Backyard Aquaponics
A place to discuss aquaponics

Not sure if this has been provided yet. the full details can be found on this website:

http://flexpvc.com/WaterFlowBasedOnPipeSize.shtml

I have found it useful if only to understand the difference in flow rates through different size pipes based on gravity vs. pressure. Hope it is useful.

I would strongly recommend not using this table.

The low pressure/gravity column states that the water velocity would be about 6'/s. That is ~1.8m/s. At such a high water velocity the flow through a pipe is not going to be:



Sizing your pump pipe with this data would significantly reduce your flow and sizing your drains this way could easily lead to them being undersized and cause tanks to over flow.

When they talk about gravity in the pipe and feet/s, what angle are they talking about? Perpendicular? How much decline?

Enough "gravity" to create a flow of 1.8m/s

I would strongly recommend not using this table.

+1

Maybe something like this:-

http://irrigation.wsu.edu/Content/Calcu ... e-Loss.php

and remember every 90 deg bend in the pipe will be the equivalent of 1 to 2m of pipe length.

The chart and the explanation on the site clearly states that the chart values are estimates. For what it's worth, most people who get into aquaponics are not engineers and are not sure what size piping to even use in their application. A combination of my link, which is a little more visual than a calculator, and the link from Slowboat provide a very close result.

"These 3 charts come from 3 different sources, and they all are just general guidelines. and should not be relied on as a precise source for information or as a substitute for engineering. The data between them does vary. In the chart to the left is a general guideline for how much liquid a pipe of specific size can flow in GPM (Gallons Per Minute) & GPH (Gallons Per Hour.)"

Also stated on the link I provided:

"These figures are for straight pipe only! The effect of putting direction changes in will compound the back pressure even more and could even result in failure of the system or burning up the pump. You will never be hurt by going to a bigger pipe and will gain by using less electricity due to a more efficient system which may offset the initial price difference for the larger pipe. "


Slowboat, I took the calculator link you provided and entered some of the values from the chart I provided. I found that the minimum pipe sizing calculator was very close to the values in the chart I refer to.


Flow Rate In The Pipe: 7 gpm
Pipe Length: 3
Pipe material: plastic (pvc)
Maximum Allowable Pressure Loss: 1 psi (higher pressure loss appears to reduce the min pipe size)
Minimum Pipe Size = .6 inch

As the pipe length increases per meter (3') the min size doesn't increase until you hit 3 meters. Most applications in aquaponics involves gravity except for the pump from sump to fish tank (or FT to GB if that is your method).

By no means am I promoting going with the smallest pipe size because that does cause problems over time. If nothing else, the table I provided simply gives the laymen an understanding of how much flow is achieved under perfect conditions and nothing but straight pipes. The same goes for the calculator from Slowboat. Bioslime buildup and roots from the plants can and do affect the pipe inside diameter to the point that flow will be impeded. Maybe it's a good idea to increase pipe size by, say 1/4", for each bend (90 degree elbow) or for every 3' or for each ball valve. I don't think any chart or calculator will work to state exactly what is needed for every possible situation.

The use of any chart or calculator found on a website involves some risk. I simply found it useful for myself and thought others might find it useful. If nothing else, the responses received confirms that 99.9% of us are not engineers. Plus, larger pipe is not always the best answer to someone questioning the size of pipe to use for their SLO or swirl filter, etc.

If the chart was useful to you then that is a good thing. This forum is for people to post their questions and share what has and hasn't worked for them. You felt something was good a thing and you wanted to share it, you wanted to contribute.

Conversely my experience is that such tables are not a good thing. I also want to share and contribute so feel compelled to post my opinion but my recommendation is the opposite of yours.

So what do you do?

This is just my personal opinion but I think people should (such a dreaded word should) do one of three things:

copy what someone else did that worked;
do what someone else says who has experience in whatever they are thinking of doing; or
learn how to work out what they should do themselves.

Tables like the original posting and even the calculator posted later (although much better) can give people who are not engineers answers that will cause them significant problems. For example without engineering knowledge how is someone going to know that 6'/s is extraordinarily fast for either a pump pipe or a drain pipe? How is someone without any engeering education to know that such a high water velocity is going to cause significant friction losses with resulting loss of flow?

As you have said they can't so they either copy someones solution, take someones advice or learn enough to work it out for themselves.

I want to point out again that the lowest pressure column of that table states that the flow through a pipe is calculated based on:



At 6'/s or 1.8m/s you are going to have significant pressure loss.

For example according to the table through a 1/2" pipe you will get a flow of 7gpm. The friction loss through that pipe will be about 1m of head for every 1m of pipe. So if you have a pipe running from your sump to your FT that is only 2m long you will have added 2m of dynamic head to the work the pump has to perform. In my mind that is very significant pressure loss.

Using such a table is likely to guide people to buying a bigger pump and using more electricity than they need to. If they also use the table to calculate their drain sizes then it is most likely going to lead to siphons that don't drain GBs fast enough and over flowing FTs.

You are quire right that is possible that using large pipes can cause you problems over and above the extra expense of purchasing them (specifically any pipe that will be carrying solids) but there is plenty of tested pipe sizes that people can copy or engineering advice of varying detail and complexity to guide them through the calculations.

Tee Hee "How is someone without any engeering education"

Think you will find velocities should never exceed 5 feet (1.54m) per second.

There is a good chart for velocity/head/flow at

http://www.engineeringtoolbox.com/pvc-p ... d_802.html

When you say should what do you mean?

I try and keep drain velocities above miniumum flushing velocity (depends on the size of the pipe) but as low as possible. A rough guide would be less than 0.7m/s.

For delivery pipes I try and get the speeds as low as possible 0.5m/s or less.

In siphons you can get much higher speeds but that is a little different.

Might be off topic, but how much boost does looping all pipes give? Anyone with experience able to help?

What do you mean?

It's my understanding that instead of having a T going to two ends, you are better off having it loop back together to distribute flow better? One of those things I don't know where I remember it from.

The reason I put that up is some of the sites I read recommend not exceeding velocities exceeding 5 feet per second.

http://www.harvel.com/technical-support ... ction-loss

http://www.engineeringtoolbox.com/pvc-p ... d_802.html

friction rises with increased velocity slower is always better unless there is an engineering, practical, or safety reason for high pipe velocity.

Tried putting in a chart but couldn't get it to format properly.

Fittings especially ones not glued could leak or blow apart.
Pumping higher velocities would probably require more energy

But you know all this.