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4.3
Operating and measuring impulse lines
Connection lines between
device and gas regulating
line
HON 512 with HON 650 pilot user manual
The lines must be arranged and sized in such a way that the devices' intended function will be
ensured.
▪ Measuring impulse line
▪ The measuring impulse line transmits the pressure process value from the
sensing point to the measuring diaphragm of a controller or the pilot of a gas
pressure regulator or safety relief valve or to the measuring diaphragm of the
monitoring device of a slam-shut device. It needs to be connected to the pipe
sideways or upwards separately for each device. In the case of safety equip-
ment, the measuring impulse line must be connected upstream of the first
outlet-side shut-off device in such a way that it cannot be shut off. If the
measuring impulse line is additionally connected downstream of the first
outlet-side shut-off device, 3-way ball valves with negative overlap must be
used for switching. These ball valves do not have a valve position in which
both measuring impulse lines can be fully closed at the same time.
▪ Vent line
▪ The vent line is used to connect a measuring diaphragm to the atmosphere. If
the measuring unit becomes damaged (e.g., diaphragm rupture), it can start
conveying gas. Under certain operating conditions, and following consultation
with the manufacturer, vent lines can be omitted if vent valves (HON 915) or
safety diaphragm configurations can be used instead.
▪ Blowdown line
▪ The blowdown line in a safety relief valve is used to divert gas (leaking gas,
for example) into the atmosphere.
Grouping vent lines or blowdown lines (into a header) is permissible if it does not have a
negative impact on the individual devices' operation. Within this context, it is recommended
to have the cross-sectional area of the header be at least five times as large as the total of the
individual lines' cross-sectional areas.
For primary slam-shut devices, it is recommended to route the slam-shut devices' vent lines
separately. Vent lines must not be grouped together with blowdown lines.
▪ Bleed line
▪ When using indirect acting (pilot-operated) slam-shut devices, the bleed line
is used to divert the exhaust gas from the pilot into the system's outlet
chamber. On certain devices, the bleed line will be grouped with the return
line.
▪ Return line
▪ When using indirect acting (pilot-operated) slam-shut devices, the return line
is used to return the outlet pressure to the actuator.
Basics for installing the device in a pipe
42
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