A holey perplexing problem

[J Butler]

Hello all,

I've just finished up bending my pipes for a custom spray bar I'm making but have now hit a bit of a road block with regards to the frequency and size of the holes I'm best to use. As far as I understand it, a good ball park figure to aim for is to match up the cross-sectional surface area (CSA) of the pipe to that of the sum of all the small holes' CSA, so my probably flawed calculations went a little something like:

Spray bar internal diameter = 26mm
(although the pipe feeding spray bar has an I.D. of 21mm)
Spraybar length 88cm

CSA of spraybar = pi * 13^2 = 531mm^2
CSA of 2mm hole = pi * 1 = 3mm^2
CSA of 3mm hole = pi * 1.5^2 = 7mm^2

2mm holes would require approximately 177 -> 1 hole every 0.5cm
3mm holes would require approximately 76 -> 1 hole every 1.2cm (still pretty excessive to my untrained eye...)

So, am I best to use the I.D. of the spraybar or the pipe that feeds it to base my measurements on, or have I got everything wrong? Or, am I completely over thinking everything and should just use a simple 1 3mm hole at 1 inch intervals across the length.

Might be worth a mention that on paper, the total lph of the system is 4130lph so maybe the 177 hole estimate isn't completely ridiculous considering the tank is only a rio 180

Hopefully someone more knowledgeable can set me straight (here's looking at you Clive )

Thanks in advance,
Joe

 

[ceg4048]

Hey Joe
(where you goin' with that gun in your hand?)

Sorry, couldn't resist the Jimi Hendix classic.

Anyway, why are you limiting the holes to 3mm diameter? Just use bigger holes and problem solved.

A typical Eheim spraybar is around 14 mm, so this gives an area of around 150 sq mm.
I can't quite recall but I think the pipes have 10 or 12 holes evenly spaced so this should give a hole diameter of somewher around 2-4mm but thst doesn't mean Eheim used the right numbers and it doesn't mean you are restricted to similar holes sizes. You just need to play with hole sizes and numbers that gives you good distribution and that doedn't blow your fish out of the water. Start with small holes and ream them bigger to not restrict flow.



Cheers,

 

[foxfish]

As I used pvc pipe for my spray bar & I have 100s of meters of it, I was able to experiment with hole size & spacing.
I doubt if my specs will help you much but I did find that by holding the spray bar with the holes pointing upward that gave a good indication of what was happening as I drilled experimental holes.
I wanted a good strong flow but found that 7 x 6mm holes spaced at 100mm best suited my tank & pump that is rated at 2000lph.
I now use a needle wheel pump which has the same effect as an in line atomiser in that there are millions of micro bubbles produced & these can be seen flowing around the tank.
I did find using 6mm holes was pretty critical as one hole to many & the flow would loose its effect of shooting down the front glass but they turned to be more effective than 3 or 4mm holes in my instance.
I did however, have a pretty good formula with 12 x 4mm holes evenly spaced over 880mm.

 

[J Butler]

Thanks for the replies guys (Hendrix quotes are always welcome! )

I had found a few refrences to spraybars and they all hovered around 2-3mm, so I assumed there may have been a reason for it, increasing the hole diameters by 2-3mm should make everything a lot easier. Real world experience helps put the mind at ease, thanks for posting your experiences Foxfish.