Emerson Fisher 377 Instruction Manual page 7

Instruction Manual
D200319X012
A supply regulator, if used, must have a flow capacity greater than the required combined capacity of the trip valve and
actuator. In order to ensure proper selection of a supply regulator, be sure the C
the appropriate flow path C
supply pressure to droop, which can cause the trip valve to trip again and begin a trip‐reset cycle. An example of an
appropriate supply regulator to use with a 377 trip valve is a 64 regulator; its capacity is usually great enough to meet
the demands of most trip valve/actuator combinations. Determine the requirements of your trip valve/actuator
combination for proper selection of a supply regulator.
Note
During normal operation, an adequately sized supply regulator maintains a greater supply pressure than the pressure demand of
the trip valve and control devices. However, if the normal actuator piston position is not relatively close to the actuator piston fail
position during startup, or during the restoration of supply pressure, the regulator supply pressure may droop and cause the trip
valve to trip again and begin a trip‐reset cycle. To prevent this, perform the following steps:
1. Adjust the instrument (control device) pressure to position the actuator piston as it is positioned in the fail mode.
2. Restore the supply pressure to the normal operating range.
3. Manually reset the instrument pressure for normal operation.
WARNING
If a flammable or hazardous gas is used as the supply pressure medium, personal injury or property damage could result
from fire or explosion of accumulated gas or from contact with hazardous gas. The positioner/ actuator assembly does not
form a gas‐tight seal, and when the assembly is enclosed, a remote vent line, adequate ventilation, and necessary safety
measures should be used. However, a remote vent pipe alone cannot be relied upon to remove all hazardous gas. Vent line
piping should comply with local and regional codes and should be as short as possible with adequate inside diameter and
few bends to reduce case pressure buildup.
Note
To ensure trip system integrity upon loss of supply pressure, a 377D or 377U trip system requires a volume tank and check valve as
shown in figures 7 and 9.
State and local regulations may require the use of ASME approved volume tanks. Determine requirements and applicable
regulations for proper volume tank selection.
For ASME approved applications, the volume tank is rated at 10.3 bar (150 psig) internal working pressure, and has a safety valve
with a 10.3 bar (150 psig) set pressure mounted on the volume tank for pressure relief. Avoid supply pressure too near the safety
valve set pressure. To ensure safety valve seat tightness and longevity, the recommended maximum supply pressure is 9.3 bar
(135 psig).
Standard volume tanks supplied in Europe must conform to Directive 2009/105/EC for simple pressure vessels. The maximum
pressure rating is stated on the tank.
For standard applications (not ASME approved), a DOT tank is used. This tank is rated at 14.5 bar (240 psig) in LP service. When
used with air, the rating should be considered to be 10.3 bar (150 psig), consistent with the maximum pressure allowed for the
377 trip valve.
1. Before installing the trip valve, inspect it to be sure it is free of any foreign material.
2. Be sure all connecting tubing is free of foreign material.
3. Use acceptable piping practices when installing the trip valve. Coat all external threaded connections with a pipe
compound.
value listed in table 1 for the trip valve. A regulator with insufficient capacity may allow
v
377 Trip Valve
value of the regulator is greater than
v
June 2017
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