RP, DC, PVB, SVB: what’s in your box

How it works

Two independent check valves with a hydraulically operated relief valve between them. The zone between the checks is held at lower pressure than the supply. If either check leaks, the relief valve opens and dumps water to atmosphere rather than let it flow backward.

Pass criteria

Relief valve opens at 2.0 psid or more; check valve #1 holds a differential well above the relief opening point; check valve #2 is tight against backpressure.

Where you’ll find it

• Premises isolation at the meter for high-hazard sites
• Hospitals, clinics, dental offices
• Car washes, labs, food processing
• Irrigation with chemical injection
• Boilers with treatment chemicals

Common failures

• Relief valve discharging continuously (“spitting”)
• Fouled #1 check seat
• Hardened relief-valve diaphragm
• Leaking shutoff valve

How it works

A full-size RPBA with a bypass that includes a small RP and water meter. Small, unauthorized flows go through the meter so the utility can detect leaks or theft on an unmetered fire line.

Pass criteria

Both the mainline and bypass assemblies are tested to RPBA criteria.

Where you’ll find it

• Fire sprinkler systems with high-hazard additives (antifreeze, foam)
• Fire service where the utility requires RP protection

Common failures

• Bypass meter or bypass RP failure
• Mainline check fouled by debris after a fire-flow test

How it works

Two independently acting, spring-loaded check valves in series between two resilient-seated shutoff valves, with four test cocks.

Pass criteria

Each check valve holds 1.0 psid or more in the direction of flow; shutoff #2 is tight.

Where you’ll find it

• Lawn irrigation
• Fire sprinkler systems without additives
• Multi-story buildings
• Premises isolation for low-hazard sites

Common failures

• Debris holding a check off its seat
• Worn check rubber
• Leaking #2 shutoff making the test impossible

How it works

A full-size DCVA with a metered bypass containing a small DCVA, so low flows on the fire line are recorded.

Pass criteria

Mainline and bypass are each tested to DCVA criteria.

Where you’ll find it

• Standard wet-pipe fire sprinkler service
• Commercial and multifamily fire lines

Common failures

• Bypass check fouled
• Mainline check stuck after a flow test

How it works

A spring-loaded check valve plus a spring-loaded air inlet. If supply pressure drops, the check closes and the air inlet opens, breaking any siphon.

Pass criteria

Air inlet opens at 1.0 psid or more and opens fully; check valve holds 1.0 psid or more.

Where you’ll find it

• Residential lawn irrigation
• Must be installed at least 12 inches above the highest downstream outlet

Common failures

• Freeze-cracked body or bonnet
• Air inlet stuck from mineral build-up
• Check valve not holding

How it works

Like a PVB, but designed so the air inlet doesn’t discharge water during normal pressurization — making it suitable where spillage matters.

Pass criteria

Check valve holds 1.0 psid or more; air inlet opens at 1.0 psid or more.

Where you’ll find it

• Indoor or landscaped locations where a PVB’s spitting would be a problem
• Irrigation

Common failures

• Air inlet poppet sticking
• Check valve leaking

How it works

A float/poppet that drops open to atmosphere when flow stops. It can’t be under continuous pressure and has no test cocks.

Pass criteria

Not field-testable. Under WAC 246-290-490, AVBs on irrigation are inspected at installation, after a backflow incident, and after repair, reinstallation or relocation.

Where you’ll find it

• Some older irrigation installations
• Hose bibbs and service sinks (as a device)

Common failures

• Installed with a downstream valve (illegal)
• Installed too low