MAINTAINING BURNER SAFETY CONTROLS
SAFETY THERMOCOUPLE OR PROBE
The safety thermocouple provides gas shut off in the event of flame failure. It is important that the probe is rigidly and correctly fixed to the burner head or pilot and the probe tip only (approx. 5mm) is situated in the flame. This is all that is required to provide sufficient voltage to stimulate the safety magnet allowing the gas to flow. The "cold" junction end must be only hand tightened plus 1/4 turn with a small spanner in the body. Always check for foreign matter between this junction and the safety valve body. Do not scratch the metal surface, do not use thread sealant on this joint and do not over tighten.
Most safety probes have a flattened section for identification, this is OK but if the probe is severely bent or damaged it should be replaced. It is not possible to repair these probes. Safety probes should be replaced every 18 months or so depending on use. Never subject the burner head or probe to excessive back heat by having the burner too close to the kiln port. Heat will also shorten the life of the safety valve.
These valves house the thermomagnet that provides gas shut down if the safety thermocouple is not heated. Although usually providing many years of service, over time, heat, dirt and normal use will necessitate their replacement. However if the gas flame will not stay lit, when the safety valve button is positively depressed and slowly released, it may not always be time to throw the valve out. Assuming the probe has been checked, a common problem is dirt trapped in the valve causing the button to not be fully depressed. This should not be disassembled but should be returned to the burner supplier for service. Keep the burner clean. Dirt or sealant may force its way under the safety valve seat allowing gas to flow even in the event of flame out.
CARE OF THE GAS ORIFICE
Most atmospheric burners have a gas orifice that is accurately fixed in the burner throat providing air inspiration. The hole in the orifice is necessarily small to provide the correct gas flow and to provide sufficient velocity to ensure there is a suction available for the correct air inspiration. As this is the smallest gas passage it is possible for any foreign matter in the system to be trapped here. The usual sign that there is a blockage in the burner unit is evidenced by either a yellow flame, short flame or excessive gas pressure to reach top temperatures previously effortlessly attained. The burner should generally be returned for maintenance but if the orifice is removed do not use wire to clean and remember to reseal to guard against leaks. Any enlarging of the orifice hole or scratching of the material will cause either the exact ratio between gas and air to be upset or the gas stream to fire at an angle into the burner throat. It is imperative that this orifice hole is drilled absolutely central.
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