Venturi Showers

[Softus]

To be pedantic NF, there is no such prize.

 

[Softus]

Since the cold storage cistern will commonly hold fifty gallons, and the WC cistern merely two, the head of water will reduce by no more than 4%. In practice, however, the pressure of hot water will reduce by even less. If we assume that both cisterns will fill at the same rate, then the average reduction in head will be only 2%.

Ah, but is the capacity of the cisterns relevent here? Seeing as the cold input to the venturi shower is mains rather than tanked?

I believe it's relevant - my reasoning is thus:

While the shower is running, cold water is being fed from the cold storage cistern to the hot tank. While this is happening, the mains is supplying cold water to the storage cistern to replenish it, and the water level is therefore always (slightly) below its maximum. If you reduce the mains pressure, for whatever reason, then the rate of water going into the cistern is less, and the level is even lower.

Clearly these are all small amounts and there's a degree of hysteresis involved, and I've never tried to measure or even observe this effect, but, logically, this is what must happen.

Obviously in practice the inlet to the toilet filler should be fitted with a restrictor when supplied with mains, but knowing several friends with toilets that refill in around 5-seconds it would appear many people forget to fit them.

So, for those 5-seconds or so the pressure to the shower could halve (if the mains pressure was exactly equal to the pressure you were using at the shower prior to the flush).

That's too big an "if". The shower valve could never release water at the same rate as the potential rate of the incoming mains to the house, because there is so much resistance to the flow at various points. Therefore there's residual mains pressure even with the shower running, hence you can re-fill the WC cistern while the shower is running.

However, with a 5.8 bar supply I think you could probably pressure wash your patio whilst flushing the toilet and still have enough pressure left over to run such a valve. But in a low mains pressure and/or negative head (for hot tank only, of course, fitting a venturi valve above the potential head of the mains supply will not help you at all) situation you could have the shower "stall", and stop flowing altogether whilst the toilet (presumably lower down than the shower) refills.

To be strictly correct, a negative head in the context of a venturi valve means that the shower head outlet is higher than the base of the cold storage cistern.

Glad we managed to untangle the web of fluid dynamics that was building up around us!

I agree

 

[civory]

Hi S again (I've been away this weekend) - I'm after an exposed model with slider rail.

Current situation is that plumb centre have promised me one by Wednesday (but not 100% convinced) for £192.00 plus VAT which seems a good price.

CI

 

[Softus]

Hi CI

£192 is very good for the valve and riser rail kit.

All the best.
S.

 

[Blair]

Hi all,

Sorry for dredging up an old thread, but it's usually considered "good form" rather than posting a new topic (and without looking for the answer first!).

I'm considering a venturi shower, as my Triton electric shower kindly failed this weekend.

I have a hot water tank in the airing cupboard, which is adjacent to the bathroom; the cupboard and bathroom share a wall, and it's the wall where the bath taps and shower are located. So far so good!

The hot water tank though is one of those with an integrated header tank - that is, it's "all in one" and sits right on top of the hot water tank, you couldn't split it if you wanted to (without an angle grinder anyway). The height difference between the shower head and the header tank is pretty much 0.

I have 2 questions:

1. Can I still use a venturi shower? Or do I have some odd and inappropriate hot water tank?

2. How do you vary the temperature of the mixed water? Since the hot water pressure will be pretty close to 0, and any flow as a result of the cold (pressure or flow?) thanks to the venturi, is there any way of varying the mix of hot and cold, or are you stuck with whatever comes out?


Sorry if these are stupid questions, but plumbing is a new area for me

Cheers

 

[Softus]

Hi all,

Sorry for dredging up an old thread, but it's usually considered "good form" rather than posting a new topic (and without looking for the answer first!).

Er, it's actually considered very bad form.

There's nothing wrong with referring to an old topic, but your problem is different, so please create a new topic.