Compact pressure balanced rotary valve
A pressure balanced rotary valve can be made more compact if the ports on the stator within can be located on a port pitch circle of smaller diameter. In certain circumstances for rotary valves used in pressure swing adsorption devices, it is acceptable for the spacing between the ports to be made smaller than the ports themselves. In a rotary valve comprising variable loading means (e.g. pistons) and fixed loading means (e.g. springs), this can involve reducing the piston size and increasing the load provided by the springs.
1. A rotary valve, comprising:
a stator comprising at least two ports centred on a port pitch circle, and each port providing an opening over an open arc length around the port pitch circle and thereby defining port spacings between the ports over closed arc lengths around the port pitch circle, wherein the minimum closed arc length of a port spacing is less than the maximum open arc length of a port opening
a rotor rotating about a rotor axis at the centre of the port pitch circle and comprising at least two ports centred on the port pitch circle;
variable loading means to sealingly engage the rotor to the stator;
fixed loading means to sealingly engage the rotor to the stator; and
drive means to rotate the rotor about the rotor axis relative to the stator such that the ports in the rotor come into and out of alignment with the ports in the stator.
2. The rotary valve of claim 1 wherein the stator comprises a plurality of ports.
3. The rotary valve of claim 1 wherein the ports in the stator are circular.
4. The rotary valve of claim 1 wherein the ports in the stator are essentially the same size.
5. The rotary valve of claim 4 wherein the ports in the stator are spaced equidistant around the port pitch circle and thereby all the closed arc lengths of the port spacings are essentially equal and all the open arc lengths of the ports are essentially equal.
6. The rotary valve of claim 5 wherein the closed arc length of the port spacings is less than the open arc length of the port openings.
7. The rotary valve of claim 1 wherein the variable loading means comprises pistons located adjacent each port in the stator for providing a variable load to the stator in accordance with as pressure received at that port.
8. The rotary valve of claim 7 wherein the pistons are centred on the port pitch circle.
9. The rotary valve of claim 7 wherein the fixed loading means comprises springs for providing a fixed load to the stator and the springs are located outside the pistons.
10. The rotary valve of claim 9 wherein a first set of springs is located on a first spring pitch circle larger than the port pitch circle.
11. The rotary valve of claim 10 wherein a second set of springs is located on a second spring pitch circle smaller than the port pitch circle.
12. The rotary valve of claim 11 wherein the second set of springs applies less force than the first set of springs to sealingly engage the rotor to the stator.
13. The rotary valve of claim 12 wherein the spring constant of the second set of springs is smaller than that of the first set of springs.
14. The rotary valve of claim 1 wherein the fixed loading means comprises springs for providing a fixed load to the stator.
15. A rotary pressure swing device comprising the rotary valve of claim 1 .
16. A rotary pressure swing adsorption device comprising the rotary valve of claim 1 .
17. The rotary pressure swing adsorption device of claim 16 wherein the rotary valve is at the feed end of the device.
18. The rotary pressure swing adsorption device of claim 16 wherein the variable loading means comprises pistons located adjacent each port in the stator for providing a variable load to the stator in accordance with gas pressure received at that port from an adsorbent bed in the device; and
the fixed loading means comprises springs for providing a fixed load to the stator.
19. The rotary pressure swing adsorption device of claim 18 wherein the average contact pressure between the rotor and the stator during operation is greater than 59 psi.
20. The rotary pressure swing adsorption device of claim 18 wherein the springs provide more than 10% of the total loading force applied to the stator by the pistons and the springs during operation.