I've got an R&D test I'm working on for my day job and I've run into a snag.

Essentially the problem is that we have some water collecting gutters of a unique profile but we don't have a way of detecting exactly how much water is flowing out of the end of the gutter system. The gutters are made of a PVC extrusion and are dark grey. Filming them dead on isn't going to work as they are part of an enclosed compartment with hurricane force water being sprayed directly down.

The idea we've come up with is to paint the inside surfaces of the gutters near the open end with a water soluble paint which will be removed by the flowing water, but not by any spray.

Does anyone know of a product like this?

We've tried dry-erase markers, finger paint, chalk and a powder film. The water doesn't seem to remove any of these.

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1984 300D "Elsa" odo reset 6/2011 147k
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Maybe collect the runout into a 50 gallon barrel and time how much is added per minute?

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or use an open channel equation, was that manning?

I worked on a small automated sewage treatment plant. After treatment, solids were seperated, dried (relatively), & liquid went through a 'vertical' venturi. Vacuum (after initial calibration) was used to measure volume flowing to holding tank.

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"I applaud your elaborate system of denial"

There are so many variables If your description of the problem is accurate. I agree that timed collection of the output is about the only certain way. To obtain an accurate flow rate.

As described with the hurricane force of water directed perpendicular to the bottom of the trough their may be no water collection. It could be blown out about as fast as it enters. A trick question? I cannot see much if any accumulation occurring. Certainly even a nominal slope would not be effective.

Then again you mention a closed system. Output will equal the input then.

Ok, so I can't use anything suggested so far.

I need to measure the depth of the water when it exits the gutter. This is the data I need.

No, the math doesn't give us what we want. No, I can't simply collect the water and measure it. I'm looking for flow patterns, exactly where water flows and where it doesn't.

I'm sorry I can't fully describe the problem or the environment as it's sensitive and contains proprietary information.

The best way I can describe it is to say that a gutter, much like the one on your house is suspended above an area which must be kept dry. The gutter is at an downward angle (say 3 degrees) which allows water to flow out one end. The environment includes lots of air movement and a deluge of water.

You cannot collect the water at the end of the gutters as you cannot isolate what goes into the gutters and what doesn't. What you need to know is what level the water is at the end of the gutter. Is it 1" deep or is it 1.25" deep?

This is why I'm looking for a paint or something which will wash away from constant water flow, but not wash away from spray.

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

Simple problem. Drill a small hole in the bottom of the gutter and install a nipple. Attach a hose to the nipple. Turn on the water. Water will flow out of the hose. Raise the end of the hose until the flow stops, and you will know your level.

That only works in a non flow situation.

Things like this are what my late Stepfather had to grapple with daily and listening to him is like reading this thread .

I hope you find an answer and share it here .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

So a bit of testing, but no result.

Things that don't work:

• dry erase marker
• paper/film/absorbing sheet
• washable markers
• wet erase markers
• sand coating

Here's what I'm going to try sometime this weekend:

• salt spray (white residue when dry)
• flour/egg paste
• spackle (thin layer)
• water miscible oil paint
• thermal paint

__________________
Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

What about something like tempera paint? That stuff is water-soluble and dries to a "chalky" finish. I'd imagine if diluted with water before being applied you could make a very thin layer that would do more or less what you want.

One critical piece of information missing here: How long is the water running in the trough? Is it a few seconds, several minutes, or over a period of hours?

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How fast of a reaction time? Powder wouldn’t stay in spray.

White based car wax paste diluted in water and sprayed would dry to a haze and would resist spray but would eventually dissolve in direct flow contact.

That would tell you level but what are you going after? How fast its going through? Total operational volume?

“That only works in a non flow situation.”

Think it through and tell me why flow doesn’t affect the observed measurement. Before you snap another answer, consider that the nipple is orthogonal to the gutter.

I dont understand why a mechanical or electrical sensing method couldn’t be applied.

Laser sensor.