Double Air Release Valve Ductile Iron Material Corrosion Resistance

Working Pressure:16kg/cm²
Shell Test Pressure:24kg/cm²
Seat Test Pressure:18kg/cm² 
Media:Water,Neutral Oil
Working Temperature:0-52°C

100％ Fusion Bonded Epoxy Coating for Inner and Outside Surface

Flange Drilled According to EN1092 PN10,PN16

Size:DN50--DN200

Vacuum — The Silent Pipe-Killer That a Single Air Valve Cannot Stop

A water pipeline is designed to resist internal pressure — the hoop stress of water pushing outward, typically at 10, 16, or 25 bar. Every pipe wall thickness calculation, every material specification, every hydrostatic test is designed around this outward force. But a buried pipeline also experiences an external force — the weight of the soil above it, plus atmospheric pressure — that it normally resists because the internal water pressure balances it. When a pipeline is drained without air intake, this balance is broken. The water exits; the void inside the pipe grows; the internal pressure drops. Atmospheric pressure outside the pipe is 1 bar — 10 tonnes per square metre. Soil load adds more. If the internal pressure drops below the external load, the pipe wall buckles inward, collapsing like a drinking straw. This is not theoretical: vacuum-collapsed pipes are a well-documented and expensive failure mode in water utilities on every continent. A single-orifice air release valve cannot prevent this — its orifice is too small and its float seals against reverse flow. Preventing vacuum collapse requires a valve with a large, dedicated air/vacuum orifice that opens the moment water level drops — a double air release valve. The Model 4004 is that valve: two independent float-operated orifices in one ductile iron body, designed to release accumulating air during operation (small orifice) and admit or expel large volumes of air during draining and filling (large orifice).

Product Overview

The Model 4004 is a flanged double air release valve — also called a combination air valve — PN16 rated, DN50–DN200. It houses two fully independent float-operated mechanisms in a single compact body: a small-orifice float for continuous automatic venting of entrained and released air at system operating pressure, and a large-orifice float for high-volume air discharge during pipeline filling and air intake during pipeline draining or pressure loss. Both floats are fabricated from solid-welded stainless steel 304 — corrosion-proof, cannot waterlog, permanently buoyant. The body is cast from EN-GJS-500-7 (GGG50) ductile iron and receives 100% internal and external fusion bonded epoxy coating at 250 um DFT, spark-tested at 3 kV to verify zero holidays. Flanges are drilled to EN1092 PN10/PN16. Manufactured by Shandong Huaze Valve Co., Ltd. (ISO 9001, since 1998), every 4004 is hydro-tested at 24 bar shell, 18 bar seat (both orifices), and verified for full dual-float operation before shipment.

Two Orifices, Two Jobs — How the 4004 Works

Key Features

Vacuum Protection — The Defining Advantage Over a Single Air Valve

This is the feature that makes a double air valve a double. When a pipeline is drained — whether deliberately for maintenance, or involuntarily through a downstream burst — the water exits and the water level in the valve body drops. In the 4004, the large float descends as the water falls, opening the large orifice fully. Atmospheric air rushes in at the full rate required to match the water outflow. Internal pressure stays at atmospheric — the pipe wall experiences no negative differential. Vacuum cannot form. This protects the pipeline regardless of how fast the water drains — a burst at full system pressure will drain the pipe far faster than a controlled maintenance drain, and the 4004's large orifice is sized to handle the worst case, not the controlled case. For pipelines crossing valleys, for pump station headers, for fire mains, for any pipe that might see a rapid drain event, vacuum protection is not a nice-to-have — it is engineering insurance against a failure that costs orders of magnitude more than every air valve on the project combined.

Independent Dual-Float Architecture — Each Orifice Optimised for Its Task

The 4004 does not attempt to operate both air management functions through a single float or a single orifice — a design compromise that forces the orifice to be either too large for precise air release (wasting water through carry-over) or too small for bulk air movement (creating vacuum during draining). Instead, two fully independent floats, each with its own orifice and seat, share the same body: the small float is sensitive, responding to millilitre-level air pockets and sealing instantly when water touches the seat; the large float is powerful, providing full-bore opening for bulk air movement during filling and draining. A failure in one float mechanism does not disable the other — the small orifice can continue releasing air even if the large float is stuck, and vice versa. This independent architecture is the engineering distinction between a proper double/combination air valve and a single-orifice valve with a slightly larger hole.

