Abstract:
An valve actuator in a hydronic heating and cooling system includes a motor for changing the position of a valve, a switch for switching power to the motor, and a sensor for detecting the arrival of the valve at a desired position and for stopping the motor without using a mechanical stop. The motor&#39;s power source includes a capacitive power source which can be used to drive the motor under low-power conditions.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of copending application U.S. Ser. No. 09/079,815, filed May 15, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to actuators and zone valves for heating and cooling systems. 
     Zone valves are often utilized in hydronic heating and cooling systems. The zone valves isolate specific areas or “zones” of the system. Typically, each zone valve is controlled by a thermostat, which causes the valve to open and close to achieve desired temperature changes. 
     Conventional zone valves are typically actuated by either a heat motor or an electric motor. In valves with a heat motor as the actuator, an electrically heated element causes linear movement of an actuating element that, in turn, opens the valve. In valves with electric motors, the motor and associated gears move a valve member between closed and open positions (e.g., a rubber plunger moved away from a seat or a ball element moved through a 90 degree rotation). 
     Conventional motorized zone valve actuators employ a motor which is energized in one direction by a source of power, held in some predetermined position by a mechanical or electrical braking means, and then returned to its original position by a spring. 
     Giordani, U.S. Pat. Nos. 5,131,623 and 5,540,414, describe zone valves for hydronic heating or cooling systems in which a motor-driven actuator rotates a ball valve through about a 90° rotation, between closed and opened positions. The motor rotates the valve from its normal position, which may be either open or closed, to the opposite position, e.g., if the valve is normally closed, from the closed to the open position. When the motor is de-energized, the valve is returned to its normal position by a spring so configured that it provides sufficient restoring torque to overcome the frictional torque of the ball valve. 
     Carson, U.S. Pat. No. 3,974,427, discloses a motor control apparatus having an electric motor which is driven in one direction by an alternating current power source and in the opposite direction by a spring. Holding or braking of the motor is accomplished by applying a source of direct current power to magnetize the motor and hold it in a predetermined position after the alternating current power source is removed. This holding or braking action is removed by taking away the direct current power source and momentarily applying an alternating current power source to the motor, thereby de-magnetizing or degaussing the motor so that it is free to return to its initial condition under the power of the spring. 
     Fukamachi, U.S. Pat. No. 4,621,789, discloses a valve mechanism in which the valve is prevented by a physical stopper from moving any further after it has moved to an open or closed state. 
     Botting, et al, U.S. Pat. No. 5,085,401, discloses a valve actuator in which the motor makes an electrical contact after rotating a predetermined distance, causing deenergization of the motor. 
     Fukamachi, U.S. Pat. No. 4,754,949, discloses a valve actuator in which the rotation of the valve by a predetermined amount causes electrical contacts to be turned off, stopping the rotation of the actuator motor. 
     Some motorized valve actuator systems employ a fail safe energy system to provide power to the actuator motor in the event that the main power source is lost. Strauss, U.S. Pat. No. 5,278,454, discloses an emergency, fail safe capacitive energy source and circuit which is used to power an air damper actuator or a valve actuator. A sensor detects loss of power to the valve actuator circuit or motor, activating a switch which connects a bank of capacitors to the motor, with the appropriate polarity to drive the actuator back to its fail safe position. No provision is made for interrupting the connection between the capacitors and the motor when the fail safe position is reached, and thus the motor appears to work against a mechanical stop defining the fail safe position. 
     SUMMARY OF THE INVENTION 
