Changing shower trap to lower-capacity unit i.e. MacAlpine @ 26l/m

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In the middle of an ensuite refurb at the moment and I am looking to change the trap that came supplied with the tray to the MacAlpine ST90CPB-S. The supplied trap can handle 33 l/m whereas the MacAlpine can handle 26 l/m. Should I be concerned about the reduced throughput? I have another trap I could use that can handle 48 l/m, but if it causes no issues then I would prefer to go with the MacAlpine trap.
For information, I have high pressure / flow rate and a powerful combi in the property and I assume that I could exceed the capacity of the new trap if the correct mix of mixer and head was used.
Putting aside the green issue, I assume that 26 l/m is in excess of what would be considered a typical power shower rating? Any reason I wouldn’t want to drop to the lower capacity trap?
I understand that I’ll need to match the throughput of the trap to that of the output of the shower.

TIA
 
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Why not turn on your fastest cold tap (often kitchen or garden tap as closest to mains stopcock) in the house and time how many litres per minute it produces, and compare with trap rate.

Your shower and hot water system will always reduce this best case flow rate.
 
Why not turn on your fastest cold tap (often kitchen or garden tap as closest to mains stopcock) in the house and time how many litres per minute it produces, and compare with trap rate.

Your shower and hot water system will always reduce this best case flow rate.

I already know the figures:
- Boiler 20 l/m
- Pressure 3.75 bar
- Flow (outside tap) 32 l/m

So as I mentioned, I assume with the correct mix of components that I could exceed the capacity of the trap and hence wonder if I would regret reducing the capacity!? If it is well in excess of what is required that it is not an issue, but if the excess capacity is nice to have on occasion, then it would seem best not to limit the whole design due to the size of the trap. This is what I would appreciate input on.

Basically I am at the design stage and I don’t know the values that I should be working towards.
 
Doesn't matter what the trap can handle if the outgoing pipework cant cope with the flow. Bear that in mind too. What's wrong with the supplied trap?
 
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Doesn't matter what the trap can handle if the outgoing pipework cant cope with the flow. Bear that in mind too. What's wrong with the supplied trap?

Outgoing pipework should be fine, as I am virtually over the waste pipe. As regards the existing trap, it is cheap flimsy plastic with a really poor quality seal. Bearing in mind that this tray will be going into a three-sided recess, I would rather use a much better quality trap as once it is in there there is no way that I can change the pipework or trap without ripping the whole lot out again.
Another advantage of the MacAlpine trap is that the flange will sit flush within the drain recess, as opposed to a raised plastic dome. I am thinking about using more expensive brass flange, as opposed to the plastic one. Was it you that suggested this?
 
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I am thinking about using more expensive brass flange, as opposed to the plastic one. Was it you that suggested this?

No but sensible advice, brass will always be superior to plastic. Given once in place, access will be virtually non existent, I'd give some thought also to cleaning the waste in event of an issue. Not familiar with the McAlpine trap without looking it up, does this allow cleaning of the outgoing pipework from the top?
 
Not familiar with the McAlpine trap without looking it up, does this allow cleaning of the outgoing pipework from the top?

Good point! All of the traps I am considering can have their innards removed by unscrewing the flange if required. You can also get to the hair trap without needing to unscrew the flange. Aside from that, the trap will be at the front of the tray and so I can get to it. The problem comes if I need to change the trap to a different one, so requiring adjustment to the pipework. I just don’t think that would be possible without removing the tray.
So, it is important that I get this right first time as there will be no going back without an awful lot of trouble and expense, hence the reason I am labouring the point.
My key consideration here is really, is 26 l/m sufficient or should I not restrict myself and stick with the higher capacity traps? For the sake of installing a better quality trap, albeit with a lower capacity, I don’t want to I don’t want to compromise some other aspect of installation that I might not of thought about.
 
Probably easier to keep it all on one thread to be honest. McAlpine do supply longer flanges to suit Tray thicknesses of up to 30mm.

I was trying to avoid a long rambling post around two slightly different issues, albeit there is a link. I address those longer flanges in the other thread.
 

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