Читать книгу Mechanics of the Household - E. S. Keene - Страница 19

—All steam boilers should be provided with safety valves as a safeguard against excessive steam pressures. Of the various types of safety valves, that known as the pop-valve is most commonly used on house-heating boilers. It is indicated at W in Fig. 18 and is shown in section in Fig. 21. The part A is screwed into the top of the boiler at any convenient place. The pressure of the spring C holds the valve B on its seat until the internal pressure reaches a certain intensity at which the valve is set, when it opens and allows the excess steam to escape. When the pressure is reduced, the spring forces the valve back on its seat. The handle D permits the valve to be lifted at any time as an assurance that it is in working order. This should be done occasionally, as the valve may stick to the seat after long standing and allow the pressure to rise above the point at which it should “pop.”

The valve may be set to “blow off” at any desired pressure by the adjusting piece E. House-heating boilers generally have their safety valves set to blow off at 8 or 10 pounds.