| 摘要 |
<p>A pneumatic device (10) comprises a piston (12) moveable along a cylinder (10). The piston has opposite ends (18, 26) defining a space (30) therebetween. The space is divided into two chambers (30a, 30b) by a housing (40) fixed relative to the cylinder and having a fluid flow control passageway (42) therethrough. The space (30) is filled with fluid, such as oil. The piston (12) is arranged such that movement thereof against a spring (16) causes the fluid to be displaced from one chamber (30a) of the space (30) to the other chamber (30b) through the passageway (42). The spring (16) is arranged to apply a return force to the piston (12) and the rate of return of the piston (12) is controlled by the return flow of fluid through the passageway (42). A pneumatic system (100) includes a device (10) connected between first and second members (58, 58a) of a building, such as a door and door frame. The pneumatic system comprises a source of compressed gas (C) for operating the device (10) to enable the device (10) to move the first member (58) relative to the second member (58a), i.e. to open and close the door. A switching device (72) controls the supply of compressed gas to the device (10).</p> |
