UQD Connectors: Sizes, Flow Rates & Selection Guide
UQD connectors are standardized, hand-mated quick disconnects for single-phase water/glycol cooling loops in electronic equipment. The Open Compute Project (OCP) UQD v1.0 specification defines four interchangeable interface sizes - UQD02, UQD04, UQD06 and UQD08 - plus minimum requirements for flow, pressure, temperature, durability and fluid loss.
This guide turns that specification into a practical selection process for data center liquid cooling. It also explains what "UQD-compatible" should mean, how hand-mate UQD differs from blind-mate connectors, and which information belongs in an RFQ.
Standards status checked July 2026: OCP UQD v1.0 is the accepted hand-mate specification. OCP currently lists UQD v2.0 as a beta draft workstream, not a final replacement specification.
What Is a UQD Connector?
UQD stands for Universal Quick Disconnect. OCP v1.0 defines a plug, a socket and the mating interface between them. Its scope is non-combustible, single-phase water/glycol cooling for electronics. A conforming pair is intended to be hand-mated, drip-free, hot-pluggable and leak-tight under pressure when connected and on both sides when disconnected.
"Universal" refers to dimensional and performance interchangeability between conforming plugs and sockets of the same nominal UQD size. It does not mean that every quick disconnect sold for liquid cooling will mate correctly. The supplier should identify the size and state that dimensional and performance requirements conform to the OCP UQD specification.
UQD02, UQD04, UQD06 and UQD08 Compared
The size code describes the standardized mating interface. It is not the same as the hose outside diameter. OCP also specifies minimum termination options: a barbed socket for reinforced EPDM tubing and a straight O-ring boss (ORB) plug.
| Size | Nominal interface | Minimum Cv | Recommended water flow | Maximum fluid loss at 0 psi | Minimum socket / plug termination |
|---|---|---|---|---|---|
| UQD02 | 1/8 in | 0.25 | At least 0.55 GPM | 0.020 mL | 1/4 in EPDM hose barb / -04 ORB |
| UQD04 | 1/4 in | 0.80 | At least 1.7 GPM | 0.025 mL | 3/8 in EPDM hose barb / -06 ORB |
| UQD06 | 3/8 in | 1.60 | At least 3.0 GPM | 0.035 mL | 1/2 in EPDM hose barb / -08 ORB |
| UQD08 | 1/2 in | 2.50 | At least 4.7 GPM | 0.070 mL | 5/8 in EPDM hose barb / -10 ORB |
The Cv values and flow ratings above are stated for water. Cv is a flow coefficient related to flow rate and pressure drop; a larger connector generally supports more flow with less restriction. Actual system pressure drop also depends on coolant properties, hose, bends, cold plates, manifolds and every other component in the loop.
Shared OCP UQD v1.0 Performance Requirements
| Requirement | OCP UQD v1.0 value | Why it matters |
|---|---|---|
| Maximum operating pressure | 100 psi | Normal loop pressure must remain within the supplier's published rating. |
| Minimum burst pressure | 300 psi | Provides a required pressure safety margin; it is not the operating setpoint. |
| Operating temperature | 17 - 65°C | Higher-temperature options may exist, but the supplier must publish the rating. |
| Shipping temperature | -40 - 75°C | Applies to transport and storage, including charged systems. |
| Shelf / service life | 5 years / 10-year service life | The connector must retain required performance through its defined life. |
| Durability | 5,000 make-and-break cycles | Performance requirements must still be met at the 5,000th cycle and end of life. |
OCP calls the interface drip-free, but the specification does not promise literally zero liquid. It sets a maximum fluid loss for each size, measured with water at 0 psi. This distinction matters in technical comparisons and acceptance testing.
UQD Connector Selection Checklist
1. Define the cooling loop and coolant
State whether the connector is used at a cold plate, server tray, rack manifold or facility connection. Identify the exact coolant and concentration. OCP v1.0 requires wetted-material compatibility with DOWFROST LC25 and JEFFCOOL ISF-25, while other fluids require supplier confirmation. Do not assume that a seal compatible with one glycol mix is suitable for every inhibitor package.
2. Calculate flow and allowable pressure drop
Start with the required flow per branch and the pressure budget available to the connector pair. Use supplier pressure-drop curves at the real coolant temperature and concentration. The OCP flow figures are selection references for water, not a substitute for a full loop calculation.
