Backyard Aquaponics
A place to discuss aquaponics

On the basis that I'm probably not the only "hydraulically challenged" member on this board... I thought it might be appropriate to start a thread relating to general hydraulic principles.

For instance.... what's the effect of stepping down pipe size over distance and relation to the rated head of a pump.

To be more specific....

What effect would it have if I was to use 25mm from the pump outlet with a pump rated at 3mtr head and at some stage reduce that piping to 19mm tubing to deliver to the growbeds?

Would I be better off maintaining 25mm piping throughout the delivery system?

What effect does total distance of the delivery piping have in relation to the choice ... one way or another?

Hydraulically, I'm not bad. Electrically I'm better. Fortunately, most electrical equations can be applied to hydraulics. So will be some crossover in this answer.

V = IR is the most basic electrical equation.

V = Potential, and in water can be often described as head. eg metres
I = Current, the speed of the water eg metres/second (NOT Litres/second)
R = resistance, in this case the frictional force exerted on the water.

So basically, as your head increases, the greater the current that can flow for a set pipe size.
Similarly as your pipe size increases, the greater the flow for the same head, (or in the case of a pump, the greater the head, if current is lessened)

So the biggest pipe you can afford will give you the least electrical waste, the greatest water flow, and the least load on your poor little pump.

As for reducing the pipe size part way along:

the resistance force is measured in -current/meter. so the longer you have the thinner pipe the greater the current will be resisted.

However if you were T-ing of the pipe, splitting the flows, then it only stands to reason to use smaller pipe, because it's cheaper, and you have only half the flow. Making the pipe larger part way along will have little effect.

Please be aware. Pipe cross sectional area goes up by the square of the radius. eg 50mm pipe is 4 times as big as 25mm pipe.

Splitting 25mm off into two pipes, you'd have to use 2x19, not 2x12.
25mm area = pi x 12.5 x 12.5 = 156.25 x pi
19mm area = pi x 9.5 x 9.5 = 90.25 x pi
12mm area = pi x 6 x 6 = 36 x pi
as you can see 19mm pipe increases the resistance by a factor of 1.6 or so.

Does that make sense?

That certainly helps Kuda.....



Pretty much what I had in mind.... so... does the added resistance factor therefore essentially decrease the head....

i.e will the flow be significantly diminished as the distance/length of tubing used approaches the rated "head" of the pump?

umm...Amperes (electrical current) is coulombs/sec which is analogous to liters/sec. (sorry, KP.) Everything else looks really good.

Sharp bends are equal in friction to a significant length of pipe, but I forget what (1 meter? 2 meters?).....it varies with sharp bends being worse than gentle ones of the same angle and larger angles being worse than smaller. There are tables....somewhere. Codebooks are often good. A plumbing book from your local hardware store might be good.

Rocky Mountain Institute has done a lot of work with industrial pump efficiency and really, really pushes for much larger pipes than standard and designing for straight runs as it allows designers to downsize pumps tremendously and save a lot of power.

If you allow for biofilm buildup (maybe a few mm layer...so reduces your diameter by perhaps 6mm) inside your pipes while sizing them you will avoid a lot of trouble later.

yep...for example 2x45° bends have less friction loss than 1x90° bend.
will do a bit of a writeup in the next week or so.

Rup:

http://www.epanet.com/downloads.asp?ski ... iQodoyKkaQ

Headloss of piping is related to the flow rate. The higher the flow, the more loss for a given diameter of pipe. So for a given pipe system, you would have a headloss curve that went from 0 flow with 0 headloss to turbulent flow where there would be a distinct bend in the curve to a theoretical maximum flow where the pressure drop across the piping system equals the pressure rating of the pipe. (envision a curve starting at zero on the left and rising to the right.)

A pump will have a performance curve as well. (usually a curve starting at the maximum flow rate on the left and dropping to zero on the right) Obviously, the more friction in the piping, the less water will be pumped through it. Basically the performance of a pump/piping system will be where the pump curve and the piping curve intersect.
If you are concerned about efficiency, you may also be able to get efficiency and hp curves for your pump. Basically at any given combination of pressure and flow, the pump will be drawing a different amount of electricity and delivering a different amount of horsepower. If you can't find the curves, you can get a good idea with an amp clamp, a pressure gauge, and a bucket.

Play with that epanet program. It does all the calculations for you -- add in a few extra feet for all your elbows (10) valves (5) etc.

oops

hello rupert, my name is darren and im new to this wonderland.
in answer to your question yes pipe reduction will work.
in WA there is a very famous pipeline from perth to kalgoolie. basically the pipe starts at 2m diameter (i think) and hundreds of km later it arrives in the goldfieds oh kalgoolie at 150mm.
your pumps 3m head refers to flow rate at certain height. so 3m above the ground pump the flow rate should be the same as ground level.
thus it come down to how high and how far you are pumping water.word of advice, if pumpimg a distance. step your pipe sizes down gradually donot go from 50mm to 19mm in one hit if pumping up hill and quite some distance.you can do this if pumping on same height.to maintain pressure. any pipe reduction reduces flowrate
check out some watering system web sites especially those who do golf courses
amazing what you will discover
cheers
dazndom

Welcome aboard, Darren.


Hmmm...so if we are looking for max flow rather than maintaining pressure it would be best to maximize pipe diameter? (As long as we don't mind the cost).

Some good charts on head loss are available in Thomas Glover's "Pocket Ref", a good source of an incredible pile of facts from head loss in pipes of different frictional coefficients as well as losses to various fittings to thermal conductivity and density of various materials to codes for airports. Pick one up if you see one (often in hardware stores) and take a glance....about $10 or $15 and worthwhile.