Gravity discharge cement weigh batchers are the most common in the industry, but can be impacted by weather, plant air supply, mix design, free fall distance, and batcher design.  For a typical 200 YPH dry batch plant, the discharge rate should be 110 lbs. per second.  Physically a butterfly valve is used to control the flow, while being operated by the outputs (Open/Close Pulse) of an Automated Batch Controller.  The Batch Controller compares the actual discharge rate Vs the targeted rate within a pre-determined cycle window, and makes open/close adjustments as needed to match the targeted rate.  Ideally the initial opening of the valve should hit the target rate, with adjustments every 3-4 seconds as needed.  The adjustments should be minimal so as to not over correct and/or cause the controller to close the valve, only to have it re-open in full.

If the flow of the cement is random and un-controllable double check the following;
Proper aeration (dry air @ 15 psi) to the cement weigh batcher.
Weather impact – paint the inside of the cement weigh batcher to seal the steel pores from outside moisture.
Confirm Weigh Batcher Dust Vent is operational and properly sized.

A good butterfly valve is well balanced and does not restrict the actuation of the valves disk. The improper mounting of a butterfly valve between two steel flanges can restrict the actuation.  In addition too much air CFM to the actuator can over-throw the disk of which flow controls might need to be added.  In order to determine the proper size of a valve, calculate the valve opening area and multiple by 2 lbs. / square inch / second.

As always if you have any additional questions please don’t hesitate to call us at 1.800.434.3462.