Double-Sided Metal Sealed Floating Ball Valve

Abstract: The working principles and structural characteristics of the double-sided metal sealed floating ball valve are introduced. The sealing structure of the valve seat and the packing gland is improved, and the sealing performance and service life of the metal sealing floating ball valve are improved.

1. Overview
In some special industrial fields such as petroleum, petrochemical, electric power, steel, food, etc., the working conditions of the medium in the pipeline are very harsh, so there are very strict requirements on the valve, requiring that the valve seal can completely achieve zero leakage, and the working temperature is long at 300 ~ 600 °C, and requires a very short opening and closing time. In this very demanding field of use, one-way metal sealed floating ball valves have been widely used. During the frequent opening and closing of the valve, it is easy to cause leakage of the seal between the ball body and the valve seat, the stem, and the stem packing. Since the medium conveyed in the pipeline may be flammable, explosive, toxic or corrosive, and other mediums which are very harmful to the environment and society, the unpredictable danger may easily occur after leakage. Therefore, if the valve leaks, it must be repaired and replaced immediately. However, in order to meet the actual production needs, it generally require the long service life of the valve, and the shortening of the valve repair and replacement cycle mean that the production cost will increase drastically. Therefore, the user requires the valve to have better sealing performance and a longer service life. In this context, we have developed a double-sided metal sealed floating ball valve through extensive research and experimentation. The double-sided metal-sealed floating ball valve has improved the valve seat structure and the stem packing and sealing structure of the valve on the basis of an ordinary metal-sealed floating ball valve. While ensuring the sealing performance of the valve, it also increases the service life of the valve and prolongs the cycle of repairing and replacing the valve.

2. Structural Features
Double-sided metal sealed floating ball valve (Figure 1) mainly consists of valve body, bonnet, ball body, valve seat, seat packing, butterfly spring seat, valve seat butterfly spring, valve stem, stem packing, packing gland, stop screw , cover butterfly, handle and other parts.

2.1. Dynamic Load Packing Structure
The double-sided metal sealed floating ball valve (Fig. 1) adds a pair of capping butterfly springs 13 on the basis of the original ordinary metal sealed floating ball valve (Fig. 2), so that it can be combined with the valve stem 8, the stem packing 9, and the packing gland 10 together with the limit screw 12, to form a packing seal of the valve.

2.2. Piston Seat Structure
The double-sided metal seal floating ball valve (Fig. 1) adopts a piston-type seal structure at the front and rear seats. The ball body 2 and the valve seat 3 form a metal seal surface. The seat packing 4 and bonnet 5, the valve body 1 and the valve seat 3 are respectively formed non-metal seal surface, the butterfly spring holder 6 and the butterfly spring 7 constitute a pre-tensioning device for the valve seat, which provides a preloaded pressure ratio of the valve seat to ensure the sealing of the valve.

3. How it works
3.1. Double-sided metal-sealed floating ball valve (Fig. 1) is a bi-directional flow control valve. It is mainly used for cutting and conducting medium in pipeline transportation and other industrial fields, and is fully opened and closed. The ball valve has a piston-type elastic valve seat structure with a fixed ball valve and has a very compact structure. The front and rear valve seats are designed according to the principle of the front seat seal of the fixed ball valve. Therefore, the inlet and outlet valve seats can be sealed and have the advantages of double-sided sealing, which is suitable for occasions with high sealing requirements.

When the valve is closed, the medium pressure pushes the inlet valve seat against the ball body and the outlet valve seat, so that the inlet valve seat and the ball body, the ball body and the outlet valve seat achieve the purpose of sealing at the same time, and the zero leakage of the hard seal floating ball valve can be truly realized. Because the structure of the front and rear valve seats of the valve is the same, the valve can also achieve the purpose of double-sealing the inlet and outlet valve seats when the medium in the pipeline is flowing in the reverse direction. Therefore, the valve can be installed in any direction without being controlled by the direction of flow of the medium.

In addition, in the process of opening and closing, the ball rotates along the axis of the valve body. Since the butterfly springs at the front and rear of the valve seat are always in a compressed state, the inlet and outlet end valve seats can always be in close contact with the ball under the effect of the butterfly spring to ensure that the solid particles in the medium cannot enter the sealing surface and avoid abnormal damage to the sealing surface, so the double-sided metal sealed floating ball valve can be applied to conditions containing solid particles impurities.

3.2. Ordinary metal seal floating ball valve is often concentrated in the valve seat of the internal leakage, ignoring the leakage of the filler. With the increase in the number of valve switches, the internal leakage of the valve is still not present, the phenomenon of wear and leakage occurs at the point of contact between the packing and the valve stem, which greatly shortens the service life of the valve.

The double-sided metal sealing floating ball valve adopts a dynamic load packing structure, and a pair of capping butterfly springs 13 (Fig. 1) are added below the limit screw to increase the sealing preload of the packing and when the parts in contact with the valve stem wear out. Due to the existence of the capping butterfly spring, the sealing of the packing can be ensured at all times, which greatly prolongs the service life of the valve.

4. Conclusion
The double-sided metal sealed floating ball valve is very suitable for harsh working conditions in certain special industrial fields such as petroleum, petrochemical, electric power, and steel. It has great advantages, such as small installation space, double-sealed double seal, high temperature resistance, zero leakage, short opening and closing time. These advantages allow the double-sided metal sealed floating ball valve to have more extensive development space in special applications.