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Weird manometer reading

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After installation of the Radon Reduction System and upon activation of the system the manometer had a good strong reading and then it went to just off zero. There is pea gravel underneath the slab. I have been told two things on this. One is that if you have really good air movement it might not show a good reading. This is rare but it does happen. The second was that if there is no reading then you have no suction.

Does anyone have any insight to this problem.

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One is that if you have really good air movement it might not show a good reading.
Good air movement isn't good. It means air from the house is being sucked into the system, thus no negative pressure under the floor slab. Are the perimeter drain, slab cracks and sump pit sealed?

More often than not, when there's no negetaive pressure reading, I find no sealant where the tube from the manometer enters the suction pipe.

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The fan is running.

Everything that I can see is sealed correctly. I have heard that a low reading on the manometer can mean a blockage above the fan. I will check that and maybe replace the fan. Thanks for your input.

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The fan is running.

Everything that I can see is sealed correctly. I have heard that a low reading on the manometer can mean a blockage above the fan. I will check that and maybe replace the fan. Thanks for your input.

The manometer reads a pressure differential - if the liquid is even it is not sensing a differential. If the fan is running then you can, 99% sure, rule out the fan (there is a chance that the motor is running but the blower isn't turning albeit slim). You may have something blocking the suction side of the fan or perhaps the sensing tube for the manaometer has fallen out or has a restriction.

How long did it take for the manometer to zero out after it was running?

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There are a whole of of things going on here.

If you have an open ended suction pipe and an unobstructed discharge pipe, then you will have a near zero reading on the manometer. No differential.

If your suction pipe is stuck into the dirt and the discharge pipe is wide open (unobstructed) then you have a 2" or 3" or higher reading. High reading does not indicate the system is working. The differential indicates there is a suction and does not indicate where or how large an area is affected.

We have never seen a system where the manometer slowly goes down after the fan is turned off. Guess it is possible.

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There are a whole of of things going on here.

If you have an open ended suction pipe and an unobstructed discharge pipe, then you will have a near zero reading on the manometer. No differential.

If your suction pipe is stuck into the dirt and the discharge pipe is wide open (unobstructed) then you have a 2" or 3" or higher reading. High reading does not indicate the system is working. The differential indicates there is a suction and does not indicate where or how large an area is affected.

Les, I don't understand your reasoning here. If the suction pipe is wide open and the discharge pipe is wide open, and the fan is running, then air is moving through the pipe and the manometer should show a pressure differential. This is Bernoulli's Principle.

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Hey Steve, I should have been more clear. If we restrict the suction pipe the reading will be higher. The manometer tells us there is suction.

It is Sat morning and I'll have to review what I thought I knew about Bernoulli's principle. My present understanding of the principle leads me to think it is not totally applicable here. Golly I would really hate to admit I am wrong!

we will see.

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Les, I see what you're saying. And that makes sense. If there's a blockage, the fan creates a partial vacuum in the pipe, and this shows up in the manometer.

But under normal conditions, when air is just flowing freely through the pipe, that airflow creates a reduction in pressure, the same way that air flowing faster over the top of an airplane's wings creates a reduction in pressure that causes lift on the wings.

It's not clear to me which condition would cause a greater pressure differential, or if they'd be about the same.

Personally, I think the original problem is the result of a faulty manometer, but I'm just guessing there.

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A manometer is about as simple of a measuring device as one can get. The chance of one not working is next to nil.

The manometer tube could easily come loose from the pipe.

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A manometer is about as simple of a measuring device as one can get. The chance of one not working is next to nil.

The manometer tube could easily come loose from the pipe.

No, it couldn't easily come loose from the pipe if properly installed. It's not out of the realm of possibility but it wouldn't be where I would first start.

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No, it couldn't easily come loose from the pipe if properly installed. It's not out of the realm of possibility but it wouldn't be where I would first start.

You are absolutely 100% correct.

But this forum is full of people who complain constantly about crappy installation, so I don't understand why you feel free to use the qualifier "if properly installed." Heck, the whole system is extremely unlikely to have problems, if properly installed.

I would start with the manometer partly because it's likely, and partly because it's easy to investigate. I'd rather rule that out before I climb on the roof to look at the top of the discharge pipe.

My favorite story along these lines comes from the movie Apollo 13. (It all comes back to that movie for me.) There is a scene just after Jack Swiggert replaces Ken Mattingly as the command module pilot. The crew is in the simulator, and Swiggert makes an error that causes the simulation mission to crash and fail. The mission control folks are lamenting the error, and one of them says, "I sent him a faulty indicator light. Mattingly didn't get it right the first time either." So, an enormous amount of the best scientific and engineering talent that this country could must went into designing, manufacturing, and installing that indicator light. But the message to the astronauts was: Don't trust the gauge. It might be wrong.

It might be simple, but don't trust the manometer: If it's giving you a faulty reading it might be wrong.

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More often than not, when there's no negative pressure reading, I find no sealant where the tube from the manometer enters the suction pipe.

Bill, it seems that we agree that the problem is likely to be the manometer itself. I don't want to put words in your mouth; am I reading you right?

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More often than not, when there's no negative pressure reading, I find no sealant where the tube from the manometer enters the suction pipe.

Bill, it seems that we agree that the problem is likely to be the manometer itself. I don't want to put words in your mouth; am I reading you right?

No, it's not the manometer, it's the installation.

Every radon mitigation system manometer I've seen is a simple clear U-tube, with blue non-evaporating liquid. It has flexible tubing on one end and the tubing is inserted into a hole drilled into the PVC suction pipe.

If the hole in the pipe is bigger than the tubing, and there's no sealant, the liquid in the tube is usually at zero. I'll take the tube out of the suction pipe, flare the end with my pen and re-insert it, just to show folks the system is actually creating a negative pressure.

The next most frequent issue is finding the tubing has kinked. Pushing on the bent tubing removes the kink, also quickly illustrating that the system is creating a negative pressure.

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No, it's not the manometer, it's the installation.

Yes, well, that's what I mean. I'm not separating the actual physical equipment from the way it's installed.

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