     The invention features an actuator in which a sensor detects when the valve has reached a desired position, and controls a switch that shuts off the motor driving the valve. The invention makes it unnecessary to rely on a mechanical stop or a return spring to put the valve in a desired position. For example, a valve can be moved from open to closed and from closed to open, without relying on a mechanical stop or return spring. And switching a valve from normally-open to normally-closed can be done simply by throwing a single switch. 
     In one aspect, the invention features an actuator for actuating a valve in a hydronic system, wherein the valve has a first position in which fluid flow may occur along one path and a second position in which fluid flow is either blocked or may flow along another path. The actuator includes: a motor coupled to the valve, wherein rotation of the motor changes the position of the valve from one of the first and second positions to the other of the positions; a switch controlling the delivery of electrical power to the motor, the switch having a closed position in which electrical power is delivered to the motor and an open position in which power is not delivered; a sensor configured to detect the arrival of the valve at the first and second positions; and circuitry connected to the sensor and to the switch, the circuitry being configured to respond to the detection by the sensor of the arrival of the valve at one of the first and second positions by opening the switch to stop delivery of power to the motor. 
     Preferred implementations of the invention may include one or more of the following features: The sensor may be configured so that the output of the sensor changes state upon the arrival of the valve at a desired position. The sensor may have two states, and a change of state in its output occurs at approximately the moment when the valve, having begun to move from one of the first and second positions, reaches the other of the positions. The motor may rotate the valve in a single direction. An electrical power storage element (e.g., a capacitor) can be included in the actuator for providing power for driving the motor, sensor, and circuitry (e.g., when power to the actuator is lost). The circuitry for controlling the actuator can be provided by an integrated circuit chip. The valve may be a ball valve. The sensor may be an optical sensor. The actuator may have projections on a member that rotates with rotation of the valve and the projections may cause the sensor to become blocked and unblocked, and arrival of the valve at a position corresponds to blockage of the sensor by a projection either ceasing or beginning. The actuator may include a clutch for manually rotating the valve, and the position of the clutch may provide an indication of the angular position of the valve. The actuator may include a worm gear drive between the motor and the valve. A default-position selection switch may be included to enable the actuator and valve to be transformed from a normally-open valve to a normally-closed valve by movement of an electrical switch. 
     In a second aspect, the invention feature a zone valve for use in a hydronic system, in which the valve includes a ball element; a valve casing enclosing a ball element; a valve seat in contact with the ball element and the valve casing, the valve seat having a notch to receive an O-ring; an O-ring installed in the notch; a metallic, springy washer positioned in a compressed state within the valve casing in such a configuration as to provide an approximately constant force on the valve seat; and wherein the notch is shaped so that the axial force causes the O-ring installed in the notch to be compressed to improve a seal between the valve seat and an internal bore of the valve casing. 
     In a third aspect, the invention features operating a hydronic valve actuator by, prior to initiating movement of the valve, determining the charge on a capacitive power source and determining the energy required to complete the valve movement prescribed, and then deciding to initiate movement only if the charge on the capacitive power source is sufficient to provide the energy required to complete the movement. 
     In a fourth aspect, the invention features a hydronic valve actuator including a motor for driving the valve, wherein rotation of the motor changes the position of the valve from one of the first and second positions to the other of the positions; a gear assembly coupling the motor to the valve, wherein the gear assembly includes a worm gear; and a knob shaped to be turned manually either by grasping or by use of a tool; a clutch assembly connecting the knob to the valve stem and to the gear assembly, wherein the clutch assembly can be moved between engaged and disengaged modes, wherein in the engaged mode the gear assembly and worm gear are engaged with the valve stem so that the motor can turn the valve, and in the disengaged mode the gear assembly and worm gear are disengaged from the valve stem so that the valve can be turned using the knob. 
