Abstract:
A valve actuator is disclosed for use with short throw valves. The actuator includes a plate perpendicular to the valve stem that has a slot formed of regions having different radii of curvature centered on the valve stem. An eccentric cam is attached to a handle mounted on the valve stem. The cam extends through the slot and is rotatable for positioning at a radius corresponding to the radius of the different slot regions. When the cam is rotated so that it may traverse a slot region, the handle can be turned to move the valve closing member through an angle subtended by the slot region. This permits the valve to be opened or closed in a step-wise fashion and prevents rapid opening and closing of the valve that can cause a water hammer effect.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to actuators for valves and especially to slow closing actuators for manual closing of short throw valves. 
       BACKGROUND OF THE INVENTION 
       [0002]    Piping systems, such as those used to deliver water to fire suppression sprinkler systems, handle large liquid flow rates under significant pressure. The flow to the sprinkler system is controlled by one or more shut-off valves which may be, for example, slow closing gate valves each operated by a hand wheel turning a jackscrew. Slow closing valves are mandated for sprinkler applications by various specifications, such as those promulgated by Underwriters&#39; Laboratories (UL) or Factory Mutual (FM) to prevent damage upstream of the valve due to the water hammer effect which will occur if a valve is closed rapidly. In pipes carrying high flow rates under significant pressure, the change in momentum caused by a sudden valve closing will generate high transient forces on the pipes which can cause their mountings to fail and the pipe to leak or rupture, thereby rendering the sprinkler system inoperative. 
         [0003]    It is desirable to use short throw valves such as quarter-turn ball valves and butterfly valves to control water flow to a sprinkler system due to the simplicity and reliability of such valves. However, these valves are capable of very rapid closing and may cause significant damage to the piping system due to the water hammer effect when manually operated without constraint. To use short throw valves and avoid the water hammer problem, the valves have been modified, for example, by the addition of a multi-turn handle coupled with reduction gearing to prevent quick closing. Such modifications defeat the purpose of using simple quarter turn valves, however, as the modifications render the valves more complicated, more expensive and less reliable. There is clearly a need for a short throw valve that is operable in a manner that avoids the water hammer effect but maintains the simplicity and reliability inherent in such valves. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention concerns an actuator for a valve having a stem rotatable about a first axis of rotation. The actuator comprises a plate mountable on the valve. The plate is substantially perpendicular to the stem. A guide slot is positioned in the plate. The guide slot has a plurality of regions including at least a first slot region having a first radius of curvature, and a second slot region having a second radius of curvature. The second radius of curvature is different from the first radius. The actuator also has a handle mountable on the stem. A cam is mounted on the handle. The cam is rotatable about a second axis of rotation oriented substantially perpendicular to the plate. The cam is eccentric to the second axis of rotation and extends through the guide slot. The cam may be rotated to a first orientation positioning the cam at the first radius thereby permitting the handle to be turned along an arc traversing the first slot region. Further rotation of the cam to a second orientation positions the cam at the second radius thereby permitting the handle to be turned along an arc traversing the second slot region. In one embodiment, the guide slot is formed of only two slot regions. 
         [0005]    The guide slot also includes a radially extending slot region connecting the first and the second slot regions to one another. The cam is rotatable within the radially extending slot region between the first and the second positions to position it at either one of the first or second radii for traversing one of the first or second slot regions. Preferably, the radially extending slot region is positioned between adjacent ends of the first and second slot regions. 
