Planning PVC pipe layout for central air

[zendog]

I picked up an Alita air pump in the last group buy for a central air system to replace all the little pumps and gang valves. I've read all the posts I could find here on what size PVC to use, etc. and am left with a few questions.

I'm basically working with 2 walls with tanks, so I'll have the pump on one side feeding that bank of tanks (10), then have the tubing go up across the ceiling to the other bank of tanks (12). So there is no simple way to just do a loop around the room.

Assuming I need to create a loop by having one pipe over as supply and one back as a return the first question relates to the diameter of tubing connecting the 2 sections. I'm thinking of larger pipe where I have my air valves for tanks (probably 1" or maybe 1 1/4"), but could I reduce it to say 1/2" for the up and across the ceiling part without a major hit to performance? It is in the basement so not a huge issue, but the smaller pipe will be easier to hang and lighter, plus not as big an eyesore. I'm particularly interested in this since I'll need to run two pipes across if I'm doing a loop.

My second question relates to a comment from Frank I read somewhere that you don't really need to do a loop if you have large enough PVC - at least 2" plus. If this is true, it simplifies my life a lot. Maybe I could run 2" behind the tanks and have single 1" across, with the air pump feeding into the 1" part so it isn't going through a bottleneck in one side. I'm planning to have 20 valves on one side and 30 on the other, although they wouldn't immediately all be in use, but just there for when I need to add a breeder box or airstone.

Thoughts?

 

[JLW]

You do not absolutely need a loop, but you will get better performance from it. The way this was explained to me, you want to air wooshing around the pipe. Your excess air, rather than bleeding out, will push the air around, increasing pressure everywhere. If you're at or near capacity anyhow, you won't see any benefit making it a loop or not, but ... if you're under utilising your pump, you'll extend its life and get better pressure by creating a loop. 95% of us underutilise our pumps.

You'll want to keep your tubing size consistent. Any narrowing of it creates an "air jam" of sorts, and reduces the performance. However, I don't think 2" pipe is necessary in the least.

Once you get above 1", you really start seeing diminishing returns on increasing your pipe sizing, though it is easier to drill into it for the valves. I don't see a big difference when I've tried going to 1.25", and stepping up to 1.5" makes no discernible difference. I've never experimented with 2", but I suspect you won't get any real benefit over 1.5", though it would depend a bit upon your pumps capacity. The big place you will see a difference, though, is in cost. A 1" x 10' PVC pipe is $4 at home depot, while a 2" is $9. A 2" elbow is $3, while a 1" elbow is less than a buck. So, to make a simple square, 10' on each end, your PVC would run $20 for 1", and nearly $50 for 2".... for almost no benefit.

 

[Becca]

The way Fran ( mscichlid ) explained it to me, the loop doesn't have to go to one side and then back, you can create a loop at the end of your line so the air circles back on itself. I was able to assemble mine from recycled pieces of Fran's old system. It took some cutting and pasting, so to speak, but it goes to two walls across the ceiling.

If you can mount your pump on a shelf attached to a foundation/load bearing wall, you'll get less noise/vibration. I mounted a shelf directly into the cinder block wall of my utility/fish room. There are enough joints/joins that I'm able to modify it fairly easily. I've added onto it twice. Make sure you have LOTS of T's and elbows, as well as plenty of the straight connectors. If you have all of that plus some extra PVC pipe around, you'll be able to modify it at will pretty easily, without an extra trip to the hardware store. I'm running 17 or so tanks (10s, 20's, 40's, plus some smaller ones) off of mine and pressure is really good. My fish room is probably about 12x8 and most of the tanks are on one wall, but there are 3 filters running on the opposite wall. I think I put a short video of the airline set up in my "I have a serious problem" post...

 

[cabinetmkr39]

We have all done this with a single pipe , The airlines closest to the pump get the most volume as you get to the far end you greatly diminish your volume of air. A loop has the same volume no matter where you tap into the pipe. I have always used a 1" pipe with no problems. I've plumbed air in six fish rooms with no call backs.

