Читать книгу Mechanics of the Household - E. S. Keene - Страница 13

—These vents depend for their action on the expansion of a part of the valve due to the temperature of the steam. The valve remains closed when hot and opens when cold. The difference in temperature between the steam and the expelled air from the radiator is the controlling factor. In the automatic vent shown in Fig. 11, the part A is screwed into the radiator loop. The discharge C is open to the air or connected with a drip pipe, which returns the water to the basement. The cylinder D, which closes the passage B, is made of a material of a high coefficient of expansion. The piece D, when cool, is contracted sufficiently to leave the passage B open to the air. When the steam is turned on, the expelled air from the radiator escapes through B and C, but when the steam reaches D the heat quickly expands the piece and closes the vent.

Most automatic vents require adjusting when put in place and occasionally need readjustment. The cap O, of Fig. 11, may be removed with a wrench and a screw-driver used to adjust the piece D, so as to shut off the steam when the radiator is filled with steam. The expanding piece is simply screwed down until the steam ceases to escape.

Fig. 12 is another style of automatic vent, constructed on the same principle as that of Fig. 11, but probably more positive in action. In this vent the part A attaches to the radiator. The expanding portion B is made in the form of a hollow cylinder, through which the air and steam escape to the atmosphere. It is longer than the corresponding piece in the other vent and is more sensitive because of its greater length and exposed surface. As the piece B elongates from expansion, the upper end makes a joint with the conical piece D. The shape of this latter piece gives better opportunity for a tight joint than in the other form of vent and in practice gives better service.

Fig. 13 is a cross-section of the Allen vent. This is an example of a vent which depends for its action on a float. Whenever sufficient water accumulates in the body of the vent to raise the float, it closes the vent by means of its buoyancy. The body of the vent shown in Fig. 13 is composed of two concentric cylinders. The float E occupies the inner cylinder, while surrounding it is the outer cylinder D. The outer cylinder is entirely closed except a little hole at G. The float is made of light metal and fits loosely in the inner cylinder. The steam from the radiator condenses in the vent until the inner cylinder is filled with water, up to the opening A. The float by its buoyancy keeps the opening in B stopped, and no steam can escape. The air of the outer cylinder D is expanded by the heat of the steam and most of the air escapes through the hole G. When the radiator cools, the rarefied air in D contracts and draws the water from the inner cylinder into the space D; this allows the float to fall and unstop the opening in B. When the steam again reaches the vent, the heat expands the air in D and forces the water into the inner cylinder; the float is again raised and stops the opening in B.

Many other air vents are in common use but most of them operate on one or the other of the principles described. Fig. 11 is a relatively inexpensive vent, while Fig. 12 is higher-priced.

Fig. 14.—Steam radiator valve.

Fig. 15.—Sectional view of a steam radiator valve.