Data Center Coolant Fill Carts: First Fill and Flush Reference

PARTS ON THIS PAGE: RH-FC-150 · $18,700 RH-FC-300 · $26,600 RH-FC-600 · $43,700 RH-FC-FE25 · $265 RH-FC-HK-UQD · $2,600 RH-FC-ADP-U · $2,000 RH-FC-SPILL · $810 RH-CSK-JMP-06 · $360 RH-CSK-JMP-06-10PK · $2,250

Why you flush new piping before the first fill

A brand-new loop is not a clean loop. Between the factory and first power-on, the piping picks up thread sealant shreds from gauge ports, hose lube from assembly, weld discoloration flakes, plastic shavings from cut-to-length tube, and the dust that settles into any open pipe end sitting on the white space floor during install. None of that matters in a chilled-water barrel. All of it matters in a cold plate, where the finest passages run a small fraction of a millimeter and sit downstream of everything else in the loop. Debris that lodges there shows up weeks later as one GPU running hot, and by then the diagnosis is expensive.

The flush itself is simple in principle. Close the empty server positions with bypass jumpers — our RH-CSK-JMP-06 drops into a UQD06 supply and return socket pair for $360 — then circulate fluid from the cart through the loop and back through a 25-micron absolute filter element, at higher flow than the loop will see in service. Watch the differential pressure across the filter housing; a loading element means the flush is working. Change elements as they load, and call the flush done when a fresh element stops picking up pressure drop and the reservoir sight runs clear. One more rule: flush with the same fluid family you intend to fill with. Flushing on water and filling with PG25 leaves dilution behind that a refractometer will catch on day one.

A first-fill sequence that avoids airlocks

Filling is mostly about managing air. This is the sequence we run when we wet-test carts before shipment, adapted for a rack loop:

Once the loop is full and deaerated, the hold test comes next. Pressure decay criteria, test-circuit hardware, and what a passing number looks like are covered in our coolant pressure test cart guide at /coolant-pressure-test-cart.

• Stage the work: drip tray under every connection point, coupling series verified against the cart hose ends, and enough premix in the reservoir to cover system volume plus the cart's own hold-up.
• Connect supply at the lowest available point and fill from the bottom up, so fluid pushes air ahead of it instead of trapping it mid-loop.
• Circulate at moderate flow through the cart filter and bleed the high points until the reservoir level stops dropping and entrained air stops showing in the return.
• Check concentration with a refractometer against the premix spec, and record the fluid lot numbers in the commissioning file.
• Top off to operating level and hand the loop over for its pressure hold test.

Handling PG25 premix

Buy premix and resist the urge to blend on site. Facility water carries chlorides and hardness you have not measured, and hand-blending leaves the inhibitor concentration a guess — the two things a glycol package exists to control. Premix from the drum, verified with a refractometer at the rack, closes both questions.

Storage is unglamorous but it matters. Keep drums sealed and bunged between sessions; a drum breathing through an open bung pulls in moisture with every temperature swing. Do not top up one vendor's PG25 with another's — inhibitor packages are not formulated to mix, and the failure mode is quiet. If a loop needs different fluid, drain it and refill. On the hardware side, all three carts run EPDM and PTFE seals on a 316L wetted path, so PG25, PG30, and DI water are all in bounds without changing a seal or a gasket.

Sizing the cart: RH-FC-150 vs RH-FC-300 vs RH-FC-600

Two questions size the cart: how much loop you fill in one session, and what power the white space can actually deliver. A single rack loop holds gallons; a row with its CDU distribution holds tens of gallons, and the reservoir should cover the volume you plan to fill plus fresh fluid for flushing — recirculating dirty coolant through a loop you just cleaned defeats the point. The RH-FC-150 is the rack-at-a-time cart: 26 inches wide on 120V wall power, light enough to ride a freight elevator without a rigging crew. The RH-FC-300 covers row-scale work with a 55-gallon reservoir and a dedicated gear-pump test circuit. The RH-FC-600 is for facility commissioning where the paperwork matters as much as the fill — programmable routines and CSV logging on a 110-gallon platform.

All three models: 316L wetted path, EPDM/PTFE seals, 25-micron absolute filtration, PG25/PG30/DI water compatible. Prices in USD; carts ship in 10-15 business days.

What to put on the same PO

The cart shows up ready to work; the consumables are what keep it working through a deployment. All of these ship from stock in 5-7 business days:

• RH-FC-FE25 filter elements, $265 per 3-pack — plan one element per two to three loop fills, more on first flushes of new piping. Standard 2.5 x 20 in double-open-end format, so any industrial filtration house can cross it in a pinch.
• RH-FC-HK-UQD hose kit, $2,600 — 12 ft supply and return pair, 1 in ID EPDM with 316L overbraid, UQD08-compatible dry-break ends machined in our shop.
• RH-FC-ADP-U adapter set, $2,000 — 14 pieces covering UQD02 through UQD08 to NPT and JIC threads, for the one loop on every job that does not match the hose ends.
• RH-CSK-JMP-06 bypass jumpers, $360 each or $2,250 for a 10-pack — close out empty server positions so a partially populated rack can be flushed and filled.
• RH-FC-SPILL drip tray and spill kit, $810 — glycol on a data hall floor is a slip hazard and a change-control incident; this keeps it in the tray.

Common questions