Adjustable packing gland assembly for movable blade damper
This invention relates to an improved packing gland assembly for providing a gas-tight seal at the point where a damper blade shaft passes through the damper frame of a movable blade damper.
One type of damper known to the art utilizes a peripheral frame which surrounds several movable damper blades. Each of the blades is mounted on a respective shaft which passes through the damper frame, and the shafts are rotated in coordinationso as selectively to close and open the damper.
In the past, packing glands have been used around the damper blade shafts to provide a gas-tight seal at the point where the blade shafts pass through the damper frame. One commonly used approach of the prior art is to weld individual packingglands in place on the damper frame to prevent gas leakage such as flue gas leakage around the damper blade shaft.
Though this prior art approach can, if properly implemented, provide a suitable seal around the damper blade shaft, it provides a number of important disadvantages. Once the packing gland has been welded into place on the damper frame, nolateral adjustment can be made of the blade shaft without affecting the concentricity between the blade shaft and the packing gland. Excessive eccentricity between the blade shaft and the packing gland can cause unacceptably high rates of gas leakagethrough the packing gland. Thus, prior art packing glands which are welded in place to the damper frame can restrict the amount of lateral adjustment that can be made to the blade shafts without physically removing the packing gland. If the bladeshafts are not adjusted properly, openings between sealing surfaces on the blades caused by the inability to adjust the blade clearances as desired can also allow unacceptably high rates of gas leakage through the damper when in the closed position.
Furthermore, when packing glands are welded in place to damper frames, replacement of the packing material within the packing gland can be a difficult operation since the gland is open at one end only. In addition, surfaces of the blade shaftwithin the packing gland are relatively inaccessible due to the fixed location of the gland. Any shaft surface defects in the region of the gland may promote gas leakage through the gland or increase torque requirements to rotate the shaft. Suchsurface defects can be difficult to detect or correct because they are concealed by the gland. Moreover, packing glands which are welded in place are difficult or impossible to replace due to the need to cut or burn them out.
The present invention is directed to an improved packing gland assembly for a movable blade damper which to a large extent overcomes the aforementioned disadvantages of the prior art.
According to this invention, an improved packing gland assembly is provided which is held in place on the damper frame by means of fasteners such as threaded fasteners. The packing gland assembly of this invention is mounted to the frame in aremovable and adjustable manner such that, within a predetermined range of adjustability, the packing gland assembly is free to follow the shaft as necessary in order to preserve the desired degree of concentricity between the packing gland and theshaft.
In the preferred embodiment described below, the packing gland assembly is held in place by two threaded fasteners such as bolts which pass through elongated slots in the packing gland assembly. Whenever it is desirable to adjust the position ofthe packing gland assembly, the fasteners are loosened and the gland is allowed to follow the shaft as the shaft position is adjusted. Once the shaft position has been properly adjusted, these threaded fasteners are then tightened to lock the packinggland assembly in position and to provide an excellent seal preventing the escape of gases out of the damper around the shaft.
The improved packing gland assembly of this invention provides a number of important advantages. It maintains excellent concentricity between the packing gland assembly and the blade shaft to ensure that a positive seal is created to prevent theleakage of gas out of the damper around the shaft. Since the packing gland assembly is held in place by means of fasteners rather than by means of welds, the fasteners can be loosened as necessary to allow the packing gland assembly to move laterallywith the blade shaft when the position of the blade shaft is adjusted. The packing gland assembly of this invention provides two seals: one between the packing gland assembly and the damper frame and a second between the blade shaft and the packinggland assembly. Together, these two seals cooperate to provide an effective seal against the escape of gases out of the damper. Since the packing gland assembly can readily be removed when necessary for service, the packing gland assembly of thisinvention is readily replaced when necessary. Furthermore, since both ends of the packing gland assembly are accessible, the packing material can readily be removed and replaced when necessary.
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