| 摘要 |
<p>A pressure indication device comprises a housing (ll) including a bore (l3) in which is received a slidable piston (l4). The piston (l4) has two end faces (l9,40), one of which is for connection to a source of fluid at higher pressure and the other of which is for connection to a source of fluid at lower pressure. The device produces an indication when the pressure differential reaches a predetermined value. In an inoperative position of the piston (l4), a portion (2l) of the upstream face (l9) operates with the bore (l3) to provide a seal which reduces leakage between the bore (l3) and the piston (l4) and which also reduces the effective area of the upstream face (l9). In addition, a labyrinth seal (l8) is provided between the bore (l3) and the piston (l4). When the predetermined pressure is reached, the piston (l4) moves, and as it does so, the effective area of the upstream face (l9) is increased. This causes increasingly rapid movement of the piston (l4) so providing a very positive indication that predetermined pressure has been reached and so overcoming any tendency of the piston (l4) to stick or move only very gradually as the predetermined pressure is reached. <IMAGE></p> |
