UQD Blanking Plugs and Caps: UQD04, UQD06, UQD08

PARTS ON THIS PAGE: RH-CSK-CAP-04 · $350 RH-CSK-CAP-06 · $440 RH-CSK-CAP-08 · $400 RH-QDP-04 · $50 RH-QDP-06 · $65 RH-QDP-08 · $60

Why open couplings on a staged rack get wrecked

A UQD's poppet keeps the bulk fluid in, but the seal face and poppet seat sit exposed the moment the halves separate. One particle of grit across the poppet seat is enough to make the coupling weep after reconnection, and by the time you notice it the rack is populated and the drop is buried behind a server. Dust that settles into residual glycol dries to a film, and that film goes into your loop on mate-up.

Mechanical damage is the quieter problem. Coupling ends hang at rail height during fit-out, exactly where ladders, server rails, and tool bags travel. The seal face on a plug half is the sealing surface — ding it and you are replacing the coupling, not polishing out the mark.

Then there are the drips. A disconnected drop holds a trapped volume between the poppet and the face, plus whatever static head the loop puts on it, and it will keep weeping for days. A $350 to $400 set of caps and plugs closes all of this out for less than the cost of one replacement coupling.

Cap versus plug: which half takes which

Both halves of a quick disconnect get called "the QD," which is how the wrong covers end up on order. Per the OCP UQD specification, the male half is the plug and the female half is the socket. Protection follows the geometry:

A cap fits over a plug (male) half. It covers the seal face and the outside diameter that the socket's seals ride on. A plug fits into a socket (female) half. It fills the bore and shields the internal O-ring and poppet from grit.

Connections open in pairs — every broken connection exposes one male and one female half — which is why our sets ship 6+6: six caps and six plugs per box, enough for six opened coupling pairs. Count your open connections, not your total couplings, when you order.

Sizes, SKUs, and set pricing

One set covers six coupling pairs in a given size. UQD06 is the workhorse on most ORV3 server loops; UQD04 shows up on cold plates and low-flow loops; UQD08 handles manifold feeds and CDU-side connections — the openings you least want exposed to the room.

UQD cap and plug sets — 316L body, EPDM seals, 6 caps + 6 plugs per set

• All three sets: 316L stainless machined from bar, EPDM O-rings compatible with PG25 and treated DI water
• Sized to mate with couplings built to the OCP UQD specification
• Sealed against residual pressure to 50 psi (3.4 bar) static
• Cleaned, DI-rinsed, and double-bagged — open the bag at the rack, not in the truck

Threaded blanking plugs for terminations and spare ports

If what you actually need to blank is a threaded port — an unused manifold stub-out, a spare instrumentation boss, or a termination during hydro and leak-down testing — the coupling caps above are the wrong part. Use a G-thread BSPP blanking plug with an EPDM boss seal instead. It seals on the O-ring shoulder, so there is no tape or paste anywhere near the coolant, and it installs and removes repeatedly without dressing threads.

Threaded BSPP blanking plugs — 316L, passivated per ASTM A967, designed to 500 psi

• Designed to 500 psi (34.5 bar) — comfortably above our 225 psi manifold hydro test and 150 psi working class
• Hex head takes a proper wrench, not an allen key you will strip at 2 a.m. during commissioning
• Cheap enough to leave installed permanently on a spare port

Materials, lanyards, and residual-pressure sealing

Both families use 316L stainless on every wetted surface and peroxide-cured EPDM O-rings, the same seal chemistry as the rest of our PG25 loop hardware. The threaded plugs are citric-passivated per ASTM A967.

Every coupling cap and plug is cross-drilled for 1/16 in lanyard cable. Tether them to the rack and they are there for the next service event instead of riding home in someone's pocket. On a big deployment that detail is the difference between reusing hardware and reordering it.

On residual pressure: the coupling caps and plugs are designed to seal 50 psi static. That covers the trapped volume between poppet and seal face and the static head on a disconnected drop, so an opened connection stays dry through the rest of the build. It is not loop isolation — if the drop is still connected to a pressurized loop, isolate at the manifold valve first. For blanking under full test pressure, use the threaded RH-QDP plugs on a threaded termination.

Common questions