     Preferred implentations of this aspect of the invention may include one or more of the following features: The clutch assembly may be disengaged by pushing the knob axially. The clutch assembly may include teeth on two rotating members that are separated by axial motion of the knob to disengage the clutch. The knob may have a marking indicating the position of the valve. 
     Other features of the invention will be apparent from the following description of preferred embodiments, including the drawings, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a valve and actuator according to the invention. 
     FIG. 2 is an isometric view of the interior of the actuator. 
     FIG. 3 is an isometric, exploded view of components of the clutch mechanism of the actuator. 
     FIGS. 4A-4D are diagrammatic views of the optical sensor and drive member of the actuator in four different positions. 
     FIG. 5 is a schematic of the electronics of the actuator. 
     FIGS. 6-13 are flow charts of the processes followed by the microprocessor in controlling the actuator. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a preferred zone valve  10 . Ball valve  12  is driven by actuator  14 . The actuator is coupled to the valve body  26  (bronze forging) by a rotate-to-lock fastening arrangement  23 . Flat-sided stem  16  extends from ball element  18  into a matching opening  19  in the actuator. The actuator is electrically operated, and has wires for coupling it to conventional power and control circuitry. 
     Fluid flows through the ball valve in a conventional manner. When the ball is in the open position, fluid flows through the ball element  18  from port  37   a  to port  37   b . The valve is bidirectional, and thus either of ports  37   a ,  37   b  can be an inlet or an outlet. 
     Ball element  18  (brass) seals against seats  20   a ,  20   b  (Teflon), which are, in turn, sealed to the internal bore  25  of the valve forging by O-rings  22   a ,  22   b , which sit in O-ring notches  21   a ,  21   b . A wavy washer  30  (stainless steel) provides an axial force on the seats  20   a ,  20   b  (the curvature of the washer is exaggerated in the drawing). Notches  21   a ,  21   b  are shaped so that the axial force compresses the O-rings, causing them to press outwardly against the bore of the valve casing, to effect a seal between the valve seats and the bore. The wavy washer presses against backing ring  24  (stainless steel), which presses against O-rings  22   a . By making the wavy washer out of a springy metallic material (e.g., stainless steel), it retains its resiliency over time. As O-rings  22   a ,  22   b  compress over time, the wavy washer expands while maintaining adequate axial force. Over the life of the valve, the wavy washer will compensate for the tendency of the Teflon valve seats to cold flow and/or wear; the washer will expand slightly, to maintain the seats in contact with the ball. 
     Referring to FIG. 2, a motor  40  turns a pinion  42 , which in turn drives a cluster gear  44 , consisting of a large and small spur gear molded as one plastic part. Cluster gear  44  drives a second cluster gear  45 , consisting of a small spur gear  47  and a worm gear  34  also molded as one plastic part. The worm gear engages drive gear  31 , which, in turn, rotates drive member  47 , which, in turn, rotates valve stem  16 . The entire gear train (pinion gear  42  through drive gear  31 ) provides a 960:1 increase in torque. The worm gear  34  and drive gear  31  provide an 80:1 increase. 
