Compound Air Release Valve

Compound air release valve is a three-in-one automatic air vent device exclusively mounted on high points, uphill sections and terminals of large municipal water supply, water conservancy and sewage trunk pipelines. Integrated with a large rapid exhaust passage and a separate tiny micro-vent orifice, it realizes three critical functions: fast bulk air evacuation during pipeline filling, continuous micro air release under normal running status, and vacuum breaking during pipeline draining, which cannot be fully achieved by single orifice air release valves. It effectively eliminates air pockets, suppresses destructive water hammer, reduces pipeline vibration and protects pumps, gate valves and pipe fittings from fatigue damage induced by trapped air or internal negative pressure.

When newly constructed or maintained pipelines start water filling, massive air is sealed inside empty pipes. The large main orifice of this compound air valve opens completely to discharge huge volumes of air at high speed, greatly shortening the priming period of the whole pipe network. As water level rises and lifts the primary stainless steel float, the large exhaust outlet is tightly sealed by elastic EPDM gasket to prevent water leakage under full nominal pressure. During stable daily transportation, dissolved air continuously precipitates from liquid and accumulates at the pipeline top. The independent small micro vent keeps exhausting tiny air bubbles separately without disturbing pipeline pressure and flow rate. If air accumulates without timely discharge, effective flow cross-section shrinks, pipeline resistance surges, pump energy consumption rises sharply, and violent water hammer may crack pipe walls or break flanges during sudden pump shutdown. When pipelines drain water or stop operation unexpectedly, liquid level drops and the main float falls down, opening the big orifice again to draw external air into pipes and balance pressure, avoiding deformation, collapse or rupture of HDPE plastic pipes and thin-walled ductile iron pipelines caused by vacuum suction.

The valve body is integrally cast from high-toughness ductile iron EN-GJS-500-7. Its internal and external surfaces are covered with fusion-bonded epoxy coating thicker than 250μm, featuring outstanding anti-rust, anti-scaling and mild corrosion resistance while meeting international drinking water sanitary standards. Two independent floating assemblies are installed inside the valve chamber: a large main float matched with the primary exhaust port and a lightweight auxiliary float supporting the micro vent. All sealing contact surfaces adopt high-elastic rubber cushions to realize bubble-tight shutoff under PN10 and PN16 working pressure. The split top bonnet allows convenient disassembly for sediment cleaning and float replacement, without detaching the entire valve from the pipeline. The whole device operates automatically relying fully on liquid buoyancy, requiring no power supply or manual adjustment and cutting long-term operation and maintenance expenses.

Standard specifications range from DN50 to DN300 with standard flanged connections complying with GB and DIN industrial standards. Applicable media cover tap water, fire-fighting water, raw river water, agricultural irrigation water and low-corrosion wastewater, with a working temperature range of 0°C to 80°C. Every finished product undergoes shell strength testing at 1.5 times nominal pressure and strict air tightness inspection before factory delivery to guarantee stable sealing performance under long-term full-load pipeline operation.

Compared with single orifice air release valves, the compound structure separates large-volume exhaust and micro venting functions to avoid mutual interference, delivering more comprehensive and reliable protection for long-distance large-caliber trunk pipelines. It is widely applied in municipal main water supply networks, reservoir water conveyance tunnels, large farm irrigation trunk lines, sewage treatment plant piping and urban fire protection infrastructure. By stabilizing pipeline flow and pressure, eliminating air blockages and lowering water hammer risks, this air valve reduces energy waste of water pumps, cuts equipment failure frequency and significantly extends the overall service life of the complete fluid transportation system.