Valves for special applications

Valves with low external emissions

Used where the escape of fluid to the atmosphere is undesirable for environmental, safety or economic reasons. The stem seal needs special attention in these cases and is often reinforced by special measures. For valves with small diameters (up to 6″), a bellows seal can be used to prevent fluid leakage and a secondary stem seal in the form of a baffle plate or o-rings in the event of a bellows failure.
Bellows seals are often used for salient stems (globe or gate valves) but can also be used for quarter-turn valves (ball valves, butterfly valves, etc.).

Valves for cryogenic use

Valves for cryogenic applications (below -50 °C) must comply with BS 6364. They normally have elongated stems that allow a reasonable temperature gradient up to the packing and operating point. They also allow liquefied gases to reach vapourisation temperature. The smallest leaks considered normal in other applications are not accepted for cryogenic service because in this case fluid leaks could freeze and prevent operation. Seats and gaskets are often chosen in KEL-F, and resilient seated valves require precautions to relieve the overpressure caused by thermal expansion caused by temperature rise.

Valves for high temperatures

Gate, globe and check valves must be selected according to the materials of the body and internal parts with reference to the respective pressure class.
The materials of the body and seals of ball valves must be selected more precisely to ensure tightness.
They often have an extended stem to dissipate the high temperature.
Depending on the degree of temperature (200° C to 1,000° C), body and seal materials will be proposed according to the process conditions.

Valves for vacuum service

Valves with resilient seats, including High Performance butterfly valves and absolute vacuum valves, must be specifically requested for such service and an additional sealing mechanism will probably be required.
The bellows stem must be expressly requested and a secondary seal may be required.
The stem seal must be suitable for a pressure of 25 mm Hg.

Flood valves

They are used for the fire-fighting water deluge service.
They open virtually instantaneously while a process control valve may take several seconds to activate. They remain functional despite damage to the detection or pneumatic actuation system.

Emergency shut-off valves

Valves intended for ESD service must achieve the highest degree of reliability and integrity.
Actuators are generally hydraulic or pneumatic “fail-safe” and affect the valve's ability to perform its closing function.
The main requirement is that the valve can be fully relied upon to close under all operating conditions.
To ensure this, new-generation “Partial Stroke” devices are applied to the actuator in order to test the functionality of the valve periodically.

Double Block and Bleed valves

Double Block and Bleed valves provide double isolation by means of two plugs in a single body and provide the bleed function by means of a drain or vent system located between the two plugs (ball, gate or disc). Different configurations are available, floating or trunnion, full or reduced passage, with the following advantages: