Quote:
Originally Posted by laka
There are 2 powerheads that i'm looking at. One pumps 3800 litres/hr with a head of 2 metres. The second powerhead pumps 3000 litres/hour with a head of 3.5metres. Which powerhead will have a higher flow rate through a 6 foot spray bar if the powerhead is situated level to the spraybar?
LAKA
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Without knowing the pump curves for each of these it's really difficult to accurately compare them. The problem is that you have the flow for each one at different heads (resistances). Most likely the heads they list aren't the head you'll be seeing too.
This is a common trap by manufacturers. They list the optimum performance of their unit but don't give you the data to compare it to other manufacturers. It makes their product look good and prevents you from seeing that a competitor’s product may actually be better for you.
On the surface it sounds like the second one (3000 L/h @ 3.5m) may give you more flow at a given head, but it depends on the shape of the pump curve.
Here's a link to a nice, brief description of the relationship between head, flow, pumps, etc... Give it a read and it should help you a lot.
http://www.aquaticplantcentral.com/f...he-basics.html