max out at 75 deg. But this is not the case with small pumps, which react more to the total volume of fluid and rpm then anything else.

Closed impellers control total fluid and can therefore if well designed increase velocity, which in turn increases pressure, with the cost being flow.

It's all a balancing act between flow, pressure and more important motor load, which is why people should not mess around with factory pump chambers.
Almost any DC pump can produce more flow or pressure, but at the cost of overloading the motor or bearings and reducing long term life.

This is the issue we had with the retail MAG, which we needed to design so that people trying to change chamber will have very limited success. This was quite the challange, and I will not discuss how we manage this.

The only issue with the MAG like any other small pump is fluid. You can not pump oil with a MAG and expect it to last. We have other impellers for higher fluids if needed.

Last edited by Dave; 04-16-2005 at 05:38 PM.
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