Differences Between Hard Sealed Ball Valves and Soft Sealed Ball Valves
Abstract: As for hard-sealed ball valves, metal/hard materials are used for high temp/pressure (up to 800℃/42MPa). Soft-sealed valves employ elastomers (PTFE/EPDM) for zero leakage in clean systems (≤200℃). Selection depends on conditions (temp, pressure, medium) and cost priorities.
Hard sealed ball valves and soft sealed ball valves are two core types of valves in industrial pipeline systems, and their differences stem from sealing materials, structural design, and adaptability to operating conditions. The following analysis will be conducted from three dimensions: technical principles, performance characteristics, and application scenarios:
1. Sealing mechanism and material properties
Hard sealed ball valves: rigid mechanical seal
The core principle: The sealing is achieved through direct contact between the sealing surfaces of metals (such as stainless steel, alloy steel) or hard non-metallic materials (such as ceramics, tungsten carbide). The sealing surface needs to be precisely ground or coated with a hard layer (such as tungsten carbide spray), and a micrometer level gap seal is formed using mechanical pressure.
Material characteristics:
Temperature and pressure resistance: The working temperature can reach -20 ℃ to 600 ℃ (high-temperature alloy materials can reach 800 ℃), and the pressure resistance range is from 1.6 to 10MPa (up to 42MPa).
Wear resistance: It is suitable for solid particles and crystalline media (such as slurry and coal powder), with a sealing surface wear rate of less than 0.01mm/year.
Chemical compatibility: Nickel based alloys (such as Hastelloy C-276) are resistant to strong acids and alkalis, while titanium alloys are suitable for corrosive environments such as seawater.
Soft sealed ball valves: elastic deformation seal
The core principle: Elastic materials such as rubber (NBR, EPDM) and plastic (PTFE, PPL) are used as seals, and the gap between the ball and the valve seat is filled by the compression deformation of the material itself to achieve no leakage.
Material characteristics:
Temperature and pressure resistance: Working temperature -40 ℃ to 200 ℃ (PTFE can reach 260 ℃), pressure resistance ≤ 2.5MPa (partially reinforced up to 4.0MPa).
Sealing: Complies with API 609 Class VI standard, with a leakage rate of ≤ 0, suitable for scenarios such as pharmaceuticals and food that require zero leakage.
Chemical compatibility: PTFE is resistant to strong corrosion (such as aqua regia), and NBR is resistant to oil but not solvents.
2. Structural design and performance comparison
A. Hard sealed ball valves: precision machining and complex structure
Typical design:
Double eccentric/triple eccentric structure: reduces sealing surface friction and reduces switch torque by 30%.
Floating valve seat: The valve seat automatically adheres to the ball under high pressure, and it is suitable for the working conditions of Class 150 LB to Class 2500LB.
Fireproof design: Following API 607 standard, the metal sealing surface can still withstand pressure during a fire.
Performance limitations:
High processing cost: The flatness requirement for the sealing surface is less than 0.001mm, and the manufacturing cost is 2 to 3 times that of that if soft sealed ball valves.
High switching torque: it requires a gearbox or electric actuator, making manual operation difficult.
B. Soft sealed ball valves: simple structure and low cost
Typical design:
Floating valve seat: Spring loaded design, utilizing medium pressure to assist in sealing.
Full diameter structure: flow resistance coefficient ≤ 0.2, strong ball passing ability.
Sanitary design: The valve body has no dead corners, complies with FDA certification, and is suitable for the food and pharmaceutical industry.
Performance limitations:
Short lifespan: Rubber seals have an aging cycle of 3 to 5 years and need to be replaced regularly.
Poor vibration resistance: High pressure vibration environment can easily cause the sealing surface to loosen.
3. Adaptability to working conditions and typical applications
1. Core scenarios of hard sealed ball valves
High temperature and high pressure: such as steam pipelines in power plants (300 ℃, 4.0MPa) and petroleum cracking units (500 ℃, 10MPa).
Granular media: mining slurry pipelines (including quartz sand), coal chemical powder transportation (including dust).
Long term operation: natural gas long-distance pipelines (maintenance free for 20 years), submarine pipelines (corrosion-resistant titanium alloy).
Core scenarios of soft sealed ball valves
Civil and light industry: water supply and drainage system (water, sewage), air conditioning chilled water pipeline (≤ 120 ℃).
Gas and Low Corrosion Media: Compressed Air, Natural Gas Low Pressure Pipeline Network (≤ 0.4MPa).
Cost sensitive projects: municipal engineering projects with limited budgets, agricultural irrigation systems (priced at only one-third of hard sealing).
4. Key factors in selection decision-making
Medium characteristics:
Containing particles/high temperature → hard seal (wear-resistant and high temperature resistant).
Clean liquid/gas → soft seal (tight seal, low cost).
Pressure and temperature:
>200 ℃ or>4.0MPa → hard seal.
≤ 200 ℃ and ≤ 2.5MPa → Soft seal.
Leakage level:
Zero leakage requirements (such as pharmaceuticals, gas sampling) → Soft sealing.
Allow slight leakage (such as liquid bypass) → hard seal.
Economy:
Short term use → Soft seal (low initial cost).
Long term critical operating conditions → hard sealing (low maintenance cost).
The above is the specific difference between hard sealed ball valves and soft sealed ball valves. If you want to learn more about hard sealed ball valves, please feel free to consult us at any time.
