Difference between soft and hard seals in ball valve applications
In terms of usage conditions:
Soft seals generally achieve very high sealing performance, while hard seals vary depending on requirements. Soft seals require fire resistance because the material can leak at high temperatures, while hard seals do not have this problem. Hard seals can generally handle very high pressures, while soft seals cannot. Due to the nature of the media they handle, soft seals are unsuitable for some applications (such as corrosive media). Hard-seal ball valves are generally more expensive than soft-seal ones. In terms of manufacturing, there is little difference between the two, mainly in the valve seat; soft seals use non-metallic seats, while hard seals use metallic seats.
In terms of equipment selection:
The selection of soft or hard-seal ball valves mainly depends on the process medium, temperatuur, en druk. Generally, hard seals are preferred for media containing solid particles, abrasive materials, or temperatures exceeding 200 degrees Celsius. For valves with a diameter greater than 50 mm and a large pressure differential, the valve opening torque should also be considered. When the torque is high, a fixed hard-seal ball valve should be selected. Regardless of whether it is a soft or hard seal, both can achieve a sealing rating of Class 6.
In terms of structural mechanism:
Hard seals in ball valves are metal-to-metal seals, where both the sealing ball and seat are metal. Machining precision and processes are relatively difficult, and they are generally used for high pressure applications, typically above 35 MPa. Soft seals are metal-to-non-metal seals, such as those made of nylon or PTFE, and their manufacturing standards are the same.
In terms of sealing materials:
Hard and soft seals refer to the sealing materials of the valve seat. Hard seals use precision-machined valve seat materials to ensure a precise fit with the valve core (ball), typically made of stainless steel or copper. Soft seals refer to non-metallic sealing materials embedded in the valve seat. Because soft sealing materials have a certain degree of elasticity, the machining precision requirements are relatively lower than for hard seals.
In terms of manufacturing process:
Manufacturer environments in many chemical and mechanical industries are complex, often involving high temperatures and pressures, high frictional resistance, and strong corrosiveness of the media. Advances in technology and the use of various materials have improved, and machining processes have also kept pace, leading to the widespread adoption of hard-seal ball valves.
In fact, the principle of hard-seal ball valves is the same as that of soft-seal ball valves. However, because it’s a metal-to-metal seal, the hardness relationship between the metals, the operating conditions, and the medium being transported must be considered. Generally, hardening treatment is required, and the ball and seat must be continuously ground to achieve a seal. Hard-seal ball valves have a long production cycle and are more complex to manufacture; producing a high-quality hard-seal ball valve is not easy.
