PIETRO FIORENTINI VS/AM 58, Техническое руководство, Страница: 5 / 14

Technical Manual MT 302-I
4
1.0
INTRODUCTION
The purpose of this manual is to provide essential information for the
installation,
commissioning, disassembly, re-assembly and
maintenance of the safety valves model VS/AM 58.
It is also considered appropriate to provide a brief illustration of the
main features of the valve.
In figure 1 a functional diagram of the valve is shown.
1.1 MAIN FEATURES
The VS/AM 58 valves are safety devices suitable for use with
previously filtered, non-aggressive gaseous fluids.
Such valves may be installed either on ducts or on pressure vessels.
Without external control sources aside from the process fluid itself,
these valves discharge a certain amount of gas at a certain calibration
pressure and then close when pressure is restored below the set
value.
The VS/AM 58 valve is a spring-loaded direct-acting valve with the
following main features.
- body design pressure (PS): 100 bar
- design temperature: -20 ÷ 60° C
- triggering range (Who): 15 ÷ 43 bar
1.2 SETTING SPRINGS
The calibration fields are the following:
ORANGE spring (2702080) - 15 ÷ 18 bar
RED spring (2702290) - 18.001 ÷ 25 bar
GREEN spring (2702460) - 25,001 ÷ 30 bar
BLACK spring (2702660) - 30,001 ÷ 43 bar
1.3 DESCRIPTION OF OPERATION
It is based on the comparison between the thrust on the piston 4
deriving from the gas pressure to control and the thrust deriving from
the setting spring 21.
The weight of the mobile unit and the static and dynamic residual
thrusts on the obturator 4 affect this comparison.
When the thrust deriving from the gas pressure exceeds that of the
setting spring, the obturator 4 is raised and a certain amount of gas is
discharged.
As soon as the pressure drops below the set value, the obturator re-
closes. Triggering of the relief valve can be controlled and adjusted by
appropriately turning the adjusting ring nut 9.
The device is designed in such a way that any breakage to one of the
main constituent parts of the valve or the pilot device leads to the
opening of the valve itself; in fact:
1.4 VALVE SIZING
The VS/AM 58 valve is sized using the given formula:
Q
𝑚
= 𝑝
0
𝐶 𝐴𝐾
𝑑𝑟
√
M
ZT
0
Where:
Q
m
= maximum flow rate to discharge in kg/h
K
d
= discharge coefficient
K
dr
= declassified discharge coefficient (0,9K
d
)
C = expansion coefficient
p
0
= calibration pressure plus 10% in absolute bars
A = minimum passage area in mm
2
(see table 1)
M = molecular weight of fluid in kg/kmol
Z = compressibility factor of the fluid under discharge conditions (= 1 if
unknown)
T
0
=temperature of fluid at valve inlet in Kelvin degrees
C = 3.948√k (
2
k + 1
)
k+1
k−1
k = isentropic equation coefficient
Table 1
Rated inlet size 1”
Minimum diameter [mm] 23
Minimum passage area [mm 2 ] 415.48