Environmental Engineering Reference
In-Depth Information
Table 4.2 valve TriM
Metal seating
Commonly used in gate and globe valves, particularly in the
latter for control applications where seatings may additionally
be coated with hard metal.
Soft seating
Commonly used in ball, butterfly, and diaphragm valves;
seatings may be made from a wide variety of elastomers and
polymers including fluorocarbons.
Lined
Usually made in cast iron with an internal lining of elastomer of
polymer material. Inorganic materials such as glass, together
with metals such as titanium, are also used for lining. Lining
thickness will depend on the design and type of material used.
In many cases, the valve lining will also form the seating trim.
Table 4.3 valve end ConneCTions
Flanged
Valves are normally supplied with flanges conforming to
either BS4505 (equivalent to DIN) or BS 1560 (equivalent
to ANSI), according to specifications. Manufacturers may
be able to supply valves with flanges to other standards.
Threaded
Valves are normally supplied with threads to BS21
(ISO/7), parallel or taper.
Other
End connections include butt or socket weld, and wafer
valves are designed to fit between pipe flanges.
Tabl
e 4.4 valve sPeCial feaTures
High temperature
Valves are usually able to operate continuously on
services above 250°C.
Cryogenic
Valves will operate continuously on services in the
range of -50°C to 196°C.
Bellows sealed
Valves are glandless designs having a metal
bellows for stem sealing.
Actuated
Valves may be operated by a gearbox, pneumatic or
hydraulic cylinder (including diaphragm actuator),
or electric motor and gearbox.
Fire-tested design
Valves have passed a fire test procedure specified
in an appropriate inspection standard.
pressure depends on materials, design, and working temperature and
should be selected from the (relevant), pressure-temperature tables. The
pressure rating of many valves is designated under the ANSI class sys-
tem. The equivalent class rating to PN ratings is based on international
agreement. Valves are also covered by various codes and standards, as
are the other components of piping and tubing systems.
Usually, valve end connections are classified as
langed
,
threaded
,
or
other
(see Table 4.3). Many valve manufacturers offer valves with spe-
cial features. Table 4.4 lists a few of these special features; however, this
is not an exhaustive list and the manufacturer should be consulted for
more details of other features. The various types of valves used in fluid
power systems, their classifications, and the applications are discussed
in this section.
