Pumping requirement help?

[Work Horse]

I'm quoting a grey water drip irrigation system for a customer.

My purpose built drip line requires 100>400kPa (14>58psi) to operate correctly.

The customer already has a sump pump setup. The pump supplies 120 litres per hour and 8 meters head of water.

From what I can work out on the net, the pump will supply max 78kPa (11psi). Not nearly enough!

Have I got this correct?

[Fryday]

That's an extremely low flow (2L/min) given it's only making 8m lift.

I'm assuming it's a centrfugal pump being a sump pump... Anyway, as you say 8m is 78kPa. If you increse the head requirement of the system, you will get less flow from the pump. You really need the pump curves to work out maximum pump head (called shut off head). You'll find that it will be more than 78kPa as it's still making flow at this pressure.

You can test the pump to find out what the maximum pressure of the pump will be - just need a closed end bit of pipe capable of standing say 20m pressure, for this applciation, with a valve to allow purging of the air and to de-pressurise at the end of the test plus a pressure gauge in the pipe. fill the line with water and fire up the pump, the gauge will tell you what the shut off head of the pump is.

The pump can probably make 100kPa but flow will be virtually non existent, it will be operating at the end of the pump curve and life expectancy would be short.

[Walkinshaw]

Essentialy you could run a pair of these in series to run at 120l/hr @ 22psi. Otherwise, as noted by Fryday, the pump is well outside its flow/pressure curve.

[Work Horse]

Thanks very much for the responses Fryday and Walkinshaw.

I will break the bad news to the customer.

And continue to try and understand more about this myself. Like a lot of things the more you know the more you realise there is to know.