The pressure rating of a hydraulic fitting is a critical technical parameter during selection; however, the actual pressure it can withstand is not a fixed value. Depending on factors such as fitting type, size, connection method, and design standards, the rated working pressure can range from a few MPa to over 70 MPa, with some specialized ultra-high-pressure fittings capable of withstanding even higher pressures.
Hydraulic Hose Fittings
Pressure Rating Classification of High-Pressure Hydraulic Fittings
Low-Pressure or Light Series (16 MPa)
Light-series hydraulic fittings are suitable for low-pressure hydraulic and pneumatic systems, such as general industrial equipment, light industrial machinery, and pneumatic tools. These fittings feature thinner walls, lighter weight, and lower costs, though their pressure-bearing capacity is limited.
High-Pressure Series (35 MPa)
Suitable for standard hydraulic systems, such as construction machinery, injection molding machines, and hydraulic pump stations. This series represents the most widely used pressure rating; the fittings are forged from 45# carbon steel or stainless steel, with wall thicknesses designed to meet a 35 MPa working pressure requirement.
Ultra-High-Pressure Series (70 MPa)
Suitable for ultra-high-pressure hydraulic systems, such as mining machinery, specialized equipment, and hydraulic test benches. These fittings feature a heavy-wall design, high-strength threads, and a dual-layer composite sealing structure, enabling them to withstand pressures of up to 70 MPa.
Pressure ranges for various types of hydraulic fittings
| Fittings Type | Pressure Range | Key Features and Description |
| SAE Flange | 35 MPa ~ 40 MPa (350-400 bar) | Pressure ratings are clearly defined; in accordance with the ISO 6162 standard, they are categorized into two series: Code 61 (3000 PSI) and Code 62 (6000 PSI). |
| ORFS Fittings | 28 MPa ~ 42 MPa (4000-6000 PSI) | Features a face-seal O-ring design, specifically engineered for high-pressure, zero-leakage, and high-vibration environments. |
| JIC Fittings | 10 MPa ~ 52 MPa (1500-7500 PSI) | Based on the SAE J514 standard, it utilizes a 37° flare metal-to-metal seal. Common specifications in the product series range from 1,500 to 5,000 PSI. |
| BSP Fittings | Up to 35 MPa (approx. 350 bar) | he pressure range extends from low pressure (approximately 30bar) to medium-high pressure (up to 350 bar), depending on the design and sealing configuration. |
| JIS Fittings | 21 MPa ~ 34 MPa (3000-5000 PSI) | Complies with Japanese Industrial Standards (JIS) and is commonly found in Japanese and Korean equipment. |
| Metric Fittings | 10 MPa ~ 80 MPa (1500-11600 PSI) | The range is extremely broad, depending on the specific standards. Commonly found in the DIN (German standard) system—categorized into light (L) and heavy (S) series—DIN bite-type fittings typically operate within a pressure range of 10 to 80 MPa. |
Factors Affecting the Hydraulic Fittings Pressure Rating
Fittings Material: The material of the hydraulic fitting directly affects its pressure-bearing capacity. Common materials include stainless steel, carbon steel, aluminum alloy, brass, and industrial plastics; among these, carbon steel offers the highest strength and pressure resistance, stainless steel provides the best corrosion resistance, and aluminum alloy is the lightest.
Structural Design: Thread fit and the type of sealing structure affect not only the sealing performance of the pipeline but also the fitting’s pressure rating; a tighter sealing structure allows for a higher pressure rating. SAE fittings, for instance, are well-suited for high-pressure systems.
Manufacturing Process: Hot and cold forging during production affect the material’s service life, while tempering and quenching influence the material’s deformation threshold, thereby indirectly affecting the fitting’s pressure rating.
Operating Conditions: Environmental factors such as corrosiveness and temperature impact the fitting’s performance; higher corrosiveness results in a lower pressure-bearing capacity.
Principles for Selecting High-Pressure Hydraulic Fittings Based on Pressure Ratings
When selecting the appropriate hydraulic fitting, it is essential to consider the system’s pressure range and operating environment to choose the right material. Factors such as dimensions, hose diameter, equipment compatibility, sealing methods, specifications, and the costs associated with installation and future maintenance must all be taken into account to determine the total cost of ownership.
Among these factors, selecting the correct pressure rating is paramount; the following three points must be observed:
1. Selection Principle 1: The pressure rating must be at least 1.25 times the system’s maximum operating pressure.
For example, if the system’s maximum operating pressure is 28 MPa, the fitting’s pressure rating should be no less than 35 MPa. Maintaining this safety margin ensures the system does not experience overpressure during pressure fluctuations.
2. Selection Principle 2: Base the selection on the system’s maximum operating pressure, not the nominal (rated) pressure.
Pressure surges can occur during system startup, shutdown, or load changes, with peak pressures potentially reaching 1.5 times the nominal pressure. Therefore, selection should be based on the highest possible operating pressure the system might encounter.
3. Selection Principle 3: For reducing fittings, base the rating on the smaller tube diameter.
Reducing fittings connect tubes of different diameters; the pressure-bearing capacity is determined by the smaller diameter end, as the wall thickness is thinner at that point.
Summary
There is no single maximum pressure rating that applies to all hydraulic fittings. Standard hydraulic fittings typically have an operating pressure of around 16 MPa, while high-pressure fittings can reach approximately 35 MPa; some ultra-high-pressure fittings can operate at 70 MPa or higher.
When selecting components, the priority is not simply choosing the fitting with the highest pressure rating, but ensuring that the fitting’s rated operating pressure exceeds the hydraulic system’s actual operating pressure, while also ensuring compatibility with the hydraulic hoses, piping, thread standards, and connection methods.
If you are looking for hydraulic fittings or hose assemblies suitable for high-pressure hydraulic systems, please feel free to contact us.
Frequently Asked Questions
Q1: What is the pressure rating (in MPa) for high-pressure hydraulic fittings, and how is it determined?
A: Refer to the product’s rated working pressure; reputable manufacturers clearly mark the pressure rating. Strongflex can provide corresponding pressure test reports.
Q2: Is a higher pressure rating for high-pressure hydraulic fittings always better?
A: No. Fittings with higher pressure ratings have thicker walls, greater weight, and higher costs. It is recommended to select a fitting with a pressure rating that matches the system’s actual working pressure to avoid over-specification.
Q3: What is the difference between the pressure rating and the burst pressure of high-pressure hydraulic fittings?
A: The pressure rating (rated working pressure) is the pressure the fitting can withstand continuously under normal operating conditions. Burst pressure is the maximum pressure the fitting can withstand for a short period; it is typically more than four times the rated working pressure.
Q4: What pressure is typically used for pressure testing high-pressure hydraulic fittings?
A: The pressure test is usually conducted at 1.5 times the rated working pressure; the fitting passes if it maintains this pressure for 3 minutes without leakage. Burst testing is typically conducted at a pressure exceeding four times the rated working pressure.