8.3 DC Field Test Procedure

8.3 DC Field Test Procedure

Quick Answer: An ASSE 1015 double check (DC) field test measures check #1 and check #2 static differentials only—no relief test. Under USC-style criteria both checks must hold ≥ 1.0 psid tight in the direction of flow (forward seating under the static procedure). Use shutoffs to create a stable static condition, connect the gauge high upstream and low downstream of the check under test, record both values, then restore shutoffs and remove the kit safely.

What you are proving on a DC

A DC has two independently acting check valves, two shutoffs, and four test cocks—and no differential pressure relief valve. Protection is mechanical double seating, not a vented zone. Therefore the field test answers only:

1. Does check #1 seat tightly enough under the static procedure (≥ 1.0 psid)?
2. Does check #2 seat tightly enough under the static procedure (≥ 1.0 psid)?

There is no “opening point,” no 2.0 psid relief criterion, and no 5.0 psid first-check floor. Note the mirror-image trap too: a DC records a psid value for each check, while an RP records no psid for check #2. Do not import RP numbers onto a DC worksheet.

Even though the DC is for non-health-hazard service, it must still pass. “Low hazard” never means “optional testing” or “close enough.”

Pre-test (same professional habits as RP)

1. Notify stakeholders; confirm shutoff #2 (and if needed shutoff #1) may be closed for the test window.
2. Inspect — orientation, accessibility, test cocks present and operable, shutoffs not seized, no unauthorized bypass around the assembly.
3. Identify TC1–TC4 in flow order: TC1 on the supply side ahead of shutoff #1, TC2 between shutoff #1 and check #1, TC3 between the two checks, TC4 between check #2 and shutoff #2.
4. Plan static isolation: typically close shutoff #2 to stop downstream influence and allow true static differentials across the checks; follow your approved worksheet if shutoff #1 is also manipulated for a specific step.
5. Gauge ready — calibrated differential gauge, hoses filled and bled, high/low clearly marked.

Static condition is the rule

Differentials for DC checks are read under static (no flow) conditions created by proper shutoff use. If water is still moving through the assembly, you are not measuring pure seating differential. Wait for the needle to stabilize before recording. Unstable readings usually mean air in the gauge train, a leaking shutoff, or a check that will not seat—not a reason to invent a number.

Typical high/low connection pattern

Exact cock numbers vary slightly by body design, but the logic is constant:

To test a check:

• High pressure hose → test cock upstream of that check (higher expected pressure when the check holds).
• Low pressure hose → test cock downstream of that check (lower pressure if the check holds and you have bled/established the low side correctly per procedure).

Conceptual map (verify on the actual casting):

Your school’s ASSE-recognized procedure may specify intermediate valve positions on three- or five-valve gauges, bleed steps, and whether a small controlled bleed is used to prove tightness. Follow that choreography on the practical. The exam still expects you to know that both checks need ≥ 1.0 psid holding differentials under the valid static method.

Step-by-step DC test (teaching sequence)

Step A — Prepare

• Attach gauge per worksheet; eliminate air.
• Open needed test cocks only.
• Close shutoff #2 (typical) to establish isolation for static testing.
• Confirm supply is available at the inlet (shutoff #1 open unless the procedure says otherwise).

Step B — Check #1 differential

1. Route high/low to span check #1.
2. Establish the static condition called for in the procedure.
3. Read and record psid across check #1.
4. Pass idea: ≥ 1.0 psid tight (holds; does not bleed down through the check).

If the differential collapses toward zero, check #1 is not holding—fail check #1.

Step C — Check #2 differential

1. Re-route high/low to span check #2 (or use the manifold positions your gauge procedure specifies without breaking the static story).
2. Re-stabilize.
3. Read and record psid across check #2.
4. Pass idea: ≥ 1.0 psid tight.

Both checks must pass. A 3.0 psid first check does not forgive a 0.2 psid second check.

Step D — Restore the system

1. Close test cocks; remove hoses; reinstall plugs/caps.
2. Open shutoff #2 (and any other valves you closed) slowly.
3. Check for leaks at cocks and shutoffs.
4. Return the assembly to normal service configuration unless the site requires isolation of a failed unit.
5. Complete the report: check #1 value, check #2 value, pass/fail, tester ID, date, gauge ID/calibration as required locally.

What “tight against direction of flow” means in plain language

For DC teaching language, direction of flow means the checks are evaluated as forward-seating elements under the static test—the way they must hold when supply pressure is upstream and the downstream side of each check is the lower reference in the procedure. This is different from the RP’s special emphasis on check #2 against backpressure with a relief story in play. Do not mix the RP #2 backpressure narrative into a DC answer blank unless the question is explicitly comparing assemblies.

Common procedural mistakes on DC tests

Practical-exam tips for DC

• DC is often the “calmer” assembly after RP, but rushed students still fail on hose discipline and forgot shutoff #2.
• Say the pass line in your head: both checks ≥ 1.0 psid.
• If your program uses a slightly different cock order than a peer’s school, that is normal—criteria stay consistent even when choreography varies.
• Time management: do not reinvent RP relief steps on a DC body; there is no relief to open.

Documentation minimum

A complete DC test record typically includes site ID, assembly make/model/size/serial, location, test date, tester credential number, gauge information, check #1 psid, check #2 psid, overall pass/fail, and any remarks (leaking shutoff, inaccessible cock, owner refused isolation, etc.). Clean documentation is part of being a 5110 professional, not optional paperwork.

Master the two-check static story, the ≥ 1.0 psid twin criteria, and flawless restore—and the DC portion of the practical becomes a controlled, repeatable routine.