thermo anti gravity

[normspanners]

As per title how much anti gravity thermo flow do you get from the DHW water system ?
there must be some. ??
I have my bath and shower fed with two 22 mm from the storage tank, cold direct to the bath/shower hot though the tank then to bath shower is tee'd of then down to 15mm to the shower, which is a semi power shower single pump in the shower cubicle with a twin silicon pipe temperature adjuster ie as you go towards cold it shuts the hot and opens the cold, the two are mixed before the pump, that then pushes it out of the head.
My problem is; if the hot is turned to max hot, the pump cavitates and hardly any water comes out of the head, the pump does have anti scald, but that shuts the hot solenoid off in the event of the hot being too hot but when it cavitates I still have voltage to the solenoid.
Now if I turn it to full cold the pump runs fine. I have tapped the hot solenoid valve to see if it is sticking, makes no difference
I seem to have nearly equal flow at the bath mixer, from my experience the hot is allways slightly slower due to the rigoures of the flow throught the tank etc and the anti gravity of hot water, I believe.
The shower and bath are fed through an warrick / surrey flange, but I also have an upright tee off the flow joined as high as poss and restricted, to the tank breather because was still struggling with some kettling at times because of the immersion, but even if I close the restrictor valve it makes no difference to my issue.
I am going to back flush the shower with mains pressure but I will have to disconnect the pump electrical feed, and I could do with blocking off the breather whilst back flushing to make the water reverse flow through the whole hot feed. I dont want to damage the pump due to hammer
Any other ideas ??

 

[gaz1]

from your explanation is the pump is pumping no water due to the anti scald mode refusing enough hot water through the pump you cant pump no pressure water when its being restricted by another source

because cold is direct you have no problem theres not much you can do with an open system a pressured system is the best one to pick if your wanting to use a pressure shower

 

[normspanners]

Thanks BUT

The pump is pumping fine, its only issue, is its limited supply? why would it pump the cold better just because it is fed direct ? apart from the anti gravity effect.
I have now spent yesterday messing with it and swapped the two complete solenoid valves and had the exact opposite too much hot, which then eventually switches the anti scald and shuts the hot solenoid, then the pump cavitates again due to lack of flow, ?
so stripped the two solenoids and swapped bits over but nothing is a common fault, the diaphragms are both identical the .5 mm hole and the filters are clear, the coils are equal readings , but one complete solenoid always seems lazy and it does'nt seem to be a common issue I even swapped the metal shuffle valve from one to the other everything looks perfect but it is not working .
before any one says just replace the valve they are obsolete and the shower is the only one with left inputs apart from one other thats not suitable so now face a complete strip out and redesign of the shower.
OH why cant things last, it was brand new----------- only 25 yrs ago ?????

 

[Kayos]

Don’t over think it

If the valve or pump is over tired it will need replacing, have you tried Shower Doc or Divapor for the spares?

I recently fitted a whole house pump on an Aga heated cylinder, that needed a negative head pump, special tmv, new tank and about 60m of pipe

 

[normspanners]

Don’t over think it

Thanks for the reply
But I have to think about it, and every avenue to fix it, and IMO its the only way is to find out what is wrong, the pump is fine and the valves the look perfect ?? neither the valves or the pump are available.
yes I have tried, shower doc bought all the spares and they are no longer available.
there are some 24v dc solenoids 1/4 " but mine is not like them I may be able to mod them------- if the bits fit?

this is available https://www.showerdoc.com/grundfos-watermill-low-voltage-solenoid-valve-old-lv-models-pc500

 

[normspanners]

Well an update stripped the valves again and found one diaphragm had a tear not immediately obvious but a tear none the less, so managed to superglue it together, like micro surgery, refitted it and STILL no luck, then found the hot solenoid required two 15 thou shims making and fitting under the diaphragm tried one and it flowed water when solenoid was switched BUT without the pump electrically connected-------- as soon as the pump was reconnected and running it stopped, oh yes I made sure the tiny bleed holes in the diaphragm where clear, as it is the bleed holes in the diaphragm that make the valve operate , so then because of my success that far, I thought I would try another and made a second shim so it had 30 ish thou and bingo, working as it was years ago. No cavitation.
I have managed to order two of these https://www.showerdoc.com/grundfos-watermill-low-voltage-solenoid-valve-old-lv-models-pc500 dont know if they are the correct voltage but my coils still work so can swap them and if I have an issue its not the end of the world to rewind them and have bought this NOS it is the later version, still low voltage and the right config to fit, at least it gives me a spare pump etc and manual valves that act as a mixer body is the same ish, no cover, sold as is, but its new, its cost £118 in total but means I dont have to rip the shower tiles off and the walls out rerouting pipes and cabling etc etc etc. and gives me options to repair, as said it has lasted 25yrs up to now so hopefully will see me out.

