| 摘要 |
The servo (2) unit is constructed on a base plate (1) and consists of a rigid envelope (3). The rear shell (3b) carries an open cylindrical funnel (321), which fits into an axial opening (10) in the base plate. A mobile partition (4) forms sealed chambers, within the envelope. A piston (6), fixed to the mobile partition, slides within the funnel and has a three way valve (61), designed to connect the rear chamber with a primary (A) or secondary (D) source of pressure. The rear shell is fitted with an external (31) and internal (32) screen, where the internal screen forms a sealed wall within the rear chamber and part of the internal screen is conformed to form the funnel. The means of fixing the internal screen consist of at least two pawns (71 and 72), which are carried by the base plate, and have oversized heads (711 and 721) carried by columns (712 and 722). Two button holes (81 and 82) are provided in the external screen and these fit behind the heads of the pawns. An indexing element (9) consisting of a disk (91) is mounted to slide axially between the two screens. It is fixed in rotation to the envelope and is driven by an elastic force from the internal screen towards the external screen. It carries two locations (11) and (12), each of which is suitable to receive the head of the corresponding pawn.
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