| 摘要 |
The device, intended to be propelled in a duct (4) by applying a pressure (P), comprises catching means (6) located at the rear and at least one piston (8) whose periphery (9) can be deformed under the effect of the pressure (P). The periphery (9) of the piston (8) comprises a guide portion (10) of maximum diameter and, behind the latter, a rear portion (12) of smaller diameter than that of the guide portion (10). The shape of the rear surface of the pistons (8) thus brings about compression of the periphery (9) when the pressure (P) is applied to the rear of the device in the duct (4) and therefore reduces the friction between the pistons (8) and the internal surface (11) of the duct (4). <IMAGE>
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