Abstract: An oil filter unit at the pot body bottom of the machine body. The valve of the oil filter unit is at the rocker unit opposite end, and the other end is against the knob unit. The rocker pivot is located on rocker seat and entrance of oil box is located under the panel. The key point is that the knob unit of knob cover and knob. The knob cover is cylinder-shaped while the center of inner cylinder is equipped with column cover. Edge opening is located at the rocker end inside the knob cover and the opening is symmetrical to the balance slot in the center of the cylinder. The balance slot is against the rocker knob cover end for limit while one inner end of the balance slot is equipped with limit plate. The knob cover is driven by knob to realize rocking between knob cover and rocker.