Fluid handling – With repair – tapping – assembly – or disassembly means – With mechanical movement between actuator and valve
Reexamination Certificate
2000-01-21
2001-12-04
Walton, George L. (Department: 3753)
Fluid handling
With repair, tapping, assembly, or disassembly means
With mechanical movement between actuator and valve
C251S149500, C251S149600, C251S252000, C251S263000, C251S297000
Reexamination Certificate
active
06325092
ABSTRACT:
SUMMARY OF THE INVENTION
This invention relates to improvements in thermally responsive valves for normally closing off fluid paths and releasing fluid when a predetermined temperature is attained. A typical thermally responsive valve, used for freeze protection in railroad locomotive coolant systems is described in U.S. Pat. No. 4,815,491, issued Mar. 28, 1989. Its disclosure is incorporated by reference into this specification.
In general, the objective of a freeze protection valve is to cause a water-containing system to be drained automatically when freezing conditions are threatened, so that the expansion which takes place as the water freezes does not damage pipes and other components of the system.
The valve described in U.S. Pat. No. 4,815,491 is an improvement over older freeze protection valves, in that it comprises a plug and fitting which separate from each other when liquid is to be released. All the parts that are likely to require service are contained in the plug, which can be easily and quickly replaced on site without draining the system.
The plug includes a set of radially movable balls that cooperate with a latching surface on the interior wall of the fitting into which the plug is inserted. The balls are situated in cylindrical, radially extending openings in the plug and are normally engaged by a cam within the plug in such a way that they project radially from the plug. However, the cam is axially movable and controlled by a temperature-responsive actuator, also inside the plug. When the temperature falls below a preset limit, the cam moves axially, clearing the balls and allowing them to move radially inwardly off the latching surface. When the balls move off the latching surface, the plug is able to drop out of the fitting. A compression spring is usually provided to assist the release of the plug from the fitting.
In the plug of U.S. Pat. No. 4,815,491, the area surrounding the outer ends of the radial openings is swaged so that the outer ends of the openings are slightly smaller in diameter than the balls. This way the balls are held captive in the openings, but are nevertheless able to protrude for engagement with the latching surface. One of the problems with the prior plug is that, with the swaging process, it was difficult to obtain consistent results. Another problem was that the balls occasionally became jammed in the radial openings in the plug, preventing release of the plug even when the cam cleared the balls.
This invention addresses the problems encountered in the formation and use of the earlier radial openings by utilizing tapered openings. The balls are inserted from inside the plug into the tapered openings, which are formed by passing a drill through larger drill holes diametrically opposite the desired locations of the tapered holes.
Essentially, in this aspect of the invention, the openings are tapered, throughout a major part of their lengths, in the direction from the interior of the plug body toward the exterior of the plug body, the taper being such that the diameter of a first part of each opening is greater than that of the ball situated in the opening, and the diameter of a second part of the each opening, situated outward from the first part thereof, is smaller than the diameter of the ball situated in the opening.
The tapered holes prevent the balls from becoming jammed as they were apt to do in the older cylindrical openings. The taper also provides a sloping surface which exerts an inward force component on the balls as they are cleared by the cam. This also reduces the tendency of the balls to jam.
Another problem with the freeze protection plug described in U.S. Pat. No. 4,815,491 is the difficulty of insertion of the plug into its fitting.
A strong coil spring is provided inside the fitting to ensure ejection of the plug when the critical temperature is reached. The plug is locked in place by a cooperation of the protruding balls with J-shaped grooves formed in the inner wall of the fitting. The balls and grooves together form a bayonet fitting. When the plug is inserted, it compresses the coil spring until the balls reach circumferentially extending parts of the grooves. The plug is then twisted so that the balls move to the ends of the circumferential parts, which have axially extending, ball-receiving notches. The balls are held in these notches by the force of the coil spring.
The coil spring exerts a strong axial force on the plug, opposing insertion and requiring the plug to be pushed as it is twisted. The need to maintain a pushing force on the plug as it is twisted makes insertion difficult. The axial force exerted by the spring also results in a frictional force resisting twisting of the plug. Manual twisting during insertion of the plug is especially difficult because the plug is typically made of polished metal, e.g. stainless steel, and has a circular, cylindrical external portion which extends outwardly when the plug is inserted in the fitting.
This invention addresses the problem of twisting of the plug in two ways. First the grooves formed in the wall of the passageway of the fitting, which cooperate with the balls to form a bayonet joint, are specially shaped to assist engagement of the plug with the fitting. Each groove has a helical ramp surface extending from the circumferential portion thereof obliquely toward the entrance opening of the passageway. The helical ramp surface merges with a surface of the circumferential portion of the groove and is engageable by a ball to urge the plug into the passageway as the plug is twisted. Thus, the cooperation of the balls with the ramp surfaces pushes the plug into place against the ejection spring as the plug is twisted, making it easier to install the plug. Second, a cap tightly fits onto the cylindrical external portion of the plug. The cap has means, for example axial ribs, formed on its exterior surface for facilitating the manual grasping and twisting of the plug for engagement and disengagement with the passageway of the fitting. The ramp and the ribbed cap both facilitate manual engagement of the plug with the fitting, while allowing the coil spring to be strong enough to ensure positive ejection of the plug.
The ribbed cap has several other advantages. If made of a plastics material, it can be provided in a variety of colors which can be used, for example, to provide a ready visual indication of whether or not annual routine maintenance has been performed. The cap can also be formed with an end opening through which a label secured to the end of the plug is exposed. The cap provides a frame for the label, preventing it from being peeled off.
Still another problem encountered with the device of U.S. Pat. No. 4,815,491 is that its thermal actuator is located inside the plug adjacent to the end of the plug which projects outside the fitting. Water in the coolant system being protected by the device, flows into the interior of the plug to come into contact with the body of the actuator. Because of this, there is a risk that debris in the coolant system can come into contact with the balls, the cam or other parts of the latching mechanism, and that the coolant may cause corrosion of the balls or other components. Excessive debris or corrosion may cause failure the plug to release.
This invention addresses the problem of debris and corrosion by positioning the seal of the plug and the cooperating sealing surface of the passageway so that, when engaged with each other, they are located in the passageway between the balls and the liquid-containing system. As a result, the liquid is isolated from the balls and other moving parts.
Because the seal is located on the liquid system side of the ball mechanism, it can be of comparatively small diameter. The small diameter of the seal makes it possible to use an ejection spring that reliably ejects the plug, but is not so strong as to make insertion of the plug difficult. This also reduces the likelihood of damage to the seal.
The expansible material of the thermal actuator is located inside a metal housing forming
Howson & Hoswon
Walton George L.
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