Dear Niaz,

Make your own Pitot-tube from 4/6 mm dia pipe and transparant plastic tubing.

The length of the pitot tube can be chosen in relation to the duct you want to measure.

You need to drill ome small holes in the duct. These holes can be closed later on.

see the attache file.

success

teus

Attachments

pitot_tube (PDF)

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Nice simple design! ■

Dear Niaz,

Where you keep the Pitot-tube measuring point, you will measure the velocity as a vector in the direction of the tube.

(Also near the hood)

How meaningfull the location is, where you measure, is more or less up to your own judgement.

By measuring at various places in a cross section or space, you can reconstruct a velocity profile and decide whether that measurement gives you the information that you wanted.

By disconnecting one of the two sides of the U-tube, you can measure the static pressure or the static + velocity pressure.

(providing that the internal pressure does not empty your U-tube)

success

teus ■

Mall

An S type pitot needs to be calibrated against a standard (L type) and a correction factor applied. The factor will be something like 0.80 or 0.85, depending.

Also, velocity pressure is typically a very low number and you will have difficulty measuring it accurately with the vertical plastic tube manometer. Use an inclined manometer (expanded scale) or Magnehelic gauge or digital manometer.

Michael Reid. ■

Mall,

Yes, heavy dust load sometimes means you have to remove the pitot after each measurement and blow out the dust. Takes time.

How easy is it to read your digital manometer? If it has an averaging function, you will get good accuracy and quick readings. If not, you have to guess which of the fast-changing jumble of numbers is the correct reading. Accuracy will suffer.

Michael Reid. ■

Mall,

The S type and L pitot should give the same reading, allowing for the correction to be applied to the S type. Tube diameter does not matter.

I do not know the Dwyer 477 but my experience with other Dwyer digital manometers is that they are impossible to use because of the constant fluctuation of the digital readout. Any reading you accept has to be a guess. Much better to use one of their Magnehelic analogue gauges.

My own instrument is an Alnor AXD Mod. 560M which allows you to average the pressure readings over a set period, say 10 sec. (It also calculates flow if you give it temp., duct size and B.P. It compensates for static pressure).

Send me a sketch of your duct/fan layout and I will try to suggest more.

Michael Reid. ■

Mall,

There is a method called isokinetic sampling. It uses a sampling train consisting of a vacuum pump, sampling nozzles, probe and filters to extract a sample of gas and separate out the dust. There is also a condenser to separate the moisture of combustion.

It requires special equipment and training and is usually done by specialist contractors who do emission monitoring. Various National Standards describe the method.

Michael Reid. ■

Mall,

Maybe you could play around with a vacuum cleaner for a rough estimate otherwise, the easiest and cheapest way is to get a specialist to do the job for you. One off cost with no investment in equipment.

Michael Reid. ■

mall,

please find the attached file as the Emtronc for measuring dust load of Mikropul.de

Attachments

emtronic-c-english (PDF)

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This device still needs to be calibrated with a proper sampling test.

Michael Reid. ■