Dear Neeta,

1st consideration

A multiple feed points vacuum pneumatic conveying system requires that, when sucking from one feeder point, the other 3 feeder points are closed off from the system.

Sucking from the closest point to the filter receiver and vacuum pump, there should be no influence from the other 3 feeding points, even when they are leaking air, as this leaked air is still used for conveying.

However, when the furthest feeding point is in operation, the 3 other feeding points, if not properly closed off, could leak air into the conveying line.

This causes the airflow at the furthest feeder point to become too low to keep the particles in suspension and a blockage could occur.

2nd consideration

You are also indicating that the air mover is a fan.

I understand that as referring to a centrifugal fan.

A centrifugal fan has the property of delivering less mass flow of air at higher vacuums.

Conveying over a longer conveying length require more vacuum at the same capacity.

This higher vacuum results in a lower (probably a too low) airflow and the pipeline chokes.

The further feed points should be feeding less material into the pipeline than the closer feed points.

A centrifugal fan is not the first choice in a pneumatic conveying system, as the fan curve leads easily to instable conveying conditions.

A remedy could be a feed control system, based on the fan vacuum, which is actually keeping the airflow above a minimum value and thereby keeping the system actively stable.

A positive displacement pump (Roots type blower or screw compressor) does not have this problem of reduced airflow at higher vacuum.

If the 2 situations are combined, the system should be evaluated and probably re- designed.

Does your design calculations take into account the fan curve? (flow=function(vacuum))

As you have not supplied the installation description (material, pipe routing, filter area, fan curve, etc.), I cannot execute an indicative computer calculation.

If you are interested, submit the necessary info.

If you want to do this privately, use the private message feature of this forum.

Have a nice day

Teus ■

Dear Neeta,

A vacuum system with 4 feeding points operating simultaneously is strongly NOT advised.

There are 2 installation configurations to consider:

1-A parallel system, whereby each feeding point is connected to the same filter receiver with one vacuum pump.

This is a NON working system, because it is not possible to divide the airflow equally over the 4 pipelines under all circumstances.

Suppose one feeding point is not feeding, then that line acts as a short circuit for the other 3 pipelines, which will choke, because there is no airflow.

2-One suction pipeline, with feeding points at certain distances into this pipeline. (A series system)

The airflow is the same for all the 4 feeding points.

However, the feeding points determine the pressure drop in the various pipe sections.

If feeding point 1 is feeding too much material, this must be compensated by one or more of the other feeding points, in order to prevent a too high vacuum. (This is extra complicated by the centrifugal fan curve)

It is hard to believe that such a system can be stable.

Any system between a parallel system and a series system has a combination of the above mentioned disadvantages.

Is the indicated capacity of 1 ton/hr for the 4 feeding points combined or per feeding point?

In downward conveying, the potential energy of the material is regained and decreases the pressure drop (or even increases the absolute local pressure, if the gained energy is more that the energy losses, caused by conveying).

Best regards

Teus ■

Originally Posted by Neeta

Dear sir ,

Thanks for your reply.

I want to convey the material simultaneously from four feed point. So during conveying it should suck the material from all four points not from only the closest feed point. For that what we should take care that it will not suck the material form nearest feed point.

System is in SS-304 , capacity 1TPH , Conveying distance - 26 mtr.

Also help me rgarding vacuum or pressure conveying in downward direction. It it parctically workable ?

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++

Dear Neeta,

Vacuum type pneumatic conveying systems can be designed to simultaneously suck (feed) material from four feed points. You have to make sure that the conveying velocity at each point is enough, acceleration length after each point is enough, and the inwards leakage flow from each feed point is added to the capacity of the vacuum blower.

Regards,

Amrit Agarwal

Pneumatic Conveying Consulting

Email: polypcc@aol.com ■

Dear Neeta, Amrit,

Easier said than done under all possible circumstances.

Regards,

Teus ■

Dear Neeta,

With each reply, we get more information.

I understand that the vacuum installation is also used as a mixing system.

The 2 mixing ingredients can have different pneumatic conveying properties, which influences the design.

To have a determined and precise mixing, the feeding points must be metered exactly.

This requires accurate rotary valves or feeder screws for each feeding point.

If the feeders are located in series in the system, whereby they feed into the same pipeline is one after another (or at the same location) in the main pipeline, a system can be designed that conveys the material.

The feeder capacity is known and constant.

Feeding into 4 different, parallel conveying lines is strongly NOT recommended, due to the very difficult division of convey air over the (then) 4 pipelines.

The material outlet of the cyclone must have a rotary valve, to seal off the vacuum. (Or pressure)

The application of a centrifugal fan as air mover in a pneumatic conveying design is a challenge in itself, as the pneumatic conveying calculations must account for the fan curve.

A centrifugal fan delivers less air at higher vacuum.

Another issue is that a fan has only a limited vacuum and as the air-only resistance is a significant part of the total pressure drop, the available vacuum range for conveying material is very small.

There is no room for allowing calculation errors or inaccuracies.

A PD pump (rotary lobe blower) would be a wiser choice.

The system has then to be designed for the maximum allowed vacuum. (Cyclone)

The discussed system has 4 feeding points and one receiving point and normally a vacuum system would be chosen.

However, the requirement is that the 4 feeding points have to be in operation at the same time simultaneously and that is only feasible when the feeders are positioned in series into one pipeline.

The same system can also be built as a pressure system, using exactly the same layout.

The only difference is the location of the air mover.

The layout of your piping diagram (geometrically) becomes now very important whether your system is workable or not.

Take care

Teus

PS.

Probably a cable/disc conveyor is a better solution.

See: http://www.cablevey.com/ ■