5.1 RP (ASSE 1013) Components and Operation

5.1 RP (ASSE 1013) Components and Operation

Quick Answer: An ASSE 1013 reduced pressure principle (RP) assembly has two independently acting check valves, a differential pressure relief valve in the zone between them, two resilient-seated shutoff valves, and four test cocks (typically TC1–TC4). It is the mechanical assembly approved for health hazards under backpressure and backsiphonage. Flow enters shutoff #1, passes check #1 into a lower-pressure zone, then check #2 and shutoff #2; if inlet-to-zone differential collapses, the relief dumps the zone to atmosphere through an air gap.

Why the RP is the flagship mechanical assembly

On the ASSE 5110 exam and in the field, the RP is the highest-rated mechanical backflow preventer you will test. It is not an air gap and it is not a vacuum breaker. It is a testable assembly listed to ASSE 1013 (device/product standard—not the 5110 personnel standard). When a premises has a toxic chemical feed, a medical waste line, a treated boiler, or another contamination risk and continuous pressure with possible backpressure, the AHJ or purveyor commonly requires an RP (or an air gap). Understanding every major part—and how those parts create a reduced-pressure zone—is prerequisite to Chapter 8 field testing.

Remember the number families:

You test hardware built to 1013. You hold a 5110 credential.

Required components of a complete RP assembly

A complete reduced pressure principle assembly is more than “two checks and a relief.” Product standards and USC field-test practice treat the following as the assembly package:

1. Shutoff valve #1 (inlet / supply side) — resilient seated, full-port style appropriate to the listing.
2. Check valve #1 — independently acting, spring-loaded (typical modern design), seats in the direction that resists reverse flow from the zone back to the inlet.
3. Reduced-pressure zone — the body cavity between check #1 and check #2 where the relief valve senses zone pressure.
4. Differential pressure relief valve — opens to atmosphere when the inlet-to-zone differential falls to its design opening point (field criteria are covered in depth in Section 5.2).
5. Check valve #2 — independently acting, protects against reverse flow from the downstream side into the zone.
6. Shutoff valve #2 (outlet / downstream side).
7. Four test cocks — labeled and ordered so a differential gauge can measure the pressures needed for a full diagnostic test.

If any of those are missing, modified, or replaced with non-resilient shutoffs that prevent isolation for testing, you may not have a complete testable assembly under the standard the purveyor expects.

Test cock numbering (typical TC1–TC4)

Exact port geometry varies by manufacturer, but the logical order used in USC-style procedures is consistent enough that exams treat it as standard knowledge:

Short version: 2 is supply, 3 is the zone, 4 is downstream. That is why every published RP procedure — USC, ASSE, NEWWA — starts the differential hookup with high on TC2, low on TC3.

You will memorize the hose hookup sequence for your gauge type in Chapters 7–8. Here, commit the physical meaning: TC ports give access to inlet, zone, and downstream-of-checks regions so each check and the relief can be evaluated independently.

Flow path under normal operation

Under normal forward flow:

1. Potable water enters through shutoff #1.
2. Pressure opens check #1 against its spring (and seat friction).
3. Water fills the zone. Because of the pressure drop across check #1 (spring + flow losses), zone pressure is lower than inlet pressure during flow and also under static conditions when check #1 holds a positive differential.
4. Water opens check #2 and exits through shutoff #2 to the customer system.
5. The relief valve stays closed because inlet pressure remains sufficiently higher than zone pressure—the differential across the relief’s sensing elements keeps the disc seated.

That lower-than-inlet zone is the heart of the reduced pressure principle. The assembly does not magically create a vacuum; it maintains a controlled pressure reduction between the two checks so the relief has a clear “fail open to atmosphere” path if something goes wrong.

How the two checks create the protected zone

Think of the zone as a monitored buffer:

• Check #1 is the primary barrier from supply into the zone. In static tests it must hold a strong differential (USC requires check #1 ≥ 5.0 psid and above the measured relief opening—details in Section 5.2).
• Check #2 is the barrier from the customer side into the zone. It must hold tight against backpressure. Under USC 10th and AWWA M14 the report records only tight or leaked for check #2 — no psid value is entered for it.
• The relief valve continuously compares inlet pressure to zone pressure. If check #1 leaks badly, or if supply pressure collapses relative to the zone, the inlet-to-zone differential can fall to the relief’s opening set point and the valve discharges the zone to atmosphere rather than allowing zone fluid to be forced back toward the potable inlet without indication.

Independence of the checks matters on the exam: each check is independently acting—not a single dual-check cartridge that shares one spring in a way that fails both together by design. Field tests treat them as separate pass/fail items.

Hazard rating: high hazard including backpressure

Cross-connection programs classify protection by degree of hazard and by hydraulic condition (backpressure, backsiphonage, or both).

A double check (ASSE 1015) lacks the relief and is not accepted for health hazards in standard programs. Vacuum breakers protect against backsiphonage only. When a question describes a toxic or pathogenic load plus possible pump or elevation backpressure, the RP (or air gap) is the correct family—not a DC or PVB.

Orientation, installation notes, and body materials

Horizontal installation of the main body is the most common field arrangement for ¾-inch through larger service sizes: shutoffs horizontal, test cocks accessible, relief discharge pointed to a free air gap drain path. Manufacturers may list vertical up, vertical down, or other orientations for specific models—always follow the listing and manufacturer instructions. Wrong orientation can keep checks from seating, trap debris, or prevent the relief from draining correctly.

Practical inspection points (detailed clearance and drainage rules appear in the installation chapter):

• Relief outlet must not be submerged or hard-piped without the required air gap.
• Test cocks and shutoffs must remain accessible for annual testing.
• Freezing, vandalism, and flood risk at the relief discharge drive enclosure and drain design—not tester improvisation.

Body materials vary with size and service: bronze and brass are common in smaller assemblies; epoxy-coated ductile iron and stainless appear in larger or aggressive-water applications. Internals use resilient seats (elastomer discs or seat rings) and stainless springs in modern designs. As a tester you report leaks, corrosion, missing test cocks, non-resilient shutoff replacements, and failed test values—you do not invent substitute materials on the report. Repair authority belongs to qualified repairers (ASSE 5130 path) under local rules.

What “operation” means for the 5110 tester

On the written exam, “operation” means you can:

• Name every major component and its role.
• Trace forward flow and reverse-threat paths.
• Explain why the zone is lower than inlet pressure and why the relief exists.
• Distinguish RP from DC, PVB, and SVB by components and hazard rating.
• Recognize that annual field testing (not visual inspection alone) proves the checks and relief still meet criteria.

On the practical exam, you will hook up a gauge, isolate with shutoffs, and record relief opening and check differentials on a live or mock 1013 assembly. Component literacy from this section is what makes those steps meaningful instead of rote.

Mini case: chemical feed station

A clinic’s water softener brine and disinfectant chemical feed skid has a pump that can raise process pressure above city pressure. The purveyor requires containment at the service with an RP. At annual test you find all four test cocks present, resilient shutoffs, and a clear air gap under the relief. That physical completeness is step one; Section 5.2 and Chapter 8 tell you whether the numbers (relief opening, check #1 buffer, check #2 tightness) pass. Missing a test cock or hard-piping the relief shut would fail the installation before any gauge reading matters.

Bridge to the next section

You now know what an RP is built of and how water moves through it. Next you need the theory of the reduced-pressure zone and relief valve—why ~2.0 psid opening, why check #1 must stay well above that point, and what continuous drip means. That theory is the difference between memorizing parts and understanding protection.