GB2142709A - Fluid flow control apparatus - Google Patents

Abstract

A fluid-flow control apparatus used in the control of a domestic hot water and central heating system includes a multi-way valve (Figs. 1 and 2, not shown) having an inlet port connected to a boiler, and a valve member movable between a first outlet port connected to a radiator circuit and a second outlet port connected to a hot water circuit, a spring urging the valve member towards the first outlet port. An a.c. synchronous motor 3 drives the valve member towards the second outlet port by way of a switch-operating element arranged to operate non- simultaneously two microswitches 11 and 12 controlling operation of the motor 3. The microswitches are connected to a room thermostat 23 and a cylinder thermostat 25. In an intermediate position of the valve member, and with both thermostats 23 and 25 demanding heat, the a.c. driving current to the motor 3 is supplied only through a resistor 21, so that the motor 3 is supplied with a.c. of a reduced power, to bring the amplitude of the motor output force to such value that the valve member stalls in the intermediate position. <IMAGE>

Description

SPECIFICATION Fluid-flow control apparatus This invention relates to fluid-flow control apparatus.

From British Patent Specification 2092713, there is known fluid-flow control apparatus which is used in the control of a domestic hot water and central heating system. In this apparatus a valve unit has an inlet port and a valve member movable between two outlet ports leading to a hot water circuit and a radiator circuit, respectively. The valve member is normally held by springs against a valve seat encircling the outlet port to the radiator circuit. A shaft rotatable by an a.c. electric motor moves the valve member to a valve seat encircling the other outlet port. Two thermostats sense temperatures at different points (e.g. hot water cylinder and room). A triac when triggered by low temperature at the room thermostat supplies the motor with a.c. to open the outlet port to the radiator circuit.Switches driven by the motor are arranged so that a rectifier supplies d.c. to the motor to lock the valve member with both outlet ports open when both thermostats sense low temperatures. A very small a.c.

demagnetising current via a resistor releases the motor from such d.c. braking.

According to the present invention, there is provided fluid-flow control apparatus, comprising: a multiway valve comprising a valve housing, first, second and third ports in said housing, and a valve member movable among a first position in which it obturates the first port and leaves open the second and third ports, a second position in which it obturates the second port and leaves open the first and third ports, and an intermediate position in which it leaves open the first, second and third ports, return biassing means urging said valve member to move in the sense from said second position to said first position, an a.c. electric motor arranged to drive said valve member from said first position to said second position against the action of said biassing means, and electrical circuitry arranged to supply substantially solely a.c. to said motor and including an impedance and switch means for switching-in said impedance, the arrangement being such that, when said impedance is switched-in, the motor continues to be supplied with substantially solely a.c.

but of a reduced power, so as to bring the amplitude of the motor output force to such a value greater than zero that the motor stalls in said intermediate position.

An advantage of the present invention is the avoidance of d.c. magnetization of the motor in the intermediate position of the valve member, so avoiding the need to make provision for demagnetization of the motor.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 shows a top plan view of a control unit for a multiway valve of a domestic hot water and central heating system, but with parts omitted for the sake of clarity, Figure 2 shows a section taken on the line ll-ll of Figure 1, and Figure 3 shows electrical circuitry of the system.

Referring to the drawings, the control unit comprises a sheet material U-shaped frame 1 covered by a cover 2. Within the housing 1, 2 sb formed is an a.c. synchronous electric motor 3 provided with a reduction gear box 4 mounted on a bracket 5 attached to the frame 1. The gear box 4 has an output pinion 6 meshing with a toothed rack 7 of a valveoperating element 8. A helical tension spring 9 acting between the frame 1 and the element 8 urges the element 8 towards the right in Figures 1 and 2. The motor 3 drives the element 8 towards the left in Figures 1 and 2 against the action of the spring 9. For such movement, the element 8 is guided in a slot 10 formed in the bottom wall of the frame 1.

The element 8 is connected to the valve member of a three-port valve (not shown), of which one port is an inlet port which receives water from the boiler, and the other two ports are outlet ports to the hot water circuit and the radiator circuit, respectively. In the rightmost position of the element 8 in Figures 1 and 2, the valve member closes the outlet port connected to the radiator circuit of the central heating system, whilst in the leftmost position of the element 8, the valve member closes the outlet port to the hot water circuit of the system. In an intermediate position of the element 8, the valve member is in an intermediate position in which all three ports are open.Fixed to the frame 1 at respective opposite sides of the element 8 are respective micro switches 11 and 12, the actuating elements 1 3 and 14, respectively, of which are operable by respective shoulders 1 5 and 1 6 on the respective opposite sides of the element 8. The shoulders 1 5 and 1 6 are slightly offset relative to each other along the element 8, so that, as the element 8 moves from the right to the left in Figures 1 and 2, the element 1 3 is depressed very slightly before the element 14 is depressed.

The micro switch 11 includes two fixed contacts 1 7 and 1 8 and a movable contact 31 normally at the contact 1 7. Similarly, the micro switch 1 2 includes two fixed contacts 1 9 and 20 and a movable contact 27 normally at the contact 1 9. Connected between the contact 1 9 and one side of the motor 3 is a resistor 21, whilst the other side of the motor 3 is connected to a neutral line N of the mains. A live line L of the mains is connected to a movable blade 22 of a room thermostat 23 and to a movable blade 24 of a hot water cylinder thermostat 25.The ther mostat 23 includes a fixed contact 26 con nected to the moving contact 27 of the micro switch 1 2 and to the contact 17, the thermostat 23 closing when room heating is required and opening when room heating is no longer required. The thermostat 25 includes two fixed contacts 28 and 29 of which the contact 28 is connected to the contact 1 8 and of which the contact 29 is connected to the contact 20 and to a boiler-and-water-pump actuating line 30. The blade 24 moves from the contact 28 to the contact 29 when cylinder hot water is required and back again when it is no longer required.In the condition shown in Figure 3, which corresponds to the element 8 being in its rightmost position and thus the outlet port to the radiator circuit being closed, the motor 3 is not energised, the moving contact 31 of the micro switch 11 is at the fixed contact 17, the moving contact 27 of the micro switch 1 2 is at the fixed contact 19, the room thermostat 23 is open and the moving blade 24 of the cylinder thermostat 25 is at the contact 28.

