Hobs - Did you know?

The hob is used for boiling, frying, steaming, simmering and braising. It primarily works by the conduction of heat from the flame through the pan surface. A certain amount of radiant heat is also generated. A large volume of primary air is provided so that the pan can be located as close as possible to the burner head and so gain the heat from the flame. The flame should not be allowed to lick up the side of the pan as heat will be wasted. 

The hotplate is usually a solid steel flat plate or ceramic surface, on which the pan sits, or it can take the form of a griddle, which is used for dry-frying foods such as eggs etc. The flame is located beneath the metal and heats it to the desired temperature.

The heat setting of a hob or hotplate often has a grading, such as simmer, medium and high. The flame does not adjust to the heat requirements of the food being cooked and if set too high, the contents of the pan may boil over or burn. Some appliances have thermostatically controlled burners. They work using a contact sensor that is filled with a volatile fluid that, when heated, expands forcing the gas valve to close down to a by-pass rate. With freestanding cookers all control taps and the oven thermostat are located on a pipe, named the float rail, which is located behind the control knob fascia. During any maintenance work all these gas connections should be sprayed with leak detection fluid to ensure they are gas tight. The gas burners used with the associated parts of the cooker are generally unprotected, in terms of flame failure. This means that should the flame go out, gas is allowed to discharge freely into the room. The oven will be found to have a flame failure device fitted, usually of the liquid vapor type, which will shut down the main flow of gas but will still allow a discharge through the by-pass. Cookers supplied by LPG are controlled and all control taps generally require the operation of a thermo-electric FSD before gas is allowed to flow freely. 

The Oven - Did you know?

The oven is used for warming, roasting and baking. It works by surrounding the food with hot convection currents. The oven temperature is adjusted by a thermostat that varies the amount of heat surrounding the food to be cooked. The grading ranges from a simmer or economy setting of around 100◦C through to gas mark 9, which generates temperatures of around 245◦C. Most domestic ovens found in the UK work by natural convection currents. The burner located at the rear of the base creates a circulation of hot gases that eventually discharge from the rear of the oven by means of a flue. Owing to the relatively slow circulatory motion, temperature zones invariable develop in the oven, with the hottest region at the top. In another design of oven, the gas burner is located outside the food compartment and hot air is allowed to enter via various ports, so producing a more even spread of heat temperature throughout the oven. This design is often used with an additional fan to give improved efficiency.

                                                                Built-in Oven and Hob

                                                                Freestanding Cooker

The Grill - did you know

The grill is used for toasting, grilling or browning previously cooked food. It works

by directing radiant heat that has been produced on the surface of a red-hot fret,

mesh or gauze surface, on to the food. There are two designs of grill.

First, those referred to as conventional grills, as they have been around the longest.

The grill consists of a pressed steel burner, fed via an injector at one end and located

beneath an expanded metal fret. The flames, on leaving the burner, heat the metal fret

and cause it to glow red-hot. The combustion products rise by convection through

holes in the canopy top. The biggest problem with this design is the problem of

uneven cooking, a result of the burner failing to heat the whole surface of the fret

uniformly.

In the second design of grill, known as a surface combustion grill, the injector feeds gas

into the primary air intake, this entails some 80–90% of that required for combustion.

The mixed gas and air now travels to the centre of a sealed chamber, which has a fine

metal mesh burner surface where the ignition probe is located and where combustion

takes place, the air/gas mixture clings to its face, producing an evenly heated radiant

surface across the entire burner.