I got an add for this on YouTube.
https://saltdays.co.uk/products/rotatable-high-pressure-shower/?gclid=CjwKCAjwgviIBhBkEiwA10D2j1GIMvc09q9qSlC0XOEVK4J8aV5qr3QXGhrawEwVMJXusLQVwC5KbRoC9joQAvD_BwE
The way it “works” apparently is that the water passes over a turbine/propellor, which moves said turbine. The movement of the turbine then increases the water pressure.
Sounds like an ingredient for a perpetual motion machine to me.
It is pretty obvious that reducing the nozzle size will increase the pressure. We have all put a thumb over the end of a hosepipe to make the water go further. "Shower head uses micro nozzle technology makes the outlet holes smaller and denser, increasing the speed of the water flow, "
On the other hand - “Shower head makes water flow generates a pressurized flow through the rotating wheel, increasing the speed of the water flow, thereby increasing the water pressure.” is not only ungrammatical but sounds like woo to me.
Not only is the water going to come out faster, but you will also use less of it.
On the topic of reducing the nozzle size, it seems to me that total nozzle cross section is more important. Smaller nozzles but more of them could result in lower speeds.
If their webpage is full of typos and spelling mistakes,
and if the only contact is an e-mail and,
when then the postal adress indicated is:
a) not a return adress
b) a PNG image, so it cannot be cut&pasted and is not searchable by Google
and the product cannot work because it violates the second law of thermodynamics…
and it is reduced from 25.98 British Pounds to unbelievable 12.99 British Pounds…
then, man, it’s a bargain! Buy three of them and save triple as much!!
I’d think Bernoulli’s principle would be in play here- if you speed up the water, the pressure will actually be lower and I suspect flow will be lower as well, but it’ll hit you with more force in the shower and feel like maybe you have more pressure.
Similarly, slowing it down should raise the pressure and flow, but the speed of the water coming out will be lower. I think that’s how the turbine would work, but I’m not sure how it would make for a better shower.
Could be that the propeller actually works more like a distributor cap, and lets pressure build up on a nozzle at a time, and then uncovers it and the water shoots out a little bit higher. So it’s really a bunch of little bursts instead of a steady stream.
There is a way that something like this theoretically could work.
In many places the pressure of the cold water is much higher than the hot.
If you took a cold water feed and used a substantial proportion of the energy and volume to drive a turbine you could use that turbine to also raise the pressure of the hot water (and possibly still be able to maintain enough cold water flow to the hot water source and also for some to be introduced to a thermostatic mixer). All that would of course depend on the available cold water pressure that you have to work with, losses in the system etc. and I don’t see an elegant way of incorporating all of this into a shower head (I mean where would the cold water go that you are using to drive the turbine? back into the mains?)
But that does not seem to be anything like what this shower head is doing. That seems just be constricting and “pulsing” the flow which isn’t really what people think about when considering claims of “increasing water pressure”.
Its a scam. In industry, we use huge pumps centrifugal and turbine based to increase pressure - all of them need external power.
Just think, if the turbine is able to make more pressure than the inlet pressure, then the water will flow back into the pipe. Flows happen from high pressure to low.
Also - those small holes will very quickly clog up with mineral deposits common with household water supplies.
There are also ways to increase pressure by discarding some of the water volume - so called ‘gravity pump’ devices manage to do this.
Not that I think this is what’s going on here - it all seems pretty scammy to me.
You’re thinking that dynamic pressure isn’t ‘real’ pressure, that only static pressure is ‘real’ pressure.
And you’re thinking that ‘pressure’ is defined as ‘force*area’, but that’s assuming shower users wish to compare unequal areas.
Clearly the turbine is just eye candy. It serves no useful purpose. Had I been designing it I would have added a tiny generator and run some flashing LEDs.
Other than that they have just used small diameter jets.
The perception of pressure on the skin may well be increased as, if the design is got right, there will be a higher force per unit area versus that had with wider jet diameters. This is a pretty common idea. Overall less water is delivered but they claim the overall experience is better. Can’t say I’m a fan of them. Nothing beats a proper deluge.
I got a new shower head not long ago. It actually has two heads, one attached, and one detachable with a hose. It very much does at least increase the sensation or pressure compared to my old one.
