Low pressure at Kitchen tap (hot) - Take 2

You may remember a while back, I posted regarding not having enough pressure at my kitchen tap (the hot side) resulting is a really poor flow rate
The cold is fed directly off the mains water (well, via a water softener) but the hot is from a hot water tank in the loft (fed from a cold water tank, above it)
The tap I have got seem to restrict the flow quite a lot (but SWMBO wanted that tape of course!)
I purchased a Grundfoss home booster pump recently, and have just got round to connecting it.
The results are poor! Although the flow is better, it is still far far short of the mains pressure, thus resulting in backflow problems when the hot and cold are both on. If I fit a non-return valve, I think this will impede the flow too much, so I haven't done this yet!
My next plan, is to buy a shower pump, and try that.
If I had a twin shower pump, say 1.5 bar, and I connected the hot feed to BOTH inputs, and BOTH outputs to my tap, would this result in about 3 bar?
If not, could I daisy chain like this Hot feed to inlet 1 outlet 1 to inlet 2 outlet 2 to tap
The reason I ask is, twin pumps seem to be cheaper!
Sparks...
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Just to add,
I have just done some measurements of my flow rate
Cold (from mains) just over 12l per minute Hot (without pump) just over 2l per minute Hot with Grundfoss Home Booster just under 6l per minute
Any recommendations to get the hot to about 12l per minute!?
Sparks...
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Where is the hot suppplied from?
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Doctor Evil wrote:

Still from a tank in the loft, as per my first post!
Sparks...
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Hi,
Does sound a bit low, a tap I just bought quotes a 3m/0.3 bar min head.
Might be a blockage in the tap/flexible, try swapping the H onto the C and see if the same.
If so, BES might do an adaptor which allows a bigger flexible than supplied to be used.
Failing that, and if you don't need much HW, also consider an inline heater.
cheers, Pete.
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Done that, exactly the same unfoutunalty :(

Not an option really, as bigger pipes would interfer with the flexable pipe that connects the tap to the spout (Its removable, a bit like a shower head)

Not really an option, as there would be nowhere to put it! (Under the sink we have a water cooler, a "waste management system" (Several diferent bins for recyclable stuff) and the usual cleaning stuff.
A [better] pump is the way foward I feel!
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I have a similar problem and I so far think the pumps should be in parralell. You wont get more than the 1.5 barr in the above example but this will be maintained longer as you open the taps and increase the flow, because you have doubled the available flow.
As for in series (daisychaining) the pump manufacturers seem to just specify a maximum pressure whether its a foot under the loft tank or in the basement it makes no difference, that is the input pressure to the pump has little effect on the output.
One thing that worrys me is that pumps are rated for temperature and one side of a twin impeller might be only rated for cold.
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