[GribinIsaf]

I am experimenting with some sprinkler irrigation in a polytunnel.  I got a few standard dropdown spinklers fully expecting not to have the pressure to drive them - and that proved to be true.

The seller of the sprinklers says they need 2 bar to operate.  I tried them with an IBC store which is about 3m above the polytunnel and also the water tank in in our loft which is fed by a bore hole and maybe about 4m above the polytunnel.  The pressure from both sources is also of course decreased by the friction in the pipework.

I have got a tank sunk into the ground in the polytunnel so about 2.5 lift with minimum pipework from there.  I would like to use a 12v pump - maybe a bilge pump or waterfall pump? - got to be able to handle non-pure water, to lift from here into the sprinklers.  I have tried a couple I have lying around but they don't produce enough pressure.

Pumps seem to be rated in litres per minute or similar.  How to a calculate the pump I need to lift water and deliver at 2 bar?

cloddopper - if you see this I bet you will know

Thanks.

[arobwk]

I would also be interested in any recommends for 12v water pumps.

[mab]

I can't really advise on which pump to get, but 2bar is about 20meters/70feet vertical height ('head'). I suspect it may be more practical to find a watering system that works at lower pressure - particularly if you're not using mains or filtered water as any debris will clog the holes in a high pressure spray system.


some pumps spec sheet will include a chart of flow vs head, or at least a value of flow rate at a given head. If they only give you max flow rate (at zero head) and max head (at zero flow) I'd probably look elsewhere.

[chrismahon]

Pumps are rated at a delivery with zero head. To get a delivery at an increased head you need to look at the manufacturers charts. 2 bar is 30 metres head and I think it unlikely any 12V pump will deliver that.
To give you an example we have a 750W mains vortex pump (handles solids to 30mm diameter) rated at 4.5 litres per second, so a gallon, but at 9 metres head it reaches its limit and delivers nothing.


As Mab says, look at an alternative system.

[oor wullie]

You will need;
2 bar (pressure loss through sprinklers)
+
0.25 bar (to overcome 2.5m hydrostatic from your tank to the max height og the system (make sure you are measuring from the bottom of the IBC))
+
Pressure loss through the pipework.  If its a short distance through large ish pipe (eg 32mm) it's probably insignificant. But, small diameter pipes (in particular) and long distances can make it significant.

Your individual sprinkler might work on 2 bar but remember if you fit them in series along a pipe the pressure will have dropped by the time the water gets to the downstream ones.

My polytunnel sprinkler system needs about 3 bar to work well but that's after I've lost 2 bar in the pipework (water is piped about 450m to get to the tunnel) so I need a water supply at about 5 bar.


For a blind guess, look for a 4bar pump.

[GribinIsaf]

I suspect it may be more practical to find a watering system that works at lower pressure - particularly if you're not using mains or filtered water as any debris will clog the holes in a high pressure spray system.

yes, I thought this might be a route to take - anyone got any links?