Source: {"pile_set_name": "USPTO Backgrounds"}

The present invention relates to a combined, adjustable airing valve and fire protection valve comprising a valve head commensurate with a valve seat, a valve stem taking the form of an adjusting screw, a fusible element taking the form of a nut threaded on the valve stem, a support bracket supporting and guiding the valve stem and a biasing means arranged between the support bracket and the stop plate on the valve stem.
In the present case a fire protection valve means a valve which as known per se is provided with a fuse element which is easily influenced by heat so that the valve will automatically close when fire or overheating occurs.
From Swedish patent specification No. 204 381 there is known an airing valve having a valve head which is held in open position by means of a temperature sensitive element, e.g. a disc consisting of a fusion metal. This disc-shaped element is clamped between a lock nut and a spring-tensioned gliding piece, the lock nut abutting against a sliding sleeve so as during normal conditions to prevent the lock nut from being pulled into the sleeve. However, such a fusible arrangement is severely subjected to destruction during the calibration of the valve head, as the disc-shaped fusible element which is manufactured from a rather soft metal, is cut to pieces when the lock nut is tightened.
Due to the soft metal of the fuse disc a proper locking of the valve head in the calibrated position is difficult to obtain. This fact also entails that an unauthorized person may turn the valve head and thereby alter the original airing characteristic of the valve.
Finally, re-adjustment of the valve will be very difficult because the soft material of the fusible element will stick to the lock nut. Usually, loosening of the lock nut will, therefore, entail a cutting of the fusible element into pieces.
From U.S. Pat. No. 800 740 there is known a valve unit which is retained in a fully open position by means of a fusible element, e.g. a fusible nut, and which due to overheating is released to a fully closed position. However, this valve unit can only be used as a cut-off unit in ordinary T-couplings and will find no application as a combined airing and fire protecting valve in straight pipes or channels. Besides, the fully open position of the valve head cannot be altered by adjusting the valve head alone, since the same is secured in position by the fusible nut.