Building Code Glossary
Reduced Pressure Principle Backflow Preventer: Building Code Definition
How the IPC 2009 define reduced pressure principle backflow preventer, where the wording differs, and which chapters depend on the term.
On this page
Last updated September 7, 2026 · Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control.
Direct answer
Reduced pressure principle backflow preventer is a defined term in the International Plumbing Code (IPC) 2009, in Definitions. The code's own words are: “A backflow prevention device consisting of two independently acting check valves, internally force-loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to the atmosphere, internally loaded to a normally open position between two tightly closing shutoff valves and with a …” No other I-Code in this corpus defines it, so the IPC 2009 definition is the one to work from. The term is used in 5 chapters of this corpus, most often in Water Supply and Distribution (IPC 2009), Water Supply and Distribution (IRC 2009), General Regulations (IPC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted.
Content and cited inputs reviewed by Scott Barrington, Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.
What does this term mean?
Reduced Pressure Principle Backflow Preventer — IPC 2009, Definitions:
A backflow prevention device consisting of two independently acting check valves, internally force-loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to the atmosphere, internally loaded to a normally open position between two tightly closing shutoff valves and with a means for testing for tightness of the checks and opening of the relief means.
What must be verified before using this guidance?
Reduced Pressure Principle Backflow Preventer is defined once in this corpus, in the Definitions chapter of the International Plumbing Code (IPC) 2009:
A backflow prevention device consisting of two independently acting check valves, internally force-loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to the atmosphere, internally loaded to a normally open position between two tightly closing shutoff valves and with a means for testing for tightness of the checks and opening of the relief means.
Where reduced pressure principle backflow preventer is used in the code
The term appears in 5 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next.
| Chapter | Code | Mentions |
|---|---|---|
| Water Supply and Distribution | IPC 2009 | 24 |
| Water Supply and Distribution | IRC 2009 | 21 |
| General Regulations | IPC 2009 | 2 |
| Plumbing Administration | IRC 2009 | 2 |
| Definitions | IPC 2009 | 1 |
The term in use
How the code actually writes about reduced pressure principle backflow preventer, quoted from the 2009 text hosted here:
The water supply for hospital fixtures shall be protected against backflow with a reduced pressure principle backflow preventer, an atmospheric or spill-proof vacuum breaker, or an airgap.
Potable water openings and outlets shall be protected by an air gap, reduced pressure principle backflow preventer with atmospheric vent, atmospheric-type vacuum breaker, pressure-type vacuum breaker or hose connection backflow preventer.
Reduced pressure principle backflow preventer assemblies, double check-valve assemblies, pressure vacuum breaker assemblies, reduced pressure detector fire protection backflow prevention assemblies, double check detector fire protection backflow prevention assemblies' hose connection backflow preventers, and spillproof vacuum breakers shall be tested at the time of installation, immediately after repairs or relocation and at least annually.
The terms reduced pressure principle backflow preventer is built out of
The definition above leans on 4 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what reduced pressure principle backflow preventer covers:
- Automatic — IBC 2009: As applied to fire protection devices, a device or system providing an emergency function without the necessity for human intervention and activated as a result of a predetermined temperature rise, rate of temperature rise or combustion products.
- Backflow — IPC 2009: Pressure created by any means in the water distribution system, which by being in excess ofthe pressure in the water supply mains causes a potential backflow condition.
- Venting — IRC 2009: Removal of combustion products to the outdoors.
- Device — IRC 2009: Aunit of an electrical system that carries or controls electrical energy as it principal function.
Reduced Pressure Principle Backflow Preventer: what to open, and in what order
Every row is a document this term depends on. The ICC code library and the ICC adoption maps cover the middle rows.
| Check | Where | Confirmed |
|---|---|---|
| Read the definition in the adopted IPC | Definitions | |
| Re-check the requirement that uses it | Water Supply and Distribution (IPC 2009) | |
| Re-check the requirement that uses it | Water Supply and Distribution (IRC 2009) | |
| Re-check the requirement that uses it | General Regulations (IPC 2009) | |
| Re-check the requirement that uses it | Plumbing Administration (IRC 2009) | |
| Confirm the dependent definition | Automatic | |
| Confirm the dependent definition | Backflow | |
| Confirm the dependent definition | Venting | |
| Local amendment to any of the above | Jurisdiction's amendment list |
A research aid, not a code determination. The authority having jurisdiction decides which edition and which amendments apply.
Where can you explore related guidance?
- Explore all glossary guidance
- Automatic: Building Code Definition
- Backflow: Building Code Definition
- Venting: Building Code Definition
- Device: Building Code Definition
Sources and method
Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The ICC code library publishes the current model text and the ICC adoption maps show which edition a jurisdiction has adopted; those sources control.
Source links
Frequently asked questions
What is the code definition of reduced pressure principle backflow preventer?
The International Plumbing Code (IPC) 2009 defines it in Definitions as: “A backflow prevention device consisting of two independently acting check valves, internally force-loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to the atmosphere, internally loaded to a normally open position between two tightly closing shutoff valves and with a means for testing for tightness of the checks and opening of the relief means.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally.
Which parts of the code depend on reduced pressure principle backflow preventer?
In this corpus the term is used across 5 chapters, led by Water Supply and Distribution in the IPC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own.
What is a reduced pressure principle backflow preventer?
In the 2009 I-Codes hosted here it is a defined term rather than a description. The IPC 2009 states, in Definitions: “A backflow prevention device consisting of two independently acting check valves, internally force-loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to the atmosphere, internally loaded to a normally open position between two tightly closing shutoff valves and with a …” It is defined in IPC 2009. Because it is a defined term, whatever the adopted edition says it means is what every section using it means — so check Chapter 2 of that edition and any local amendment before relying on this wording.
What is the main difference between a double check valve and a reduced pressure backflow preventer?
Valve is a separate defined term. The IRC 2009 defines it as: “A device used in piping to control the gas supply to any section of a system of piping or to an appliance.” That is not the same as reduced pressure principle backflow preventer, which the IPC 2009 defines as “A backflow prevention device consisting of two independently acting check valves, internally force-loaded to a normally closed position and separated by an intermediate chamber (or zone) in which there is an automatic relief means of venting to the atmosphere, internally …” — read both before applying either, and confirm the wording in the edition your jurisdiction has adopted.
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