quick plumbing question

[_shorty_]

Hoping for some plumbing advice: I know the larger diameter pipe you use for return pump (climb from sump to DT) the better flow rate you will retain off the pump.
My question is this: I want to climb with 1" pipe about 6 ft - up over the edge of the DT and then down about 1.5 or 2 ft down into my overflow reservoir and back in through either 1 or 2: 3/4" inlets. If I only use one inlet - will 3/4" tubing on the descending part of my plumbing reduce my overall flow rate much? I'm assuming maybe a little bit - but how much? I have two 3/4" inlets out of four available - so I am trying to decide if it's worth it to split the plumbing into two 3/4" streams or just use the single (obviously I'd prefer to use just the single). I'm running a mag12 return pump.

[picker]

The up and back down will be "free" except for the added distance friction loss, and the flow will be determined by the smallest hole. so it won't matter where you put the 3/4 line, if its there, that will be the limiting factor of your total flow. how much it limits the flow is a function of the pump's head pressure.

ie: if your pump output is 3/4... then having more 3/4 someplace on your run will have a small impact. but if one adds a line that's smaller than the pump's output, well, then that will be the major factor in flow loss.

[_shorty_]

The up and back down will be "free" except for the added distance friction loss, and the flow will be determined by the smallest hole. so it won't matter where you put the 3/4 line, if its there, that will be the limiting factor of your total flow. how much it limits the flow is a function of the pump's head pressure.

ie: if your pump output is 3/4... then having more 3/4 someplace on your run will have a small impact. but if one adds a line that's smaller than the pump's output, well, then that will be the major factor in flow loss.

Selecting 1" pipe with a few fittings - head calc says:
Total losses are 8.57 feet of head pressure, or 3.7 PSI. with a flow rate of 949 GPH. Process took 111 iterations

Selecting 3/4" pipe with a few fittings - head calc says:
Total losses are 11 feet of head pressure, or 4.75 PSI. with a flow rate of 756 GPH. Process took 68 iterations

Just so I'm clear - The actual outlet of the pump itself (which is Mag18, not mag12 like originally posted) IS only 3/4" ... so are you saying the calculator when inputting 1" isn't accounting for that 3/4" pump outlet, and I'm actually limited to that 756GPH(ish) figure no matter what?

I am semi-familiar with the concept of smallest hole size limiting flow in gravity feed or syphon applications - but when you start to pressurize your line, it gets fuzzy in my head... :hmm5:

[picker]

> limited to that 756GPH(ish) figure no matter what?

if the pump output is 3/4, yes, sorry.

[dml931]

I'm no pro here, but I'm in the designing stage of my plumbing project as well. I have had discussions about this very topic with others here on RC and Uncleof6 recommends using 1-1/5" over 1" or 3/4" to reduce friction loss. There is less surface area to water volume using larger dia piping. Picker was correct by saying the 3/4 holes are the limiting factors in your flow rate, but reducing the friction that the piping creates will help out and increase your final gph. Hope this helps you understand it a little better.

[_shorty_]

I'm no pro here, but I'm in the designing stage of my plumbing project as well. I have had discussions about this very topic with others here on RC and Uncleof6 recommends using 1-1/5" over 1" or 3/4" to reduce friction loss. There is less surface area to water volume using larger dia piping. Picker was correct by saying the 3/4 holes are the limiting factors in your flow rate, but reducing the friction that the piping creates will help out and increase your final gph. Hope this helps you understand it a little better.

It does help... kinda. LOL. I feel kinda dense.. But in my mind the information is still a little conflicting. It makes me think that the 3/4" pump outlet is more of a 'reducing' factor - and not a 'limiting' factor as long as you can increase pipe diameter for less friction loss, increasing over-all GPH. I'm starting to think I hate fluid dynamics...

I guess my question still is: is that head loss calculator accounting for the 3/4" pump outlet based on the model that I inputted (truly limiting me to the 756ish GPH, or is the head calc correct, and I could actually see up to 949GPH)? Because if it is - that friction is a pretty big factor of head-loss.

