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Snail · 06-07-12, 04:04 PM

I've a question about the pumping heads. Once the flow is established, won't the return pipe, the down leg, be full of water? If it is, won't there be a siphon effect, effectively reducing the pumping head to the friction losses only? So you need to have a pump capable of lifting the water the full head height to prime the system, for which a relatively low flow should be OK, but it only needs to be able to pump at full flow against a much lower head.

I realise that I am almost certainly wrong here, given all the gurus commenting here, but I'd really appreciate an explanation of where my logic has gone astray.

06-07-12, 04:04 PM	#33
Snail Lurking Renovator Join Date: Jul 2011 Location: Palmerston North Posts: 20 Thanks: 3 Thanked 9 Times in 7 Posts	I've a question about the pumping heads. Once the flow is established, won't the return pipe, the down leg, be full of water? If it is, won't there be a siphon effect, effectively reducing the pumping head to the friction losses only? So you need to have a pump capable of lifting the water the full head height to prime the system, for which a relatively low flow should be OK, but it only needs to be able to pump at full flow against a much lower head. I realise that I am almost certainly wrong here, given all the gurus commenting here, but I'd really appreciate an explanation of where my logic has gone astray.