Analysis of the Sealing Principle of Electric Ball Valves

A, ball valve sealing principle analysis

Ball valves are generally composed of two parts: the stationary part (valve body) and the closing part (ball), which rotates 90º around the centerline of the valve body to open and close the valve. The ball uss the structure of the fixed shaft ball valve and its sealing principle.

The sealing of electric ball valves against gas media is achieved by the soft seal formed by the close combination of the ball and the seat seal. The sealing principle of the seat in electric ball valves varies with the seat construction and can be divided into two main types: double piston effect (DPE) and downstream self-releasing (SR).

The downstream self-releasing design ball valve is now mainly used in liquid pipelines, so this paper focuses on the double piston effect (DPE) design ball valve, which is widely used in gas pipelines.

1. Double Piston Effect (DPE) valve seat structure and sealing principle analysis

In the following schematic diagram of the Double Piston Effect (DPE) sealing structure, the forces are described as follows.

FF-Seat spring force F△A-Stem line/valve cavity pressure acting on the seat

FR - combined force on the valve seat A - combined force area

As can be seen in Figures 2.1 and 2.2, with the double piston effect (DPE) seat as the object of force analysis, the force on the seat from the mainline and cavity pressure is FR= FF+ F△A, with the combined force FR always pointing in the direction of the seat, i.e. both the mainline and cavity pressure cause the seat seal to press against the ball, always achieving a good seal on the seat of the ball valve.

Fig. 2.1 Schematic diagram of the Double Piston Effect (DPE) construction and sealing principle (mainline pressure on the valve seat)

Fig. 2.2 Schematic diagram of the Double Piston Effect (DPE) construction and sealing principle (pressure on the valve cavity against the valve seat)

Both seats of the ball valve are designed with a double piston effect seat design, i.e. a double piston effect (DPE) design, which ensures that both seats of the ball valve are sealed simultaneously. The double piston effect seal is a standard design requirement for Grove B-5 ball valves with counterbalanced orifices. Due to the good sealing performance of the double piston effect construction, many valve manufacturers have in recent years started to make extensive use of ball valve designs similar to the double seal construction.

In practice, improper maintenance of DPE ball valves or improper specification of certain DPE ball valve designs or selection of seal materials, supported by the excellent sealing design of these DPEs, has been one of the main causes of ball valve lock-up.

valve can be divided into two types of fixed shaft and floating shaft ball valves, we mainly disc