Air release valve delivery information

Fifty DN200 PN25 Double Orifice Air Valves: The Heavy End of the Range

In October we wrote that past DN200 an air valve stops being a fitting. This batch is that statement made in quantity: fifty double orifice air release valves, every one of them DN200, shipped on November 11.

The order: 50 pcs DN200, PN25, flanged to EN 1092-2, bodies cast in GGG50 ductile iron. The casting beside the flange reads DN200 PN25 GGG50, so the working class is part of the metal rather than a sticker. For the buyer it is one line item on one purchase order. For the workshop it is fifty large castings that have to be poured, machined, tested and packed to the same standard, fifty times in a row.

The loads sit at the top of the range. At 25 bar, the working pressure of this class, each DN200 flange carries around 78 kN of end thrust, roughly one and a half times the load of the same size at 16 bar. Bolts, seats and floats are all sized against that number. Buoyancy follows the cube of float diameter, so the DN200 float is its own casting with its own wall section and seat ring, and at PN25 the float has to seal against a force measured in tonnes, not kilograms.

The double orifice layout is unchanged at this size. The large orifice under the hood vents the main at full bore during filling and admits air on drain-down, so the pipe is not pulled flat. The small orifice in the side chamber releases the air that keeps coming out of solution while the line runs under pressure. What changes with size is everything around them: heavier floats, thicker walls, more bolts on the flange, and less room for error in the casting.

Every body is cast in GGG50 ductile iron to ISO 1083 and EN 1563, epoxy coated inside and out, and pressure tested before packing. Each nameplate lists the body material and the seal; the month of manufacture is cast into the body, 202611 on this batch.

Large valves do not travel like small ones. They went into wooden cases with cardboard grid cells, a few units per case, braced so the flanges carry the load and the coated surfaces do not touch. The plastic plugs on the side outlets stay on until installation.

Fifty valves, one large size, one shipment. When a transmission main needs air protection at the top of the range, this is the batch built for that duty.