Short definition
A hose-bib vacuum breaker (HBVB) is a small atmospheric vacuum breaker designed to screw directly onto a hose-bib outlet (3/4-inch male hose thread). Provides back-siphonage protection at outdoor sillcocks where a hose could be submerged in a pool, sprayer tank, or fertilizer applicator. Listed under ASSE 1011. WA code requires one on every hose bib that doesn’t have an integrated vacuum breaker.
What it is
The HBVB is a brass or chrome-plated body with female hose thread on the inlet (mates to the hose-bib spigot) and male hose thread on the outlet (the garden hose connects there). Inside is a check disc and an atmospheric vent that opens when supply pressure drops below atmospheric, breaking any siphon and admitting air to prevent back-siphonage.
Two main types:
- Integrated. Built into modern frost-free sillcocks, in the upper body of the valve. The valve and the HBVB are one unit; replacement is the whole sillcock or the upper section.
- Add-on. Screws onto the existing hose-bib threaded outlet. Cheap retrofit for older hose bibs that didn’t have integrated protection.
Some HBVBs include a tamper-resistant set screw or a one-way fitting that prevents removal by garden-hose users — keeps the device on the bib where it’s needed.
Why it matters to a homeowner
The contamination scenario is concrete: a garden hose dropped into a pool, a chemical sprayer tank, or a fertilizer applicator — combined with an upstream pressure inversion (utility main break, fire-flow draw nearby) — pulls that downstream water back up the hose and into the home’s drinking water. The HBVB’s air vent opens the moment supply pressure inverts, breaking the siphon before contamination travels back upstream.
Three places homeowners encounter HBVBs:
- Outdoor hose bib without one. Code requires retrofit. A screw-on HBVB is a $10–$25 part and a 1-minute install — hand-tight onto the threaded outlet. The tamper-resistant version costs a few dollars more.
- Modern frost-free sillcock with integrated HBVB. If it leaks, the upper section is the replacement. A $5–$15 part for the typical residential sillcock model.
- Inspection report flags missing HBVBs on older homes during a sale.
When you’ll encounter this term
- Inspection identifies a hose bib without backflow protection.
- New sillcock install — modern frost-free sillcocks have HBVBs integrated.
- Existing HBVB drips at the air vent during normal flow — diaphragm has degraded; replace.
- Tamper-resistant HBVB requested when the previous one was removed by a garden-hose user.
Common variants
- HBVB (residential, ASSE 1011) vs. PVB (irrigation, continuous pressure, ASSE 1020) vs. AVB (general, ASSE 1001).
- Integrated (frost-free sillcock) vs. add-on (screws onto an existing hose bib).
Common failure modes
- Diaphragm degradation from chlorine or freeze cycles — leaks at the vent during normal use.
- Mineral deposits prevent disc seating — water drips from the vent.
- Cracked plastic body from impact (lawn mower, kid’s bike, errant car wheel).
- Stuck-closed vent — defeats the protection function.
Washington note
WA UPC adoption (WAC 51-56) and WA DOH WAC 246-290-490 require backflow protection at outdoor hose bibs. Modern frost-free sillcocks have HBVBs integrated; older standard hose bibs require a screw-on HBVB retrofit. The retrofit is one of the most common minor inspection-report items on pre-1990 WA homes — and one of the cheapest to fix.