A negative pressure wound therapy apparatus can include a wound dressing, a fluid collection container, a vacuum pump comprising a pump motor, and tubing. In one advantageous embodiment, the polishing head comprises a wafer carrier having an outer periphery and a wafer holder. Therefore, when a control switch is replaced with another type, it is unnecessary to change the control device but just connect it to a corresponding control module, able to save manufacturing cost. A flange can be provided at a distal end of one or both of the roof and rib support arms, each flange projecting toward the mine roof or rib. The non-metallic fibers are predominantly oriented in one of the two orthogonal dimensions.