Why is this mixer unsuitable for low pressure systems?

Kernel_Sanders

I have an unfitted combined bath/shower mixer tap which states it is unsuitable for low-pressure systems i.e. traditional cylinder and header tank arrangements. It has a spring - loaded knob which only lets water through to the shower when pushed in, with no obvious way of keeping it in that position. Is it just the force of mains-pressure water that keeps it there, and is this the only reason that it is unsuitable?

EssexExile

You're probably right. It may well work on your system but it's not guaranteed.
We used to have special low pressure inlet valves for washing machines because normal ones used the pressure of the incoming water to close the valve. But the normal ones worked fine in most "low pressure" systems, just not in all.

roger-w5

The available water flow/pressure needs to be enough to hold the weight of the shower diverter bobbin in position,usually the hot & cold taps are run on full then the diverter manually activated for shower flow.
The shower part may well work but depends on how well the item is manufactured,the other consideration is safe showering temperature ie prevention of scalding.
it will be a new install and your installer will be clued up on the regulations !.

Kernel_Sanders

roger-w5 wrote: »

The shower part may well work but depends on how well the item is manufactured,the other consideration is safe showering temperature ie prevention of scalding.

So, the tap part will definitely work. But how might the thermostatic property of the shower mixer be compromised? The hot and cold water inlets will still be at the same pressure.

Ruski

You didn't say it was a thermostatic mixer in the combined filler/shower?
What brand/model is it??

Russ

Kernel_Sanders

Ruski wrote: »

You didn't say it was a thermostatic mixer in the combined filler/shower?
What brand/model is it??

Russ

I've been up in the loft to get the box (it's been there years) and I am mistaken, it's not thermostatic. If you still need to know, it's a LGA, model DIN 4109.

roger-w5

Doubt if there will be sufficient head of water to maintain a decent shower,especially if your water loft tank is sitting on the loft floor and your bathroom is on the floor below.It really needs on site investigation if you want a nice shower.
Gravity flow has its limitations,if will work for some installations and not others.

Kernel_Sanders

EssexExile wrote: »

... normal ones used the pressure of the incoming water to close the valve.

You mean to open it, Shirley?

roger-w5 wrote: »

Doubt if there will be sufficient head of water to maintain a decent shower,especially if your water loft tank is sitting on the loft floor and your bathroom is on the floor below.It really needs on site investigation if you want a nice shower.
Gravity flow has its limitations,if will work for some installations and not others.

It had a mixer fitted previously which was adequate. I don't need a power shower.

EssexExile

Kernel_Sanders wrote: »

You mean to open it, Shirley?

No, to close it. The water pressure forces the washer against the inlet pipe so closing the flow. When activated the solenoid pushes the washer away from the inlet, against the water pressure, hence allowing the flow.

If the incoming water pressure is too low, it doesn't seal the washer with enough force so the water dribbles past. Then you need a low pressure valve that has a spring to hold the washer in place.