Generally, the sealing of ball valves is divided into soft sealing ball valve and hard sealing ball valve according to the ball valve seal material. The hard seal of the ball valve is the metal-to-metal seal, and the valve body and seat are all made from metal. They are used for those working under high pressure which is usually greater than 35Mpa. While the soft seal is the metal-to-nonmetal seal with nonmetal materials such as nylon and PTFE. The hard and soft sealed ball valves have the same manufacturing standard.

1. Soft Seal Ball Valves

Soft seal ball valves are that one side of the sealing is made of metal and the other side is made of flexible non-metallic materials. Soft seal ball valve has good sealing but poor resistance of high temperature, abrasion and mechanical properties.

In general, soft seal seat made of non-metallic materials has certain intensity, hardness and high temperature resistance to ensure zero leakage. Nevertheless, service life and adaption to temperature is worse than hard seal ball valve. Besides, corrosion resistance of soft seal ball valve to some corrosive medium cannot meet the technological requirements.

 

2. Hard Seal Ball Valves

Both two sides of sealing pair are made of metal materials or other materials having high hardness. Hard seal ball valves have poor sealing but high temperature resistance, abrasion resistance, and the mechanical properties are better than soft seal ball valve.

3. Differences

The ball valve seat serves for sealing the fluid inside and uniformly distributing the seating stress. In soft seat ball valve designs, either the elastomer or polymer can be used as the seal. And due to different classification standards, thcharacteristics, performance and applicable working condition can also be different.

(1) Structural Mechanism

The Soft Seal Ball Valve

The Hard Seal Ball Valve

In terms of structural mechanism, soft sealing ball valve is easy to achieve good sealing effect and resistant to corrosion, acid and alkali. And without high temperature resistance, the sealing surface being easy to wear, relatively poor mechanical performance are the defects. This kind of ball valve is used for the working condition of high sealing performance, containing corrosive medium but no particles and normal temperature and pressure.

Oppositely, the hard sealing ball valve is with high temperature resistance, wear resistance and good mechanical properties. And its has disadvantage of poor sealing performance. It is recommended to choose hard sealed ball valve like ZJCLV trunnion ball valve if the medium contains solid particles or the medium temperature is higher than 250℃.

(3) Manufacturing  Standards

From the principle point of view, the hard-sealed ball valve and the soft-sealed ball valve are the same, but because it is a seal between metals, it is necessary to consider the hardness relationship between the metals, as well as the working conditions, and what medium to go. Hardening treatment is generally required, and continuous grinding between the ball and the valve seat is required to achieve a seal. Hard-sealed ball valves have a long production cycle and complex processing. It is not easy to make hard-sealed ball valves.

(4) Usage Conditions

In terms of conditions of use, generally soft seals can reach a high level, while hard seals can be high or low according to requirements. Hard seals can generally be used at very high pressures, while soft seals cannot. Soft seals need to be fireproof, because at high temperatures, the material of the soft seal will leak, but the hard seal does not have this problem. The soft seal cannot be used in some occasions due to the problem of the flowing medium (such as some corrosive media). Finally the hard seal valve is generally more expensive than the soft seal. As for manufacturing, there is little difference between the two, mainly the difference between the valve seat, the soft seal is non-metal, and the hard seal is metal.

The above is the main difference between the soft-seal ball valve and the hard-seal ball valve. The specific purchase and use need to be determined according to the actual use. There is no difference between the advantages and disadvantages of the two.

In fact, hard seal ball valves have the same sealing principles as seal ball valves. Owing to metal-to-metal sealing, hardness between metal and metal, operating conditions and media should be taken into consideration. In general, ball valves are required to be treated by harden. Core and seat need to be grinded constantly to realize sealing.

Hard seal ball valves have long production cycle and complex processing procedures. So, it is not easy for manufacturing hard seal ball valves.

4. Selection 

Choosing hard or soft seal ball valves mainly depends on media, temperature and pressure. In general, hard seal ball valves are better to be used due to media containing solid particle or having abrasion or the temperature higher than 200 degrees centigrade. For valves having high differential pressure, torque also should be considered. Trunnion hard seal ball valves are suitable for large torque. If you need a ball valve with better sealing performance, you can also choose a double seal ball valve.

In short, valves have quite high technical content. Various aspects must be noticed. Different working conditions require different valves and sealing rings.

Use of soft and hard seal ball valve is different, mainly depends on structural, different standards to the manufacture of the valve.

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