Either way - the 3/4" (downward) section of pipe probably causes more friction - reducing available GPH... With the help of gravity - how much? - and does this loss outweigh the pain of more intricate plumbing.... I guess I'll have to test both ways, maybe - or should I just shut-up and take someone's word for it that my flow is already limited, due to the 3/4" pump outlet?

If not - would reducing to 3/4" right at the tank return outlet yield better flow than reducing 3/4" right where the flow is starting to be assisted by gravity (at downward turn)?

Edit: something MAY have just clicked!... The way I'm thinking of friction: So - maybe that 1 1/4" pipe diameter is like kind of a magic number - where it reduces your friction but going bigger than that is not going to help any more? I picture it like a column of water flowing up through a 'stationary' hollow (pipe shaped) column of water that is what's touching the outer actual pipe - allowing the 3/4" stream of flow to flow 'unrestricted' ... causing less friction of the over-all system, increasing GPH... that 3/4" is STILL the limiting factor ... That does make more sense now.

If my thinking IS correct now - I should probably just go with the single 3/4" inlet into the tank, but reduce as close to the inlet as possible.

Does that all sound right (at least the last part) :) ?

[sleepydoc]

People often assume that if there is a 3/4" diameter segment someplace in the line, then it doesn't matter what the rest of the system uses. Remember, resistance/head loss is additive. The resistance of a 2' section of 3/4" pipe is not the same as that of a 1' section of 3/4" pipe connected to a 1' section 1.5" pipe.

Also, resistance decreases with the 4th power of the radius, so a 2" ID pipe will have 1/16th the resistance to flow that a 1" ID pipe will have. I believe that is what Uncleof6 was getting at with his recommendation to use 1.5" pipe. When you increase the pipe size, at some point the resistance in the larger diameter section will be small enough compared to the smaller diameter section and/or nozzles that it will be negligible.

I think you pretty much got it right with your edit. As picker said above, if water goes up 3' and down 1, it is the same as going up 2', except for the resistance of the pipe. So to maximize your flow, do as you said - reduce the diameter as close to the nozzle as possible.

[uncleof6]

One thing to remember is I consider the mag drive pumps to be junk. Any pump with a 3/4" outlet, that needs 1.5" pipe to operate on the flow curve--is a piece of junk. In this case, it is not just a matter of reducing the friction loss, though that is what happens, it is getting the pump output where the flow curve says it should be. I did not believe it the first time I 'heard' it. It was put rather bluntly: You gotta use 1.5" pipe on that pump if you want ANY flow out of it. The fact is, this is stated in the instructions for the pump. It uses the word "optimum," however, in this case "optimum" is synonymous with ANY. The difference is ~ 300 gph give or take--real world.

Personally, I would suggest getting a better, more modern pump, that will give you more for less--generally the recommendation is 1 pipe size over the outlet size. 1.5" on a 3/4" outlet is ridiculous.

I generally don't recommend running a pump fed flow through a "smaller" bulkhead. Though it is a short distance, and will give a brief pressure rise, rather than a lot of drag, it will still affect the total flow equal to around 7 - 8 foot of straight pipe. Similar to running the 1.5" pipe in the branch of a tee and hitting a brick wall. (Going from 1.5" pipe to a 3/4" bulkhead.)

It is to your advantage to run the return up and over the back. use a 90 and a 45, at around 6' of straight pipe--- well ok it is two foot less.

[_shorty_]

thanks guys!

[PowerNap]

Your overthinking it. 1" will be fine, and be easier to work with.

[uncleof6]

Your overthinking it. 1" will be fine, and be easier to work with.

Depends on the pump. 1" on a mag drive 9.5 or larger will not be fine. That is the whole point--it will not be fine. This is no over thought. It is right there in the instructions for the pump.

[_shorty_]

I guess it just depends on your definition of 'fine'... :) Sure - I can get by with the currently with 1". I have it plumbed in now and getting at least 700GPH climbing to 6.5 ft or more. But I'd prefer maximizing my flow and get more around 950-1000ish+... wish i would have read directions.. but I'm guessing as with most dudes in this thread, is typically not standard operating procedure... lol. I guess I just trusted the head calculator, as well. But all this discussion has definitely helped me understand things better - which is ultimately what I needed. Thanks all!