Honeywell HON 670 Component Documentation, Maintenance Manual And Spare Parts page 12

Functional diagram of the
controller
How the controller works
when the SAV responds
How the controller works
when the SBV responds
HON 670 / HON 671 Controllers Component Documentation
Figure
▪ The pressure in the system to be safeguarded is guided into the controller via the
measuring line where it is applied to the upper side of the double diaphragm system
and compared with the reference variable that is specified using the setpoint adjusting
screw (force of the pilot spring).
▪ In the normal operating state, the amplifying valve is closed. The downstream system
including the actuator of the SAV is pressureless.
▪ When the upper or lower response pressure is reached, the amplifying valve opens.
▪ Gas from the monitored system flows to the actuator of the safety shut-off valve.
▪ The piston of the pressure unit is moved and triggers the SAV's trip mechanism via the
piston rod.
▪ The safety shut-off valve closes.
▪ The pressure in the system to be safeguarded is guided into the controller via the
measuring line where it is applied to the upper side of the double diaphragm system
and compared with the reference variable that is specified using the setpoint adjusting
screw (force of the pilot spring).
▪ In the normal operating state, the amplifying valve is closed. The pressures in the upper
and lower actuator chamber of the actuator assembly are equal.
▪ When the monitored pressure reaches the set response pressure of the controller, the
amplifying valve opens.
▪ The pressure in the actuator chamber below the driving piston is reduced.
▪ The system pressure on the upper side of the actuator moves the sleeve against the
closing spring in the opening direction so that the blowdown procedure of the safety
relief valve is enabled.
▪ If the monitored pressure then once again falls below the setpoint as adjusted, the am-
plifying valve closes and the pressure in the lower actuator chamber thus rises.
▪ When the pressure between the upper and the lower actuator chamber has equalized,
the safety relief valve closes again on its own.
Description
No. / Description
color
1 Vent line
2 Bleed line
3 Measuring line
Outlet pressure
Atmospheric pres-
sure
12