An actuated butterfly valve can leak due to a possible maladjustment in the seat or the thrust bearing found. If this happens, the valve needs to be opened and adjusted for repairs. These faulty adjustments are usually caused by long periods of use.
Step 1 – Detach the Actuators
Ensure that the electric supply or the compressed air is detached from the pneumatic or electric actuator. Check the mounting devices connecting the flanges to the mounting bracket. Unlock the bolts or loosen the nuts. The nuts should be loosened in a counterclockwise direction. Detach the mounting bracket and the actuators as well. Locate the position indicator and detach it as well.
Step 2 – Adjust the Seat
Remove the mounting hardware securing the flanges. Disconnect the flanges and turn the butterfly disk to inspect the seat. Check if the seat touches the disk edge. If it is not, adjust it until it touches the disk edge. To do so, locate the bolts on the seat that allow it to be adjusted. Move the bolt until the seat is correctly adjusted. Test the disk to see if it seals completely when closed.
Step 3 – Replace the Seat
If the seat appears to be damaged, then it has to be replaced to stop the leaks. Detach the butterfly disk from the unit and remove the seat assembly. At the base of the butterfly spindle detach the bushing and plug, turn the disk open so it can allow the seat to be removed. Squeeze the seat and pull it off at the end of the spindle. Slide the butterfly disk shaft end as well to remove it.
Step 4 – Install the Replacement
Purchase a replacement that is made exactly for the particular butterfly valve model you are repairing. Check the service manual for the product number or product part. Lubricate the butterfly disk spindle as well as the new seat with a sanitary lubricant. While the butterfly disk is in the open position, insert the spindle into the seat hole. Insert the disk and the seat assembly in between the flanges while the disk is in the open position. Re-attach the bushing and the plug.
Step 5 – Re-attach the Actuators
Mount the flanges to secure the butterfly disk and re-attach the position indicator. Re-install the actuators and the mounting brackets. Afterwards, connect the compressed air or the electrical supply. Test the actuated butterfly valve if it works correctly.
Step 6 – Adjusting the Thrust Bearing
If there is gap at the bottom or top of the valve after repairing the seat, adjusting the thrust bearing will solve the problem. Locate the lock nuts securing the thrust bearing and loosen them. Adjust the lower nuts uniformly until the butterfly disk is either raised or lowered depending on the gap. When a uniform seat compression is reached, stop the adjustments. Turn on the valve and check for any other issues during operation. If none is found, the adjustment process is successful.