Safety / Relief Valves for Water & Wastewater

A surge relief valve and a safety relief valve both protect piping from overpressure, but they differ in speed of response and intended duty: A safety relief valve (spring-loaded, API 526 pattern) is designed for steady-state overpressure — it opens at set pressure and reseats after pressure returns to below set pressure. Opening and closing is relatively slow (several seconds for larger valves). It's designed for thermal expansion, blocked-in liquid, or equipment runaway conditions. A surge relief valve (also called a surge dampener or transient relief valve) is specifically designed for hydraulic transients — fast pressure waves (water hammer) that rise and fall in milliseconds to seconds. Surge relief valves must open extremely rapidly (< 50 ms from set pressure to 80% open) to divert flow before the pressure wave damages the pipeline. They are typically diaphragm-operated or pilot-operated designs with large disc area for rapid full-lift. In water utility practice, the term 'surge relief valve' often refers specifically to the fast-acting design used on pump discharge manifolds and transmission mains. Standard API 526 safety valves are not acceptable for water hammer surge protection — they open too slowly.

Yes, in the United States, safety and relief valves installed on potable water systems must be listed to NSF/ANSI 61 (Drinking Water System Components — Health Effects). NSF/ANSI 61 testing evaluates the leaching of contaminants (heavy metals, organic compounds, microbials) from valve body materials, seat materials, coatings, and lubricants into the water stream at realistic operating conditions. For safety/relief valves on potable water pump stations, PRV bypass stations, and water mains, the valve body (bronze, brass, or SS 316L), seat material (EPDM, NBR, PTFE), and any internal coating must all individually pass NSF/ANSI 61 testing. In practice, reputable water-works valve manufacturers supply a single NSF/ANSI 61 certificate that covers the entire valve assembly. Additionally, in US states with lead-free legislation (California AB 1953, federal Safe Drinking Water Act 2011 amendments), valves must also comply with NSF/ANSI 372 (wetted surface lead content < 0.25% by average weight). In Australia, the equivalent is the Watermark certification scheme administered by the Water Industry Regulators Alliance.