Shower Mixer Question

[jazz125]

Hi all,

Had a (hopefully) straightforward question about the differences between a modern shower mixer and old school individual hot and cold flow taps.

I have decent flow and pressure, and the readings in our yet-to-be renovated bathroom are:

Hot: ~12 l/m
Cold: 18-20 l/m
Average mixed flow: ~16-17 l/m (good enough for me)
Pressure: 5 bar


Our second bathroom was recently renovated and fitted with a Hansgrohe ShowerSelect (2 outlet) shower mixer (it's a manual mixer; not thermostatic). There's no flow control lever, just a button to start the shower and a temperature lever. The average flow rate at the same temp in this shower is 12 l/m (so a drop of around 4 l/m), which doesn't make sense as it supports a high flow rate at the mixer and shower heads.

The bathroom that hasn't been renovated yet has a tub and separate hot and cold taps, with attached handshower, yet has a higher flow rate. To get the 16-17 l/m flow rate, we're opening the hot tap all the way and then adjusting the cold water to get the desired temp. This way, we're getting the most hot and cold water mixed in.

As there's no flow lever in the new shower, I wanted to know if all these mixers (without a flow lever) work by using less cold and hot water to get the desired temperature. If so, is there a way of overriding that to get the maximum volume of both hot and cold? Can we retroactively adjust the new shower through the mixer (by removing the mixer panel) for more volume or do these mixers generally work this way by using less water?

The Hansgrohe mixer has a maximum outlet flow rate of over 20 l/m at 3 bar.

Thanks

 

[Madrab]

What type of hot water system do you have? Unvented? The shower output would be dictated by the supply flow and pressure up to the max flow rate. What temp is the HW set to?

You say your supply is 5bar, is that dynamic, same with the flow figures is that a dynamic reading? Ideally you want to test the pressure and flow at a given outlet with at least 2 of the same outlet open at the same time. Is this bathroom/shower fed with 15mm pipework or 22mm?

A bath will use higher flowing outlets therefore it would be expected to get higher flow figures at a bath under lower dynamic pressures than a shower. I don't believe that shower is adjustable to allow an increase to the output at the valve. They will be set to flow @ max under the supply conditions I would think.

Only other checks that would be done would inlet filters and check valves and clear and ok.

 

[jazz125]

Hi, it's a combi (Vaillant Ecotec plus 836) and the boiler temp is set to 60 C. I'm manually checking the flow in both bathrooms at 42 C using a flow cup and thermometer. Ah, didn't get a dynamic reading in that case as only one outlet was open for each reading.

22mm pipework which I think isn't ideal for combis, but it is what it is. I have a PRV at the mains set to around 5 bar (otherwise it's just above 6) and that's the reading I'm getting at the outlets as well (again with only one outlet open).

So, the bath taps have an outlet for a shower hose and that's what I'm using to test the flow. Wasn't sure if the new mixer would use a completely open hot and partially open cold inlet by default as there is no flow lever. This in place of partially opening both inlets (hot not all the way and less cold) therefore less overall volume coming through. I mistakenly assumed it would as it's spec'd at a high flow rate (<20 l/m at 3 bar).

I think the shower head has an inlet filter (not a flow restrictor) - would that impact flow?

I'll get some more readings this week. Just wanted to know if there's something I could have done differently (chosen a different mixer, etc) as the old shower is due to be upgraded soon as well and want to avoid making the same mistake.

Appreciate the quick response - thanks very much.

 

[Madrab]

Wasn't sure if the new mixer would use a completely open hot and partially open cold inlet by default as there is no flow lever

The temperature control is, in effect, a flow lever or mixer control. It will adjust the flow level between hot and cold to whatever the control is set to. If the control is on full hot does it still flow 12l/Min and is the temp say around 55deg? How much further is the new shower away from the supply compared to the old bath? Length of pipe runs , number of elbows/tees etc will also effect flow levels at the outlet.

As far as different showers are concerned then there's always alternatives. I have a Mira Activate running off of supply @ 25L/Min - 3 bar dynamic through a 250L unvented cylinder and that can maintain up to 16L/Min but that is the limit of the digital shower itself. Under full flow conditions it typically will reach around 20L/min

 

[jazz125]

I believe it was at (or just below) the 12 l/m mark, but will need to retest (as that was something I tested weeks ago). Can't recall the temp, but will definitely run that test again, thanks. The new shower is directly above the combi, so not much of a pipe run.

16 l/m mixed would be perfect for me as well as that's what we get with the older shower. I've reached out to the manufacturer as well and they asked for flow videos. They reckon maybe there's an issue with the stop cartridges (I think that's what he said over the phone). Will run some more tests and send some recordings over to their customer service team.

 

[Madrab]

Stop cartridges would be what I guess we would call the non return or check valves.