SEATS, SEAT INSERTS & SEAT SEALINGS
On request, two other Trunnion mounted valve designs are available:
DOUBLE PISTON EFFECT DESIGN.
Bi-directional, twin seats valve (with two seats, both seats are bi-directional). This means valves designed for blocking the fluid in both downstream and upstream directions, with two seats, each sealing in both directions: from the valve ends to the valve body cavity and from the body cavity to the valve ends. This seats design improves the sealing capacity of the valve adding a seating surface in line, but an external safety relief valve is needed to allow the release of the cavity over-pressure.
DOUBLE BLOCK AND BLEED (DBB).
According to API 6D definition: valve with two seating surfaces which, in the closed position, blocks flow from both valve ends when the cavity between the seating surfaces is vented through a bleed connection provided on the body cavity.
UPSTREAM SELF RELIEVING DESIGN.
Uni-directional, twin-seat valve with the upstream seat uni-directional and the downstream seat bi-directional. This combination maintains the sealing capacity of the valve in the event of failure of the upstream seat. In addition, as the upstream seat automatically releases the body cavity over-pressure, no safety relief valve is needed for this purpose.
Other seat insert materials are available on customer request or for special applications.
For temperature range greater than -10/+120°C.
For temperature range upon 250°C.
PTFE or RPTFE.
For special fluids.
For cryogenic applications.
Suggested for valves working with natural gas at design pressure up to class 600.
Hardfaced Ball and seats to provide a positive seating action in case of abrasive service or in case that the high service temperature don’t allow the use of any kind of soft seat insert material.
EMERGENCY SEALANT INJECTION.
Dafram ball valves can be equipped with ports to inject a suitable sealant to restore seat sealing in the event of damage to the soft seat inserts.
Extended bonnets and stems are available for valves working in extreme low or high temperatures (below – 46°C and above 200°C) to increase the distance between the body and the stem sealing area.
STEM FOR BURIED SERVICE.
For valves to be installed underground, suitable extended bonnets and stems are available. In this case all drain, vent and emergency sealant injection lines are extended and the relevant pipes are firmly attached to the bonnet extension.