Backyard Aquaponics
A place to discuss aquaponics

Yep googled it couldent find the bit where it said you will get better flow and preformance if you step the pipe down from 40 to 25 mm

25mm pipe will create more pressure it is true but in aquaponics we are going for the most energy efficient way to move the given volume of water so we can turn over the FT volume in an hour. The distribution grids Joel used do not require high pressure to work, they just distribute solids to multiple parts of the GB rather than just dumping in one spot. If anything the higher pressure created by using 25mm pipe would cause the water to spray into the GB causing water to be lost as it bounces off the gravel and out of the GB.

I agree that in retic you are concerned about maintaining pressure because you need high pressure to ensure the outlets operate correctly and distribute the water the desired distance, but AP is not retic, different end goal, infact most people just have the pump dump the water straight into the GB from a pipe.

Blackduck: I think the 40mm pipe would also help with volume loss with head as larger ID = less resistance and therefore less wasted pump energy.

I may have had a few beers last night which may have made my posts a bit less friendly than usual

I still stand by the comments though.

A 50mm pipe will have exactly the same pressure as a 25mm pipe at the end of it. Exactly. If you dead head the pipe, the pump will build up the pressure to the same levels.

However, if you open end the 25mm pipe the flow will appear to be stronger, because it is restricted by the pipe, hence it exits with more 'force'. If you measured the 25mm pipe flow, and then measure the 50mm pipe flow, I guarantee that the 50mm pipe will have more water emerge from it, even though it looks like less because their is no force behind it.

All this back and forth about pipe size, I don't see anyone telling blackduck that a 4000 lph pond pump moves 4000 lph at zero head. With 1m head and 3 metres of pipe, you will not move 1000 lph in 15 mins. Possibly half 500 lph. Make sure that is good enough for your system. We try to turn over 1 entire tank volume every hour.

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Its not a trade off between pressure and flow, the pressure vs flow relationship is based on the pumps performance.
Undersizing pipe simply reduces the pressure (and therefore flow) availiable at the end. Theres no trade off - just loss. Only benefit is cheaper pipe.
Static head is identical because thers no friction headloss as theres no flow.
Also its the length of the restriction, a short piece of 13mm pipe may have less restriction than a much longer piece of 19mm.
Each size you go up in pipe can handle around double the flow for the same friction loss.
Once you get these losses right down say with 40mm pipe there isnt much to be gained by going bigger.
As was pointed out these low head pumps we use in AP are VERY sensitive to restrictions and flow will drop significantly with even very small restrictions like elbows, valves OR too small a pipe.
I dont think you will reduce life of pump much by undersizing, but you will sure burn up electricity for no benefit.

What about vertical rises? I was thinking that running larger pipe from my pump on the vertical would stess my pump as it is being made to push a larger volume (and therefore weight) of water uphill. Is this a non issue? Also could I get a quick clarification on "head"? It is my understanding that head height is the distance from the water level in the container you are pumping from to the highest point you are pumping to, regardless of how deep in the water your pump sits. So, by raising the water level in my sump I would be decreasing the head height and improving the efficiency of my pump. Is this correct?

Verticle risers get a 10 meter piece of 1 in pipe and fill it with water it will give a certian pressure now get a 10 meter pice of pipe 10 in dia and fill it with water and if i an not mistaken it will read the same pressure

As long as the delivery pipe is full the static head is from the water level in the lower container to the water level in the higher container or if the pipe discharges above water level to the height of the end of the pipe.

So if a pipe goes from a sump upto a greenhouse roof along aways through a junction with an inspection port that is sealed and then down to a ft and discharges below water level in the FT then the static lift is from the water level in the sump to the water level in the FT. However if the inspection port is opened then the static lift will be from the water level in the sump to the highest point in the pipe where the water is open to the air.

The only problem with the former example is while a small pump may be able to deal with the static lift once the water is flowing through the delivery pipe it may not be big enough to start the water flowing in the first place. As long as it is capable of getting a small amount of water over the top the falling water on the down leg will creates bubbles some of the bubbles will get taken out of the pipe into the fish tank and as the air is evacuated flow will increase.

So. Say The bottom of the sump is 1 meter underground, and the FT is sitting at ground level and is 1 meter tall. If the sump is almost empty, the head would be approx 2 meters. If the sump is full the head would be 1 meter. and if I routed the pipe to the bottom of the FT I would be at 0 head.

And if the sump was full and I routed the pipe over the roof and back down to the bottom of the FT it would still be at 0 head?

So theoretically, If my pump was too fast for my system, instead of putting in a tee and returning water to the sump, I could remove water from the sump, increasing the head and decreasing the capacity of the pump?

Just trying to get this all straight for figuring my pumps working capacity.

Mostly right. If you take the inlet to the FT to the bottom of the FT you calculate the head using the value that is the greater out of the water level of the FT or the discharge height of the pipe. In above example you gave the only way you would get close to 0 head would be if the FT was nearly empty. Practically there are limits to how high you can go, basically dependent on atmospheric pressure. Apparently you can go higher but it gets a little complicated.

Thanks Stuart, that actually helps a lot. Couldn't figure out how my SLO was handling the pump just fine at one point but couldn't keep up and I was at the verge of over filling the FT at a later point. The difference was that I had filled the sump. I guess the pump was working just enough better due to the decreased head.

The stuff about routing the pipe over the roof, to bottom of FT, over the river and through the woods, etc. was just for clarification of how things work. Not fluent in fluid dynamics but with this project I am learning.

With pipe sizing friction loss is proportional to the square of the velocity of the water in the pipe. So even a little increase in pipe diameter results in a big increase in cross section, big decrease in velocity and hence big decrease in friction loss. Which means that if you increased your pipe size you would be able to use a smaller pump or get more flow from the same pump.

I dont know why you would be concerned about pressure in a delivery pipe but if you were you would get more flow if you went from the 25mm at the pump up to the size pipe that the run will be made in and then back to 25mm or whatever size you want for the shortest distance posible.

Mind you since this discusion is about running from a FT to the GBs that would mean the pump would be in the FT which is not something I'd do.

Thanks to all that helped with my 'size issue' (snickers). Hopefully I'll have some photos to put on the members systems forum in the next few days.

Mucho gracias,

the other duck

Interesting read. OBO would you be going from the pump outlet to the bigger pipe straight away or waiting till you get to the desired height then change into the bigger pipe?

I have a 20mm outlet from the pump which i will use 20mm --> 40mm --> 50mm "increaser" then to the GB if the performance of the pump is the same

The sooner you get into the larger pipe size the more flow you will have.