You haven't said whether you think the airlocks are too small or whether there is some other problem. You should really have a settling volume/chamber between the cyclone and the airlock to provide steady feed.

Go to a manufacturer of airlocks and give them:

particle size,

bulk density,

flow rate,

pressure differential.

Michael Reid. ■

There are several points to consider:

1. Correct size and type of valve for the capacity

2. Size of discharge port on cyclone should match RA.

3. Leakage characteristic of RA

4. Differential pressure of RA

5. Temperature of material

6. Physical arrangement of equipment

7. Material physical and bulk properties (bulk density, particle size, hardness, Tg, etc.)

Since you are discharging from a dryer, I assume that the material is hot. If the material temperature is greater than 60C, the RA may need to have greater than normal internal clearances, which then causes higher leakage rates. If the leakage is not vented, then all of the leakage gas must travel up through the cyclone which has the effect of reducing the volumetric efficiency of the RA.

A leakage bypass vent can reduce, but will not eliminate, the leakage gas flow through the cyclone. You can make a connection from the RA leakage port (or adaptor port) to the conveying pipe at a positon immediately upstream of the cyclone inlet. A lateral connection, entering the pipe from above, angled towards the cyclone will provide a good way re-entrain the leakage gas, and any particles that carry-over, into the cyclone without disturbing the flow patterns inside the cyclone.

With more detailed information, we can recommend a valve for your application. Please contact me directly to continue.

Bob ■

If leakage is reducing your convey rate, its because the total vacuum provided by your air mover is now split between the leg of pipe which carries your product and the leakage across the valve, into the cyclone. The leakage is acting like a branch in your convey line, reducing the total vacuum available to move the product.

An easy way to determine leakage would be to tap a straight section of pipe on each side of the cyclone, then measure the airflow using a pitot tube and manometer. The location for your measurment should be as close to the cyclone as possible, in a straight run of pipe whose length is equal to 6-10 pipe diameters. The measurement location should be placed approximately in the middle of this pipe run.

Once the airflows before and after the cyclone are tabulated, the difference between the two will give you a good indication of the leakage into the cyclone through the valve. However, be aware that some leakage could also be occuring at other locations, such as flanged joints and pipe connections, that are located anywhere between the two measurements.

Leakage across the valve is inevitable, but can be controlled based on proper design and manufacturing processes that account for the actual internal operating temperature of the rotary valve. If proper operating temperature is carefully determined, the valve manufacturer can use this to provide you a valve with close tolerances between rotor and valve body when operating under actual conditions.

Our line of rotary valves are precision CNC machined for actual operating conditions, and can help minimize leakage. Combined with a inlet vent, we can help solve your dilema.

Please contact us directly to disuss the application further and for assistance in measuring vacuum.

Darrell Malczewski ■

Hello,

you might want to consider to measure the flow with a airflow meter. There are insertion probes available where you can measure pressure, flow, and temperature and have directly the calculated details on a datalogger. One design which is really innovative and that I like using is from Europe. You can buy these at Bolder Products Group in Vancouver or see www.monitoring-flow.com for the North-American markets.

Best regards

Tim Petterson ■

There are some valid suggestions already and to properly tackle the situation more information about the application is required. However, there are some basics to consider.

If you feel leakage is causing your convey issues it is because either the leakage is greater than it should be or was not accounted for in the original design.

Leakage being larger than it "should be" is a function of clearance on the airlock. Wear on the valve creating larger clearances is probably not an issue with plastic unless you see wear in other places in the plant as well. It is possible the airlock was designed for the elevated temp (with increased clearance) to account for the rotor growth. If actual temps don't reach the design temp, then the valve has artificially increased clearances. Replacing the valve with an adjustable tip valve would at least give you adjustability.

One thing that was not discussed is the effect of temp on your air movement device. Blowers, fans, etc will all be rendered less efficient when the convey air gets heated by the product. Check the discharge temp on the cyclone air outlet to analyze.

In any of the cases listed above, increasing the speed of your air movement device would alleviate the symptom of the problem, but this may not be possible.

Jonathan Thorn

MAC Equipment ■

Sure leackage from the rotary valve will hurt the feeding rate and reduce cyclone effecient.

You can modify your vacuum suck nozzle to increase the feed rate. ■

no vent for RA is necessary ■