Thread: Anyone good with irrigation pipe/pump calcs?

First off 9metre head is only 88kPa, flow rate you need is no. of drippers x 1.6l/hr divided by 60. Add 25% pressure loss (guess only) you should have head pressure of 137kPa /14metre minimum at your calculated flow rate. This aint no transfer pump rating, a higher pressure house pump might work.

busy forum again

as described above and out of my hydraulics books....

110Kpa is more or less a 11m head height + 25% for 14m head (roughly) (this 25% is to account for pumping ineffeciencies, minor deviations in head heights, minor flow restrictions after the pump)

your flow rate is # drippers X flow rate @ pressure per hour.

so assuming that the calculated flow rate of 1.6l/hr is based on the 110kpa working pressure stated.

500m of drippers at .6m spacing is 500/.6= 833.3---- drippers call it 840.

the drippers drip 1.6l/hr so thats 840*1.6 thats 1344l/hr

flow per minutes is that /60 1344/60 = 22.4 call it 23l/m

you need a pump that can push 22.4l/min into an operating head of 14m.

sans out the 25% fudge factor and round the numbers down.... and

830*1.6/60=22.13---- call it 22l/m into an 11m head.

you hit the nail on the head when you said the down hill ones to get pressure out of your system always push water up hill , can you run a pipe from your pump to the bottom of your system ?

Originally Posted by richard4u2

you hit the nail on the head when you said the down hill ones to get pressure out of your system always push water up hill , can you run a pipe from your pump to the bottom of your system ?

Won't matter. Drip line being used is pressure compensated. Pressure consumed to raise the water to the highest point in the line is gained back on the downhill run ... less pipe friction losses.

Kev..

For mechanicing call Dave, for hydraulic engineering call me.

How about you check your numbers Dave

300m x dripline @ 0.6m spacings = 500 drip emitters

500 emitters X 1.6l/hr = 800l/hr

800l/hr / 60(min) = 13.33l/min. TOTAL FLOW

Head loss is calculated for the longest run of pipe only. The shorter runs need less pressure.

Longest run = (35m x 25poly supply line) + (170m x 17mm dripline - 284 drip emitters @ 1.6l/hr = 455l/hr = 7.6l/min

The loss in 35m of 25 poly at a flow rate of 7.6l/min (0.126l/sec) is SFA. (My head loss curves are at work, but it is neglible).
25 poly is good for 45l/min (0.75l/sec). More than that and the velocity exceeds 1.5m/sec and the head losses become a J curve.

19mm poly (i realize 17mm is being used) is good for 20l/min or 0.333l/sec ... our flow into the 17mm poly is only 7.6l/min, and every 0.6m we take out 0.0256l/min, and the flow (& velocity & loss) in the next 0.6m drops ... and every 0.6m ... the loss in the drip line for this installation is negligible.

... so without splitting hairs add 1m head required.

110kpa = 16psi + 1.4psi head loss (1m) and we want 17.4psi ... don't dick around, call it 20psi.

So our head required is 20psi - 14.1m - 138kpa

Our total flow is 13.33l/min.

You need a pump that can deliver AT or BETTER than 13.33l/min at 20psi ...

This all assumes a flat ground delivery ... if you need to raise the water thru 4m to clear the highest point in the system, ADD 4m to my workings ... deduct if your going down hill lower than the pump.

1psi = 2.31ft

1m = 3.28ft

1psi=6.895kpa

You can do the math.

... PLUS your suction losses on the pump need to be added to the above calc's ... it will have a loss at flow that needs to be overcome (but I'm guessing your using a submersible pump by the flow rates/heads you're quoting ... right ? They don't develop the head required for your application. small/medium subs 150-400l/min are usually shut head (no flow) of around 8 to 12m (17psi and NO FLOW) ... they are designed to move big volumes of water quickly over small heads ... for dewatering.)

So if it is a sub .... and your pipe runs quoted are correct ... this is the calculated INPUT your system needs to work ....

15l/min @ 20psi - 15l/min @ 11m - 15l/min @ 138kpa .... or BETTER. Always choose a slightly bigger than required pump.

Nuff now.
Kev..

... sorry, just to add. The reason you existing pump won't do the job is it cannot overcome the inherent losses in the system it's connected to. Those flow/pressure figures you quote are probably maximums ... ie:max' flow & max' pressure ... you can have one or the other but NEVER both at the same time ....

Nobody makes pumps for this type of application, and subs are cheap, so that's what gets used, but I bet your 9m pump has ZERO flow AT 9m head ... got a pump curve for it ?

ahhh so thats what happens when you transpose a number.....

least I got the head pressure right.

Originally Posted by Blknight.aus

ahhh so thats what happens when you transpose a number.....

least I got the head pressure right.

but if he decides to run 500m of pipe he can use your numbers