Earthing central vacuum cleaner in our plant

Use conductive plastic.
Del

Or, paint the existing piping with conductive paint. Or keep the RH above 60%.

I think somebody is pulling Omar's leg. Maybe he can put screens or metal nozzles at the places of concern, and bleed off the static charge to ground. Ground the machine, too.

Static electricity can play havoc with paper,textiles,cats,and electronic components.

Thanks Yusef1 for your reply but how to measure the electrostatic charges so I can say it possible to make explosion. Do you know any standard or regulation that I can use galvanized steel as an earthing points for discharging.

The only way to avoid static electricity in non-conducting liquids is to keep the velocity down.

It is not possible to earth a non-conductive material.

Adding earthing wires to non-conductive systems is like putting a lightning conductor up in a thunderstorm.

"Adding earthing wires to non-conductive systems is like putting a lightning conductor up in a thunderstorm."

Actually, a correctly grounded, sharp pointed, high (compared to other surrounding objects) lightning conductor can emit or receive enough charge to reduce the field intensity in that region and reduce the probability of a lightning strike to that area significantly,

Now if you were referring to installing that device during a thunderstorm, that's a whole different story...

You asked me how I got rid of it, not how to measure it. The iron filings used to accumulate on the inner surface of the plastic, they don't collect any more, so I know my method works. But also, I was not using conductive polyethylene tubing, which you SHOULD use when working with potentially explosive atmospheres. I was just cheaping out here...

(And yeah....I grounded the wire to the frame of the machine, which in turn is grounded to the ground conductor on the plug. Which in turn is grounded to a spike in the ground. I thought that went without saying...grin!) However, I note that this method is not recommended on at least one site because they feel that a single wire doesn't provide sufficient wide spread protection. However, they point out that it is better than nothing. The answer of course, is to replace all that plastic tubing with metalic ductwork. They you won't have ANY problem.

Copper will conduct with less voltage drop than galvanized wire, however static electricity has no amperage, and therefore who cares about the voltage drop. I would suggest however that you check with the manufacturer of your system, and see what they recommend.

http://www.scif.com/safety/losscontrol/Article.asp?ArticleID=627

one more question is do electrostatic charges accumulate only in outer side of the pipe or also in the inner side of the pipe. Also when say explosion happen inside or outside the pipe since we are cleaning differnet types of material such dust,flour,bran....etc

The charges are originally generated by the motion of the particles and gasses inside the pipe, but as soon as there is any accumulated charge inside, those charges will attract opposite charges on the outside. You then effectively have a large capacitor, sort of like a large Leyden Jar, but with no conducting plates, so it can't discharge quickly. An appropriate conductive path from the outside to the inside of the tube will prevent the accumulation of significant charge. Perhaps a coating of aluminum foil or conductive paint would help. There must be someone, more expert than I, on the subject!

To have the explosion, you must have the standard: fuel, oxidizer, and ignition. Your dust is the fuel, the air is the oxidizer, and the static spark is the ignition. Prevent the spark and you have no explosion. Outside the pipe, there should be insufficient dust (fuel) to allow the explosion unless you are in a silo or something of the kind (or if the vacuum system has not been used regularly, so dust has accumulated). I am aware of one explosion (don't remember where or when) that was caused by the ignition of accumulated sugar powder on the ceiling beams, so it can happen...

It is very good that you are aware of the danger and doing something about it!

I want to ask do the electro static charges build in inner wall of PVC pipes or only outside because this may cause dangerous problem if generated inside.

Unless I'm mistaken, YES, charge will accumulate on the inside of the PVC pipes.

BUT:

1. The entire inside of the pipe will be charged the same way, so there is little to no ∆V between different points inside the pipe, so no problem with sparks there.

2. Since the charge is accumulated on the surface of an insulator, it is not free to move around rapidly, so no significant current can flow.

3. The flowing dust could carry a charge, like one side of the belt of a Van-de-Graaff generator, but if metal parts at both ends of the tube are properly grounded, the charge will be carried away as fast as it arrives, so there will be no accumulation of charge, therefore no chance of spark.

If anyone has evidence to the contrary, please give that evidence!