Flowserve Vogt Forged Steel Gate - Manual (Page 14)

Flow Control
Vogt Valves
14 Forged Steel Gate, Globe and Check Valves FCD VVENIM2000-02
2.11 Trapped Pressure
When a closed valve containing liquid is heated (e.g., from process
condition, radiation or solar heating) the cavity pressure will increase
due to volumetric expansion or vaporization of the liquid. Conversely,
cooling an un-drained cavity below the freezing point may also result
in volumetric expansion of the media. These types of expansion can
result in extremely high pressures in the valve.
(1)
A bonnet cavity relief can be added to Vogt gate valves when the
user determines that the conditions for over-pressurization of the
“locked-in bonnet cavity” exist. Globe and check valves do not have
a “locked-in volume” when the valves are closed and are not subject
to this trapped pressure.
(1) Paragraph extracted from MSS SP 92.
2.12 Material Compatibility
It is significant that forged valve materials and lubricants used in
construction be chemically consistent or compatible with the con-
necting piping system components, line fluids, applications and the
environment. Flowserve, or the system design engineers, should be
consulted whenever there appears to be reason for such concern.
Flowserve Vogt Valves has construction procedures for valves used
in various applications, one being “food service”. These procedures
ensure that valve materials, and lubrication used in manufacture are
compatible with food standards. Flowserve should be consulted on
proper valve selection when applications require special cleanliness,
materials and/or lubricants.
2.13 Operating Effort
Vogt valves are designed to require a reasonable amount of physical
effort applied to a handwheel to open or close at rated working pres-
sure. Maximum handwheel torques at maximum pressure ratings
are listed in Section 5 of this manual.