The wearing of components is one of the most common problems in pneumatic conveying system and certainly one of the most frustrating. It does not only lead to deficiencies but may also impact your overall production flow. Especially in running systems where the rotary valve is feeding the pneumatic conveying system, wearing is not always easy to detect. As dismantling the system outside of your regular maintenance cycle is a time-consuming task, you should have a strong suspicion that progressed wear of your valve is causing the problem before dismantling.
So what are the signs your rotary valves are affected by wearing?
Drop in the conveying rate – The number one factor that your valves are wearing
Without being product specific the first notable sign would be a drop or reduction in the conveying rate. Generally speaking, it would be most evident in a pressure conveying system due to the higher air leakage passing through the clearances on the rotary valve. Air typically follows the path of least resistance; thus as more air is moving up into the feeding hopper, feeding device (such as a screw conveyor), or whatever device you have feeding the rotary valve, the system airflow will continue to drop. The result of additional air leakage at the rotary valve may also affect the blower’s ability to consistently convey the material in the conveying line. If the leakage becomes excessive, the system airflow may cause your material to drop below the required pickup velocity. Pickup velocity is the minimum velocity that is needed to convey your material. The condition is often times referred to as slugging, which can be identified as an irregular swooshing or rushing noise in the conveying line. As the rotary valve wear worsens, pressure spikes and the slugging will become even more evident until finally the air loss becomes too high and the line will plug.
How to detect that your rotary valve is wearing in a vacuum system?
With a vacuum system it is harder to identify a wear problem with your rotary valve. In some cases a slight increase in the overall vacuum and rate will happen as more material is able to leak past the clearances. In fact, in most cases, a rotary valve would have to be worn severely in order to see a significant change in the system rate (subject to blower performance). As the valve wear becomes worse the vacuum may tend to convey higher volumes of material and eventually plug the line.
If you suspect your valve is exhibiting signs of wear the sure shot method for detecting the problem is to inspect the clearances in your rotary valve and compare them to the manufacture’s specification for proper valve tolerances. If the variance is significant, you will have your answer.