What is an RP Assembly ?

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The RP is the most protective type of assembly available for backflow prevention. They are regulated by two main specifications, ASSE 1013 and AWWA C511, depending on the codes and systems used ( Plumbing for ASSE, Water Distribution for AWWA ) they will have to adhere to one of these specifications or sometimes both, if you read both specifications, they largely say the same things with very small differences in the wording. Typically they are installed either for domestic water containment protection which protects the water purveyor's lines from an entire facility, or the they are used to isolate hazardous systems from the potable water supply inside of a plumbing system in a building, for example an HVAC make up water connection or a connection to irrigation. They will always have some type of outlet to atmosphere on the bottom  or side, called the Relief Valve, which differentiates the RP from a Double Check which may look the same but without the relief valve.

The RP Assembly incudes:

No. 1 Test Cock - This test cock is not normally used during testing, but can be used to flush components of the valve during repair, or used to bypass a leaking No. 2 Shutoff during testing.

No. 1 Shutoff Valve - This valve is normally open during testing, but would be closed if repair is required for the valves. During some single hose testing methods, you would also use the No. 1 Shutoff.

No. 2 Test Cock - This test cock shows the pressure in the zone upstream of No. 1 Check Valve and the Relief Valve, which is also equal to the static line pressure for the system.

No. 1 Check Valve - This Check Valve is extra heavy ( Minimum 5.0 psi Differential ) and, although would stop backflow in an extreme situation, under normal operation should never be in a Backsiphonage or Backpressure Condition, and serves as a component of the Relief Valve System by reducing the pressure between the upstream and downstream sides of the relief valve. The Relief Valve should remove all water or contaminating liquids from the Reduced Pressure Zone in the event of a Backpressure or Backsiphonage event.

No. 3 Test Cock - This test cock shows the pressure in the zone downstream of No. 1 Check Valve and the Relief Valve, and upstream of No. 2 Check Valve, also referred to as the "Reduced Pressure Zone"

Relief Valve - The relief valve is hydraulicly dependent on the No. 1 Check Valve, meaning that if the No. 1 Check Valve leaks, the Relief Valve will discharge continuously. This valve will discharge any contaminants that may leak through No. 2 Check Valve in a Backpressure or Backsiphonage condition, such that even if the components of an RP are broken, as long as the relief valve is not stuck closed, backflow will not occur.

No. 2 Check Valve - This Check Valve is normally the component that stops backflow in a Backpressure condition, holding backpressure continuously in some applications, and holds the system's water inside the building during a Backsiphonage condition, until pressure is restored. This check valve has a normal pressure differential ( Minimum 1.0 psid )

No. 4 Test Cock - This test cock shows the pressure in the zone downstream of No. 2 Check Valve, which is used in testing to determine No. 2 Check Valve tightness against backpressure and Differential Pressure ( if required ).

No. 2 Shutoff Valve - This second shutoff valve is normally used during testing and interrupts the flow to the building or the hazardous service being isolated.

More info on how the RP works on our YouTube Video here