Air Valves for Offshore and Seawater Applications

GA VALVES LTD TEL: 01484 711983 JOHNSTONE HOUSE FAX: 01484 719848 BIRDS ROYD LANE EMAIL: [email protected] BRIGHOUSE WEBSITE: www.gavalves.co.uk WEST YORKSHIRE VAT No: GB 516235956 HD6 1LQ

Certificate Number LRQ0921762 Supplier Number 70091 Supplier Number 10042395

REGISTERED IN ENGLAND 2535998, REGISTERED OFFICE: 19 LONG FALLAS CRESCENT, BRIGHOUSE, WEST YORKSHIRE, HD6 3TN

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Air valves in high corrosion resistance materials for seawater / offshore duty.

Abstract Air valves are normally required on piping systems to either vent air from a pipeline or admit air back into the system under vacuum conditions. For the water industry, such as water utility companies, iron valves are used with a WRAS approved coating. For seawater duty, or indeed any other corrosive media, more exotic materials are recommended. Commonly used materials are aluminium bronze, super duplex, duplex, hastelloy, stainless steel (various grades), which give a high corrosion resistance. As well as excellent corrosion resistance, these materials also offer the advantages of high strength and toughness. Introduction On a regular basis air valves are overlooked with little thought going into them, yet they play an important part within the system. They need to be correctly specified, as there are many options available. Due to GA Valves experience and wide range of air valves, we are able to work with the client to ensure that the correct air valve is used. We have been supplying our Hivent range of air valves for many years and it is a well-proven product. We can offer technical support so that the correct specification air valve is supplied Why use air valves and which type There are three basic types of air valve which all perform different functions. Below is an explanation why you may need an air valve and which function each type of air valve does. 1). Air release valves. (Also known as; single small orifice air valve, purge, bleed valve) Air that is entrained within a flowing liquid will naturally rise and collect at high points within the system. This accumulation of air within the pipeline adds resistance to the liquid flow causing the pump to work harder, resulting in an increased energy consumption and stress within the system. Such a situation can continue unnoticed adding to the systems operating costs. Air release valves will automatically exhaust these small accumulations of air which collect at the high points whilst the system is flowing and under pressure. This ensures that the system will remain free of trapped air, thus increasing efficiency. Air release valves are installed at high points in the system. Air bubbles entering the valve displace the liquid within the air valve, which lowers the liquid level. Once the level drops to where it no longer buoys the float, the float drops pulling the seat away from the orifice allowing air to be vented to atmosphere. As the air is vented, liquid re-enters the valve lifting the float so the seat presses against the orifice. This cycle is automatically repeated as necessary. These types of valves are not normally sized as they only vent small accumulations of air.




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2). Air vent / vacuum valves. (Also known as; single large orifice air valve, bi-functional, vent / vacuum relief) Filling and draining are critical times in the operation of a pipeline. During filling, air within the empty pipeline must be vented in a controlled manner. This minimises surge and water hammer, thus reducing system stress and inefficiency. During draining air must be admitted into the system to prevent vacuum formation. Air vent / vacuum valves allow the air to be vented from the system ensuring complete filling of the pipeline. Once the air has been vented, the liquid enters the air valve pushing the float against it seat and will not open until the system is drained or a negative pressure occurs. It then opens admitting large volumes of air into the pipeline, thus eliminating vacuum conditions. Air vent / vacuum can be fitted at the top of a riser. Usually the riser will need to be vented quickly with the use of a fast-start pump, for example, an offshore fire system. Air valves do not like fast-start pumps due to the fact that the water column is moving at a high velocity. When this water column enters the air valve it can cause high stress, surge, water hammer and even damage. This can be reduced by the fitment of an adjustable throttle device or surge arrestor, which creates an adjustable orifice to regulate the discharge rate of the air, thereby controlling the rising column of water from the pump. This provides a solution to these potential problems. These types of valves require sizing correctly as they are passing large volumes of air at high velocity. By sizing the air valve correctly the system will be more efficient and, in extreme cases, reduce the risk of pipe collapse during vacuum conditions. 3). Combination air valves. (Also known as; double orifice air valve, tri-functional, air release / vacuum relief) Combination air valves combine both previous 1 and 2 functions. Filling and draining are critical times in the operation of a pipeline. During filling, air within the empty pipeline must be vented in a controlled manner. This minimises surge and water hammer, thus reducing system stress and inefficiency. During draining air must be admitted into the system to prevent vacuum formation. Air vent / vacuum valves allow the air to be vented from the system ensuring complete filling of the pipeline. Once the air has been vented, the liquid enters the air valve pushing the large orifice float against it seat. Once the large orifice float has seated, the large volumes of air have been vented from the system and only the small accumulations of air remain. This is where the air release function activates, which will automatically exhaust these small accumulations of air whilst the system is flowing and under pressure. This ensures that the system will remain free of trapped air, thus increasing efficiency. During draining or if a negative pressure occurs, then the large orifice part opens admitting large volumes of air into the pipeline, thus eliminating vacuum conditions. These types of valves require sizing correctly as they are passing large volumes of air at high velocity. By sizing the air valve correctly the system will be more efficient and, in extreme cases, reduce the risk of pipe collapse during vacuum conditions.




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Add-on features GA Valves offer many options that can be fitted to our air valves. These include; Adjustable throttle device Surge arrestor Inflow check device Outflow check device Vented non-return device Materials available for seawater / offshore duty We have been supplying special material air valves for many years worldwide. Using the materials listed below gives our air valves a long life in arduous environments, which standard material air valves cannot provide. Aluminium Bronze Super Duplex Duplex Hastelloy Stainless steel (various grades) Monel Titanium Others on request Material testing can be offered as per client requirements, such radiography, corrosion test and various non-destructive testing. Material testing to NORSOK MDS or specific Oil Company specifications are also available. We also have the facility to use NORSOK approved foundries. Enquiry information required In order for GA Valves to deal with an enquiry we would ideally require the following information. Line fluid Pipeline diameter and length (for riser pipes) System operating conditions Connection detail Pump start-up time (if applicable) Valve size Conclusion At GA Valves, we can offer one of the largest ranges of air valves available in the World. In conjunction with technical support, UK based foundries and manufacture, excellent delivery times, various testing capabilities, detailed documentation packages and fast quotations we can fulfil our client needs.




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Assorted Aluminium bronze & Super Duplex air valves.

Documents

Air Valves for Offshore and Seawater Applications