     Referring to FIG. 3, the ball valve  12  may be manually opened and closed by depressing and turning a knob  70  (FIG. 3) exposed above the top cover (not shown) of the actuator. The knob is connected to stem  16  of the ball valve via drive member  47 , and can be manually disengaged from drive gear  31  using a clutch mechanism  38 . Normally, valve clutch teeth  48  on the drive member interlock with valve teeth  50  on the drive gear. A compression spring  32  (FIG. 1) wraps around shaft  49 , and provides an upward force on drive member  47  to keep the teeth engaged. Manual movement of the valve is not possible with the teeth engaged, as such movement would require that drive gear  31  turn worm gear  34  in reverse (the 80:1 torque ratio of the worm and drive gears prevents that from happening). To manually rotate the valve, the valve clutch teeth  48  are disengaged from the valve teeth  50  by pressing downward on knob  70  (FIG. 3) and rotating drive member  47 . Because the drive member is directly connected to the valve stem  16 , rotation of knob  70  results in rotation of the ball valve. Once the clutch is disengaged, the valve may be rotated in either direction. After the valve has been manually rotated to a desired position, pressure is removed from the knob, spring  32  causes the clutch teeth to reengage. A valve position indicator  54  is molded into knob  70 , to provide a visual indication to the valve operator of the current position of the valve. A notch  56  is provided in the knob to permit a screwdriver, or other thin rigid object, to be used to turn the valve. 
     The electronic circuitry controlling operation of the actuator depends on an optical sensor U 2  (FIGS.  3  and  4 A- 4 D) to determine the position of the valve. The sensor is positioned so its light path is alternately blocked and unblocked as drive member  47  is turned. Projections  72 ,  74  extending from the drive member pass through the optical path of the sensor. 
     FIGS. 4A-4D illustrate operation of the sensor. Projections  72 ,  74  are positioned on drive member  47  so that the sensor is blocked in two quadrants of rotation of the drive member. Each of projections  72 ,  74  blocks the optical sensor over 90° of travel, leaving 90° between them in which the sensor is not blocked. In operation, the circuitry controlling motor  40  will turn the motor on and keep it on until a change of state occurs at the optical sensor. E.g., if movement of the valve were to begin with the drive member in the position shown in FIG. 4A, in which the optical sensor is blocked by projection  72 , movement would continue for approximately 90 degrees of travel, until the drive member rotated to the position shown in FIG. 4B, wherein projection  72  has just moved out of the path of the optical sensor. (A natural lag between the moment that the sensor detects a change in state and actual cessation of movement assures that the actuator stops a small angular displacement beyond the position at which the optical sensor became unblocked; this assures that vibration will not cause the sensor to become blocked again and restart.) This 90 degrees of movement would have either opened or closed the ball valve. If further movement of the ball valve were called for (e.g., if the valve were now open, and the circuitry called for the actuator to close the valve), the motor would be turned on and the valve would continue to rotate for approximately another 90 degrees of travel to the position shown in FIG. 4C, at which point the optical path is again blocked, this time by projection  74 . 
     FIG. 5 is a schematic of the electronic circuitry of the actuator. At the heart of the circuitry is a microprocessor U 1 , which has programmable pins GP 0 , GP 1 , GP 2 , GP 3 , GP 4 , and GP 5 , a power supply pin Vdd, and a ground pin Vss. Power (24V AC) is supplied to the circuitry through two-pin connector CONN 1 . Typically, a 24V AC transformer is connected to CONN 1  through a thermostat. When the thermostat turns on, 24V AC flows through CONN 1  and into the power supply circuitry (diode D 1 , resistors R 1  and R 2 , and transistor Q 1 ), which sets supply voltage Vcc. 
     A capacitor C 1  with a capacitance of 3.3 F is connected between Vcc and ground. During normal operation, the capacitor C 1  charges to 2.5V to provide power to the motor  40 , as described below. A switch SW 1  is used to configure the zone valve  10  to be either normally open or normally closed. The position of switch SW 1  can be changed by an operator by means of a slide knob  58  accessible on the exterior of the actuator assembly  14  (FIG.  2 ). 
     Power to optical sensor U 2  is provided at pin GP 0  of the microprocessor U 1 . When the light path to the optical sensor U 2  is blocked, pin  4  of the sensor outputs a logical LO. When the light path is not blocked, pin  4  outputs a logical HI. 
     A two-pin motor connector J 1  provides power to motor  40 . Supply voltage Vcc is delivered at one pin. The other pin is connected to gating transistor Q 2 , which is in turn controlled by the microprocessor. When microprocessor pin GP 4  is HI, transistor Q 2  turns on, supplying power to the motor  40 . Otherwise, power to motor  40  is cut off. 
