Because of the relatively large cost of pressure transducer in quantity, a scheme has been devised for using one transducer to measure a number of pressures-up to 48 or more. This scheme is the comnutation of pressures using a device known as a "pressure scanner valve". In using the scanner valve, model pressures are allowed to stabilize in the lines leading from the model through the stator of the scanner valve. The rotor is then turned through one revolution. connecting each model pressure in turn to the pressure transducer through a slot. Seals between the individual model pressures at the scanner valve are commonly maintained by the very close contact of the hardened steel surfaces of the stator and rotor which are lapped together. The force holding the two surfaces in close contact is sometimes provided by a pressure equal to or greater than the highest model pressure. Obviously, the mating surfaces must be kept very clean in order to avoid leakage of pressures. If the two surfaces should be accidentally separated, for example by loosing the balance pressure, the rotor should be turned through several revolutions to pulverize any dirt that may have gotten between the surfaces. If the valve leaks after this has been done, it will be necessary to disassemble and clean the valve. Lens tissue is normally used for cleaning and a single drop of light silicone oil is put on the surface before reassembly.

由于使用大量压力传感器需要耗费相当多的资金，所以现已设计出一种应用一个压力传感器测量多点压力的方案——最多可达48点或更多。这个方案利用一台称为“压力扫描阀”的装置来进行压力切换。使用压力扫描阀时，先使模型压力在由模型通往扫描阀定子的测压管道中达到稳定。然后将转子旋转一周，通过沟槽把模型上各点压力顺次接到压力传感器上。扫描阀内各单独模型压力之间的密封，通常靠磨合在一起的定子和转子的淬火钢表面之间的紧密接触来维持。维持这两个表面处于紧密接触的力，有时由一个等于或高于模型最高压力的压力来提供。很明显，为了防止压力泄漏，上述两个配合面必须保持非常干净。假如这两个面因偶然的原因，譬如平衡压力松弛而脱开，那么，就应将转子旋转数周、把可能落入配合面间的任何脏东西辗碎。如果这样做了之后，扫描阀还漏气的话，就必须把它拆开弄干净。通常用擦镜纸来进行擦拭，并在重新装配前在表面上滴一滴轻硅油。

When using a scanner valve in a blowdown wind tunnel, a common mode of operation is as follows. The pressure in the lines will be allowed to equalize over a period of time during the run. At the end of this time, a guillotine (or other type) clamp is used to trap the model pressures in these lines. The tunnel is then shut down and the lines are sequentially connected to the transducer and pressure readings taken. The volumes of the lines in which the pressures are trapped are large compared to the scanner valve and transducer volume (more than 100 times) so that the volume when vented to the transducer is not materially affected. This mode of operation requires a minimum use of air for blowdown tunnel operation.

在下吹式风洞中使用扫描阀时，通常采用如下操作方法。让管道里的压力在风洞运行中的一段时间内达到平衡。达到平衡后利用截止钳(或其他类型的钳）将模型压力封闭在这些管道中。然后风洞关车，再按顺序把测压管道接到压力传感器上，并记下压力读数。收集压力的管道容积比扫描阀和传感器的容积大得多（超过100倍)。因此，接通传感器实际上对容积没有影响。采用这种操作方法时，对下吹式风洞而言，所需要的气量最少。

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