Short, numeric briefs on the parts that make or break a liquid loop: the OCP UQD interface with its four sizes from UQD02 to UQD08 (0.55–4.7 GPM), the blind-mate vs hand-push decision, and the manifold pressure-drop budget that the LBNL open specification caps at 1/40 of the IT loop. Written by the engineers who quote, machine and helium-test the parts — the numbers we build against, not vendor poetry.
Read the standard summary before your first UQD RFQ, the coupling comparison before you freeze the tray interface, and the pressure-drop brief before you sign off a manifold drawing. The deadline is real: liquid-cooled AI servers went from 15% of shipments in 2024 to a projected 76% in 2026, and every one of those racks multiplies the number of mating cycles that have to end dry.
The OCP Universal Quick Disconnect specification (Rev 1.0, published September 2020) defines four interface sizes with flow floors from 0.55 to 4.7 GPM and spillage capped at 0.020–0.070 ml per disconnect. We walk through what the standard locks in, which numbers belong on your RFQ, and what it deliberately leaves for the buyer to specify.
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UQDB describes an interface form — blind-mate, latch-free, self-aligning. UQ04 describes a size class — the dash-04 (1/4") OCP tier with a Cv of 0.80 minimum and 1.7 GPM rated flow. The two are orthogonal, and mixing them up at design time is the most common selection error we see. A side-by-side table settles it.
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The LBNL open specification puts a hard ceiling on rack manifolds: combined supply and return pressure drop below 1/40 of the IT equipment loop they feed. We run the sizing arithmetic at the 1.2 L/min/kW industry baseline — an 80 kW rack moves about 96 L/min — and show where the rest of an 18 psi rack budget actually goes.
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Next in the queue: ORB stud ends vs hose barbs on UQD terminations, ISO 4406 cleanliness codes (why 18/16/13 keeps showing up in GPU loop tenders), and glycol versus dielectric fluid from the seal's point of view. If a loop question is blocking your design, email the engineering desk — the answer usually becomes the next brief.
Send the loop diagram or tray drawing — UQDB, UQ04 or manifold, quoted within 48 hours. MOQ from 50 pieces, standard sets ship in 15 days, test reports in every carton.