High-Volume Air Discharge — Fast Filling, Fast Commissioning

When a drained pipeline is refilled, the air ahead of the water front — the entire internal volume of the pipe section — must be expelled before water can occupy the pipe. The fill rate is limited by the air discharge rate: if the air valve orifice is small, the fill pump must be throttled back to a trickle to prevent air compression that stops the fill. A kilometre of DN200 pipe contains over 30 cubic metres of air. With a small-orifice single air valve, venting at perhaps 1–3 cubic metres per minute, that filling operation takes hours — not because the pump is small, but because the air valve is the bottleneck. The 4004's large orifice opens during filling and provides full-bore air discharge. The pipe fills at the pump's design rate. The water front moves at normal velocity. A fill that takes a full day with a single air valve is completed in under an hour with the 4004. When the water reaches the valve, the large float rises and seals — the small orifice then takes over for continuous operational air release.

Continuous Air Release — The Everyday Function That Never Stops

Even in a well-maintained pipeline, air enters continuously. Pump suction vortices draw in dissolved air. Pressure drops at high points and after control valves release dissolved gases. Temperature changes alter the solubility of air in water. Gland seals on pump shafts and valve stems allow microscopic air ingress over months and years. The small-orifice float mechanism in the 4004 operates silently and automatically to vent this accumulated air. As air collects in the body chamber, the water level drops; the small float descends; the small orifice opens; air vents to atmosphere. When the air is released and water rises to the valve, the float lifts and seals the orifice water-tight. This cycle repeats — perhaps a few times a day, perhaps continuously in high-air-entrainment systems — without any operator awareness, any electrical power, any control signal. The result: no air pockets, no flow restriction, no reduction in pumping efficiency, no air-related water hammer.

Corrosion Resistance — SS304 Internals, FBE Body, Designed for the Air-Water Interface

An air valve operates in the most corrosive zone in any pipeline: the air-water interface. Repeated wetting and drying concentrates dissolved minerals and chemicals. Oxygen is continuously present at atmospheric concentration. Temperature cycles from ambient air and solar radiation accelerate electrochemical reactions. The 4004's material selection directly addresses each corrosion mechanism: the solid-welded SS304 floats cannot rust, pit, or absorb water — they maintain buoyancy and dimensional stability for the valve's design life. The SS304 float guides and linkage components operate smoothly without binding from corrosion. The orifice seats — stainless steel or bronze — maintain precision sealing geometry despite years of exposure at the interface. The GGG50 ductile iron body is protected by 100% FBE coating (250 um DFT, 3 kV spark-tested) inside and out — the iron never touches water, never touches air, never corrodes. And all fasteners are SS A2-70 — removable without cutting after years of exposed outdoor service.

Ductile Iron Body — GGG50, 500 MPa, Survives What Grey Iron Cannot

Air release valves are installed at exposed locations — on risers at pipeline high points, in valve chambers that flood seasonally, on bridge crossings subject to vibration, on pump station roofs exposed to accidental impact. The 4004's GGG50 ductile iron body provides 500 MPa tensile strength with 7% elongation — twice the strength of grey iron and, critically, ductile behaviour. If a ductile iron valve body is overloaded — excessive pipe strain from settlement, impact from a dropped tool or vehicle, thermal stress from direct sun followed by cold rain — it deforms before it fractures. The deformation (a visible crack, a weeping flange, a distorted bolt pattern) warns before failure. Grey iron provides no such warning; it shatters. For a valve that will sit on top of a pipeline for 30, 40, or 50 years — in sun, rain, frost, and heat — the ductile iron body is the difference between a valve that survives its environment and one that eventually becomes a leak point.

