Spoke to a guy in Dublin, his job is just to recondition/repair these pumps and he confirmed exactly as your schematic shows, a straight through length of 15mm pipe, the only restrictor he said is the 4.1mm washer at the pressure vessel. (which presumably cannot restrict the flow through that pipe in any way.)
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Stuart Turner Pump Strange Temperature Fluctuation
- Thread starter Mrtrana
- Start date
Bit late to the party but .....
The thing I can't get my head around with this is when the pump is running then there shouldn't be any crossover through that pipe. The reason for that is that the pressures should be exactly equal, as originally suggested, so the flow should always take the straight path of least resistance and that should be out of the flow side of the pump and outwards to the outlet.
If there is somehow an imbalance created at the outlet or in the pipework, then that could create an imbalance at the pump then that could potentially allow crossover. I have installed many of these universal pumps though, from the old green bodied to the new black bodied and never had an issue like that.
Only other thought would be there is an imbalance between the hot and cold supplies which is limiting the supply to the cold
The thing I can't get my head around with this is when the pump is running then there shouldn't be any crossover through that pipe. The reason for that is that the pressures should be exactly equal, as originally suggested, so the flow should always take the straight path of least resistance and that should be out of the flow side of the pump and outwards to the outlet.
If there is somehow an imbalance created at the outlet or in the pipework, then that could create an imbalance at the pump then that could potentially allow crossover. I have installed many of these universal pumps though, from the old green bodied to the new black bodied and never had an issue like that.
Only other thought would be there is an imbalance between the hot and cold supplies which is limiting the supply to the cold
3.0Bar Monsoon Twin.
If one assumes no 15mm connecting pipe and assuming the Hot End is pumping through a single HW tap to give a flow rate of 10.0LPM, the Hot end will be running at a 2.4bar head, the Cold End, will be running at 0.0LPM at a dead headed pressure of 3.0bar, if a (this) 15mm connecting piece is installed, then, yes, both pumps will run at the same head since both are now, in effect, in parallel. For the same HW tap opening the flowrate will only rise to ~ 10.75LPM but both pumps will now be running at ~ 2.78bar head, to give a flow rate each of 5.38LPM with resultant huge dilution of the HW supply, if the HW flowtemp is as high as 60C and the cold at 10C, then the water temperature at the tap is only 35C and only 30C if the HW is 50C.
The 15mm by pass, say 0.5M long will only have a pipe friction loss of 0.003bar at 5.5LPM so virtually no restriction to flow. As the flow demands from both Hot&Cold ends start equalizing like in a shower then the bypassing will decrease as the two pump heads will be far closer together.
If one assumes no 15mm connecting pipe and assuming the Hot End is pumping through a single HW tap to give a flow rate of 10.0LPM, the Hot end will be running at a 2.4bar head, the Cold End, will be running at 0.0LPM at a dead headed pressure of 3.0bar, if a (this) 15mm connecting piece is installed, then, yes, both pumps will run at the same head since both are now, in effect, in parallel. For the same HW tap opening the flowrate will only rise to ~ 10.75LPM but both pumps will now be running at ~ 2.78bar head, to give a flow rate each of 5.38LPM with resultant huge dilution of the HW supply, if the HW flowtemp is as high as 60C and the cold at 10C, then the water temperature at the tap is only 35C and only 30C if the HW is 50C.
The 15mm by pass, say 0.5M long will only have a pipe friction loss of 0.003bar at 5.5LPM so virtually no restriction to flow. As the flow demands from both Hot&Cold ends start equalizing like in a shower then the bypassing will decrease as the two pump heads will be far closer together.
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