Air pump for generating excess pressure in a fuel tank for liquid fuel in a portable heating device

An air pump for generating excess pressure in a fuel tank for liquid fuel for running a portable heating device which is provided with a burner, to which the fuel can be fed from the fuel tank under pressure, the air pump being configured as a reciprocating compressor and comprising:

• a cylinder fitted on the fuel tank;
• a piston rod which is disposed coaxially in the cylinder and is axially displaceable;
• a handle which is designed to actuate the air pump and is supported on the piston rod at an end of the piston rod lying farther from the fuel tank;
• a piston which is axially movable in the cylinder and is disposed so as to form a one-way seal and which is fitted at the other end of the piston rod lying closer to the fuel tank and divides the interior of the cylinder into two chambers, of which
• one said chamber lying closer to the fuel tank communicates with the fuel tank via a first one-way valve which lets air enter into the fuel tank but prevents air and fuel from escaping from the fuel tank, and
• another said chamber lying farther from the fuel tank is able to communicate essentially unchecked with the atmosphere;
• one-way sealing of the piston against the cylinder permitting passage of air past the piston in a first direction from the chamber lying farther from the fuel tank to the chamber lying closer to the fuel tank, but prevents passage of air past the piston in a second direction which is counter to said first direction;
• said piston rod being provided with a coaxial duct and with a second one-way valve controlling the passage of air through this duct;
• the two chambers being able to intercommunicate via the duct and the second one-way valve;
• said first and second one-way valves each having a direction of one-way flow, said directions of one-way flow being opposed to one another, and
• from a predetermined pressure, the second one-way valve allowing air to escape from said predetermined pressure, from the chamber lying closer to the fuel tank in the direction of the atmosphere, but preventing air from escaping in a counter-direction.