Читать книгу Mechanics of the Household - E. S. Keene - Страница 18

—Steam pressure is measured in pounds to the square inch above the pressure of the atmosphere. The gages used for indicating the pressure of the steam are made in several forms but the type most commonly used is that shown in Fig. 20. It is known as the Bourdon type of gage and takes its name from the bent tube A, which furnishes its active principle. The Bourdon barometer invented in 1849 employed this form of sensitive tube. In the drawing the face of the gage has been removed to show the working parts. The sensitive part is the flat elastic tube A, which is bent in the form of a circle. When the pressure of the steam enters at S the air in the tube is compressed and the tube tends to straighten. The movement of the tube caused by the steam pressure is communicated to the pointer by a link connection and gear as shown in the drawing. The amount of straightening of the tube will be in proportion to the steam pressure and is indicated by the numbers marked on the face of the gage. When the pressure is released, the tube returns to its original position and the spiral spring C turns the hand back to its first position.

Fig. 21.—Cross-section of a pop valve.