| 摘要 |
An inexpensive and yet highly reliable device for indicating when the pressure in a receptacle is above or below a predetermined value comprises a housing means, a diaphragm means in the housing means, the diaphragm means having first and second side surfaces and a translucent viewing means having an inner surface, at least a portion of which is adjacent to the second surface of the diaphragm means. The first side surface of the diaphragm is adapted to be in pressure communication with the receptacle so the the diaphragm means may be movable between a first position in which the pressure is below a predetermined value and a second position in which the pressure is above a predetermined value. The inner surface of the viewing is relatively frosted except for at least one portion or area which is relatively clear so that when the diaphragm is in the second position it will be in contact with the inner surface of the viewing means and obscure the differences between the relatively frosted portion and the relatively clear portion. With the diaphragm in the second position the second surface of the diaphragm will be clearly visible through the viewing means and hence indicia on the second surface may be easily read. In one embodiment the word "full" may be used. In the first position with the second surface out of contact with the inner surface of the viewing means the relatively clear area will be readily distinguishable from the relatively frosted area. If the relatively clear area forms the word "empty" this may be clearly read.
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