Emergency Vent is available in 250 mm (10”) and 500 mm (20”) sizes with flat face flanges to match a 10” ASA Class 125 and a 20” API Roof Manhole respectively. For normal service Applications, the steel manhole base has a weld deposited stainless steel seat facing and is fitted with a neoprene ‘Tite’ seal diaphragm. For chemical/low temperature service Applications, the manhole base is of stainless steel Construction and a PTFE coated glass cloth ‘Tite’ seal diaphragm completely covers the underside of the hinged cover.
250 mm (10”) Minimum set pressure with alum. pallet = 84 m m (3.3”) W.G. Minimum set pressure with steel pallet = 165 m m (6.5”) W.G. Maximum set pressure with alum. pallet = 1435 mm (56.5”) W.G. Maximum set pressure with steel pallet = 1516 mm (59.7”) W.G. 500 mm (20”) Minimum set pressure with alum. pallet = 51 m m (2.0”) W.G. Minimum set pressure with steel pallet = 112 m m (4.4”) W.G. Maximum set pressure with alum. pallet = 640 m m (25.2”) W.G. Maximum set pressure with steel pallet = 701 m m (27.6”) W.G.
When set pressure is reached, the pallet starts to lift and flow efficiency rises rapidly to approximately 60% of a perfect orifice when tank pressure is 40% in excess of the set pressure.
At higher overpressure the flow efficiency can reach 75%. Where 40% overpressure cannot be tolerated. Flow capacity formulae have been estimated for 30%, 20% overpressure.