With the development of fracturing and acidizing application technology, fracturing pumps with high pressure and large flow are required. The working condition of fracturing pump is extremely bad: high pressure, high acidity, high sand content and high sand hardness. Poor working conditions make the service life of the plunger pump seals short and the maintenance frequent. Sometimes, the seals made of rubber and plastic are broken, and a large amount of pumping liquid is ejected into the crankcase at the power end, causing serious deterioration of the lubricating oil in the crankcase and loss of lubrication, resulting in serious wear, ablation and corrosion of some key parts in the crankcase (such as crosshead, gear, pull rod, bearing, etc.), leading to major accidents. A key problem encountered in the development of fracturing pump is the sealing of plunger.

The plunger can only do linear reciprocating motion when constrained; After the plunger is sealed, the pressure cap has a pressing and adjusting effect on the seal; The sealing body is composed of three rubber seals and three PTFE backing rings. This structure can ensure that the sealing rings work in turn, that is, when the first sealing ring loses its function, the pressure difference is transmitted to the second sealing ring, and the second sealing ring can also play a sealing role, so as to improve the overall service life; The back-up ring is an important component supporting the V-shaped sealing ring; The function of the pressure ring is to form an initial compression amount for the V-shaped sealing ring to make it fully contact with the sealing surface. The end face width of the pressure ring should be slightly smaller than the cavity width, and the gap between it and the plunger is about 0.12-0.20mm, so that the pressure can better act on the sealing lip to make it fully open. The small hole on the sealing function is the inlet of forced lubrication. It is obvious that the unclean pumped liquid will damage the seal. The fracturing pumps produced at home and abroad take the following measures: inject engine oil into the small hole on the seal body, and the injection pressure of engine oil is slightly higher than that of the whole pump. Its purpose is not only to provide good lubrication between the plunger and the seal, but also to form a high-pressure oil film between the plunger and the seal to prevent unclean fracturing fluid from entering the sealing gap and protect the seal.

Two kinds of sealing materials are selected: one is woven polytetrafluoroethylene, which has the characteristics of small friction coefficient, high strength and wear resistance; The other is cloth rubber, which has the characteristics of good elasticity, high strength and wear resistance. These two materials are more suitable for high-pressure plunger sealing occasions.