Greetings from my corner of the frozen eastern wildernes @ 1140 feet above mean sea level.

your biggest problem will be cleaning the screen as it does not really matter who makes it for you.

If youy want an inline screen you will need to have butterfly clamps with flanged fittings or a "Victaulic clamp" mated to the entry part of the discharge line.

The problem is how big a screen? If you want a screen sized to the diameter of the discharge/delivery pipe it will take some time to fabricate it and at best you should have two of them one for actual useage and the second for a spare to replace the first while it is being cleaned.

The other option is to build an air tight box with

the screen facing in a backslash position to allow for dumping rock and quick return to service.

This is accomplished by building a hinged gasketed door and installing it on the bottom of the box and allowing it to swing down to allow the build up of material to drop out and not impede product flow.

The box could be made of oversize delivery pipe or a standard size welde box and by doing some welding you will have an easily done project with little trouble. It will take timne to make it but it can be done. If the screen

ever needs replacing all you would have to do is slip out the piece of screen as it is just resting in the frame of the box and replace it.

What ever you do do not use cheap material or components. ■

Wouldn't it be easier to screen the product before feeding into the p.c system?

Michael Reid. ■

Dear Mr Van der Putten

I assume from your question, that the pneumatic system is a pressure system.

Then it is not clear where the screen should be located.

At the beginning of the pipeline, where the pressure is high or at the end of the pipeline. where the pressure is almost atmospheric or somewhere in between.

The simplest way for separation of lumps from the cement should be on top of the silo, using an ordinary screen.

The application of a filter receiver in combination with a silo filter (both with ventilators, to control the pressures in the system) is well feasible.

The lumps should be taken out of the system by trickle valves or manually from a bin from time to time.

This is done before.

The design should be calculated properly and sized accordingly.

While operating the pressures in the system have to be monitored to secure proper working

best regards ■

Dear Mr Van der Putten

In case the bigger particles have to be separated right after the bulk truck outlet, the equipment used must be able to withstand a pressure of at least 3,5 – 4 bar(o), as the bulk truck can unload at 2,5 to 3,0 bar(o).

That can become a quite heavy structure in case a vibrating screen is used.

In some cement conveying installations a so called lump catcher is mounted.

For 2 mm lumps the aperture size should be less than 2 mm f.i. 1 to 1,5 mm.

In case the total area of the holes in such a lump catcher is large enough to let the cement (60 – 100 micron) with a velocity of approx 4 m/sec it might work.

But it is also possible that the differential pressure over that screen blocks the system.

Even if it works, I expect a considerable amount of wear, althoughthat can be solved by changing the screen frequently.

The volume of this lump catcher depends on how much lumps have to be catched from one bulktruck.

Another solution might be a lump crusher of sufficient capacity. The lumps will not be catched but crushed to a size below 2 mm.

success ■

I have read all the replies and agree with some:

1. scalping at truck is common and suits a vibrating screen application well.

2. I saw an angle mentioned at 30 degree, if you put wirecloth on a slope of 30 deg........you can put 2mm opgs and probably a little bigger, say 2.5 mm opgs to make your 2 mm cut FOR LUMPS. The fines will just pour through and any overs should be scalped off.

At a 30 degree slope, the material WILL NOT SEE the full opening in the wirecloth, DUE TO FORESHORTENING of the opening, created by the angle. So you can actually CHEAT UP a tad....and still do your CUT at 2mm.

3. LUMPBREAKER theory: This is a very viable suggestion as well, cement lumps are very friable, easily breakable and properly sized would be a possible solution.

Regards, ■

I understand it is not a lump catcher. It is a small lump scalper to remove oversize.

RPM on a screener like this would be around 1000 to 1200 RPM with a nominal 3/16" circle stroke size.

A test would be adviseable prior to buying on a lab sieve shaker unit. ■

Interesting, do you have a small vibrator on the stationary grid to help keep clean or? ■

Dear Mr Van der Putten

The systems to separate lumps or stones (less than 1 kg at 25 tonnes, which is very little),

which are discussed so far are :

A vibrating screen , a sieve and a lump catcher

A vibrating screen and a sieve work under gravity forces.

But, in a pneumatic conveying system, the convey air has to pass also through the screen or sieve, together with the cement and maintain pneumatic conveying at the same time.

(That is also the reason why the 4 m/sec is mentioned).

Then the screen or sieve operates suddenly as a lump catcher.

Actually we are trying to use the vibrating screen principle as a lump catcher.

I am afraid that I have to agree with all the arguments of RPD, that a 2mm separation in line with a pneumatic conveying installation will not work properly.

Greetings ■

Dear Sir

Have you considered the use of in-line Cyclone? Cement will flow with the air thrugh centrifugal outlet, while large particles will exit through bottom air lock. ■

A cyclone would cause too much pressure loss too soon at the position under discussion.

I presume the oversize will be trapped on the underside of the screen medium & the undersize carried on (against gravity) along the pipe. Oversize could then be driven to the downstream end of the screen by the impinging undersize if the angle was shallow. The usual clout with a rubber hammer would dislodge material into the screen underpan at the end of unloading.

Mesh support requirement would detract slightly from the otherwise substantial screen area & wear would be high; which is endemic in pneumatic conveying situations anyway. ■