FLANGED GATE VALVES
اين شيرها بيشتر در محل هايي به کار مي روندکه بخواهند جريان سيال را به طور کامل بسته يا باز نمايند. از خواص اين شير ميتوان به کم بودن افت فشار در طول آن اشاره نمود. به همين دليل در سر راه لوله هاي با طول زياد از اين شيرها استفاده ميشود. يک شير کشويي براي محدوده وسيعي از سيالات ميتواند مورد استفاده قرار گيرد و در هنگام بسته شدن آببندي خوبي دارد. مهمترين موارد استفاده از اين شيرها در مايعات ويسکوز (چسبنده) همانند گريسهاي سبک، روغنهاي سنگين و ساير سيالات غير قابل اشتعال ميباشد. مجرابند اين شير وقتيکه بطور کامل باز ميشود، از مسير عبور جريان حذف ميشود. اين خاصيت باعث از بين رفتن هرگونه مقاومتي در شير هنگامي که باز است ميگردد. وقتي که شير کاملاً بسته شد يک حلقه مجرابند را آببندي ميکند. با قرارگيري مجرابند درداخل حلقه آب-بندي، نشتي به مقدار زيادي کاهش مييابد و حتي امکان دارد مقدار نشتي به صفر نيز نزديک گردد.
• HANDWHEEL The spoked handwheel is fabricated from steel pipe. The hub is coupled with the yoke sleeve by means of a key. Larger valves are equipped with a bevel or spur gear gearbox unit.
• YOKE SLEEVE The yoke sleeve is made from cast aluminium bronze having high resistance to wear and a high melting point. It is designed to simplify removal from the bonnet or the yoke whilst the valve is in service. Gate valves 6" class 600 and above are fitted ball thrust bearings.
• GLAND AND FLANGE They are in forged steel and are supplied in two pieces, self aligning design in order to allow the gland to slide parallel to the stem even if the eyebolts are unevenly tightened.
• GLAND BOLTS AND NUTS The forged steel gland bolts are of the eyebolt type which can be swung outward for ease of gland repacking. They are fixed to the bonnet by hinge pins.
• BONNET BOLTING Bonnet studs and nuts are manufactured from alloy steel to the relevant ASTM standard. The body to bonnet connection is designed according to ASME VIII DIV 1 standard.
• BODY The body is cast in carbon or stainless steel and is available in many other CRA. It is carefully designed for total reliability and simple maintenance. The basic dimension, i.e. wall thickness, face to face and flanges comply with the relevant API and ANSI standards. The body-to-bonnet flange is circular, expect in the Class 150 which is oval. The body-to-bonnet joint are flat face on Class 150 valves, male-and-female on Class 300 and ring joint on Class 400 and above. The body is basically supplied with renewable seats. Bosses are provided for drain taps or by-pass piping.
• The internal surfaces in contact with the fluid can be fully lined or cladded for improved corrosion or erosion resistance.
• BONNET As the body, the bonnet is cast in carbon or stainless steel and is available in many other CRA. It is machined to accept yoke sleeve and incorporates a stuffing box sized in accordance with the API standard.
• Lifting lugs can be provided integrally cast on the bonnet surface.
• BONNET BUSHING The bonnet bushing or backseats is part of the valve trim. Its design allows valve repacking without valve's bleeding or draining. Hardfacing can be provided on stem seating surface.
• STEM The stem is part of the trim and is available in a wide range of material in accordance to API 600 or customer's requirements. The stem is provided with a T-shaped head. A ground backseat is provided to ensure a perfectly tight seal to the stuffing box when the valve is fully open. The stem is highly finished in order to minimize friction and prevent damage to the packing. The thread is trapezoidal ACME type. All the stem sizes comply with the API 600 standard.
• SEAT RINGS Welded-in seat rings are supplied as a standard. The rings are part of the trim of the valve. They can be externally threaded and internally notched for easy installation and dismantling. Special attention is given to the sealing surface which are ground and lapped for a tight seal.
• WEDGE The wedge is the main part of the trim. It is forged steel or alloy for diameters up to 12" and is in cast for larger valves. It is normally supplied as the solid wedge type. It is connected to the stem by means of a T -shaped joint. The guides on each side of the wedge are machined. Special care is given to the seating surfaces which are ground and lapped, integral or handfaced.
• A cladding or lining can be applied to the wedge to improve its resistance against erosive and corrosive environments. For improved seating and unseating easiness, it can be machined with the flexible option.
FLANGED GATE VALVE DATA SHEET