     The circuitry shown in FIG. 5 may be powered by AC power supplied at connector CONN 1  ranging from approximately 8V to approximately 40V. Diode D 1  converts the supplied power from AC to DC (the same power supply would also function if supplied with DC power). When transistor Q 1  is on, capacitor C 1  is charged by the power supplied at connector CONN 1  minus the voltage drop across the circuit consisting of diode D 1 , resistor R 1 , and transistor Q 1 . Capacitor C 1  will charge when at least 2.5V is present at Vcc. Taking into account the voltage drop across D 1 , R 1 , and Q 1 , and the power necessary to run the microprocessor U 1  and the motor  40 , the circuitry shown in FIG. 5 can operate with a minimum of approximately 8V AC. As the supplied voltage is increased, capacitor C 1  will continue to charge and sufficient power will be supplied to the microprocessor U 1  and to the motor  40 . 
     FIG. 6 is a flow chart of the process followed by the microprocessor U 1  in controlling the motor  40 . When power to the microprocessor U 1  is turned on (step  310 ), state variables and other parameters are initialized (step  315 ). Next, the main control loop is entered. The loop begins by checking the voltage at the microprocessor&#39;s Vdd input, and determining whether there is sufficient power to power the motor  40  (step  320 ). The output of the optical sensor U 2  is then checked to determine whether the zone valve  10  is passing in front of the optical sensor (step  325 ). The microprocessor U 1  then obtains the current state of switch SW 1  (step  330 ), and detects whether an AC signal is present at pin GP 5  (step  335 ). Next, the microprocessor U 1  decides whether or not to continue charging capacitor C 1  (step  340 ). 
     In steps  345 - 365 , the microprocessor U 1  decides whether the motor  40  should be turned on or off. If the zone valve  10  is normally closed (decision step  345 ), then the Result register of the microprocessor U 1  is assigned the value OPTO XOR AC (step  355 ). If the zone valve  10  is normally open, (as indicated by switch SW 1  being in position 1) (decision step  345 ), then the OPTO flag is toggled (step  350 ) before assigning to the Result register the value OPTO XOR AC (step  355 ). A Result register value of TRUE indicates that, if there is sufficient power, the motor  40  should be turned on. A Result register value of FALSE indicates that the motor  40  should be turned off. 
     The process  300  shown in FIG. 6 is now described in more detail. 
     Referring to FIG. 7, initialization (step  315 ) proceeds as follows. First, the optical sensor U 2  is turned off by de-asserting pin GP 0  (step  410 ), in order to conserve power. Next, a flag V_READY, which is used to indicate whether the capacitor C 1  has been fully charged, is initialized to FALSE (step  415 ). A variable AC_PREVIOUS, used by the method of FIG.  11  and described in more detail below, is initialized to LO (step  417 ). Next, the motor  40  is turned off by de-asserting pin GP 4  in order to conserve power (step  420 ). Next, if pin GP 5  is HI (decision step  425 ), indicating the possible presence of an AC signal (or DC signal in the event that the power supplied to the actuator is DC instead of AC), the microprocessor U 1  delays for one tenth of a second, and then checks pin GP 5  again to verify the presence of an AC (or DC) signal (step  440 ). If pin GPS is not HI during both steps  425  and  440 , then the presence of an AC signal has not been verified, and the microprocessor U 1  goes into sleep mode (step  430 ). Once in sleep mode, the microprocessor U 1  will wake up again in approximately one second and begin again at step  315 . If pin GP 5  is HI at steps  425  and  440 , then control proceeds to FIG. 9 (step  445 ). 
     Note that if an AC signal is present and the microprocessor U 1  is either turned off or in sleep mode, then pin GP 2  will act as an open circuit (exhibit high impedance), in which case transistor Q 1  will turn on, allowing the AC signal to charge capacitor C 1 . 
     Referring to FIG. 8, the microprocessor U 1  estimates the voltage at pin Vdd by as follows. First, a local variable COUNT is initialized with a value of 25, and a local variable VCNT is initialized with a value of zero (step  510 ). Next, the microprocessor U 1  determines whether pin GP 1  is HI (decision step  515 ). If GP 1  is HI, then VCNT is incremented (step  520 ). This process repeats 25 times (steps  515 - 530 ). Whether pin GP 1  is HI is an indicator of the voltage at pin Vdd because pins GP 1  and Vdd are internally connected by a single 25 kΩ resistor (not shown). The microprocessor U 1  estimates the voltage Vdd as Voltage=2.3+0.1* VCNT (step  535 ). If Voltage&gt;2.5 (decision step  540 ), indicating that the capacitor C 1  has been fully charged, then a flag V_READY is set to TRUE (step  545 ). Otherwise, the V_READY flag is set to FALSE (step  550 ) 
