135. A steam trap is a device for retaining the steam in a heating apparatus while permitting the Water of condensation to escape.

136. Fig. 52 shows a bucket trap in section. Water of condensation flows by gravity into the trap body a through the inlet pipe b, as shown by the arrow. As the water rises in the trap, it floats the empty pot, or bucket e, and the spike valve shown in the center of the pot bottom is forced into the opening at the base of the tube i, which leads through e to the outlet pipe d, and which is really the outlet opening of the trap.

When the float has risen to its full height, that is, when the spike valve has reached its seat, the water continues to flow into the trap and will finally overflow into the pot. When the pot is nearly filled with water it loses its buoyancy and sinks to the bottom of the trap, thereby opening the spike valve, but, as the lower end of i is now submerged in water, it follows that steam pressure within the trap will force the water in the pot up and out through i, e, and d, to the point of discharge. Before the water becomes low enough in the pot to expose the valve opening to the steam, the pot again rises and the spike valve closes the opening as before, and the trap again fills with water, only to be partly emptied when the pot is again sunk with an overflow of water into it. It will be observed that the action of this trap is thus automatic and intermittent; also that the steam pressure in the trap must be greater than that of the atmosphere, otherwise the water cannot be discharged to the outer atmosphere without the aid of some other contrivance, such as a pump, which will draw it, as it were, from the trap and force it into a space of higher pressure-a sewer, for instance.

Fig. 52.