 

[Frank Cowherd]

If you go to this link, https://www.new-line.com/informatio...ressed-air-flow-at-100-psi-length-of-run-feet , you will see that the size of the pipe needed depends on the amount of air you want to transport and the distance you want to move it. The longer the distance and the higher the volume the bigger the pipe needed. Since you really do not want to get into the calculations (they are available if you use fluid dynamics equations), just go with IMHO anything over 1.5 inches and I would recommend 2 inches. The bigger pipe also makes it easier to drill and put in your valves.

My manifold is in a h shape with a 30 foot pipe connected to an 8 ft pipe that has a 20 ft pipe connected to it. ALso there is another branch coming out of the knee of the h that is 10 ft long.

If any of my valves appear to have less air to them, I take out the valve stem and stick a wire down it to clean it out. I have drilled many new valves in place without shutting down the pump and have gotten some PVC shavings inside the manifold which occasionally block a valve. Do not put your valves on the bottom side of the manifold, since that makes it easy for any debris to clog the valves.

The table in the link is basically volume of air versus distance with the points being the size pipe needed.

No loop is needed. You just need a big enough pipe so the pressure at both ends is the same to every valve. If the pipe is too small the valves closest to the pump get more air.

 

[Becca]

If any of my valves appear to have less air to them, I take out the valve stem and stick a wire down it to clean it out.

Amen. Pipe cleaner, wire, twist tie... Every time I've found myself puzzling over why flow is bad, this fixes it. I have the plastic type valves and sometimes I also need to completely unscrew the plug that regulates flow and stick a wire in that, too.

 

[zendog]

Thanks everyone for some great feedback. So it seems like I can go 2" loopless or 1" with a loop.

One more question is do I need the PVC to be higher than the top of whatever tank it is feeding to avoid it possibly back syphoning into the PVC in case of a power outage? And if so, I take it that would just be the section of PVC where the airline is connected, not the entire pvc run, correct?

 

[Becca]

Thanks everyone for some great feedback. So it seems like I can go 2" loopless or 1" with a loop.

One more question is do I need the PVC to be higher than the top of whatever tank it is feeding to avoid it possibly back syphoning into the PVC in case of a power outage? And if so, I take it that would just be the section of PVC where the airline is connected, not the entire pvc run, correct?

This is probably a good idea. It would only back siphon to a certain point, but if your pump is on the ground, that might be the point. I actually put my pump on a shelf in order to keep it higher than all of the tanks.

 

[zendog]

I'll have my pump above all the tanks, but since some of the tanks are small, I would worry that the total volume of PVC below say a 5 gallon might be enough to drain all or most of the water. Also, if it back syphons into the PVC, then I'd need to figure out how to drain it out...

Although I don't think I'll be able to keep all of the PVC above all the tanks, I think I'll just make sure that whatever part of the PVC the air tube for a tank connects to that it is higher than the tank.

 

[Becca]

Although I don't think I'll be able to keep all of the PVC above all the tanks, I think I'll just make sure that whatever part of the PVC the air tube for a tank connects to that it is higher than the tank.

That's what I meant. I don't think it would be likely for a tank on a top rack to back siphon into a tube on the bottom rack if that's not the pipe it's connected to...

 

[FishEggs]

Of course you could always add a check valve if it becomes a problem.

 

[Pat Kelly]

Thanks everyone for some great feedback. So it seems like I can go 2" loopless or 1" with a loop.
QUOTE]
I am late to the conversation but I agree. My old fishroom had 1 1/2 inch and no loop. I now have a loop but 1 inch. I had better air
with the 1 1/2 and no loop.

 

[zendog]

I am late to the conversation but I agree. My old fishroom had 1 1/2 inch and no loop. I now have a loop but 1 inch. I had better air
with the 1 1/2 and no loop.

Very interesting. Did anything else change that might account for that besides the different size pipe? More tanks or a different pump maybe? Just asking since I know you redid your entire fish room, masterfully I should add.

 

[zendog]

Of course you could always add a check valve if it becomes a problem.

I've considered that, but I wonder if it might be a problem with central air with some lines having check valves and others not. I think the higher air pressure required for the check valve might make it hard to balance the air flow across all the outlets.

 

[Pat Kelly]

Same size tanks and number of outlets. I bought a new linear pump but the same size.