         [0006]    In one embodiment, the first slot region has a shorter arc length than the second slot region. In this embodiment, the valve is preferably in the closed configuration when the cam is positioned at the end of the first slot region that is positioned distal to the second slot region. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a valve having an actuator according to the invention; 
           [0008]      FIG. 2  is an exploded perspective view of the valve shown in  FIG. 1 ; 
           [0009]      FIG. 2A  is a perspective view of a diverter valve having another embodiment of an actuator according to the invention; 
           [0010]      FIG. 3  is an end view of the valve shown in  FIG. 1 ; 
           [0011]      FIGS. 4 ,  6  and  8  are top views showing operation of the actuator shown in  FIG. 1 ; 
           [0012]      FIGS. 5 ,  7  and  9  are sectional views taken, respectively, at lines  5 - 5 ,  7 - 7  and  9 - 9  of  FIG. 3  showing the position of the valve closing member corresponding respectively, to the positions of the valve actuator shown in  FIGS. 4 ,  6  and  8 ; and 
           [0013]      FIG. 10  is a perspective view of another embodiment of a valve having an actuator according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0014]      FIG. 1  shows a valve  10  on which is mounted an actuator  12  according to the invention. Valve  10  (shown in phantom line) is a short throw valve, such as a ball valve or a butterfly valve, which requires only a quarter turn (a rotation of 90°) of the valve closing member to fully open or close the valve. 
         [0015]    As best shown in the exploded view of  FIG. 2 , actuator  12  comprises a plate  14  that is mounted on a flange  16  of the valve  10  by fasteners such as bolts  18 . A hole  20  in the plate allows a valve stem  22  to pass through. Valve stem  22  and plate  14  are oriented substantially perpendicular to one another. The valve stem is connected to a valve closing member (described in detail below) and is rotatable about an axis of rotation  24  to rotate the valve closing member between open and closed positions. A handle  26  is attached to the valve stem  22  to permit manual turning about axis  24 . The handle may be attached to the valve stem using an elongated aperture  25  as explained in detail below. 
         [0016]    A cam  28  is mounted on the handle  26 . The cam is rotatable about another axis of rotation  30  which is also oriented substantially perpendicular to the plate  14 . A turning knob  32  is attached to the cam for rotating it about axis  30 . Knob  32  has a detent mechanism  34  that cooperates with indentations  36  in the handle  26  to fix the rotational position of the cam about axis  30 . A retaining head  38  is attached to an end of cam  28  opposite the knob  32 . As shown in  FIGS. 1 and 3 , when the actuator  12  is properly assembled, the cam  28  extends through a guide slot  40  positioned in the plate  14 . The knob  32  rides on handle  26  above the upper face of plate  14  and the retaining head  38  engages the bottom face of the plate. The retaining head  38  is sized larger than the width of the guide slot to prevent the cam from being pulled out of the guide slot. 
         [0017]    Guide slot  40  is formed of a plurality of slot regions differentiated by their respective radii of curvature. The radius of curvature of each slot region is centered on the axis of rotation  24  of the valve stem. In the example actuator shown in  FIG. 2 , guide slot  40  is formed of two slot regions, region  42 , having a radius of curvature  44 , and region  46 , having a radius of curvature  48  greater than radius  44 . It is also noted that the arc length of slot region  42  is smaller than the arc length of slot region  46  for reasons described in detail below. 
         [0018]    The slot regions  42  and  46  are connected to one another by a radially extending slot region  50 . Guide slot  40  may also have an enlarged slot region  52  positioned at one end. The enlarged slot region is sized to permit the retaining head  38  to pass through the plate  14 , allowing assembly and disassembly of the actuator  12 . It is also feasible to make the retaining head  38  removable from the cam  28 , by attaching it to the cam by screw threads for example. If the retaining head is removable then there is no need for the enlarged slot region  52 . 
         [0019]    In another embodiment, shown in  FIG. 2A , guide slot  40  is formed of three slot regions  43 ,  45  and  47 . The three slot regions are connected to one another by two radially extending slot regions  49  and  51 . Slot regions  43 ,  45  and  47  subtend an angle of about 180 degrees and such configurations are used with valves having a longer throw, such as diverted valves which may be closed or opened to a first or a second outlet. 
         [0020]    As best shown in  FIG. 4 , the cam  28  is positioned eccentrically to its axis of rotation  30 . Rotation of the cam about axis  30  thus moves the cam toward and away from the axis of rotation  24  of valve stem  22 , allowing the cam to be positioned at different radii of curvature corresponding to the respective radii  44  and  48  of the slot regions  42  and  46 . Rotation of handle  26  is constrained by the position of cam  28 , which is used in conjunction with guide slot  40  to control the speed at which the valve is opened and closed as described below. 