The operation of the apparatus will now be described.

Assuming that there is a demand for heat at the thermostat 25, the blade 24 moves from the contact 28 to the contact 29, so that the line 30 is energised to actuate the boiler and the water pump of the system. When the demand has been satisfied, the blade 24 returns to the contact 28, so that the line 30 is de-energized to turn off the boiler and the pump.

Upon the room thermostat 23 closing to demand more heating of the room, the motor 3 is energised by way of the contact 1 7 of the micro switch 11 and moves the element 8 leftwards, thereby opening the outlet port to the radiator circuit. As the element 8 nears its intermediate position shown in Figures 1 and 2, the micro switch 11 is operated to bring the moving contact 31 from the contact 1 7 to the contact 18, whereupon the motor 3 continues to be energised via the cylinder thermostat 25. Shortly afterwards, the element 8 operates the micro switch 1 2 to bring the moving contact 27 from the contact 1 9 to the contact 20. Thereby, the line L is connected via the micro switch 1 2 to the line 30 to activate the boiler and the pump of the system.The element 8 then continues to advance to its leftmost position in which the outlet port to the domestic water circuit is closed. When the thermostat 23 has sensed that the heat demand for the room has been satisfied, it opens, thus de-energising the line 30. The motor 3 continues to maintain the element 8 in its leftmost position. Assuming that now there is a demand by the thermostat 25 for hot water to be supplied to the cylin der, the blade 24 moves from the contact 28 to the contact 29. This energises the line 30 and de-energises the motor 3. Thereupon, the element 8 is returned towards its rightmost position.As this occurs, the moving contact 27 of the micro switch 1 2 returns to the contact 19, and the moving contact 31 returns to the contact 1 7. When the demand at the thermostat 25 has been satisfied, the blade 24 returns to the contact 28.

If, while the thermostat 23 is demanding heat and, before the micro switches 11 and 1 2 have consequently been operated, the thermostat 25 demands heat, the line 30 is immediately energised. However, when the contact 31 moves from the contact 1 7 to the contact 18, the motor 3 is now supplied only through the room thermostat 23, the micro switch 12 and the resistor 21, so that the a.c.

power supply to the motor is considerably reduced. The resistance of the resistor 21 has been pre-set to such a value that the amplitude of the output force from the motor 3 is just sufficient to hold the element 8 against the action of the spring 9 in the intermediate position shown in Figure 1, in which the shoulder 1 5 has just depressed the element 1 3 and the shoulder 1 6 has almost contacted the element 14, so that the valve supplies hot water to both the radiator circuit and the domestic hot water circuit.It will be appreciated that, if the room thermostat 23 next becomes satisfied, the motor 3 will become de-energised and the valve member returned by the action of the spring 9 to close the radiator circuit outlet port; whereas, if instead the cylinder thermostat 25 becomes the next satisfied, the motor 3 will become energised through the thermostat 25 and the micro switch 11 with a full power supply, and thus the element 8 moved to its leftmost position in which the domestic hot water circuit outlet port is closed.

If, after the room thermostat 23 has demanded heat and the micro switches 11 and 12 have both been operated, the cylinder thermostat 25 demands heat, then the moving of the blade 24 from the contact 28 cuts off the power supply to the motor 3 so that the spring 9 reutrns the element 8 towards its rightmost position. When the shoulder 16 allows the element 14 to return to its projecting position, the moving contact 27 comes to bear on the contact 19, so that the motor 3 is supplied with reduced power a.c. via the resistor 21 and then holds the element 8 in its intermediate position shown in Figure 1 against the action of the spring 9.

Claims (6)

1. Fluid-flow control apparatus, comprising: a multiway valve comprising a valve hous ing, first, second and third ports in said housing, and a valve member movable among a first position in which it obturates the first port and leaves open the second and third ports, a second position in which it obturates the second port and leaves open the first and third ports, and an intermediate position in which it leaves open the first, second and third ports, return biassing means urging said valve member to move in the sense from said second position to said first position, an a.c. electric motor arranged to drive said valve member from said first position to said second position against the action of said biassing means, and electrical circuitry arranged to supply substantially solely a.c. to said motor and including an impedance and switch means for switching-in said impedance, said impedance being in a bi-directional current path such that, when said path is switched-in, the motor continues to be supplied with substantially solely a.c. but of a reduced power, so as to bring the amplitude of the motor output force to such a value greater than zero that the valve member stalls in said intermediate position.

2. Apparatus as claimed in claim 1, wherein said switch means comprises first and second electromechanical switches.

3. Apparatus as claimed in claim 2, wherein driving current is supplied to said motor through the first switch to move said valve member in the sense from said first position to said second postion.

4. Apparatus as claimed in claim 2 or 3, and further comprising a switch-operating element arranged to move linearly to transmit drive from said motor to said valve member, said element comprising first and second switch-operating portions arranged to operate the respective first and second switches nonsimultaneously during movement of said valve member from said first position to said second position and from said second position to said first position.

5. In a domestic hot water and central heating system, apparatus as claimed in any preceding claim and having the three said ports connected respectively to a boiler, a hot water circuit and a radiator circuit.

6. Fluid-flow control apparatus, substantially as hereinbefore described with reference to the accompanying drawings.