Patent Application
20130056668
This invention relates to temperature control systems typically used in office or apartment buildings in order to control the flow of hot or cold water, refrigerants, or steam.
Ball valves heretofore were a preferred type of flow control device used for this purpose.
U.S. Pat. No. 3,678,556 may serve to show the principle elements of construction of a ball valve. Here the flow controlling element is a ball 56 having a pierced opening 15 and being wedged between two compressed seal rings 36, typically made from a deformable plastic. This then creates a good deal of friction, whenever the ball is rotated from a given position. Such high friction requires large and costly operating devices on the one hand, and it also creates a hysteresis, or, dead-band effect whenever the travel is reversed from a given position, typically in automatic control applications. This dead-band translates into “dead time” using the parlance of automatic control theory. Such dead time, in turn causes instability of the control loop. In other words, it becomes very difficult to maintain a constant desired temperature.
My invention, on the other hand, overcomes these difficulties by providing a swinging ball, unhindered by any friction causing seals (save for a minor shaft seal). We therefore offer a device which is virtually dead-band free, and is therefore ideal for automatic control purposes.
In addition, my design has fewer parts and weighs at least 40% less than a comparable ball valve, an important economical advantage.
Finally, a wide-open ball valve has a bore through the ball, whose diameter is basically equivalent to the adjacent pipe size. Such a large port offers no fluid restriction and is therefore useless for control purposes. As a matter of fact, such valves have to operate at less than 50% open in order to generate a desired pressure drop (fluid restriction). This then restricts the controller's operating signal to only less than 50%. Here the dead-band has twice the negative impact on the available signal. My invention, on the other hand, can utilize close to 100% of the available travel for control purposes, another important advantage.
Referring to
Opening 11 encompasses a retainer 12 and a seal ring 13. Opening 11 and with it shaft 10 are off-set by a distance “X” from the centerline connecting both ports equivalent to about 20% of the radius “R” of the ball. This causes ball 9 to make a rotating or camming motion in and out of orifice 8 upon rotation of shaft 10, typically operated by an actuating device 14 (not part of my invention).
A portion 15 of shaft 10 passing through said ball is profiled, matching a similar profiled bore of the ball. This allows the shaft to transmit precisely rotary motion; yet, it allows the ball to slide freely along the length of shaft 10 in order to line up with the center of orifice 8. An enlarged cavity 25 within housing 5 allows the ball to freely rotate by 90 degrees as shown by dotted lines. Cavity 25 narrows in diameter into a conical section 16 towards orifice 8. This allows the ball to self-center itself against the orifice in order to provide tight shut-off. The relationship between the exposed flow area between housing interior surfaces and the ball, and the angular rotation of the stem is basically linear.
Shaft 10 furthermore has an enlarged diameter portion 17 co-operating with a similarly sized recess in retainer 12, thus preventing the shaft from being expelled from housing 5 by internal fluid pressures.
The controlled flow area, determining the amount of fluid passing the valve, is determined as follows: Any rotation of the shaft by an angle α will lower the upper surface of the ball by a distance d equal to the eccentricity “X” times one minus cosine α. This creates a flow area equal to d×R×π/2. The flow area is mostly dependent on the cosine of α, and since the cosine varies exponentially, we have a non-linear flow characteristic.
While my invention has been described in a preferred embodiment, nothing shall preclude from making additional modifications without departing from the scope of the following claims. For example, the shape of the section of the shaft connecting to the ball could have a serrated profile instead of a square, and the housing could have flanged ports instead of the shown pipe threads.
