Understanding Hydraulic Coupling Pressure Ratings: ANSI/ISO vs. Low Cycle, Non-Pulsating

When selecting hydraulic couplings, one critical factor to consider is their pressure rating. However, not all pressure ratings are the same. The existence of two distinct ratings—ANSI/ISO and Low Cycle, Non-Pulsating—reflects the different operational demands of hydraulic systems. Understanding these ratings and their test methods helps ensure safety, efficiency, and cost-effectiveness in your application.

1. ANSI/ISO Pressure Rating: Designed for High-Stress, Dynamic Systems

Application Context

ANSI/ISO-rated couplings are built for systems that experience frequent pressure changes, hydraulic shocks, and cyclic stress. These include applications such as:

• Agricultural equipment
• Hydraulic presses
• Construction machinery

These systems often experience rapid pressure spikes, vibrations, and repeated loading/unloading, requiring couplings that can endure extreme conditions.

Test Method

ANSI/ISO-rated couplings undergo rigorous impulse testing at 125–133% of their rated pressure. This overpressure testing simulates unpredictable hydraulic shocks and validates:

Fatigue resistance over many cycles

The ability to withstand sudden pressure surges

Leak-proof performance in demanding environments

Purpose

The primary goal of the ANSI/ISO rating is to ensure durability and safety in harsh operating conditions. This rating provides a critical safety buffer, reducing the risk of coupling failure that could lead to costly downtime or hazardous situations.

2. Low Cycle, Non-Pulsating Pressure Rating: For Steady-Pressure Applications

Application Context

Unlike dynamic systems, some hydraulic applications experience relatively stable pressure with minimal fluctuations. Examples include:

• Hydraulic jacks
• Mine roof supports
• Fluid transfer pumps

In these cases, pressure remains steady, with only minor variations, such as small pump ripples, and the coupling does not undergo frequent cycling.

Test Method

Couplings with a Low Cycle, Non-Pulsating rating are tested at 100% of their rated pressure without an overpressure multiplier. This test focuses on:

• Structural integrity under constant load
• Ensuring the coupling can handle occasional use without failure

Purpose

This rating prioritizes reliability over extreme durability testing. Since these couplings are not exposed to high-frequency pressure changes, they do not require the same level of cyclic fatigue resistance as ANSI/ISO-rated couplings. This avoids overengineering and keeps costs in check.

Why the Difference?

Safety & Industry Standards

ANSI/ISO ratings align with stringent industrial and agricultural standards, ensuring that couplings can absorb hydraulic shocks and cyclic stress without failure. Meanwhile, Low Cycle ratings cater to applications where overtesting would be unnecessary.

Material Fatigue Considerations

Dynamic systems degrade faster due to repetitive stress cycles. High test pressures ensure an additional safety buffer. In contrast, low-cycle applications do not require extreme durability, allowing for a more application-specific approach.

Cost vs. Performance Optimization

By defining two separate ratings, manufacturers provide customers with the ability to choose couplings suited to their exact needs. This prevents unnecessary costs associated with overbuilt components in low-cycle applications while ensuring high-performance options for demanding environments.

Key Takeaways

• Match the rating to your system’s pressure profile. Dynamic, high-shock applications require ANSI/ISO-rated couplings, while steady-pressure systems can use Low Cycle-rated couplings.
• Prioritize safety and efficiency. Overengineering low-cycle applications can add unnecessary costs, while underengineering high-cycle applications can lead to failure risks.
• Ensure compliance with industry standards. Selecting the right pressure rating ensures durability, performance, and regulatory adherence.

Final Thoughts

Understanding the difference between ANSI/ISO and Low Cycle, Non-Pulsating pressure ratings is crucial when selecting hydraulic couplings. Choosing the right rating ensures longevity, safety, and cost-effectiveness in your hydraulic system. Always analyze your operational cycles, pressure demands, and industry standards to make the best choice for your application.