The Pipeline's Air Management Lifecycle — Day 1 to Year 20

Materials of Construction

Technical Data

Applications — Where Double Air Release Valves Are Standard Specification

• Long-Distance Water Transmission Mains: Cross-country pipelines 10–100+ km long, crossing undulating terrain. Every high point must be vented; every section must be drainable for maintenance. The 4004's vacuum protection is mandatory during emergency burst drains — a vacuum-collapsed section of a transmission main can require kilometres of excavation and replacement. Fast filling via the large orifice reduces commissioning time from days to hours.
• Pump Station Headers — Suction and Discharge: During pump start-up, the empty discharge header must fill quickly, and air must vent at the fill rate. During pump shutdown or maintenance, the header must drain without vacuum. The 4004 handles both, plus continuous air venting from pump-entrained air during operation — protecting downstream equipment and next-stage pumps.
• Valley Crossings and Pipeline Low Points: Pipelines descending into and ascending out of valleys create siphons that amplify vacuum forces during draining. The water column in the descending leg pulls water from the ascending leg, creating negative pressure at the low point. The 4004 at the valley low point acts as a vacuum breaker — air enters, siphon breaks, pipeline stays intact.
• Fire Protection Mains: Fire water networks are static for years between tests. Air accumulates and must be continuously released to keep the system fully charged. When drained for testing or modification, vacuum protection prevents collapse of fire mains that pass under buildings, roads, and critical infrastructure where excavation is exceptionally expensive and disruptive.
• Irrigation Networks with Seasonal Operation: Agricultural and landscape irrigation systems that are drained for winter freeze protection and refilled each spring. The 4004's large orifice enables fast spring fill across large pipe networks; the small orifice handles air release throughout the irrigation season; the vacuum protection prevents collapse during the autumn drain-down. One valve, three seasonal duties.
• Water Treatment Plant Interconnecting Pipework: Multiple unit processes — aeration basins, flocculators, clarifiers, filters, clear wells — connected by pipe runs that must be isolated and drained for vessel maintenance. The 4004 at high points between treatment stages ensures safe draining and fast refilling with no air carryover from one process to the next.
• Cooling Water and Industrial Process Loops: Recirculating cooling and process water systems that cycle between operation and maintenance shutdowns. The 4004's dual-float mechanism handles all air scenarios — filling, operating, draining — without operator intervention, protecting heat exchangers from air binding and vacuum collapse.

Quality Assurance

• 100% Shell Hydrostatic Test — 24 bar, 60 sec hold — every valve body
• 100% Dual Seat Test — 18 bar, zero leakage — independently verified on both small and large orifices — every valve
• 100% Float Buoyancy Test — Water immersion, mass measurement — every small and large float — zero water ingress
• 100% Dual-Float Operational Test — Full stroke exercise — air release, air discharge, air intake — every complete valve assembly
• 100% FBE Coating DFT Verification — Minimum 250 um, all internal and external surfaces — every valve
• 100% Spark Test — 3 kV continuous holiday detection, full coverage — every valve
• 100% Dimensional Inspection — EN1092 flange drilling, body height, face-to-face, vent connection thread
• EN 10204 3.1 Material Certificates — Available on request for body, floats, and pressure-retaining components

Ordering Information

About Shandong Huaze Valve Co., Ltd.

Established 1998 in Qingdao, China. ISO 9001 certified manufacturer with 100–200 employees, 300 containers annual production capacity, and USD 5–6 million annual turnover. Huaze manufactures a comprehensive range of pipeline products for water, wastewater, fire protection, HVAC, irrigation, process water, and industrial applications: Gate Valves (DIN 3352 / EN 558, BS 5163, SANS 664), Swing Check Valves — flanged and wafer (DIN, BS 5153, Silent Metallic, Silent Resilient, Corrosion-Resistant Wafer), Strainers — Y Type and T Type Basket (Quick-Release, Low Maintenance), Air Valves — Single Air Release (Model 4002) and Double Air Release (Model 4004), Globe Valves, Flap Valves, and Fire Hydrants. All products are individually factory-tested to the relevant standards, coated, spark-tested, and shipped from Qingdao Port to distributors, water utilities, EPC contractors, pump OEMs, and building services contractors in 30+ countries worldwide.