The Hydraulic Fusible Loop Charge panel is similar to the pneumatic type, but with components suitable for hydraulic operation. The Fusible Loop Charge panel will always be used in combination with a fusible loop at low pressure (approx. 7 BAR).
The Fusible Loop Charge Panel is intended to charge (pressurize) the fusible loop and intended to cause an emergency shutdown in event of heat (fire) detection in certain areas where the fusible loop with fusible plugs are installed.
The heat (fire) is detected by the fusible plugs, only if these are installed close to the possible heat source, therefor it is of great importance to know where a possible heat generation/fire can occur.
Usually this is a few meters above the Christmas tree valves and nearby the Choke Valve.
A loop van be a single run of tubing with fusible plugs at well selected location, or a complete loop or circuit with several side branches.
The fusible plugs can be selected with a wide variety of melting temperatures and sizes, but usually a 1/4” NPT plug is selected with a melting temperature between 158°F (70°C) and 281°F (138°C).
The fusible plug panel can be part of a complete system or a standalone system with electrical interface to a ”Fire and Gas” system. This is done by adding a pressure switch or pressure transmitter in the fusible plug panel and connect it to the external system.
The medium used in the fusible plug panel should not be flammable (preferred is to use nitrogen). In case of heat (fire) near one or more fusible plugs in the field, the plug(s) will melt and cause a pressure drop in the field line. This pressure drop will be detected inside the Fusible Loop Charge panel. The hydraulic supply line to the field will then be block and the pressure switch or pressure transmitter will give a signal to the remote system to take further action. When a plug melts a very small amount (a few drops) of the hydraulic medium will vent through the melted plug.