| 摘要 |
<p>PURPOSE: To efficiently recover the vaporized substance in safety by continuously measuring the effective concentration of a mixture, and comparing the same with at laest one threshold value indicating that a mixture is explosive for momently adjusting a rotating speed of a positive displacement pump actuating on a return pipe. CONSTITUTION: A pump actuating on a return pipe 31 is a positive displacement pump 21, and a motor 36 of this pump is controlled by a means for momently adjusting its rotating speed as the function of the delivery capacity of the supplied fuel. On this occasion, the effective concentration of the mixture is continuously measured in consideration of the quantity of excess air depending on the pressure difference, the temperature of an underground tank, and the temperature of vapor-air mixture to be compared with at least one threshold value indicating that the air is very rare and the mixture is explosive by a logical unit 14. Whereby the vaporized substance can be efficiently recovered in safety without using a system for recovering the vapor in safety, particularly a bellows type sealing element, and without the possibility of explosion and the undesired pressurization of the underground tank.</p> |
