ALFA T2/T3 RB/FB ANSI 150 – ANSI 2500 TRUNNION BALL VALVE

GENERAL DESCRIPTION

ALFA VALVOLE "TRUNNION MOUNTED" Ball Valves are designed to satisfy all the requirements of API 6D for pipeline service by utilizing the proper materials to meet the requirements of the service conditions for different fluids and pressures up to ANSI class 2500/PN 420. ALFA VALVOLE "TRUNNION MOUNTED" Ball Valves are designed to withstand hydrocarbon corrosion as well as the severe service conditions that occur during start-up, ensuring a long life. The technical solutions drawn up for the petro-chemical industry can be successfully used in other industrial fields.

Easy maintenance can be carried out in the dynamic seal areas.

CONSTRUCTION

BODY

The body of the ALFA VALVOLE "TRUNNION MOUNTED" Ball Valve is manufactured from forged pieces in compliance with ASTM standards. This type of design gives a good homogeneous material structure ensuring a long working life for the valve.

STEM

The stem is constructed separately from the ball. The stem is designed with an integral pin which permits perfect positioning with the ball. The stem is of an anti blow out design. The load pressure on the ball (thrust) is absorbed by special bearings fitted on the ball trunnions (upper and lower), thus ensuring no side thrust on the stem, which permits a very low operating torque and a long life.

STEM SEAL

The stem seal is obtained by a set of three gaskets (triple barrier) ensuring perfect tightness. Furthermore, if required, the upper gasket can be easily replaced by disassembling the upper part only. On request a lubricator is available in order to inject lubricant and/or sealing grease, if necessary.

BODY/CLOSURE SEAL

A set of two gaskets ensures tightness even in the case of an environmentally harmful medium.

SEAT SEAL

ALFA VALVOLE "TRUNNION MOUNTED" Ball Valves are designed to guarantee a perfect thightness between ball and seat, by means of a primary soft seal of suitable material and of a secondary metal seal. Tightness is obtained by providing the necessary seat thrust on the ball.

ALFA VALVOLE "TRUNNION MOUNTED" Ball Valve seats are manufactured in two basic types:

1) SELF RELIEVING SEAT

fig. 1) Shows that inlet pressure works on seat area "A" which is wider than area "B"; therefore the differential area creates a piston effect which forces the seat against the ball surface producing a tight effective seal.

fig. 2) Shows the self relieving feature when the pressure in the body cavity exceeds the inlet or the outlet pressure. In this case area "C" is wider than area "D" and when the piston effect created becomes greater than the constant spring load, the self relieving effect is obtained.

2) DOUBLE PISTON EFFECT SEAT

fig. 3) Shows that inlet pressure works on seat area "A" which is wider than area "B"; therefore the differential area creates a piston effect which forces the seat against the ball surface, producing a tight effective sea-ling.

fig. 4) Shows the pressure inside the body on seat area "D" which is wider than area "C"; therefore the differential area creates a piston effect which forces the seat against the ball, producing a tight effective seal.

LOW OPERATING TORQUE

The ball operates on a fixed axis established by bearing blocks located on the upper and lower ball trunnions. The ball trunnions revolve in an oilless bearing which does not require lubrication. The main feature of this bearing is a reduced friction factor with a better load resistance.

This feature combines to assure lower operating torque.

DOUBLE BLOCK AND BLEED

This is the capability of a valve, in a pipeline under pressure, to have its body cavity bled down to atmospheric pressure when the valve is in fully closed position.

ALFA VALVOLE "TRUNNION MOUNTED" Ball Valves are designed for services requiring "double block and bleed". The upstream and downstream seat bubble-tight design permits venting and draining of line fluids from the body cavity. Small body cavities permit rapid drainage.

Bubble-tight sealing is achieved without lubricants, which completely eliminates product contamination. Double block and bleed design with emergency grease seal is available on request.