Hi Guus,

Pulse-jet cleaning is achieved partly by the propogation of a shock wave down the length of the filter bag, partly by reverse flow of the compresssed air and also by cleaned process air being entrained by the jet.

The venturi is intended to enhance the cleaning action by entraining more of the cleaned process air.

Bag filter makers differ about whether venturies make any difference to the efficiency of cleaning. Some use them, many don't.

All makers will have done testing of various arrangements (or copied someone else's). Their results will be proprietary and not available to the rest of us.

The flow characteristic of the pulse valves is probably more important than venturis. Note, the pressure loss across the tube plate will be higher with a venturi than without.

Bags up to 8 m long are cleaned without them in many applications.

Cheers,

Michael Reid. ■

I reckon you've got the makings of a good university research project here. ■

In the early days, a lot of pilot scale testing was done by various makers to determine the optimum shape for a venturi, for pulse tube diameters, for nozzle hole sizes etc. Venturis were considered to be essential for conserving compressed air and enhancing reverse flow. Filter bags were rarely longer than 4 m.

Later, the larger, global companies began to use longer and longer filter bags (f.i., when converting electrostatic precipitators to bagfilters) 8 m and above. At the same time, they developed their own improved systems including new pulse valves.

In simple terms, the cake of dust is supposed to break away from the surface of the filter bag when it comes to a sudden stop when fully inflated. There should be some residual dust left in the surface layer of the fabric. It is this “filter cake” which does the actual filtering. The shock wave is probably more important than the reverse flow.

Hope this helps.

Cheers,

Michael. ■

I just trawled Google

http://www.steelspinnings.com/SteelS...s/Welcome.html

http://www.metalspinningdirect.com/

http://www.spin-tec.co.uk/ ■

Originally Posted by Dusty Mill

Dear All

One of our pulse jet filters has got a whole load of damaged alloy venturi sections. The filter manufacturer is only interested in selling us a new filter! I am therefore looking for a UK supplier who can manufacture such an item, I believe they are made using a spinning process.

Can anyone help?

Half a world away, but I am getting the same reaction from dust collector suppliers here.

You can go the expensive way and try and have exact duplicates made, however you can also make something that is a close enough match using two cones and a short straight section of straight tube.

You are in the fortunate position where you appear to have ready access to your existing venturis, whereas I am having to "wing it" because my client does not have damaged ones, but we are trying to build ourselves a small 5 bag filter over a charge hopper. The only filter that has venturis is in operation and it is a case of having to wait over a month before we will get access when the dome of the dust collector will be removed for a clean down. For some reason, the filter manufacturers are reluctant to sell these items separately.

You could also try http://www.slyfilters.com/replacement-parts/cages.html

You may have better luck logging in. For some reason, I cannot find where to register for the technical literature.

I have been trying to get standard concentric reducers, however the ones I have managed to locate have a standard length. It might be a case of finding someone to make up the two cones of different lengths and get them welded together with a short straight piece.

The venturis here are cast aluminium and not stainless steel.

Good luck, and I will be checking to see if you have been able to find something. ■

Just a follow up

I mentioned http://www.slyfilters.com/replacement-parts/cages.html who were very helpful. They told me who the agents were in Australia (Goyen) where I was able to get some information on their venturis. I was contacted by Goyen/Tyco and they are coming out to see how things go.

Interestingly, while waiting for contact I decided to investigate concentric stainless steel tube reducers. Given we use 6" cages elsewhere, I tried a 6" x 3" reducer and then showed a 40 mm length of straight 3" tube welded to the small end.

It turns out that this was pretty close to what the venturis are. It gives me some flexibility depending on availability.

Anyhow, if you can't get the spun ones, you can get a shop to make them up out of tube and reducers. ■