The output valve coupling is another pair of precise coupling of the injection pump, whose shape is shown in figure 2-4. The oil injection pump adopts the up-set oil outlet valve. The top surface is the spring seat of the oil outlet valve, and the bottom is the conical valve surface, which falls on the conical surface of the upper part of the oil outlet valve seat. Four oil grooves are milled on the cylinder body. The cross section is a cross-shaped valve body. The valve diameter affects the flow section of the outlet valve. Between the body and the head, there is a convex shoulder with a precise fit with the seat hole, that is, the relief belt. When the relief belt enters the seat hole, the high pressure tubing is separated from the low pressure oil chamber that has formed in the plunger top. After that, the oil outlet valve drops another distance until the valve face is seated. This process expands the fuel in the high pressure tubing, causing the oil pressure to drop rapidly and the injection to stop quickly.