In AI computing power clusters and high-density data centers, rack mounted cooling distribution units (CDUs) play the role of the "cooling heart" - they transfer the cooling capacity of the building side chilled water to the secondary side cooling liquid of the servers, driving the cooling liquid to circulate between the chip cold plate and the manifold. The flexible inlet and outlet pipes connecting the CDU to the cabinet manifold and server nodes are the elastic joints in this "cardiovascular system", which need to withstand a working pressure of 1.0 MPa (about 10 bar), meet the requirements of curved piping in narrow spaces, and maintain zero leakage during 7 × 24 hours of operation. The flexible inlet and outlet pipes of CDU with a pressure resistance of 1.0MPa are a systematic solution for this working condition - using EPDM/PEX material to ensure pressure bearing and medium compatibility, using standardized quick plug connectors to achieve maintenance plug and break, and UL94 V-0 flame retardant to meet the safety red line of data centers, becoming the "flexible artery" connecting CDU and IT equipment in rack level liquid cooling distribution systems.
1、 Pressure adaptation: matching logic between 1.0MPa grade and CDU system
As the core hub of liquid cooling systems, rack mounted CDUs have clear engineering boundaries for their secondary rated flow and working pressure. Taking Rittal's 150kW rack level CDU as an example, the rated flow rate on the secondary side is 225L/min and the allowable working pressure is 5bar; The flow rate of the secondary circuit of the 1.4MW inline CDU in the Cooler Master reaches 1500L/min. The actual working pressure of the end hose assembly from the manifold to the cold plate inside the server cabinet is usually only 0.1-0.3 MPa. The pressure resistance level of 1.0MPa (10bar) is much higher than the conventional end demand, but this redundant design precisely covers the water hammer impact during CDU pump start-up, instantaneous overpressure during pipeline misoperation, and pressure fluctuations during multi node parallel liquid supply.
CEJN liquid cooled hoses explicitly set the working pressure to 10 bar (1.0 MPa), which directly matches the outlet pressure rating of mainstream CDU secondary side pumps. CEJN uses high-quality reinforced EPDM material reinforced with high-strength synthetic fiber yarn to ensure that the hose maintains good dimensional stability under compression and does not experience "breathing effects" due to pressure fluctuations that may cause loose joints. For the main connection section between the CDU and the cabinet manifold, Schneider Electric provides PEX-AL-PEX material flexible pipes with a pressure resistance rating of 150psi (approximately 1.03MPa), which is also aligned with the 1.0MPa rating.
2、 Material selection: Mainstream status of EPDM and scene supplement of PFA/PEX
The liquid cooling pipeline system in the data center presents a three-layer architecture of "backbone branch end", with different levels of hose material selection logic. The end connection section is the core application area of hose assemblies, and EPDM has become the mainstream solution with a market share of about 58%.
The advantages of EPDM hoses are reflected in three dimensions: firstly, the temperature resistance range covers -40 ℃ to+100 ℃ and even 150 ℃, compatible with commonly used water ethylene glycol coolant in data centers (such as PG-25), and has passed compatibility testing; Secondly, the material has excellent flexibility and bending resistance, allowing it to pass through gaps of several centimeters inside the cabinet without twisting or collapsing; Thirdly, with UL94 V-0 flame retardant certification, it can self extinguish within 10 seconds in the event of an open flame without producing ignition droplets, meeting the rigid requirements for material safety in the "white space" of data centers. The liquid cooling pipeline matching scheme of Liwang Fluid further points out that EPDM hoses with peroxide sulfurization formula should be given priority in selection to eliminate the risk of sulfate leaching contaminating the coolant.
For immersion liquid cooling systems or fluoride liquid transportation scenarios, PTFE/FEP perfluorinated material hoses are a better choice - their temperature resistance can reach -200 ℃ to+260 ℃, with almost no dissolved substances, ensuring that the dielectric properties of the fluoride liquid are not contaminated. In the main pipeline from CDU to the cabinet, Schneider Electric uses PEX-AL-PEX (cross-linked polyethylene aluminum cross-linked polyethylene composite pipe) material, with a pressure resistance of 150psi, temperature resistance of 6-60 ℃, and a small bending radius of 203mm, suitable for long-distance and high flow backbone routing.
3、 Supporting integration: quick connector and system reliability
The practical engineering value of CDU flexible inlet and outlet pipes lies not only in the pipe body itself, but also in the system integration with the end joints. The maintenance scenario of liquid cooling systems in data centers requires pipelines to have "hot plugging" capability - operation and maintenance personnel can replace faulty server nodes without shutting down, which poses a dual challenge to the pressure plugging performance of quick connectors and the connection reliability of hose ends.
The UQD series liquid cooled quick connector is a standardized solution for the OCP open computing project, supporting one handed quick locking and separation, with clear red and blue markings to distinguish the supply and return liquid ports. Its flat leak free sealing design ensures that there is no leakage during the insertion and extraction process, and the mechanical insertion and extraction life can reach more than 5000 times. Stainless steel quick connectors dominate high reliability scenarios, while nylon quick connectors are entering the high-density cabinet market with the advantages of cost reduction of 50% and weight reduction of 40%.
In terms of bending radius and spatial adaptation, the connection channels between server nodes inside the cabinet are often only a few centimeters apart. CEJN liquid cooled hoses are designed with high flexibility, making them easy to install and navigate in complex liquid cooling systems that are difficult to reach. The "connection unit+flexible supply and return liquid pipeline" solution in technology combines the hose with a sliding installation guide rail, allowing the hose to slide with the connection unit during insertion and maintenance of IT equipment, avoiding excessive bending.
Cleanliness control is the core difference between liquid cooled hose assemblies and traditional hydraulic hoses. The microchannel size inside the cold plate is extremely small, and any trace ion precipitation or particle detachment may cause channel blockage. Therefore, EPDM hoses need to use low precipitation formulations, while PTFE/FEP materials, with their extremely low solubility, become chip level connectors.
In summary, the flexible inlet and outlet pipes of the server rack mounted liquid cooling distribution unit with a pressure resistance of 1.0MPa perfectly meet the strict requirements of the rack level liquid cooling distribution system for "pressure stability, space adaptation, and plug and break" due to its precise matching of EPDM/PEX material with 1.0MPa pressure, UL94 V-0 flame retardant safety guarantee, and UQD quick connector and flexible pipe system integration. From CEJN's 10 bar reinforced EPDM hose to Schneider's 150psi PEX-AL-PEX main pipeline, from the mainstream EPDM solution with 58% market share to PTFE fluorine liquid special material, every technical detail points to the same goal: to provide safe, reliable, and flexible flexible connection guarantee for coolant transportation between CDU and servers in the era of AI computing power density continuous increase in liquid cooling.
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