Hydraulic Pipe Fittings and Sealing Standards for Engineering Machinery

1. Purpose

This document aims to systematically outline the widely applied pipe fittings and sealing standards within hydraulic systems of engineering machinery, assisting design, procurement, and maintenance personnel in promptly identifying and selecting hydraulic connectors compliant with international regulations to ensure system safety and reliability.

2. Scope

Applicable to connections involving steel pipes, hoses, and hydraulic components within hydraulic circuits, with a maximum operating pressure of up to 630 bar, encompassing metric, imperial, and US customary thread standards.

3. Overview of Mainstream Connector Standards

Standard Number	Standard Name	Sealing Type	Thread Type	Typical Application
ISO 8434-1	24° Cone Connection Without O-Ring (Heavy/Light Series)	Metal-to-Metal (Cone Seal)	Metric Thread (M)	High-Pressure Hydraulic Systems, Construction Machinery, Injection Molding Machines
ISO 8434-2	37° Flare Connection	Metal-to-Metal (Flare Seal)	UN/UNF Thread	Aircraft, Low-Pressure Hydraulic & Fuel Systems
ISO 8434-3	O-ring Face Seal (ORFS)	O-ring Face Seal	UN/UNF Thread	High-pressure applications with stringent leak-tightness requirements
ISO 6149	Metric O-ring Port	O-ring (Axial Seal)	Metric Thread (M)	Ports of hydraulic pumps, valves, cylinders
ISO 1179	British Pipe Thread Port (with Elastomeric Seal)	ED Seal Ring (DIN 3869)	British Pipe Thread (G)	General Hydraulic Component Ports, Low to Medium-High Pressure
ISO 9974	Metric Thread Port (with Elastomeric Seal)	ED Seal Ring (DIN 3869)	Metric Thread (M)	Modern Design Replacing ISO 1179
SAE J514	37° Flare Fitting	Metal-to-Metal (Flare Seal)	UN/UNF Thread	North American hydraulic systems, fuel & lubrication systems
SAE J1453	O-ring Face Seal (ORFS)	O-ring Face Seal	UN/UNF Thread	High pressure & stringent leakage prevention requirements
DIN 3869	ED seal ring (compatible with ISO 1179/9974)	Elastomeric seal (ED ring)	—	Standard for sealing elements used in face seal joints

4. Sealing Element Matching Standards

Sealing elements	Corresponding joint standards	Material	Operating temperature
ED seal ring (DIN 3869)	ISO 1179、ISO 9974	NBR、FKM	-30℃ ~ +100℃（NBR） -20℃ ~ +200℃（FKM）
O-ring	ISO 6149、ISO 8434-3	NBR、FKM、EPDM	Material dependent
Metal seal	ISO 8434-1、ISO 8434-2、SAE J514	Steel, stainless steel	Dependent on material and medium

5. Selection Recommendations

For high-pressure heavy-duty applications (≥350 bar): preferentially select ISO 8434-1 (24° cone) or ISO 8434-3 (ORFS) fittings, which provide reliable sealing and vibration resistance.
Compact installation space: ISO 1179 or ISO 9974 face seal connectors utilizing ED seal rings may be employed, facilitating convenient assembly and disassembly.
International standardization: SAE J514 (37° flare) or SAE J1453 (ORFS) is recommended for inch-based systems; ISO 8434-1 series is recommended for metric systems.
Sealing materials: NBR is selected for mineral oil-based hydraulic fluids; FKM or EPDM is selected for high-temperature or special media, such as phosphate esters.

6. Precautions

Installation torque must conform to the connector manufacturer's specifications; both overtightening and undertightening can cause leakage.
ED seal rings and O-rings are single-use components and must be replaced after removal.
Interfaces of different standards must not be interchanged (for example, ISO 1179 ports cannot be directly connected to ISO 6149 fittings) and require adapters for proper connection.

Note: This document is primarily compiled with reference to the Parker Industrial Steel Pipe Fittings Product Manual 09-09-B Conn-CH-350P-0085. For selection inquiries, please contact the technical team of Hunan Haiyitai Technology Co., Ltd. for assistance.