     FIG. 9 shows a method used by the microprocessor U 1  to determine whether the optical sensor U 2  is blocked. The result of the method of FIG. 9 is to set the OPTO flag to TRUE if the optical sensor U 2  is not blocked, and to set the OPTO flag to FALSE if the sensor is blocked. First, power to the optical sensor U 2  is turned on by asserting pin GP 0  (step  610 ). Next, an arbitrary 8-bit binary code is transmitted through pin GP 0 , one bit at a time (step  615 ). As the microprocessor U 1  transmits the code, the microprocessor U 1  monitors the input at pin GP 1 . If the value of the bit received at pin GP 1  is the same as the value of the bit transmitted at pin GP 0 , then the optical sensor is not blocked. If all of the bits in the transmitted code are correctly received at pin GP 1  (decision step  620 ), then the OPTO flag is assigned a value of TRUE (step  630 ). Otherwise, the OPTO flag is assigned a value of FALSE (Step  625 ). In either case, the power to the optical sensor U 2  is then turned off by de-asserting pin GPO (step  635 ). Eight bits, rather than a single bit, are transmitted and tested in order to take into account manufacturing imperfections in the zone valve  10  which might cause spurious readings of the optical sensor when an edge of the drive member  47  is in front of the sensor. Requiring that eight consecutive readings of the optical sensor output all match the expected readings ensures that the zone valve  10  has completed a state transition. 
     Referring to FIG. 10, the NORMALLY_OPEN flag, which indicates whether the zone valve  10  is normally open or normally closed, is set as follows. If pin GP 3  is HI (decision step  710 ), then the NORMALLY_OPEN flag is assigned a value of TRUE (step  715 ). Otherwise, the NORMALLY_OPEN flag is assigned a value of FALSE (step  720 ). 
     Referring to FIG. 11, a flag AC is assigned a value of TRUE when an AC signal is detected at pin GP 5 , and is assigned a value of FALSE when no AC signal is detected for a period of time. In addition, a flag AC_TRANSITION is assigned a value of TRUE when the flag AC changes value, and is assigned a value of FALSE otherwise. 
     More specifically, the values of AC and AC_TRANSITION are assigned as follows. First, the microprocessor U 1  determines whether pin GP 5  is HI (decision step  810 ). If it is not, then the microprocessor U 1  initializes a variable COUNT to a value of 150 and assigns the value TRUE to the flag AC (step  815 ). Then, if AC is not equal to AC_PREVIOUS (decision step  820 ), then the value of AC_TRANSITION is set to TRUE (step  835 ). Otherwise, the value of AC_TRANSITION is set to FALSE (step  837 ). The value of AC_PREVIOUS is then assigned the value of AC (step  840 ). 
     If pin GP 5  is HI (decision step  810 ), then COUNT is decremented (step  825 ). If COUNT=0 (decision step  830 ), then AC is set to FALSE (step  845 ). 
     Referring to FIG. 12, the microprocessor U 1  decides whether to continue charging capacitor C 1  as follows. If V_READY is FALSE (see FIG. 8) (decision step  910 ), then capacitor C 1  is charged by putting pin GP 2  into input mode, causing pin GP 2  to act like an open circuit (step  915 ). If V_READY is TRUE (decision step  910 ), then the microprocessor U 1  stops charging capacitor C 1  by putting pin GP 2  into output mode and asserting LO, causing pin GP 2  to act like a short circuit (step  920 ). This turns off transistor Q 1 , which prevents capacitor C 1  from charging. 
     After the method of FIG. 12 has completed, the microprocessor decides whether the motor should be turned on or off. If the switch SW 1  is in position 1, indicating that the zone valve  10  is normally open (decision step  345 ), then the OPTO flag is toggled (step  350 ). Then, the Result register is assigned the value OPTO XOR AC. A Result value of TRUE indicates that the motor  40  should be turned on, if there is sufficient power. A Result value of FALSE indicates that the motor  40  should be turned off. The expression OPTO XOR AC results in the appropriate values for the Result register as follows. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Result 
                 Result 
               
