dual spraybars w/scwd and mag12

cjburden

Non-member
im setting up a single corner overflow 90g rr AGA.

I am trying to determine whether or not I want to make dual spraybars for the return, or if I should just have 90 degree outlets.

I figure that the advantage of a spraybar of the single outlet is of course more evenly dispersed water flow.

Are there any disadvanteges? If I place the spraybars below the surface of the water I need to drill a 1/8" hole at the top of the return to keep them from back siphoning in the event of a power outage correct? What exactly does drilling that hold do, and does it add any extra noise or bubbles to the tank?
 
You actually want to drill the hole just an 1/8 inch or so under the water surface in the tank. The small hole drilled will allow water to siphon only until the tank's water level drops below the hole, at which point the siphon will suck air through the hole, and stop the flow of water.
 
cjburden said:
If I place the spraybars below the surface of the water I need to drill a 1/8" hole at the top of the return to keep them from back siphoning in the event of a power outage correct? What exactly does drilling that hold do, and does it add any extra noise or bubbles to the tank?
Yes, you will need to drill an anti-siphon hole. A siphon is hard to describe without complex terminology, but basically, you may think of it as the case where the weight of water in a line pulls more water into the line, and that water, in turn, pulls more water, and so on...

As a simple example, let's say you have a rigid pipe, full of water, submerged on one end in a reservoir of water, and open to the air on the other end. Water is an incompressible fluid (for the sake of argument here). Therefore, when you pull water out of the rigid pipe through the open end, the water doesn't expand or get less dense to fill the volume in the pipe like a gas would. Rather, the plug of water simply pulls more water in on the other end.

Conversely, if there is a break in your pipe, and you go to pull water out on one end, two things can happen: 1) more water will be pulled in on the submerged end, and/or air will be pulled into the pipe. Whatever is easiest will happen, and typically, this involves sucking air into the system.

So in the end, the anti-siphon hole simply allows air to be pulled into the line in place of water, thereby breaking the siphon. With air occupying the high point of the system, it is not possible for the weight of the water to go over the overflow and pull more water in.

I am not sure about how much noise and air bubbling the anti-siphon hole will add. As long as your line pressure is sufficiently high, there should be no air entrainment. Be careful, as the opposite to air entrainment may occur; water may spray out of the anti-siphon hole. Also, remember that an anti-siphon hole simply has to allow air to be sucked in. As such, it can be connected to some tubing. I have a problem with water jetting out on my frag tank, so I shield the hole with some plastic to deflect water back down into the tank,

Matt:cool:
 
If I design the spraybars so that they have holes just below the water surface in the tank than that should suffice and take care of any possible noise and spray?

This is my first attempt to do any sort of a plumbing job so you'll have to excuse the ignorance.
 
The only problem I see with a spray bar return is that it reduces the velocity (flow) of the return water. If you have other flow devices (power heads or closed loop) then I guess that would not be such a problem.
 
hrmm..

I assume that it reduces the velocity based on diameter and number of holes in the spray bar itself. Any way to estimate how much flow you lose? I don't like the idea of losing any flow :(.
 
I don't thing you will loose the gph flow with enough holes but I also don't think you will get the same velocity or power and Turbulence behind the flow that you get form a straight return for those SPS's IMO ;)
 
Spray Bars

You need to determine what size pipe and outlets you will use. Obviously the smaller the outlet, the more pressure. I just built mine with the help of Scott M. on my 120...love them.

I am using 3/4" pipe and sockets with a Mag24
 
Mag 12 question

I don't understand why if my mag12 has 3/4" female intake and 3/4" male return why the instructions that come with the pump would say " 1 1/2" ID is the MINIMUM hose size that should be used for maximum flow"

Would using a larger ID hose make any difference? I'm using a scwd on the return, which has 3/4" intake, if I were to use 1 1/2 tubing it would just reduce again to 3/4". If using 1 1/2" tubing WOULD make a difference, would it be wise to "T" off the return and reduce from 1 1/2 to 3/4 at the T and going dual scwd?

Thanks in advance...
Chris
 
cjburden said:
I don't understand why if my mag12 has 3/4" female intake and 3/4" male return why the instructions that come with the pump would say " 1 1/2" ID is the MINIMUM hose size that should be used for maximum flow"
Again, this question is hard to go into without resorting to fluid mechanics terminology.

Basically, centrifugal machinery (such as your pump) requires an optimal velocity for water entering and exiting the pump casing. This velocity is independant of and unrelated to the velocity in the pipe that carries water to or from that pump; the pipe is sized to produce minimal frictional loss and a reasonable velocity. The two are completely separate.

In practice, the line coming (to or) from a centrifugal pump is always one to two sizes larger than the influent and effluent flanges of that pump.

1 1/2" does seem awfully large, though. You could probably get away with 1 1/4" or maybe even 1"...

cjburden said:
I assume that it reduces the velocity based on diameter and number of holes in the spray bar itself. Any way to estimate how much flow you lose? I don't like the idea of losing any flow .
I don't know how much flow you will lose, but in order for a spay bar to work properly, you need manifold flow. (i.e., you want an equal amount of water exiting each hole). To ensure that this happens, the diameter of the spray hole must be sufficiently less than the diameter of the manifold. This is to cause the head loss through each spray orifice to be at least 10-20 times greater than the friction loss of flow from one end of the manifold to the other.

So yes, you need to lose some flow in order to create equal flow exiting each hole, but I don't know how much that is, and whether it is acceptable to you. I suggest using threaded fittings, and trying a number of different spray bar attachments until you find the one that you think works best. Trial and error can be a very effective method,

Matt:cool:
 
Thanks Matt.. that makes enough sense to me.

Guess its time to get to work and see what I can come up with :)
 
The point that I was trying to make is this. Let?s say you have a return at the tank of 500 gph. In case one you have it going through a ?? nozzle. And in case two you have a spray bar with a number of holes that will give you the same 500 gph. IMO I don?t think you will get anywhere near the water movement at 4 feet away on the other end of the tank as you would with one ??
 
Yeah,

I can't tell you which option will generate more flow for you either:confused: (I suspect the open 3/4" line will generate more water movement). Yet PVC is usually pretty cheap, so that is why I am a strong advocate of: 1) threaded fittings and 2) monkeying around until you find what works best for you:)

Matt:cool:
 
I use a spray bar the length of our 75g. I would agree that there is less water movement from the return that there would be with a nozzle output. That's why I use powerheads for water movement. I only use the return for circulation through the sump. I never turn off the return pump for anything (except when I clean the pump), and always have good circulation regardless of how long I turn the powerheads off for directed feeding, cleaning, etc...
 
I am a fan of either splitting the return multiple times or using a spray bar. If you run 600-700 gallons per hour through 1 one inch return you will probably power wash the tissue off anything in its path.
 
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