Manual reset

Usually, the closed liquid drain header is run as a separate line to the drum and provided with a high level cut-off valve with local manual reset. In some cases the closed drain system is segregated into a number of subheaders, as described earlier. Hydrocarbon liquids may be bypassed around the drum through a connection from the closed drain header directly to the pumpout pump suction, provided that the liquid can be routed to a safe disposal location, considering its vapor pressure and temperature. Emergency liquid pulldown connections, if provided, are routed to the blowdown drum via the closed drain header. 

If, during the ignition sequence or the running sequence, flame failure occurs, a lockout will result, which will require manual resetting. 

Three-Way Solenoid Valve Latch Type With Manual Reset... 

The slam-shut valve cuts off the gas supply in the event of predetermined pressure criteria being exceeded. It must be manually reset, having made safe the downstream pipework and the cause of the abnormal pressure removed. 

An independent overriding second low-water control. This will be set below the level control in (2). It will give an audible alarm on shutting off the fuel and air supply and require manual reset before the boiler may be brought back into operation ... 

All electrical equipment for the water-level and firing controls should be designed so that any fault will cause the boiler to shutdown and require manual resetting before the boiler may be restarted. 

ESD valves should lock in the fail safe mode once activated and be manually reset once it has been confirmed the emergency has passed or has been resolved. 

An overspeed shutdown device with manual reset arranged to shutdown the engine at a speed of 20% above rated engine speed. 

Some machines by nature generate transients that can affect machine operation if they contain sensitive circuits. Figure 3.25 shows a waveform produced by a foodprocessing machine. The transients occurred several times each day as the machine automatically turned on and off. Severe transients caused the machine to go into a lockout mode which required the operator to manually reset the machine. The problem was fixed by providing a dedicated circuit of low impedance for the machine. This reduced the transient to levels that could be lived with. 

This pressure relief device is designed to actuate by means of the process fluid and remains open after operation. A manual resetting or replacement will need to be provided after a pressure upset. The different design types include ... 

A non-redosing pressure rdief device is a pressure relief device designed to remain open after operation. A manual reset may be provided on certain valves. 

A good oxy/fuel ladle preheater incorporates several safety features. These include double block and bleed, flame supervision, low and high flow interlocks on oxygen and natural gas, a high-temperature interlock and manual reset (see Chapters 9 and 10). The entire system must conform to current NFPA (National Fire Protection Association) safety standards. 

Emergency stop (E-stop) switches, common to machinery and some products, use red mushroom buttons on a yellow background, which is universally recognized by operators and service personnel. E-stop devices have special requirements such as, positive opening, manual reset, fail-safe, and should be type-approved as E-stops (see Emergency Stop Switches section). 

Emergency stop devices are required for machinery They shall have a red button on yellow background, be self-latching, positively opening, readily accessible to operator, manually activated, require manual reset. Resetting the E-stop switch shall not restart any part of the machine. 

There are many kinds of thermal switches. Some are normally open some closed. Different switches have different preset action temperatures. Some operate one time, whereas others reset automatically after the temperature returns to a preset value. Others have a manual reset button. 

The nuclear system protection system initiates the rapid insertion of the control rods to shut down the reactor. The system is of the fail-safe design where it will trip on loss of electrical power but will not trip and cause a scram on the loss of a single power source. The four trip channels are physically separated from each other and from other equipment precluding the possibility of interactions that could cause possible false scrams or failure to scram. The logic requires a manual reset by the operator, which is automatically inhibited for 10 s. One reset switch is used for each trip channel. Failure of a single trip channel, division logic, or a system component will not prevent the normal protective action of the nuclear system protection system. 

A momentary trip of any channel is annunciated and causes that channel to lock out until manually reset. Sufficient annunciation trip signals are used so that the operator can determine the particular sensor or sensors, which caused the channel trip. The computer also prints out the identificahon of sensors, which have caused scram and, if several variables are involved, it prints out the sequence of events in which they occurred. 

This resetting can be done manually or automatically. With manual reset, a potentiometer is used to electrically shift the proportional band. The amount of shifting has to be done in small increments until the controller power output matches the process power demand as setpoint temperature. 

Overloads—Use overloads of the manual reset type. Overload reset buttons shall be installed in the panel enclosures to allow manual reset, unless specifically provided for in separate motor starter control boxes. 

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