Technical manual
MT 208-E
9
Tab.5
The speed of the gas must not exceed the following
values in the piping downstream from the regulator:
Vmax = 30 m/s for Pd > 5 bar
Vmax = 25 m/s for 0,5
< Pd
≤
5 bar
2.3
DOWNSTREAM VOLUME REQUIRED
FOR INSTALLATION
In the case of a service regulator of the ON-OFF type (stopping or
starting of burners), you should remember that though the
APERFLUX
101
apparatus is classified as being of the fast reaction type, it requires
an appropriately dimensioned volume of gas between the apparatus
itself and the burner so as to partly absorb the pressure swings caused
by fast flow rate variations.
3.0 IN
LINE
ACCESSORIES
3.1 RELIEF
VALVE
The relief valve is a safety device which releases a certain quality of
gas to the exterior when the pressure at the control point exceeds the
set-point as a result of short-lasting events such as, for example, the
very fast closing of the on/off valves and/or overheating of the gas with
zero flow rate demand. The release of the gas to the exterior can, for
example, delay or block the intervention of the slam-shut valves for
transitory reasons deriving from damage to the regulator.
Obviously the quantity of gas released depends on the extent of the
overpressure with respect to the set-point.
The different models of relief valves available are all based on the
same operating principle which is illustrated below with reference to the
valve
VS/AM 65
(fig. 10).
It is based on the contrast between the thrust on the diaphragm
24
deriving from the pressure of the gas to control and the thrust from the
setting spring
20
. The weight of the mobile assembly, the static thrust
and the residual dynamic thrust on the obturator
4
also contribute to
this contrast. When the thrust deriving from the pressure of the gas
exceeds that of the setting spring, the obturator
4
is raised and a
certain quality of gas is released as a result.
As soon as the pressure drops below the set-point, the obturator
returns to the closed position.
Proceed as indicated below to control and adjust intervention of the
relief valve.
3.1.1 DIRECT INSTALLATION IN THE LINE (fig.
11)
When the relief valves fitted directly in the line that is, without the
interposition of an on/off valve, we recommend proceeding as follows:
1) Ensure that the downstream on/off valve
V2
and the bled cock
6
are closed;
2)
To increase pressure in the downstream pipe until the envisaged
intervention value in one of the following ways:
- If allowed by the spring installed on the pilot (see tab.2),
increase the setting of the same pilot until the desired value is
reached;
- Connect a stand-by controlled pressure to the atmosphere
drain tap
6
and set it to the desired value.
3)
Check intervention of the relief valve and ad just it if necessary by
turning the internal adjustment ring
14
appropriately (clockwise to
increase the set-point, anticlockwise to reduce it)
fig. 10
fig. 11
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