         [0021]    The description of operation of the actuator  12  begins with  FIGS. 4 and 5 .  FIG. 4  shows the handle  26  in the closed position, and  FIG. 5  shows the valve closing member  54  (in this example, a plate of a butterfly valve) in the closed position corresponding to the aforementioned handle position. The enlarged view of  FIG. 4  shows the cam  28  rotated about its axis  30  so that it is positioned at a radius  44  from the axis of rotation  24  corresponding to the radius of slot region  42 . With the cam in this position, the handle  26  may be turned counter clockwise toward the open position, but only over the limited angle subtended by the slot region  42 . The cam  28  traverses the slot region  42  and is stopped by contact with the radially extending guide slot region  50 . The arc length of the slot region  42  is purposely limited so that the valve closing member  54  is only opened a small amount, calibrated to prevent a significant surge of water from passing rapidly through the valve and thereby avoiding the water hammer effect. 
         [0022]    With water now flowing through the valve at a controlled rate, the cam  28  is rotated within the radially extending guide slot region  50  by turning knob  32  so that the cam is positioned at the larger radius  48 , corresponding to the radius of curvature of slot region  46 . As shown in  FIG. 6 , this position of the cam allows it to traverse the slot region  46 , thereby allowing the handle  26  to be turned through an angle subtended by this slot region to further open the valve as shown in  FIG. 7 . In this example, the arc length of the slot region  46  allows the valve to be opened fully when the cam  28  traverses the entire length of the slot region, as shown in  FIGS. 8 and 9 . It is understood that the guide slot  40  could be divided into more than two regions in order to further slow the opening and closing of the valve by requiring the motion of the valve closing member to be halted while the cam is rotated to the proper radius for a particular guide slot region. 
         [0023]    To close the valve, handle  26  is rotated clockwise from the position shown in  FIG. 8  with the cam  28  traversing slot region  46  as shown in  FIG. 6  until it encounters the radially extending guide slot region  50  which prevents further rotation of the handle. With only a partial rotation of the handle being permitted, the valve closing member is prevented from closing fully and a severe water hammer effect is thus prevented. The motion of the valve closing member  54  is halted while cam  28  is rotated to position it at the radius  44  of the slot region  42 . The handle may then be rotated further in the clockwise direction to complete the valve closing illustrated in  FIGS. 4 and 5 . Note that pausing the motion of the valve closing member with the valve in the partially open position limits the transient forces due to the change in flow rate and gives them time to settle out without a significant water hammer effect. After rotating the cam to position it at the radius  44  corresponding to slot region  42 , the handle may be turned to complete closing of the valve without fear of damage to the pipe network because the flow rate at this point is small enough such that no matter how quickly the handle is moved, significant force from the water hammer effect will not occur. 
         [0024]      FIG. 10  shows a ball valve  56  having the actuator  12  according to the invention. Valve  56  is also a supervised valve in that it has within a weatherproof cover  58  a cam  60  that rotates with the valve stem. The cam  60  interacts with a sensor  62 , for example, a switch, which generates a signal indicative of the status of the valve. For example, the cam may close the switch when the valve is in the open position, and the switch may be used to control a lamp on a control panel, an illuminated lamp indicating that the valve is open, an unlit lamp indicating that the valve is closed or vice versa. Other configurations are also feasible using multiple cams and switches to further define the state of the valve. Additionally, the valve may have a visual indicator, such as plate  64  that is attached to the valve stem and rotates with it. The orientation of the plate indicates the status of the valve. When the plane of the plate is perpendicular to the flow direction as shown in  FIG. 10 , the valve is closed. When the plane of the plate is aligned with the flow direction, the valve is open. 
         [0025]    Valve actuators according to the invention, when used on short throw valves such as ball valves and butterfly valves, prevent damage due to the water hammer effect by controlling the manner in which the valves are opened and closed. This allows such valves to be used in applications for which they were previously considered unsuitable without sacrificing the advantages of simplicity and reliability inherent in their design.