As shown in the figure, it is a schematic diagram of the stove head of a domestic gas stove. When in use, the gas valve is opened, and the ignition device is rotated, so that gas and air are mixed and

As shown in the figure, it is a schematic diagram of the stove head of a domestic gas stove. When in use, the gas valve is opened, and the ignition device is rotated, so that gas and air are mixed and flow at the entrance for combustion. Because the faster the flow rate, the smaller the pressure of the fluid, so the gas at the entrance has a large flow rate and the pressure is less than atmospheric pressure, and the gas and air flow to the combustion head under the action of atmospheric pressure, but the gas will not leak into the air.

So, the answer is: big; Less than.