The rear opening of the penstock is provided to give access to the tuyere for cleaning out and for plugging with clay in case of a stop, or the like. The cap which closes this opening is called the "wicket." This joint also is made spherical so that the cap will be tight in any position and is held in place by key bolts which can be operated with a hammer in spite of being very hot when in use.

The wicket is provided with a small hole through which a pricking rod can be run to punch out the tuyere, and this hole must be kept shut by some apparatus which permits it to be opened freely and which contains a peep glass through which the action of the tuyere can be directly observed. Much ingenuity has been expended in meeting these conditions. The wicket design here shown gave good satisfaction, which is more than can be said for many that have been used. The outside end of the hole through the wicket is turned to fit a ball of 3-inch diameter. This ball is loosely held by two pins which go into holes in its sides. These pins are at the lower end of an angle lever which has heavy weights cast at the ends of its horizontal branches. These force the ball up against its seat in the wicket, and the ball being loosely held is free to take a position which makes a tight joint. The pressure is applied to it, not through the pins, but by a loosely fitted cap which is a part of the weighted lever. The hole in one side of the ball is square and the end of the squared pin on that side fits loosely into it. The outer end of this pin is bent down into a handle so that the ball can be rotated on the horizon axis transverse to the line of the tuyere. The ball has a half-inch hole bored through its inner half and a larger tapped hole through the outer half with a squared seat at the bottom. In this tapped hole fits loosely a screw plug with a half-inch hole through it. This is screwed down on to a a glass set in the base of the larger hole and holds it firmly in place. Normally the ball is turned at right angles to the position shown and its blank face is presented to the seat, when it is desired to look into the tuyere, the ball is rotated by turning the handle a quarter turn so that the peep hole through the ball is in the axis of the blow pipe. The reason for this is that at all furnaces, but especially charcoal furnaces, the gas leaking back even for a few seconds when the blast is off, clouds up the glass so that after a short time it is impossible to see through it. By this design the glass is only exposed to this action when the blast is on the furnace for a minute or two at a time. In addition four holes are drilled through the ball in such position that by turning it to different angles a strong jet of blast may be blown through these holes to impinge on the glass in such a way as to blow it clean. By turning the blank side of the ball to the seat, the sight glass can be changed with the blast on the furnace. The hole through the wicket is unnecessarily large in this design and exposes the ball to too great a pressure. The design could be improved by making the hole smaller and putting the joint surface next to the hole instead of at the outside so that the area of the ball exposed to the blast pressure could be reduced to a small fraction of that in this design, then the same weights would keep the joint tight against a much higher pressure.

Fig. 177. Wicket.

This design of penstock wicket, etc., was made under the supervision of the writer to fit the conditions of a small furnace which was being reconstructed. While the general design is right certain details worked out badly owing to some conditions which could not be altered. The first of these was that the vertical leg of the penstock was too short, and the inner end of the penstock was about a foot too close to the furnace, the blow pipe being as much too short, so when swung back it did not give as much room to work as was desirable. If the vertical leg had been 2 feet longer so as to give a proportionately greater swing, it would have been very much better. These defects were due to the location of the bustle pipe and the openings through it, which we did not desire to change. In a new plant these difficulties could be avoided, while using the general principles of this design, which are, in my judgment, correct.

Since these wickets were made, I have seen in use a simpler apparatus which obtained the same general result and gave good satisfaction. . This design is in essence a large plug cock mounted in the line of the hole through the wicket and arranged to open or shut the hole exactly as a plug cock does. It was found that by making the taper of the plug just right, the tendency to bind, due to unequal expansion, could be overcome. I would have supposed that this scarcely could have been done, but this simple arrangement seemed to work very well. I saw it at the Lorraine blast-furnace and I believe it was the design of Mr. A. J. Boynton, the superintendent of that plant.

It may be thought that too much stress is being laid upon these details, but as a matter of fact there is scarcely anything which has a greater influence on a decent, orderly and successful operation of the furnace than these parts. If a correct design be not used, a tight joint cannot be made, or if it be tight when made, as soon as the parts become heated in operation it is no longer tight and the blast howls out at every leak in a way that is distressing to the ear and apt to be ruinous to the cost sheet.