It has thinner nozzles for the first mode. It has another mode that concentrates the water. But it also has a mode where it produces this sputtering effect, which does seem to make the pressure feel even higher, to the point I would call it too high unless you have both shower heads running.
It would not surprise me at all if the actual pressure is not any higher. But it definitely produces the sensation that it is.
That said, I didn’t get it from any website. It was just a showerhead offered in the bathroom fixtures at our local hardware store. I don’t currently remember which one. I don’t think it’s anything special.
However, looking online, this appears to be it:
Indeed; huge amount of woo in the advertising blurb there, but it is an interesting gadget. While the turbine might not be able to break the laws of physics and increase the water flow, it does make for a rather unique water jet pattern by continuously changing the entry (and hence exit) angle of the water jets to/from the outer perforated disc. The $64k question is: will this rinse the shampoo out of my hair quicker than a standard shower head? It may well at that, and I’d be tempted to buy one just for a laugh were it not for a couple of showstoppers: I’m in a hard water area, and this thing will get jammed solid with limescale flakes within a week; and we have an electric shower that won’t take kindly to this device’s on/off switch blocking off the water output (electric showers have a low water pressure safety switch to cut the power to the heaters if the water pressure drops too low, but if the outlet is blocked then the heater will only get turned off after it overheats and trips/blows the thermal safety switch).
The business address for Saltdays is this house in a residential road in London (on the left, behind the privet hedge):
https://www.google.co.uk/maps/@51.4335637,-0.0240445,3a,55.4y,274.53h,96.88t/data=!3m6!1e1!3m4!1sWPYhEWsW0ffRefowcoMnnA!2e0!7i16384!8i8192?hl=en
They seem to be an online version of the old Innovations catalogue, which sold gadgets that seemed like a great idea at the time, but when purchased it soon became apparent why they were only sold by one niche company and not stocked by a wider variety of distributors. That said, I am won over by the appalling rudeness of this Saltdays party banner and would like to know if they have a wider range:
https://saltdays.co.uk/products/3-pieces-please-leave-by-9-party-banner/
If they don’t, then may I offer some suggestions?
“We only invited you out of obligation”
“Did you check your children for nits?”
“Double-dippers will be expelled”
Could be onto a winner here.
No - I am not thinking that.
I am thinking what process/mechanical engineers call surge in centrifugal compressors / fans and what aerospace engineers call stall in airplane engines.
12 months ago (shortly after my last post in this thread) my curiosity got the better of me and I bought one of these propeller shower heads, albeit not from the OP’s link as I found one half the price (there are loads of copycat versions out there). This is a dangerous item to fit to an electric shower like ours as the shower head’s water on/off and flow control knobs can reduce the water flow through the electric heater to such a point that the over-temperature safety switch trips, or the heater can explodes (and indeed there are several Amazon reviews that claim this item has damaged the reviewer’s electric shower), so I was careful to leave those controls fully open.
My first impression was that this shower head generates a huge amount of thrust, although not quite enough to blast itself out of its holder and do the out-of-control firehose thing. My second impression was that the water flow leads to massive shower curtain billowing, which is inconvenient. My third impression was that the water pressure from the narrow-bore jets is so high that it’s painful (and possibly damaging) if the head is too close to the skin. It worked nicely for exactly one shower, and then started leaking everywhere, so I shelved it and put the original shower head back in.
51 weeks later and the UK is in the middle of an energy crisis and widespread water shortages, so I dug it out again and did a few modifications to overcome some design flaws, and to make it safer for an electric shower. Mostly this involved glueing open the on/off switch and water control valves so the flow can’t be reduced or cut off, but as the aperture was still a bit small I drilled it out to widen the bore as much as possible, then lined the bore with epoxy resin to prevent leakage from the bored-out gubbins. I also made various modifications to stop water leaks, and stop the water pressure from blowing off the threaded end of the head, cheap PoS that it is. Having done this, I am pleased to report that it works exceedingly well at rinsing, to the point where I can set both the shower heater power and water flow to 50% and still get the same rinsing effectiveness as the original shower head that used twice the electricity and water to get the same result. The previous issues of curtain billowing and painful jets go away with this lower water flow, which is an additional bonus.
