A Lagit question on a Bakki Shower Installation

[Mike T]

If you have 4 Bak Trays would the perfomance be different if you stacked them 4 high or split them into two stacks of 2 to keep the height lower...

Thanks in advance for your answer (s)...

Aloha! Mike T

[Bob Hart]

Hi Mike,

I do know that Mike Snaden suggests that they be 4-high, so the velocity of the water is high as it drops through the showers.

[D@z]

Yes, water velocity and impact are key. adding that fourth tier makes a huge differnce over a 3 tier system.

[Bancherd]

It's not clear to me why water velocity passing through EACH tier would depend on the number of tiers.

Could someone please help me out?

[James P]

Interesting! Mike S can you explain how the volicity and ( force? ) increases if there are four trays vs. two trays? JR

[Ryan S.]

Quote: Originally Posted by JR Interesting! Mike S can you explain how the volicity and ( force? ) increases if there are four trays vs. two trays? JR

[not mike s. but] If ponder has one pump and 4 trays total, stacking 4 trays high in a single stack would give greater velicity than 2 stacks of 2. Of course this is not how it was worded in this thread, but I think that was the intent of the post.

Running a heavier flow you have less buildup in the shower. At least that is how it has worked in my ponds, with LR, BioBalls, and K1, all of which stay clean for extended periods of time in my ponds, even without FIRs.

[luke frisbee]

he might try.....

The only reason I can think that the 4 tier high set-up would be better is that the water becomes cleaner as it passes through a single tier...not CLEAN, but LESS dirty.....and as it passes through each tray it becomes more clean (exponentially less effective but none the less "cleaner")...so dirty water leaving a four tier system would have been sent through 2x the media as a two tier set up, and therefore would have been more "cleansed" than the same amount of water passing through two tiers.

I AM not saying that is the reason, but that is more plausible than the people that have not been able to understand that the media slows the water flow down so that each time the water exits a tier it is traveling at the same speed as it was exiting the tier above it. Which explains that the speed of the water is NOT the reason for a 4 tier system working better.
If the distance between the trays was increased the speed would increase, but the increase in speed is negligible between a two and four tray system...it is facinating to see people espouse a theory developed from a lack of understanding of the exact topic they are purporting to understand....

(here again the Manufacturer of the product wisely maintains silence. If this were a British product the consumer would have been given a detailed explanation. The manufactuer's decision on how to market the media is to allow the product to become shrouded "mystical properties" and whatever the consumer wants to believe)

oh and tewa...if you read the post HERE where JR questioned the gentleman on his flawed understanding of fluid dynamics/friction/ gravitational pull and such, he Knows the fellah is flawed in his logic....AND HIS QUESTIONS LOOK VERY SIMILAR TO YOURS BACK WHEN i THOUGHT YOU WERE BEING POLITE TO THE FRACTIONATED MIND THAT STILL BELIEVES FIR IS THE REASON BM WORKS. I sincerely thought you were smart enough to know that FIR had nothing to do with the effectiveness of the BMS...which I still believe is a very good, over-priced bit of filtration kit....surrounded by BS so that a segment ( a very large segment) of the hobby can validate spending a considerable amount of money, and believe that there is no ontehr media that can work because of FIR....which they know exiists but haven't used their resources to understand. besides people want to believe their is a god...and a filter system that works all by itself FOREVER...

Porous media Showers are the best thing I can think of to put on a pond After a coarse mechanical filtration apparatus. BM is a good media.
The "science" and logic purported as to why a BMS is the be all end all is extremely flawed and that needs to be understood by today's hobbyist NOW.

[Valarc]

EDIT: in my haste to write out the math here, I forgot a factor of 1/2 in the energy calculations... this is now the corrected numbers

The three top trays in a stack of 4 would of course have the same velocities as the three trays in a stack of 3, so the velocity in those wouldn't have any difference from before. I'm going to bore you all with a little math, just so we know exactly how much of a velocity difference we're dealing with here.

Everything I'm going to be calculating here is a theoretical maximum. This is the best possible velocity you could get without any air resistance, and no media changing flow direction and slowing the water down. This calculation is basically the water flowing straight down in a vaccuum. Actual velocities would be much lower, as would their difference.

Also, I can't find exact dimensions for the towers with some cursory googling, so I'm going to do a calculation GROSSLY over-estimating the size of the towers. Basically, I'm going to assume each section is a full meter high - which is of course MUCH taller than reality, so again the actual velocities and their differences would be much smaller.

The easiest way to do this calculation is with conservation of energy. It eliminates the hassle of using calculus to solve newton's equations, and makes the math short and sweet. That is, the potential energy at the top of the tower is conserved, and converted into kinetic energy at the bottom.

Potential energy - U = m * g * h

where m is the mass, g is the acceleration due to gravity, and h is the height. If we set the height to be 0 at the bottom of the tower, U at the bottom is then 0 as well.

As far as kinetic energy, E = (1/2) * m * v * v

Because we know energy is conserved E_bottom = U_top, therefore
0.5 * m * v * v = m * g * h, or v = square root (2 * g * h).

Therefore, for a 3 story bakki, with meter-tall units, the velocity AT THE BOTTOM OF THE LAST TRAY is...

v = sqrt(2 * 9.8 * 3 ) = 7.67 m/s

For 4 stories

v = sqrt( 2 * 9.8 * 4 ) = 8.85 m/s

So, for meter-tall units, the velocity at the BOTTOM of the lowest tray differs by a theoretical maximum of 1.87 m/s between a 3-tray and 4-tray system. To put this in perspective, adding a fourth tray gives a maximum theoretical velocity change of 15% at the end of the shower.

For half-meter trays, we get for 3 trays v=5.42 m/s, 4 trays - v=6.26 m/s. In this case, the difference is only 0.84 m/s, but this is again 15% of the 3 tray velocity.

I can't judge whether these velocity effects would be enough to make any difference in the filtration properties of the media, but I thought it was important for folks to understand the scale of the velocities we're talking about. I'm curious for those who have seen the effects of adding a fourth try - did you TRY it with the fourth tray stacked separately first, or did you just add the tray to the tower? My point is, it could simply be the extra media and accompanying biofilm that's making the difference, and not the extra height. The only way to know for sure would be to test both configurations.

[Valarc]

Luke, good point about the extra filtration in one row due to stacking 4-high instead of two that are 2-high. I hadn't considered that, and that makes a LOT more sense than extra velocity effects. I would strongly suspect that would indeed lead to better filtration in a taller stack. I guess the only way to test the velocity effects would be to separate the stacks by larger spacings to give additional height.

[luke frisbee]

DAng V,
You can still do the math? you are a freak.

Question though...what would having BM in the trays do to the flow rate through an individual tier.....wouldn't it slow it down so that the velocity leaving each shower would be about the same no matter how high they were stacked?