Liquid cooling
UQD02, UQD04, UQD06, and UQD08: Flow and Pressure by Size
Pick the OCP size whose rated water flow covers the loop, then read that maker's pressure, because the pressures are not the same on every sheet.
On this page
For a loop that follows OCP UQD specification v2.0.0, use the smallest size whose rated water flow covers the design flow: 0.6 GPM on UQD02, 1.7 GPM on UQD04, 3.0 GPM on UQD06, and 4.7 GPM on UQD08, as listed in Table 6, effective September 22, 2026. That table lists one maximum operating pressure, 100 psi, for every size. Danfoss's fact sheet, read October 20, 2026, keeps those GPM figures and then lists 290 psi on UQD02 and 100 psi on UQD06. Gates's 2025 sheet lists 290 psi as the maximum working pressure for UQD02 through UQD08. The size code and the maker's pressure are both part of the request.
What OCP Table 6 assigns to each size
OCP v2.0.0 says a product complies when it meets or exceeds Table 6. The scope line is non-combustible single-phase water and glycol for liquid cooling of electronics. Rated flow in that table is 2.27 L/min (0.6 GPM) for size 02, 6.44 L/min (1.7 GPM) for 04, 11.36 L/min (3.0 GPM) for 06, and 17.79 L/min (4.7 GPM) for 08. Minimum Cv, reported for water, is 0.30, 1.1, 2.2, and 3.6. Maximum Cv is 0.43, 1.6, 3.3, and 5.6. Maximum fluid loss per cycle is 0.02 mL, 0.03 mL, 0.04 mL, and 0.07 mL. Minimum burst pressure is 300 psi. Operating temperature is 5°C to 65°C (41°F to 149°F). Those limits are the specification's limits, opened October 20, 2026. A catalog that uses the letters UQD still has to be read against this table.
Maximum flow is not a fourth GPM cell. The table points the reader to the coupling supplier and describes a general limit based on a maximum velocity of 5 m/s. Note 1 says coupling cycles under flow must currently sustain a minimum of twice rated flow, as a limit on seal washout. The supplier and mating comparison covers hand-mate UQD and blind-mate UQDB. This page stays with the size ratings.
| Size | Rated flow | Minimum Cv | Maximum Cv | Maximum fluid loss per cycle |
|---|---|---|---|---|
| 02 | 2.27 L/min, 0.6 GPM | 0.30 | 0.43 | 0.02 mL |
| 04 | 6.44 L/min, 1.7 GPM | 1.1 | 1.6 | 0.03 mL |
| 06 | 11.36 L/min, 3.0 GPM | 2.2 | 3.3 | 0.04 mL |
| 08 | 17.79 L/min, 4.7 GPM | 3.6 | 5.6 | 0.07 mL |
Danfoss pressures are not one number for every size
The Danfoss Hansen fact sheet, copyright 2026, says the UQD complies with OCP and lists rated flow as the reference used to measure pressure drop and publish Cv. The GPM column matches Table 6: 0.6, 1.7, 3.0, and 4.7. The L/min column is 2.1, 6.4, 11.4, and 17.8, which is close to OCP's 2.27, 6.44, 11.36, and 17.79 and is not the same rounding. Cv on the sheet is 0.33, 1.37, 2.37, and 5.32 for UQD02 through UQD08.
Operating pressure on that sheet changes with size, as read October 20, 2026. UQD02 lists 20 bar (290 psi) on the connected coupling, the socket, and the plug, with a minimum burst of 60 bar (870 psi). UQD04 lists 16 bar (232 psi) operating and 48 bar (696 psi) burst. UQD06 lists 6.9 bar (100 psi) operating and 20.7 bar (300 psi) burst. UQD08 lists 8.9 bar (129 psi) connected and 6.9 bar (100 psi) on the socket and on the plug, with 20.7 bar (300 psi) burst. A 290 psi loop can sit on the UQD02 line of this sheet and still sit above the 100 psi line in OCP Table 6. Ask Danfoss which figure the quote is using.
