Twin Impeller Shower Pump

However at the midpoint of the circuit the pump is neither pushing or pulling the water are no pressure either positive or negative is being applied.

I'm not sure of your logic there. That's like saying there can't be any current flow at the centre tap of a transformer - and I think Mr Kirchhof has something to say about that. All else being equal every metre of pipe will have the same pressure difference along it's length - and it's that that pushes the water around, not the difference between the pressure inside and outside the pipe or the centre of the pump.


Neutral points are handy concepts in plumbing especially when you have two or more separately pumped (or gravity driven) circuits interconnected - they provide a common reference pressure for the whole system. Rather like us referencing everything to earth. Note that the neutral point isn't necessarily half way around a pumped circuit - you can have almost an entire circuit at +ve or -ve pressure relative to the neutral point, depending on the position of the pump.


   - Andy.

so which animal has the highest blood pressure?

I'm going to guess something like a blue whale.....


  - Andy.

Round here the highest blood pressure is project manager I think, or possibly the senior design authority, depending how well the projects are going.

In the animal kingdom, the giraffe, but it has a long length of thin plumbing between heart and head, so I imagine the highest blood pressure is measured at the giraffe ankle when it is standing up. At the head end it will be less, and I understand they have special valves to prevent them fainting when they stand up suddenly. (the giraffe not the manager and SDA.)

Andy J.


Years before there was a oil installs registration scheme I Installed secondhand AGA and Rayburn cookers, Some of which heated the hot water alongside wood burning stoves and central heating boilers.

To interconnect the various water heater flows and returns required the neutral point in the pipework to be fixed by using a Dunsley Baker neutraliser


Generally the water will flow past the neutral point in closed loop heating water pipework, unless there is a restriction or airlock, but fitting a bigger pump may not resolve issues with badly installed plumbing and a positive head shower pump may also not resolve the issues with badly installed plumbing as it may not even turn itself on, at least a negative head pump should turn itself on.

To interconnect the various water heater flows and returns required the neutral point in the pipework to be fixed by using a Dunsley Baker neutraliser

Ah ha - indeed. That's exactly what I had in mind - came across them when working out the plumbing for my Dunsley Yorkshire log burner. Ended up just using the thermal store to do the job of the neutraliser. You don't actually need anything fancy - just a way of interconnecting the pipes in a way that flow in one circuit doesn't cause an inadvertent flow in any of the others - one very wide pipe (so very low resistance) does the job nicely (which in effect is what the neutraliser, or my thermal store) is.


  - Andy.

Blue whale is an interesting suggestion, but without Googling the subject, I expect that it would be quite low given that they are usually horizontal and immersed.

But, at the bottom of the ocean where the pressure is already under hundreds, if not thousands, of metres 'head' of water pressure. The pressure differential between heart and head may well be small, but the absolute pressure must be massive.


   - Andy.

indeed, and the electrical equivalent of the whale is the flying deck supplies, such as the old heater windings for the EHT rectifier valves  in the sort of black and white tellies I used to top up my pocket money by repairing. Half a dozen volts AC across the heater for the kathode, derived by a thickly insulated over-winding on the HT transformer, but flying around at several kV above the chassis (which itself was connected to the mains, not strictly earthed-  with a modern health and safety view it is amazing any of us lived to tell the tale, but you soon get used to working with one hand out of the way, when to forget the do not touch rule would carry the death penalty.)

The idea of a single reference 'ground' that is magically always at 0v is not always a useful one, it is perfectly fine to take your reference with you.


Thinking of the TVs, there are even more impressive things made where very delicate sensing electronics running off self contained supplies of  a few volts operates inside little metal boxes that bounce up and down by many tens of kV when pulsed power kit is fired, and so long as there is no penetration into the box, the violent change in the external potential is not 'visible' to the kit inside, and  it  is blissfully unaware of anything changing during the pulse. Equally, just leaving a couple of screws out can impair the screening such that it dies an EMP death immediately.