How Do Water Hammer Effects and Pressure Impulse Testing Influence Liquid Cooling System Reliability?

Author: Liquid Cooling Series

May 05, 2026Artificial Intelligence / Testing and certification of products

Why AI Server Liquid Cooling Systems Need Fatigue Durability Validation?

Data centers operate continuously 24/7 throughout a year, placing extremely high reliability requirements on electronic components. In most cases, components are expected to achieve an annual failure rate (AFR) below 0.3% and maintain a product lifespan of more than six years. As generative AI continues to rise up and high-power platforms such as the NVIDIA GB200 become more widely adopted, liquid cooling systems have gradually become a key technology.

The reliability challenge of liquid cooling systems often lies not in cooling performance, but in mechanical pressure fatigue. Once liquid cooling components crack, deform, or experience connector loosening, coolant (PG25) leakage may occur, increasing the risk of short circuits, hardware failure, and unexpected system downtime in high-value GPU clusters.

In practical applications, especially during early stage of product development, liquid cooling system manufacture must consider more than just maximum pressure resistance. Long-term pressure cycling and pressure pulsation can also gradually cause material fatigue and increase the risk of component failure.

To evaluate these risks, tests such as Water Hammer, Pressure Impulse, and Pressure Cycle testing are commonly introduced based on the system design. These validation methods help ensure long-term reliability and stable operation of liquid cooling systems.

水錘與壓力脈衝測試：兩者差異在哪裡？

雖然兩者皆透過壓力變化來模擬管路內部異常升壓的情境，但在流體動力學行為上仍存在本質差異。其觸發機制、壓力波形特徵、能量傳遞方式，以及對材料所造成的疲勞損傷模式皆不相同。

因此，如何區分水錘效應與壓力脈衝，是制定測試方法並正確評估液冷零組件壽命的重要前提。

1. 水錘效應（Water Hammer）：瞬間壓力衝擊特性

水錘效應又稱液壓衝擊(Hydraulic Shock)，是一種短時間內發生的高壓衝擊現象。當管路中的冷卻液流速或流向突然改變，例如CDU內部的泵浦因斷電而急停、閥門快速關閉或 UQD 插拔時，原本流動的動能會瞬間轉換為壓力，形成強烈的壓力波。

這些壓力波會在管路中來回傳遞與反射，對系統產生瞬間的高壓衝擊，進而提高零組件破壞或洩漏的風險。

【Water Hammer Schematic Diagram】

2. Pressure Impulse: Long-Term Cyclic Fatigue Behavior

Pressure impulse, also known as pressure cycling, refers to a continuous pressure fluctuation phenomenon that occurs during system operation. Unlike water hammer, pressure impulse is not an instantaneous shock but a long-term, repeated variation in pressure.

In AI server liquid cooling systems, pressure impulses mainly come from two sources: periodic fluid movement generated by pump operation, and flow adjustments made to maintain cooling performance under varying system loads. These factors create continuous pressure fluctuations in the secondary loop. Over time, this repeated stress can lead to material fatigue and component aging.

【Comparison Table of Water Hammer and Pressure Impulse】

These pressure-related tests are primarily used in the secondary loop of AI server liquid cooling systems. Under pressure pulsation, different component designs and materials can result in different stress conditions and fatigue issues.

Common validation targets include:

Cold Plate
In-Rack Manifold
Universal Quick Disconnect (UQD / UQDB)
Hose Kit
Manifold Supply / Return System
Various liquid cooling valves (Reducing Valve, Check Valve, Flow Control Valve)

Following International Standards to Ensure Test Consistency

Pressure pulsation testing is typically conducted in accordance with international standards and industry specifications to ensure consistency in testing methods and reliability of results, including:

OCP (Open Compute Project): Systems must pass at least 5,000 dynamic pressure impulse cycles.
SAE J343 / ISO 6803: Flexible hose assemblies (Hose Kits) must withstand more than 200,000 pressure impulse cycles under specified working pressure conditions.
ISO 19879: Rigid metal tubing and connectors (Manifold & Quick Disconnect) must withstand up to 1,000,000 continuous high-cycle fatigue test cycles.
ASSE 1061 (American Society of Sanitary Engineering): This standard verifies the water hammer performance of building hot and cold water distribution systems and valves.

When Fatigue Durability Reaches Its Limit: How Do Failures Occur?

Pressure pulsation testing helps identify how liquid cooling components fail under extreme pressure conditions, such as:

Cold Plate: Cracking, expansion deformation, liquid leakage, flatness exceeding tolerance limits
Manifold: Weld cracking, external deformation, liquid leakage
Universal Quick Disconnect: Thread stripping, O-ring deformation, liquid leakage during disconnection, sleeve jamming
Flexible Hose Assembly: Hose rupture, connector pull-off

These practical failures not only reflect the limits of a product under extreme conditions, but also help to improve structural optimization and overall system reliability level.

DEKRA iST–Professional Validation Services

With the rapid growth of AI servers and high-power liquid cooling applications, DEKRA iST provides comprehensive burst testing and pressure validation services for liquid cooling systems. We support companies in ensuring product reliability from product development through mass production.

Key Advantages

Testing conducted in accordance with international standards.
Precise pressure control and measurement capabilities.
Comprehensive support for a wide range of critical liquid cooling components.
Customized testing and validation solutions tailored to customer requirements.

Through systematic validation and professional testing expertise, we help customers reduce risks, enhance product quality, and accelerate time-to-market.