 

[normspanners]

I am still not sure what has caused the issues with the valves it maybe the tear but the water has to flow through the diaphragm to work anyway ! fixing it didnt alter it, or it maybe the hot water has effected the rubber? making it less flexible, but they both are and feel identical?
The new ones should arrive sometime today for me to compare physically and any resistance difference readings.

 

[normspanners]

As a matter of interest does anybody know of a chart for the different vertical flow rates of hot water to cold ?
I would think that it would be taught to plumbers in college ?

 

[Kayos]

As a matter of interest does anybody know of a chart for the different vertical flow rates of hot water to cold ?
I would think that it would be taught to plumbers in college ?

To be honest water is very odd stuff, every other liquid when frozen sinks in the liquid, but ice floats.

The difference is so small it doesnt matter in a domestic property, you can search for pressure loss in a given size pipe, there are tables of that

 

[normspanners]

The difference is so small it doesnt matter in a domestic property,

but you can see the difference, I realise it takes a more arduous route through the tank etc but hot always seems to flow slower
BUT I found this which belies the reality

Dear Chris,

Hello, my name is Tommy Czaczkes, and I am a PhD student at the University of Sussex. My question is; why does boiling water sound different to room temperature water when poured into a mug?

Yours,

Tommy Czaczkes


Answer
Chris - If you've noticed, when you turn the shower on the morning, the cold water comes through from the pipe first and it will splash and sound different against the bottom of the shower compared with when the hot water, which comes along shortly afterwards, comes in; the note will change. This is a real observation; your ears aren't deceiving you.The reason for it is that water changes its viscosity - its stickiness - according to its temperature. If you could zoom in with a really powerful microscope and look at some water molecules, what you'd see is they are shaped like miniature boomerangs. At the apex of the boomerang you would see an oxygen atom and on each of the arms, you'd see hydrogen atoms. Oxygen loves electrons, so it pulls the electrons of itself and the hydrogen towards itself very tightly, and that makes the oxygen a bit minus. The hydrogens are correspondingly therefore a bit plus. As a result, when water molecules are sitting together side by side in solution, the positively charged hydrogens are attracted to the negatively charged oxygens of an adjacent molecule and this is called hydrogen bonding. It makes water sticky, and it gives it some of its special properties that in fact help it to make life happen on Earth. So it's pretty important that this happens. But, when you heat the water up, the particles start to move much more quickly. They have more kinetic energy which is a function of the temperature. This means that they're zipping past each other much faster. They're therefore gluing onto each other less well and this makes the water runnier or less viscous. So when it comes splashing out of the shower and hits the shower pan, the water fragments into smaller particles and makes a higher pitched splashing noise than when it goes into the cup or goes into the sink when it's cold. Have a listen next time you're in the bath for the shower and you will see that the note is different.

 

[normspanners]

And found this
http://www.johnhearfield.com/Water/Water_in_pipes.htm

IT is the Reynolds number !! same as FI aerodynamics ! and seems that even though it should flow better it is actually slower !!

Chaos rules
About 120 years ago, in Manchester, a man called Osborne Reynolds was trying to understand - or at least describe - the flow of fluids in pipes. After many careful experiments, he decided that what happened to the flow depended on four things - the viscosity and density of the fluid, the diameter of the pipe, and the speed the fluid was moving. He put these four quantities together like this to make a dimensionless number:

Reynolds number

Speed x Diameter x (Density / Viscosity)

The number has been known ever since as the Reynolds number, Re. Respect!

Reynolds found that when the fluid moves slowly, the flow stays smooth and even, but as the speed is increased it eventually becomes rough and turbulent - chaotic, we would say now. The transition to turbulence always happens at a Reynolds number between 2,000 and 3,000, no matter what fluid is used. (The reason for the uncertainty is probably to do with small variations in initial conditions - chaos is like that.)

In other words, the simple equation above relating flow rate to pressure drop is only valid when the moving water has a Reynolds number of 2,000 or less. If Re is higher than this, the water starts bouncing around unpredictably, and it takes more energy - more pressure - to shift it along.

