Two or three pieces bolted body construction designed for maximum rigidity against pipeline forces. Bolted construction allows easy service and on site maintenance.
A primary positive sealing action of O-rings and a secondary fire-proof graphite gasket assure no leakage in all static body joints.
PRESSURE RELIEF (API 6D, 6.8).
All standard trunnion ball valves shall be provided with self relieving seats allowing automatic body cavity relief exceeding 1,33 times the valve pressure rating at 38°C.
All Dafram trunnion mounted ball valves have a drilled and threaded drain connection as per API 6D.
All Dafram trunnion mounted ball valves have a threaded vent anti-blow-out valve as per API 6D.
VALVE ENDS (API 6D,6.7).
Standard end flanges shall be furnished in accordance with ASME B16.5 for sizes up to and including DN 600 (NPS 24), except MSS SP-44 for DN 550 (NPS 22) and ASME B16.47 Series A for DN 650 (NPS 26) and larger sizes. Standard welding ends shall conform to ASME B31.8 and ASME B16.25.
The ball is fixed and the two spring loaded seat rings are floating, free to move along the valve axis, always in contact with the ball to provide an effective tight seal also at low differential pressures.
BALL POSITION AND POSITION INDICATORS.
Proper position stops assure fully open and fully closed position of the ball. Valves fitted with manual or powered actuators shall be supplied with position stops adjusted in the factory. Wrenches or gear and actuator position indicators shall indicate the ball position. Stems have proper provisions for the verification of open and close alignment when the wrench, gear or actuator have been removed.
LOW FRICTION BUSHING.
Side load due to line pressure acting on the ball is supported by special maintenance free dry bearings.
SEATS, SEAT INSERTS & SEAT SEALINGS
FLOATING SEAT RINGS.
Indipendent floating pressure loaded seat rings grant a positive tightness of the valve. Springs action pushes always the upstream seat ring in contact with the ball to provide an effective tight seal also at low differential pressures.
SELF RELIEVING DESIGN.
According to API 6D definitions, in the standard design all DAFRAM trunnion mounted ball valves are bi-directional, twin-seat (with two seats, both seats uni-directional) valves. This means valves designed for blocking the fluid in both directions, with two SELF RELIEVING seats, each sealing in one direction (from the valve ends to the valve body cavity) able to relieve the body cavity overpressure generally downstream.
Nylon seat inserts are used as standard in the Dafram ball valves for general services for service temperatures of -10 to + 120°C.
STEM & STEM SEALINGS
Strict machining tolerance, accurate surface finish, a primary positive sealing action of two O-rings and a secondary fire-proof graphite gasket assure zero leakage of stem sealing.
STEM RETENTION (API 6D, 6.18).
All valves have been designed with an anti-blow-out stem to prevent his ejection by internal pressure. The stem design don’t preclude replacement of damaged stem sealings.
ANTI-STATIC DEVICE (API 6D, 6.20).
In all DAFRAM ball valves an anti-static spring loaded device assures electric continuity, with controlled low resistance, between the ball and the valve body and between the stem and the valve body.