Boiler Accessories Steam Traps

BOILER ACCESSORIES: STEAM TRAPS Steam traps are used for collecting the water of condensation from steam pipes. They consist of a receptacle with an inlet and outlet valve so arranged that the condensation which collects may flow out, but steam cannot pass.

In the float trap shown in Fig. 62, the float rises and falls with the change in water-level. When the water-level rises above a certain point, the float opens the discharge valve. The trap shown in Fig. 63 is similar, the float being replaced by a weight W, which is nearly counterbalanced b y the weight T. The raising of W by the water opens the valve V.

There are other forms called bucket traps. In the one shown in Fig. 64, the water enters at W. While there is only a little water around the bucket F, it floats, and the valve V is closed; but when the water rises high enough to flow over the edge, the weight of water in the bucket causes it to sink, and opens the valve V. Water is forced up the passage M, and out through the pipe N, by the pressure of the steam on the surface of the water surrounding t h e bucket.

Another form of trap, called the differential steam trap, depends upon a head of water acting on a flexible diaphragm. Water enters at either top or bottom by the pipes E, Fig 65.

When the waterlevel rises, it fills the chamber G and the pipe N. This causes a pressure on the under side of the diaphragm greater than that caused by the spring H, which spring acts on the upper side of the diaphragm and tends to keep the valve open. While the pressure below the diaphragm preponderates, the valve P remains closed. When the water rises and fills the chamber J so as to flow down the pipe M, the water-pressure on the upper and lower side of the diaphragm will become equal, because the head of water in M is practically the same as that in N. The spring will now open the valve P, and water will be discharged from the pipe I. When the head in At falls, the pressure on the under side of the diaphragm again becomes greater, and the valve accordingly closes.

Return Traps. Traps that are used for returning water of condensation to the boiler are called return traps. There are a variety of forms, but the principle of action in all is similar, and is shown in Fig. 66. B represents the boiler, and T the trap, which is placed a few feet above the boiler. The trap is supplied with steam from the boiler. It is also connected with the boiler by the pipe P, in which is a check-valve at C. Water of condensation enters the trap through the pipe E, in which is a check-valve II, until it reaches a depth sufficient to raise the float F, which opens the balanced steam valve V, called an equalizing valve. Steam from the boiler then enters the trap and equalizes the pressure. Since the pressures are equal, water in the trap, because of its height above the water-level of the boiler, will flow to the boiler until the level in the pipe 1' is nearly the same as the water-level in the boiler. As the water-level in the trap falls, the float F drops, and the equalizing valve is closed.

In some forms of return traps, buckets are used instead of floats.