Difference between Soft‑seat and Hard‑seat Valves
Add time：2022/5/10 15:30:09 Page views：8885
First of all, whether it is a ball valve, butterfly valve or other valve types, there are both soft‑seat and hard‑seat designs. Taking ball valves as an example, soft‑seat and hard‑seat ball valves differ mainly in structure and adopt different manufacturing standards.
Soft‑seat Butterfly Valves
1. Structural Mechanism
For hard‑seat ball valves, sealing is achieved between metal‑to‑metal surfaces. Both the ball and valve seat are made of metal. They demand high‑precision machining and sophisticated manufacturing processes, and are generally applied under high‑pressure conditions, typically above 35 MPa.
For soft‑seat ball valves, sealing occurs between metal and non‑metallic materials such as nylon and PTFE. They follow identical manufacturing standards.
2. Sealing Materials
The terms soft‑seat and hard‑seat refer to the sealing material of the valve seat.
Hard‑seat valves adopt precisely machined metallic valve seats to ensure fitting accuracy with the valve core (ball). Common materials include stainless steel and copper.
Soft‑seat valves have non‑metallic sealing materials embedded in the valve seat. Thanks to the elasticity of non‑metallic sealing materials, the requirement for machining accuracy is relatively lower compared with hard‑seat valves.
3. Manufacturing Process
Many chemical and mechanical industries operate under harsh working conditions: high temperature, high pressure, high medium friction resistance and strong corrosiveness. Thanks to technological advances, improved material performance and mature machining techniques, hard‑seat ball valves have been widely promoted.
In fact, hard‑seat and soft‑seat ball valves work on the same principle. Nevertheless, for metal‑to‑metal sealing, factors such as metal hardness matching, working conditions and service media must be taken into account. Hardening treatment is normally required. Repeated lapping between the ball and valve seat is necessary to achieve effective sealing. Hard‑seat ball valves feature long production cycles and complex machining procedures, making them difficult to manufacture properly.
4. Service Conditions
Soft‑seat valves can generally achieve excellent sealing performance, while the sealing performance of hard‑seat valves can be adjusted according to actual requirements.
Soft‑seat valves require fire‑protection consideration, because their sealing materials may leak under high temperatures, whereas hard‑seat valves are free from such risks.
Hard‑seat valves can withstand much higher pressure than soft‑seat valves.
Due to medium compatibility, soft‑seat valves are not suitable for certain working scenarios, for example, services with corrosive media.
In addition, hard‑seat valves are usually more expensive than soft‑seat ones. From the manufacturing perspective, the two types have few differences except for the valve seat: non‑metallic for soft‑seat valves and metallic for hard‑seat valves.
5. Equipment Selection
The selection between soft‑seat and hard‑seat ball valves is mainly based on process medium, temperature and pressure.
Hard‑seat ball valves are preferred for media containing solid particles, abrasive media, or operating temperatures above 200 °C.
For valves with a nominal diameter larger than 50 mm and large pressure differential, the valve opening torque shall also be considered. Fixed‑type hard‑seat ball valves shall be selected when high torque is expected. Both soft‑seat and hard‑seat valves can reach sealing level VI.
Company News
Chinese
English
