Detecting ice in water pipes....by using a motor? 16

[schnell]

Hello,

We design domestic water temperature controlled showers.

Stepper motors adjust hot and cold flow rates.

If the water in the pipes is ice, and we try and rotate the stepper valves, these valves break.

So do you know how we can detect if the water is ice or liquid.?

...its not terribly useful to use a thermistor....anyway, we already have a thermistor in the "mixed" pipe outlet....since water can be at zero degrees and liquid if it is agitated ....(made to flow a bit)

...the problem is that if our thermistor reads zero degrees or therabouts, we don't know if its ice or water....and we have to disallow the shower form turning on.....and customers are unhappy when there shower does not work.


I was thinking that we could put like a small rotary "fan" in the water pipe, and energise it.........we could then measure the current flow to it to see if the water was ice or not....because if it was ice, then the "fan" would not be able to rotate and it would be in "locked rotor" state.....as such ...would more current flow to its coils?

...i would have thought so , since the back EMF would be lower.(?)

....because if less electric current did flow, then we could measure this current to assess whether we had ice or liquid water in the pipes.?

 

[MiketheEngineer]

How about a water detector on the floor below the pipe. Because if you have ice in the pipe - the pipe has broken.

Where in the world are you that the pipes can get that cold in a shower?? I sure don't want to take a shower in those conditions!!

 

[Compositepro]

Most stepper motor systems are designed to stall rather than break. Make whatever is breaking stronger. If ink jet printers broke whenever a motor stalled none would last a year.

 

[schnell]

Hi,

the shower unit is placed in the attic...which is very cold in winter in many parts of USA and uk.

sorry it isn't so much the steppers breaking, as the cold water is frozen solid, and so the hot can come through alone and scald the person becasue theres no cold water mix.

 

[btrueblood]

"Most stepper motor systems are designed to stall rather than break. Make whatever is breaking stronger."

Or use a lower torque stepper motor, or a magnetic torque-limiting clutch, or...

" it isn't so much the steppers breaking, as the cold water is frozen solid, and so the hot can come through alone and scald the person becasue theres no cold water mix. "

What commands the stepper motors? Presumably a fairly sophisticated circuit. A simple flow switch, or a pressure sensor between valve and shower head on the cold water side would tell you if the flow is inadequate. Presumably a thermistor in the shower head would command the hot water valve shut when the temperature spiked, is the valve speed to slow to do this?

 

[MiketheEngineer]

Could you wrap the hot & cold water lines together with insulation or such - so that both stay warm??

 

[badservo]

What about checking the pressure after the valve, no pressure=no flow, or listen for flow with a microphone.

 

[Compositepro]

I'm glad I've still got my 30 year old hot and cold valves in my shower.

 

[schnell]

btrueblood:
steppers are commanded by a microcontroller.
-the uC reads thermistor temperature of a thermistor in the mixed pipe, just after the stepper valves.

....you're right we can't risk too-hot water getting up to the shower-head as scalding is then a risk.

badservo:
Unfortunatley, we cannot just command the water flow and then check to see if its flowing...because then it would be too late and hot water (not mixed with cold) would be on the customer.

hot, with cold water must always be able to flow together so that we can decrease risk of scalding...if theres no cold becasue its frozen, then the pure hot water can get through and scald before the uC has time to shut off the valve.


MiketheEngineer:
It wouldnt help to wrap hot and cold together because when the shower is not used, the cold will eventually still cool down to the point where it gets to around zero degrees.

 

[waross]

Adapt a moisture meter that works on capacity. If the meter reports that the water is drier than water that is because it has frozen. Resistive measurements may help also.
I've never seen this done though. I Canada we have quite a few techniques to prevent the water from freezing in the first place.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

A flow switch in the cold water (ice) line that would cut off the motor power supply either at the start or even during the showering. (Pity the guy who had just shampooed his hair)

Muthu

http://www.edison.co.in

 

[schnell]

edison123
Thankyou...........

-with our showers, if the customer switches it on...it won't actually come on in the first place if the thermistor reports a temperature of zero degrees Centigrade.

-This also applies to our bath fillers too.

so hopefully our customer won't have started to shampoo their hair

 

[wayne440]

Heat trace the "cold" water pipe, maybe?

 

[cloa]

Why not instead make a place for the water to freeze safely without going through the pipes- e.g. Silver Iodide is much better seed than some random location in your pipe (why cloud seeding works) and when it freezes there- you can detect it easily and do something.

 

[OperaHouse]

If some micro controls the stepper with a thermistor you could determine the last time water was flowing and how long it would take for pipe to likely freeze. It could even cause some water to flow and warm up the pipe.

 

[Skogsgurra]

An impeller and a motor, where the current is not very much dependent on rotation or not, is not a good idea. At least not in small AC motors. DC motors will not last long in that environment, but react more to stalled shaft.

The simplest frozen water detector I can imagine is an AC coil with a plunger with a return spring that you put inside the coil. When you apply AC voltage, the plunger is sucked into the coil and current goes down. If the water is frozen, the plunger stays out and current will be high.

Of course, there are a lot of practical considerations, space, rust-proofing, keeping water from the electric parts and such things. But probably a lot easier than using a motor and impeller.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[lukin1977]

Dont let the hot valve open until a signal from cold water running comes first. This way your customer wont get burned

 

[schnell]

skogsgurra,
....your idea is along the lines i should have been looking for in the first place....much better than a motor....in fact, as you no doubt are aware.....your idea basically describes a solenoid.

In fact, on that point, we were considering adding some power-fail normally-closed solenoids into the cold and hot pipes, in order to handle the case when mains fails but the stepper valves are open (in some places its a legal requirement that showers shut off water in the event of a mains power fail)..now i am wondering if there is such thing as a solenoid that won't open if the water in the pipe is ice?...because if there was , then that would be "2 birds with one stone".

lukin1977, yours is a good idea also, , though slightly less sleek for our discerning customers who may find it bizarre that their shower "dribbles" before it starts up properly...though maybe we could only have the dribbling when thermistor reported zero degrees....

..anyway, i have not heard of many cheap, off-the-shelf electronic flow meters for inside water pipes, -that don't give much resistance to water flow...but worth looking in to.

 

[waross]

Browse Omega.com for devices. If you see something that will do the job, then search for quantity pricing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

They are called "turbine flowmeters", essentially a small magnetic paddle wheel in a plastic housing that spins with flow, and a magnetic pickup on the outside of the housing that looks for (or counts) the pulses as the magnet spins. No spin, pulse count is less than or equal to 1, disable the hot water flow.

types:

By the way, forgive all my fellow North Americans who are not yet used to the concept of "electric showers" that provide instantaneous hot water on demand. We mostly have large hot water tanks and separate pipes throughout the house so "freeze protection" is an entirely different issue for us.

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