UQD to NPT Adapters for Direct-to-Chip Cooling Loops

PARTS ON THIS PAGE: RH-QDA-06-NM08 · $120 RH-QDA-06-NF08 · $110 RH-FC-ADP-U · $2,000 RH-QDA-MC18 · $1,650 RH-QDP-06 · $65

UQD terminations: what thread you are actually adapting

UQD is the Universal Quick Disconnect defined by the Open Compute Project for direct-to-chip liquid cooling, and UQDB is its blind-mate variant used on ORV3 (Open Rack V3, 21-inch) rack manifolds. The coupling half you buy — plug or socket — is supplied with a BSPP female termination, and the size of that port tracks the body size:

• UQD02 — G 1/8 BSPP female termination
• UQD04 — G 1/4 BSPP female termination
• UQD06 — G 3/8 BSPP female termination
• UQD08 — G 1/2 BSPP female termination

Where NPT shows up around a coolant loop

The permanent wetted loop should stay parallel-thread and elastomer-sealed end to end. NPT belongs at the boundary — the equipment that connects to the loop temporarily or lives outside it. In practice that means four places:

A good habit during commissioning: put the NPT joint on the rig side of the quick disconnect wherever you can, so the joint that relies on thread sealant gets made once and left alone, while the connection that gets cycled is the UQD itself.

• Pressure-test rigs — hand pumps, hydro pumps, and calibrated gauges are almost universally 1/4 or 1/2 in NPT
• Fill and flush carts — cart plumbing, sight glasses, and drain valves typically carry NPT ports
• Temporary instrumentation — temperature and pressure transmitters landed during flush and leak-down, then removed
• Facility-side and legacy hardware — older CDU ports, building water stubs, and gauge tees that predate the ORV3 ecosystem

Availability matrix: UQD size vs NPT end

The UQD06 to 1/2 in NPT transitions are the two we stock as singles, because that pairing covers most rack-manifold and CDU bench work. The rest of the matrix is quoted — small-batch 316L turning is the core of our shop, so a quoted combination is a short conversation, not a special project.

If you need coverage across sizes rather than one fitting, two kits solve it. The RH-FC-ADP-U universal set ($2,000) packs 14 adapters covering UQD02 through UQD08 to 1/2 and 3/4 in NPT plus -8 and -12 JIC in a foam-lined case. The RH-QDA-MC18 master set ($1,650) carries two of every adapter and blanking plug in our QD category, including both NPT transitions. And for capping a coupling or stub-out during a pressure test, the G 3/8 blanking plug RH-QDP-06 ($65) is cheap enough to leave installed.

316L UQD-to-NPT transition availability. Stocked singles ship in 5-7 business days; quoted combinations typically ship about 15 business days after drawing approval.

Sealing: O-ring boss on one end, tapered thread on the other

The two ends of these adapters seal by completely different mechanisms, and treating them the same is how coolant ends up on the floor.

The BSPP end seals on a peroxide-cured EPDM O-ring compressed against the boss shoulder. Parallel threads carry the load; the elastomer does the sealing. Wrench it home against the shoulder and you are done — no sealant of any kind goes on this joint, and it can be made and broken repeatedly. Inspect the O-ring each time and replace it if it shows a set.

The NPT end seals by thread interference, and a tapered joint needs sealant to be reliable. Use a low-shed anaerobic thread sealant rated for glycol service, applied to the male threads only, keeping the first two threads clean so nothing gets pushed into the flow path. Assemble hand tight plus one and a half to two turns with a wrench. Going harder than that gains nothing on a stainless joint.

Skip PTFE tape entirely on coolant service. Tape fragments shear off during assembly, migrate with the flow, and end up lodged in cold plate microchannels or loading up your filter elements. A quality center pulling shredded tape out of a plugged cold plate is an expensive way to save four dollars on sealant.

Pressure ratings and materials

Our NPT transitions are designed to 500 psi (34.5 bar), which puts the adapter well clear of being the weak point in any joint it lands in. The loop hardware around it is 150 psi working class, our manifolds are hydro-tested to 225 psi with serialized certificates, and ORV3 secondary loops typically run below 50 psi in service. The margin is there so a hydro test or a pressure spike during commissioning never involves the adapter in the conversation.

Construction is the same across the category: 316L stainless machined from bar with citric passivation per ASTM A967, EPDM 70A peroxide-cured O-rings compatible with PG25 and DI water, and a service temperature range of -4 to 194 F (-20 to 90 C). Each fitting arrives cleaned, capped, and bagged for coolant service, so it can go from the bag straight into a loop without a solvent wash first.

Common questions