3. Match the UQD size and termination separately
Select UQD02, UQD04, UQD06 or UQD08 for the mating interface, then specify the required hose barb, ORB thread or another supplier-supported termination. A 1/4-inch hose does not automatically mean a UQD04 interface. Include tube inside diameter, outside diameter, hose material and clamp method in the drawing or RFQ.
4. Verify pressure, temperature and coupling force
Check maximum working pressure, surge conditions, burst rating, coolant temperature and ambient conditions. OCP requires suppliers to publish coupling force versus pressure. This is important where technicians must service densely packed 1U equipment by hand.
5. Specify fluid loss and service expectations
Use the OCP fluid-loss limit as a maximum, then add any stricter system requirement. Record expected connection cycles, shelf time, service life and maintenance procedure. For critical deployments, request production test data rather than relying only on a catalog headline.
6. Confirm identification and color coding
OCP requires identification of UQD conformity and nominal size. Suppliers must also offer visible red or blue color options to reduce the risk of crossing supply and return lines. Define the color convention consistently across racks and service documentation.
Hand-Mate UQD, Blind-Mate UQD and the v2 Draft
The accepted UQD v1.0 document covers a hand-mated plug and socket. OCP also publishes separate blind-mate work for equipment that connects as a tray slides into a rack. These are related liquid-cooling interfaces, but they should not be treated as the same mechanical requirement.
OCP's Cold Plate project currently lists a UQD Specification v2.0 workstream covering hand-mate and blind-mate versions. The linked v2 document is identified as a beta draft intended to close design, production and test gaps in v1. Until a final revision is accepted, procurement documents should name the exact specification and revision required instead of writing only "UQD v2 compatible."
Why AI Racks Make Connector Selection More Important
NVIDIA's GB200 NVL72 is a rack-scale liquid-cooled system with 72 Blackwell GPUs and 36 Grace CPUs. NVIDIA's OCP design contribution describes approximately 120 kW of cooling capacity, enhanced liquid-cooling manifolds and floating blind-mate tray connections. The GB200 NVL4 is also compatible with liquid-cooled NVIDIA MGX modular servers.
This does not prove that every GB200 implementation uses a particular UQD model. Rack builders may use different hand-mate or blind-mate interfaces at different points in the cooling path. The correct approach is to work from the system drawing and approved vendor list, then verify the exact interface, termination and compliance evidence.
What to Include in a UQD Connector RFQ
- UQD size: UQD02, UQD04, UQD06 or UQD08.
- Plug, socket or complete matched pair.
- Termination type and size, including hose dimensions or ORB thread.
- Coolant chemistry and concentration.
- Target flow, allowable pressure drop and working pressure.
- Operating and shipping temperature range.
- Seal and wetted-material requirements.
- Red or blue identification requirement.
- Required OCP revision and compliance documentation.
- Manufacturer, part number, quantity and requested delivery date.
Dasenic can help locate specified UQD connector part numbers and alternatives through the independent supply channel. For an accurate cross-reference, submit an RFQ with the complete checklist above rather than only a hose size or a product photograph.
Frequently Asked Questions
Are same-size UQD connectors interchangeable across manufacturers?
Interchangeability is the purpose of the OCP interface: conforming plugs and sockets of the same nominal size should mate. In production, verify that both suppliers explicitly claim conformity to the same OCP revision and validate the mixed pair for pressure drop, leakage, material compatibility and coupling force.
Does "drip-free" mean a UQD releases no coolant?
No. OCP v1.0 permits a small maximum fluid loss per couple/decouple cycle: 0.020 mL for UQD02, 0.025 mL for UQD04, 0.035 mL for UQD06 and 0.070 mL for UQD08, measured with water at 0 psi.
How do I choose between UQD04 and UQD06?
Compare required flow and allowed pressure drop first. UQD04 has a minimum Cv of 0.80 and a recommended water flow of at least 1.7 GPM; UQD06 has a minimum Cv of 1.60 and at least 3.0 GPM. Then confirm available space, hose termination, coupling force and the supplier's coolant data.
Is OCP UQD v2 already final?
No. As of the standards check for this guide, OCP lists UQD v2.0 as an active workstream and links to a beta draft. Use the accepted v1.0 requirements unless your project documentation explicitly approves a later draft or final revision.