The same sheet prints a separate flow at 5 m/s: 2.4 L/min (0.62 GPM), 9.4 L/min (2.5 GPM), 14.7 L/min (3.9 GPM), and 23.6 L/min (6.2 GPM). That column is higher than rated flow on sizes 04, 06, and 08. It is the sheet's 5 m/s reference, not a replacement for the rated-flow cell. A marketing line on the sheet says flow ratings are exceeded by at least 25 percent. The rated-flow GPM cells match OCP's GPM cells, so this guide does not repeat the 25 percent line as a rated-flow increase.
Gates publishes one pressure and a minimum Cv for each size
The Gates sheet, copyright 2025, lists 316L stainless steel, EPDM seals, a maximum working pressure of 290 psi (20 bar), and a minimum burst pressure of 1,160 psi (80 bar) for the UQD family. Operating temperature on that sheet is -40°F to 248°F (-40°C to 120°C). Minimum Cv, as read October 20, 2026, is 0.54 for UQD02, 1.53 for UQD04, 2.45 for UQD06, and 4.25 for UQD08. Force to connect at 0 psi is 34.5 N, 44.4 N, 54.6 N, and 70.1 N. Force to connect at 100 psi is 64.5 N, 110.4 N, 170.0 N, and 251.0 N.
Set those Cv numbers next to OCP's minimum and maximum, without treating them as the same test report. Gates's minimums sit above OCP's minimums. Gates's UQD02 minimum of 0.54 also sits above OCP's maximum of 0.43 for size 02. OCP says a complying product meets or exceeds Table 6, and Table 6 also has a maximum Cv. This page does not decide whether a Cv above that maximum still complies. Ask which OCP revision the 2025 Gates sheet was checked against. The temperature and pressure windows keep Gates, Danfoss, and the OCP operating line in one place.
Hose barb size follows the code
OCP v2.0.0 lists push-lock hose barbs of 1/4 inch for size 02, 3/8 inch for 04, 1/2 inch for 06, and 5/8 inch for 08, and says the barb is intended for reinforced EPDM hose. The Gates socket-with-barb rows use those same barb sizes: 1/4 inch, 3/8 inch, 1/2 inch, and 5/8 inch. Gates part numbers on that sheet, as of October 20, 2026, include 7245-0000 for the UQD02 socket with barb and 7245-0006 for the UQD08 socket with barb. A red and a blue option share the dimensional row. Color does not change the size code. Hose assemblies still have to name the hose the barb is allowed to grip.
What to write down before asking for a price
Write the design flow, the fluid, the size code, the specification version, and the pressure you need the quote to meet. If the mate is blind, say UQDB and the same size number. OCP's 0 psi coupling-force line is noted as applying to UQDB, so a hand-mate force from the Gates sheet is a different row.
- Design flow, with the units, and the fluid.
- Size: 02, 04, 06, or 08.
- Hand-mate UQD or blind-mate UQDB, and the specification version.
- Working pressure and temperature the loop uses.
- Maker and part number, once a sheet has been chosen.
- Barb or thread on each end.
Questions the size code does not answer
Should the next size up be used for margin?
Table 6 already states a rated flow and a minimum Cv for each size. Moving from UQD04 at 1.7 GPM to UQD06 at 3.0 GPM is a different barb, a different body, and, on the Danfoss sheet, a different published pressure. Add margin by confirming the pressure drop at your flow with the maker, which is what OCP's unfinished pressure-drop coefficient row still leaves open.
Can one maker's Cv be used with another maker's pressure?
Keep each maker's Cv with that maker's pressure. Gates's 290 psi and Danfoss's size-by-size pressures are each maker's table. OCP's 100 psi line is the specification's operating pressure. Quote the pair of numbers that appear on the same page as the part number.
Sources
OCP figures are from specification v2.0.0, effective September 22, 2026. Danfoss figures are from fact sheet AI423953312825en-001401, copyright 2026, including a drawing release date of April 2, 2025 inside the file. Gates figures are from the UQD spec sheet marked 2025. Air-inclusion and fluid-loss cells on the Danfoss table were left out because the column alignment in the file was too tight to quote. Pages were opened October 20, 2026.