               
                   
                   
                   
                 (Normally 
                 (Normally 
               
               
                 SENSOR 
                 OPTO 
                 AC 
                 Open) 
                 Closed) 
               
               
                   
               
             
             
               
                 BLOCKED 
                 FALSE 
                 FALSE 
                 TRUE 
                 FALSE 
               
               
                 BLOCKED 
                 FALSE 
                 TRUE 
                 FALSE 
                 TRUE 
               
               
                 UNBLOCKED 
                 TRUE 
                 FALSE 
                 FALSE 
                 TRUE 
               
               
                 UNBLOCKED 
                 TRUE 
                 TRUE 
                 TRUE 
                 FALSE 
               
               
                   
               
             
          
         
       
     
     Referring to Table 1, consider, for example, the case in which the zone valve  10  is normally closed (i.e., switch SW 1  is in position 2). In this case, if OPTO is FALSE (i.e., the optical sensor is blocked, indicating that the zone valve  10  is closed) and AC is FALSE (indicating that the thermostat is not requesting that the zone valve  10  change its state), then the zone valve  10  is in the correct position. Therefore, the value of Result is FALSE, indicating that the motor should be turned off. Consider next, for example, the case in which the zone valve  10  is normally open (i.e., switch SW 1  is in position  1 ). In this case, if OPTO is FALSE (i.e., the optical sensor is blocked, indicating that the zone valve  10  is closed) and AC is FALSE (indicating that the thermostat is not requesting that the zone valve  10  change its state), then the zone valve  10  should return to its default position of open. Therefore, the value of Result is TRUE, indicating that the motor  40  should be turned on. The values in the remaining cells in Table 1 can be verified similarly. 
     Once the value of Result has been calculated, the microprocessor U 1  decides whether to actually provide power to the motor  40  as shown in FIG.  13 . If V_READY is TRUE, then pin GP 4  is asserted, turning the motor  40  on (step  1015 ). If V_READY is FALSE, then the motor  40  is not turned on. This ensures that the motor  40  is not turned on unless there is sufficient power. 
     Other embodiments of the invention are within the scope of the following claims. For example, the invention may be used to provide other types of valves, e.g., a mixing valve or a two-way valve. 
     In the case of a mixing valve, a different ball element, with a central aperture communicating with port  37   c  (FIG. 1) at the base of the valve body, replaces the ball element shown in FIG.  1 . Ports  37   a ,  37   b  become inlets (e.g., hot and cold water) and port  37   c  is the outlet. The left-to-right aperture in the ball element, which is straight in the embodiment of FIG. 1, becomes curved so that rotation of the ball element causes a change in the proportions of fluid flowing through the valve from the two ports. By using a noncircular cross motion for the aperture (e.g., tear drop), a linear relationship can be achieved between ball rotation and flow. Projections  72 ,  74  are also configured differently so that the output of the optical sensor changes state after the ball element has turned sufficiently to complete close off one of the ports. E.g., one of the projections might block the sensor to indicate that port  37   a  was shutoff, and the other of the projections might do the same for port  37   b . In operation, movements of the mixing valve are controlled by activating motor  40  for short durations to make small adjustments to the position of the ball element. Polarity of the power is reversed to change the direction of rotation. During these movements the optical sensor does not provide information; it is only when the ball element has reached a point at which one or the other of the ports is closed off that the sensor functions. In effect, it replaces the mechanical stop that would be found in a conventional mixing valve. 
     For a two-way valve, the right-to-left aperture in ball element extends from the center of the ball in only direction, so that by rotating the valve 180 degrees, central port  37   c  can be connected to one or the other of ports  37   a ,  37   b . The same configuration of projections  72 , can be used, or alternatively, a single projection ending 180 degrees could be substituted.