Powerhead MFR rating VS. Actual

[parkinsn]

I thought this artical was pretty interesting. Thought I would share it. Not sure if it was posted on here or not but here it is.

http://www.advancedaquarist.com/2011...aign=clickthru

[parkinsn]

Digging on RC I found tunzes response to this:

I wouldn't draw any conclusions just yet, we don't dispute that we got our flow numbers wrong, I attach our press release about this issue. However, gph is not the only factor at play, to say this is so would be equivalent to saying a 400W MH with no reflector puts out more light and is therefore superior to a 250W HQI with a reflector. I have yet to meet anyone who has done a side by side comparison and not reached the conclusion by observation that our comparably rated pump is stronger, the reason is this ability to direct the flow.



Where did we get our flow numbers?
We derived our flow numbers in two ways, by a test termed a “bag test” and by theoretical calculations. The bag test is just as simple as it sounds, a collapsed bag is placed over the end of the pump and inflated by the pump with water, the time to fill the bag is measured and the flow is calculated. This method has definite limitations, it places backpressure on the pump, and it cannot be used on larger pumps given the limits of bag volume and reliable timing. For all pumps a theoretical calculation is made based on propeller surface area and rotation frequency.
Our bag test results are consistent (within + or – 10%) with theoretical results on the pump models 6015, 6025, 6045, 6055, 6065 and 6085. This led us to rely on theoretical numbers. The biggest pump that a bag test can be performed on is the 6105 and the inaccuracy of flow numbers on the 6105 has a different origin than 6205 and 6305 inaccuracies. The 6205 and 6305 flow numbers were only based on theoretical calculations. The 6105, when released, was near specified flow and was bag tested with a result of 90% of theoretical, however, later modifications to reduce noise relied on theoretical flow numbers and flow was lost to these modifications. On models 6205 and 6305 the fundamental issue is that the theoretical flow cannot be reached due to overly constricted intake and output.
Going Forward.
Over the next 6 months we will perform numerous tests aimed at improving our pumps. We believe pump volume alone does not equal effective flow, the ability to direct that flow is also important. In much the same way as the light available from a bulb means little if it cannot be properly directed into the aquarium, the flow rate at a pump is not as important if there is not sufficient flow at the corals.. We have since purchased two flow meters, one uses comparable sonic technology and the other uses a propeller akin to a common wind gauge and while we have found that using the comparable meter and methodology our results are the same. We have also found the propeller based meter gives divergent data, this data indicates that our more forceful targeted flow draws in current as the distance from the pump increases and that our total flow produced may be well higher than the flow of the pump itself. Use of a different methodology may very well give the opposite results, but this does not dispute the results of this study, it will only show that flow is complex and has numerous aspects which we are only beginning to understand. At this point we conclude that the study is correct for the flow produced by the actual pump itself and we will improve the pumps in a retrofittable manner, though this will take time as new parts must be designed and produced. Improvements will be based on increasing intake surface and reducing output restrictions on models 6205 and 6305 and increasing rotational speed for 6105. We would like to thank Sanjay Joshi, Bill Straka and Michael Sandford for performing this study, graciously informing us of the results and giving input on proposed solutions. We believe it is a step forward in uncovering many of the mysteries of high volume, low pressure flow which until recently was nearly impossible to quantify.

[lastlight]

I still love Tunze. I applaud their response and can't wait to see what they do about this. I had 6101s and thought they just ripped. If they had twice that flow in my old tank I'd have been struggling to balance just two with a sandbed. They're going to have to unrestrict those covers tho and I'm sorta scared for all the little critters that love to climb over them. That or make the covers bigger but we don't want that I'm sure.

[Delphinus]

Seems pretty much all over the blogosphere. I dunno if there's really anything much to dwell on it though. I kind of wonder if people get hung up on #'s too much. If you liked the flow patterns and you thought it was 2000gph but you find out now that it's really 1500gph is that really enough to invalidate the first premiss that you thought you liked it? And on the flip side, if you didn't like it in the first place anyhow then likely the gph value had little to do with that. I'm sure owners of Vortechs will particularly like this study so I guess good for them on that, but it doesn't change the fact that they are a more expensive option for starters. Don't get me wrong, I like several features of the Vortechs but I'm rather fully invested in Tunze due to that I've had had time to build up the inventory over 5 or 6 years now and I can just add to what's already there. It's sort of like how when DSLR's first came out, I had a nice collection of lenses for Nikon so I chose a new Nikon body despite that Canon makes some incredibly awesome cameras as well - but why switch out EVERYthing and take that financial loss when you don't need to because what you have technically fits the bill? So back to Tunze vs Vortech, without anything already in hand it might be an easier decision to go one way or the other, but neither option is really leaving the consumer out in the lurch so to speak. Plus I love that I can play around with positioning and aiming of the Tunzes, so I'm still happy with what I've got, even if the #'s are not what I first thought they were.