Shoddy construction aside, here are some observations on the design and operation:
In short, playing around with this thing has been a fascinating exercise in fluid dynamics, though I can see why the reputable shower companies don’t sell them (every model I’ve seen is cheap no-name junk, and all have water flow controls that make them dangerous when fitted to electric showers). One other issue I’ve seen is that the rose holes are so small that they very soon become jammed with tiny flakes of limescale, making such a shower head useless in hard water areas. I have a mesh limescale filter in line with ours, and though this works well to keep conventional shower heads un-fouled, it lets through enough tiny particles to cause issues with the small-bore holes of this be-propellered beast. The holes don’t get completely blocked; rather, they cause the individual jet to go off at a random angle, both impairing the action of the jets in shaping the water spray, and soaking various hitherto dry areas of bathroom.
If there are any fluid dynamics engineers reading this (or even the idly-curious), shout and I’ll post some pics. There’s some interesting things going on with the physics of this item, and I can’t explain how it generates a spray with a curved profile.
The apparent bell shape is most likely a optical illusion akin to the curved shapes outlined in things like string art. You get a family of parabola outlined by straight lines drawn in a regular grid.
Here is a neat overview:
The Waterpik shower-head linked to earlier is interesting. The company has been around for some time and has quite a few patents. 35 for shower heads alone. One thing the patents don’t claim is any pressure increasing function. The turbines inside the head are there to drive the on/off pulsating of the massaging modes. Cheap and nasty plastic versions with visible turbines are just cosmetic.
This one is extensive in its description and variations on the theme:
Disregarding any curvature of the the individual spray jets due to gravity and/or aero drag, the 3D shape produced by the overall array of spray jets constitutes a ruled surface:
In particular, the shape produced is a hyperboloid of one sheet:
I was fairly sure it was some kind of non-linear effect due to air-coupled interactions between the two concentric spray rings - particularly as they twist in opposite directions - but having had a few hours to chew over your theory, followed by a shower and a good contemplation of the spray pattern, I reckon you’re correct. There probably is some complicated dynamic going on, but the dominant effect seems to be good old euclidean geometry.
Those Waterpik patents look very interesting - I didn’t know such exotic heads were available as all I’ve ever seen in the usual shops are variations on the rose spray. I’m going to be checking some of those out, thank-you.
Thank-you too, Machine_Elf, those diagrams illustrate the effect nicely. I like the idea of a hyperboloid shower head - sounds much more credible than a propeller shower head, which is only one small mental leap away from a propeller hat.
Here’s some pics of various propeller shower heads:
In this one the outer ring jets can clearly be seen to exit the head with a clockwise bias. It’s harder to see the inner ring jets, but it can be inferred that they’re going counter-clockwise by the diamond pattern made when viewed against the outer jets. It’s much easier to see up-close IRL.
Here’s a longer view showing the overall shape of the rose, which nicely correlates with what Francis_Vaughn and Machine_Elf have pointed out.
There’s a nice little GIF video at Showery. It’s a bit pricier than the one I bought as it’s got an inline filter - necessary in hard water areas as those tiny rose holes are devils for clogging with limescale flakes. I doubt it’s constructed to higher standards than all the others though, as they’re all essentially clones of the same design, and all are from no-name manufacturers. I note that no reputable shower head manufacturers have anything like this in their ranges; might be they’re more vary of infringing patents, might be they’re aware of issues that could cause problems (even without the electric shower-killer flow control switch/knob), might be they don’t want to taint their brand by association with all the cheap junk out there. It’s a shame no-one produces a decent version of these as they are very effective at rinsing at low water pressures, so could save a lot of heat energy and water.
Now what I can’t work out is why the outer and inner spray rings are biased in opposite directions. The water is swirled clockwise inside the head by angled vanes on the head’s inner circumference, so I would expect both rings to have jets pointing in a common direction. It’s not the action of the propeller as it works pretty much the same with that removed, but the countersinks on the inside of the rose plate are important as the jets exit at a normal 90 degrees without these. I might take it apart at some point and get the rose holes under a microscope - I’ll post the pics if I do.
