Comparing the Differences Between Elastic Soft and Hard-Sealed Gate Valves

Hard sealing involves a metal-to-metal seal, where both the sealing sphere and the valve seat are made of metal. This type of sealing requires high machining precision and advanced manufacturing techniques, making it typically suitable for high-pressure applications—usually above 35 MPa. In contrast, soft sealing uses a metal-to-nonmetal interface, such as nylon or PTFE, while still adhering to the same manufacturing standards.

　　1. On sealing materials

　　Elastic soft-seal gate valves and hard-seal gate valves refer to the sealing materials used for the valve seat. Hard sealing involves precisely machining the valve-seat material to ensure tight fit and precise alignment with the valve core (typically a sphere), commonly made from stainless steel or copper. Soft sealing, on the other hand, uses non-metallic materials embedded in the valve seat as the sealing element. Because soft-seal materials possess some elasticity, the precision requirements for manufacturing are relatively lower compared to hard sealing.

　　II. In Manufacturing Processes

　　Due to the complex working environments in many chemical and mechanical industries—often involving high temperatures, high pressures, significant media friction resistance, and strong corrosiveness—advances in technology have now enabled the effective use of a wide range of materials. As a result, manufacturing processes have improved significantly, allowing hard-sealed ball valves to be widely adopted and increasingly popular across these sectors.

　　Actually, the principle behind hard-sealed gate valves is the same as that of soft-sealed ones—however, since the sealing occurs directly between metal surfaces, it’s crucial to consider the hardness relationship between the metals, as well as the specific operating conditions and the type of medium being handled. Typically, hardening treatments are required, and the ball and valve seat undergo continuous grinding to achieve a reliable seal. As a result, hard-sealed gate valves have longer production cycles and more complex machining processes, making it challenging to manufacture high-quality hard-sealed ball valves.

　　III. Usage Conditions

　　Soft seals generally achieve very high sealing performance, while hard seals can be tailored to meet requirements—either high or low—as needed. Soft seals require fire resistance because, at elevated temperatures, their material may start leaking, whereas hard seals do not suffer from this issue. Hard-seal valves are typically capable of handling much higher pressure levels, a capability that soft seals lack. Additionally, soft seals are unsuitable for certain applications due to the nature of the media being handled—for instance, in cases involving corrosive substances. Finally, hard-seal valves usually come with a higher price tag compared to their soft-seal counterparts. In terms of manufacturing, the two types aren’t significantly different; the main distinction lies in the valve seat: soft seals are made of non-metallic materials, while hard seals use metallic ones.

　　4. Regarding equipment selection

　　The selection of soft- and hard-sealed gate valves primarily depends on the process medium, as well as temperature and pressure conditions. Generally, if the medium contains solid particles, is abrasive, or operates at temperatures exceeding 200°C, a hard-sealed valve is recommended. Additionally, for valves with diameters larger than 50 mm and significant pressure differentials, the required opening torque should also be considered. If the torque is particularly high, a fixed hard-sealed gate valve is the better choice. Notably, both soft- and hard-sealed valves can achieve a sealing grade of up to Class 6.