How to choose the right gate valve? Soft seal or hard seal? Selection guide for gate valves under different operating conditions.

Soft seal: Excellent sealing performance, but not resistant to high temperature and wear.
Hard seal: wear-resistant and temperature resistant, but zero leakage sealing is relatively more challenging.
Detailed comparison and selection guide.
1、 Comparison of core differences
2、 Selection guide: When to choose?
Priority selection of soft seal gate valve:
In situations where zero leakage is required:
This is the biggest advantage of soft sealing. For example, in urban gas systems and chemical medium transportation, there are strict requirements for leakage. The soft seal can achieve ANSI Class VI (zero leakage) sealing standard.

The medium is clean and particle free:
For example, tap water, drinking water, domestic sewage, non abrasive oil products, air, nitrogen, etc.
Low working temperature
Conventional soft sealing materials (such as rubber and nylon) are typically suitable for temperatures below 80 ° C; Enhanced PTFE (polytetrafluoroethylene) can reach up to 200 ° C. Hard seals must be used beyond this temperature.
Strict cost control for ordinary working conditions:
Under the premise of meeting the above conditions, soft sealed gate valves are a more cost-effective choice.
The situation where [hard seal gate valve] must be selected:
High temperature working conditions:
For example, steam pipelines (saturated steam, superheated steam), thermal oil systems, high-temperature flue gas, combustion systems, etc. The temperature usually exceeds 200 ° C.
Wear resistant media:
The medium contains particles, powders, ash, crystals, etc. For example:
Power plant ash removal system (fly ash)
Coal chemical industry (coal powder, slag water)
Pipeline for transporting slurry and mud
Cement industry
Chemical media with crystalline particles
High fluid (throttling condition):
Gate valves are usually not used for throttling, but in certain operating conditions that require partial opening, high-speed fluid can erode the valve seat. The erosion resistance of metal hard seals is much stronger than that of soft seals.
Special requirements:
Fire safety requirements: In the event of a fire, the soft sealing material will burn out and cause serious leakage, while the hard sealing gate valve can maintain a certain degree of sealing and comply with fire safety standards such as API 607/API 6FA.
Pigging operation: When a pipeline needs to be cleaned with a ball, it is required that the inner diameter of the valve be consistent with the pipeline, and a full bore hard seal gate valve is a standard configuration.
3、 Special solution: Combination seal
In order to balance the "zero leakage" of soft seals and the "temperature and wear resistance" of hard seals, combination sealed gate valves have emerged on the market.
Working principle: Valves usually use metal hard seals as the main seal, while embedding a soft sealing ring on the gate.
Working process:
When closed normally: the soft sealing ring first contacts and achieves ultra tight zero leakage.
Under high temperature or wear conditions: If the soft sealing ring is damaged, the metal hard seal serves as a backup seal to ensure that the valve is not completely penetrated and can still be used.
This type of valve combines the advantages of both, but has a more complex structure and higher cost.
summary
The decision process for choosing between a soft seal or a hard seal can follow the following steps:
Check temperature: Does the medium temperature often exceed 200 ° C? Yes → Choose a hard seal.
Check the medium: Are there hard particles or powders in the medium? Yes → Select hard seal.
Requirement: Do we need absolute zero leakage (such as gas) and mild operating conditions? Yes → Choose soft seal