Math and or Fluid Flow Gurus. Spraybar hole calculations

[Jgray152]

Wouldn't you want the holes smaller toward the end and larger toward the hose side?

When I see spray bars run, the lower flow is always toward the beginning of the bar. This would be due to the fact that its easier for the fluid to flow to the end of the spraybar which will create lots more pressure than up near the beginning which would have lower pressure

I do like the loop system, I would just make it more fluid friendly because spliting a flow like that could cause a loss in flow but I get the idea.

 

[Jgray152]

I just did some more math using the fluid flow calculations.
I found this most interesting!!!
No matter what volume of flow or velocity of flow I use for the calculations, I come up with the same diameter for the holes. 0.258". Interesting!

I tried it with 600 GPH, 700GPH and 1000GPH. I then found the fluid velocity for each flow volume and I kept coming up with the same exact answer when figuring for a 1" diameter hose!

Problem is, this is a hard version of simple geometry

 

[svtim]

mmmk. so what size bit will you use a 1/4 inch bit and how long will the pvc be on the drilled tube?

 

[deeda]

I second houie925's math calculations.

What you also need to consider is the length of the spraybar and any 90 degree fittings that you add. You need to make the holes smaller at the beginning of the spraybar (closest to the pump) and larger at the end.

We did a 6' spraybar using 1/2" CPVC. There are three 3/4" 90's to get over the tank rim and up against the side of the tank. Then a 3/4" x 1/2" street elbow connected to 1/2" CPVC (with no holes) along the tank side, then one 1/2" elbow to the spraybar which runs along the front of the tank at the top. The spraybar is 72" long and the holes are spaced 1" apart. The holes are 3/32" diameter for the first 36" and then 1/8" diameter for the remaining 36" length. The end of the pipe is capped. The flow velocity appears to be evenly distributed along the entire spraybar.
BTW, this is using an Eheim 2262 (900 GPH @ 0' head) filter filled with 5L of Ehfimech, 3 pads of Matala filter media (1.5" thick ea.), 5L of EhfiSubstrat Pro and 1" filter foam pad. I never did check the actual GPH output using this configuration. I need to pick up a flow meter one of these days.

 

[svtim]

Thats cool. i thought that you want a spraybar to flow forward at a small angle to get that front to back flow going. im prob wrong just going on what ive seen.

 

[Oosh]

Any hole/hose can theoretically achieve any flow (simplification), what changes is the pressure required, and that pressure is what slows down your pump.

Frankly, you can do a lot of complex math and still achieve an approx. answer, or just experiment (Computation Fluid Dynamics is just a simulated experiment not plugging A&B into a formula to get C).

This is route I'll be taking:

1) Make the spray bar (loop or single end) but drill smaller holes than you think needed.
2) Provide a way of tee-ing a hose (diameter relatively unimportant) in to the furthest end away from the inlet.
3) Attach the length of hose a run it vertical (I'd say at least 1m/3').
4) Fire up the pump.

What'll happen is water will flow along and climb the hose, the higher it goes the more pressure it has to over come, when the water reaches the max height it'll be forced out the holes at the same rate as if the tube was sealed.

Note: If you have a particularly powerful pump or, more accurately, too short a hose you'll make a mess. S
Safest way is to make the hoses total height exceed the max operating head of your pump.

Now you just enlarge the holes until you get the velocity you desire at the minimum possible "extra head" in the tube. 1
Then remove the hose and close it all up and you're done.

 

[Jgray152]

Any hole/hose can theoretically achieve any flow (simplification), what changes is the pressure required, and that pressure is what slows down your pump.

Yup, I know that.

This is route I'll be taking:

1) Make the spray bar (loop or single end) but drill smaller holes than you think needed.
2) Provide a way of tee-ing a hose (diameter relatively unimportant) in to the furthest end away from the inlet.
3) Attach the length of hose a run it vertical (I'd say at least 1m/3').
4) Fire up the pump.

What'll happen is water will flow along and climb the hose, the higher it goes the more pressure it has to over come, when the water reaches the max height it'll be forced out the holes at the same rate as if the tube was sealed.

Note: If you have a particularly powerful pump or, more accurately, too short a hose you'll make a mess. S
Safest way is to make the hoses total height exceed the max operating head of your pump.

Now you just enlarge the holes until you get the velocity you desire at the minimum possible "extra head" in the tube. 1
Then remove the hose and close it all up and you're done.

Thats very interesting. Tell me if I understand you correctly.

You are using this hose that is connected to the end of the spray, running it verticle (far above the top of the tank) and you are going to see how far the pump can push the water up the hose. You then drill the holes larger and larger till the water in the tube gets lower and lower since more and more of the pressure within the pumping system will be reduced and relieved through the holes.

Correct? I never thought of doing that and that is a really good idea.

 

[Jgray152]

mmmk. so what size bit will you use a 1/4 inch bit and how long will the pvc be on the drilled tube?

You can make it as long as you want. The more holes you have, the smaller the holes will be. I would start with 1/8" bit and according to others, start to enlarge the holes at the end of the spraybar using a 1/4" bit. I for sure thought I saw my rena spray bar on my fluval 304 of less pressure at the beginning than at the end of it. I have to check it again, maybe get a video of it.

What you also need to consider is the length of the spraybar and any 90 degree fittings that you add. You need to make the holes smaller at the beginning of the spraybar (closest to the pump) and larger at the end.

We did a 6' spraybar using 1/2" CPVC. There are three 3/4" 90's to get over the tank rim and up against the side of the tank. Then a 3/4" x 1/2" street elbow connected to 1/2" CPVC (with no holes) along the tank side, then one 1/2" elbow to the spraybar which runs along the front of the tank at the top. The spraybar is 72" long and the holes are spaced 1" apart. The holes are 3/32" diameter for the first 36" and then 1/8" diameter for the remaining 36" length. The end of the pipe is capped. The flow velocity appears to be evenly distributed along the entire spraybar.
BTW, this is using an Eheim 2262 (900 GPH @ 0' head) filter filled with 5L of Ehfimech, 3 pads of Matala filter media (1.5" thick ea.), 5L of EhfiSubstrat Pro and 1" filter foam pad. I never did check the actual GPH output using this configuration. I need to pick up a flow meter one of these days.

That is great. I love it

The length of the piping horizontally has little effect on flow volume, to a point that is, depends on the flow you are trying to achieve and if you are using a high or low pressure system.

I do not like using 90* bends at all. If I can go without I will, they are bad for fluid flow.

 

[deeda]

That is great. I love it

The length of the piping horizontally has little effect on flow volume, to a point that is, depends on the flow you are trying to achieve and if you are using a high or low pressure system.

I do not like using 90* bends at all. If I can go without I will, they are bad for fluid flow.

That's why I used 3/4" 90's to get the CPVC into the tank. The output hose from the Eheim is 5/8" so using the 3/4" reduces the restriction of the flow. I actually only have one 1/2" 90 fitting in the spraybar setup.

 

[Oosh]

Thats very interesting. Tell me if I understand you correctly.

You are using this hose that is connected to the end of the spray, running it verticle (far above the top of the tank) and you are going to see how far the pump can push the water up the hose. You then drill the holes larger and larger till the water in the tube gets lower and lower since more and more of the pressure within the pumping system will be reduced and relieved through the holes.

Correct? I never thought of doing that and that is a really good idea.

Exactly, the vertical tube is essentially a pressure gauge, and you just use it to help adjust the back pressure in your spray bar.