As the upper thrust force on the upper valve core and the lower thrust force on the lower valve core are basically balanced, the entire valve core suffers from unbalanced forces. The features of the straight-through double seat valve are as follows.

1 The unbalanced force received is small and the pressure drop allowed is large. For example, the DN100 double seat valve allows a differential pressure of 280 kPa.

2 The circulation capacity is large. Compared with other control valves of the same caliber, the double seat valve can flow more fluid. The flow capacity of the same-caliber two-seat valve is about 20%-50/% larger than that of the single-seat valve. For example, the DN100 double-seat valve has a flow capacity of 160. Therefore, in order to achieve the same flow capacity, the two-seat valve can use a smaller thrust actuator.

3 positive body valve and reversing valve are easy to modify. Since the double seat valve adopts dual guides at the top and bottom, only the reversed installation of the valve plug and the valve seat can change the positive body valve to the reverse body valve, and the reverse body valve to the positive body valve, without the need to change the position of the actuator. Effect or reaction type. The double-seat valve structure shown in Figure 2-4 simply reverses the body and is connected to the stem.

4 large amount of leakage. The double seat valve's upper and lower valve cores cannot be closed at the same time. Therefore, the double seat valve has a large amount of leakage and the standard leakage is 0.1%C. When the poppet and valve seat of the double seat valve are used in different villages or used in low temperature or high temperature occasions, the amount of leakage caused by the different amount of expansion of the village feed line will be greater.

5 poor anti-erosion ability. The flow path in the valve is complex. In high pressure differential applications, the high pressure fluid scours more severely, causing flashing and cavitation of the fluid at high pressure differentials, which aggravates flushing of the valve body. Therefore, the double seat valve is not suitable for use. High pressure differential application places. Due to the complicated flow path, it is not suitable for the control of fiber-containing media and high-viscosity fluids.

Since the balanced sleeve valve can eliminate most of the static unbalance forces, the advantages of the double seat valve are not obvious, and the disadvantage of its large leakage volume is even more obvious. Therefore, in the industrial production process, the double seat valve was originally used. On occasions, a sleeve valve with a balanced structure may be used instead. Foreign manufacturers also use a two-seater direct-through valve of an overall structure to reduce the amount of leakage.