The fault is characterized by a slow descent of the drill pipe after the stop. The reason may be floating solenoid valve stuck or brake skid and so on.
if the floating solenoid valve is stuck, even if it does not stop, the drill pipe may fall slowly. At this point, you can open the floating solenoid valve, the valve will be removed, cleaned, or replace the valve. Long wearing of the
brake will cause it to fail to provide sufficient braking force, which will cause brake failure and slow down of the drill pipe. Replace the brake pads at this time.