In-depth analysis of pneumatic connectors and threaded sealing types

Introduction
Threaded pneumatic fittings rely on threads for mechanical fastening, and their sealing performance depends on the choice of sealing form. Correctly understanding the type of sealing is the key to preventing leakage.

Comparison of main sealing forms

1. End face O-ring seal:

   • Structure: The joint end surface is equipped with a groove and an internal O-ring. When tightened by threads, it is compressed onto the flat end surface of the mating component to achieve sealing.

   • Advantages: reliable sealing, low requirement for thread machining accuracy, reusable, easy to disassemble and assemble.

   • Application: The international standard ISO 1179 interface is widely used in pneumatic and hydraulic systems.

2. Taper pipe thread sealing:

   • Structure: Sealing is achieved by relying on the plastic deformation of the thread profile itself (PT threads) or by using a sealing compound (NPT threads).

   • Advantages: Compact structure, no need for additional seals.

   • Disadvantages: High precision is required for thread machining, and repeated disassembly and assembly may easily lead to seal failure, thus it should be used with caution.

   • Application: Traditional pipeline systems, such as NPT (American Standard) and PT (British/Japanese Standard).

Key points of selection and installation

• Priority principle: In modern pneumatic systems, it is strongly recommended to use connectors with end face O-ring seals (such as those compliant with ISO 1179 standards), as their reliability and ease of maintenance are significantly superior to those with taper pipe thread seals.

• Thread identification: It is necessary to accurately distinguish between parallel threads (G) and tapered pipe threads (R/PF, NPT), and they must not be mixed.

• Tightening torque: Follow the manufacturer's specifications. Over-tightening may damage the O-ring or threads.

• Sealant usage: When connecting with taper pipe threads, select appropriate thread sealant or thread tape, and prevent it from entering the interior of the pipeline.

Common problems
Leakage at tapered pipe thread fittings is one of the most common installation issues, mostly stemming from mismatched thread types, improper tightening force, or thread damage. Switching to face seal fittings is a fundamental solution.