As well as speed and pipe size, the Reynolds number Re depends on the ratio of the water's density to its viscosity, so to save having to work out (ρ/μ) each time you need to calculate Re I've included a table so that you can simply look it up.

Table 1: Viscosity and density of water
Temp oC Viscosity μ Density ρ ρ/μ
10 0.00133 999.7384 753,000
20 0.001 998.2 998,000
30 0.000753 996.6739 1,320,000
40 0.000567 995.1502 1,760,000
50 0.000427 993.6288 2,330,000
60 0.000321 992.1097 3,090,000
70 0.000242 990.5929 4,100,000
80 0.000182 989.0785 5,440,000
90 0.000137 987.5663 7,210,000
Example - Reynolds number
Cold water is flowing through a 15mm pipe run. How fast can it go before it starts to become turbulent?

The Reynolds number for this flow is

Re = (Speed) x (14/1000) x (753,000) = (Speed) x 10,500

(assuming "cold" means 10 deg.C and the pipe's internal diameter is 14mm), so if Re is to be 2,000 or less, then

Speed < 2,000/10,500 ... or Speed < 0.19 m/sec

Not very fast, then. How about hot water (at, say, 70 deg.C)?

Re = (Speed) x (14/1000) x (4,100,000) = (Speed) x 57,400

so Speed < 2,000/57,400 ... or Speed < 0.035 m/sec

which is really slow. Don't get too hung up on the numbers, by the way. Chaos is not exact. It's enough to say that turbulence is likely to start at around 0.2 metres/sec.

Is turbulent flow essential in domestic water systems?
Cold water flowing in 15mm pipe starts to become turbulent at the slow speed of 0.2 metres/sec. In 22mm pipe, the speed is lower still (0.13 m/sec). Does it matter that the water is moving so slowly?

The question is, how long are you prepared to wait for the sink or the bath to fill? A flow rate of 0.2 metres/second means that just 0.2m (20cm) of the pipe's contents come out of the tap in one second. Now, 22mm pipe (the size normally used to plumb in a bath) has an internal cross-sectional area of 320 sq.mm, so the volume occupied by 20cm of water is just:

Volume = Length x Area = (320 x10-6) x (20 x10-2) = 64 x10-6 cubic metres = 0.064 litres.

A bath holds typically 100 litres. It would take nearly half an hour to fill at this rate. Clearly 0.2 metres/second is far too low a speed to be useful. If a higher speed means turbulence, then so be it.

The trouble is that allowing turbulence is really not a good idea. For one thing, the particles of water are bashing into each other all the time, and that takes energy, and that means a much bigger force has to be applied to move it. For another, the force you need can't be calculated. It has to be inferred from other peoples' experiments.

 

[Kayos]

Yes, but in the real world the hot water may be a bit slower or more turbulent, if you are noticing it you have other issues

Don’t over think it

 

[normspanners]

Don’t over think it

Cant stop my brain asking why, and it demanding answers, very interesting to me the reason why it is slower when it actually should be faster

if you are noticing it you have other issues

I think the difference between 0.19 m/sec and 0.035 m/sec = 5 X slower would be quite noticeable to be honest.

 

[normspanners]

Another update; Carries out a 'blow back' purge from the hand basin mixer, there was no excessive pressure felt though the 'sensor' (my thumb!)
bits have arrived but after fitting the 30 thou shims to the hot solenoid the shower is working faultless, adjusts perfectly which it never really did and no cavitation, that is the big problem as cavitation kills pumps,
To me it is amazing to see how it erodes even solid steel away, all done by micro eruptions in water, the eruption and evaporation of microscopic gas bubbles occurring repeatedly causes this phenomenon , and it provides sufficient power to overcome the particle-to substrate adhesion forces of steel so plastic would have no chance against it
If you look at a large impeller it makes it easier to see it is quite remarkable that it is caused by evaporation within cold water .

http://webwormcpt.blogspot.co.uk/2008/04/why-cavitation-is-destructive.html

 

[normspanners]

After leaving the shower as is to test the modification the general consensus in the family who all like different shower temperatures is it has never been as good, I realise that this must have been a problem from the offset 20 yrs ago and that the solenoid valve with least flow, have been sucked virtually shut that being the hot one and by adding the shim it equalises the differences in immediate flow,
As the showers were modified by the manufacturers to a manual valve it seems that the original design didnt work so well as expected .