AUTOMATIC DRAIN VALVE FOR A COMPRESSED AIR FILTER

Abstract: The automatic drain valve comprises a valve body (11) having first and second fluid inlets (13) and (14) and a fluid outlet (15), a first valve member (18) for opening and closing a fluid communication path between the first fluid inlet (13) and the fluid outlet (15), a second valve member (19) for opening and closing the second fluid inlet (14), and a float (20) operable in use as water collects in the filter to move the second valve member from a first position in which it closes the second fluid inlet to a second position in which it opens the second fluid inlet. The first valve member (18) is responsive to compressed air entering the second fluid inlet (14), when the second valve member (19) moves to its second position, to open the fluid communication path between the first fluid inlet (13) and the fluid outlet (15) to allow water to drain away from the filter and is responsive to the pressure at the first fluid inlet (13), when the second fluid inlet closes as the water level in the filter falls, to close the fluid communication path between the first fluid inlet (13) and the fluid outlet (15).

Description: AUTOMATIC DRAIN VALVE FOR A COMPRESSED AIR FILTER This invention relates to an automatic drain valve for a compressed air filter. It is important to eliminate water and debris from compressed air used to operate pneumatic tools as otherwise the water and/or debris could cause damage to the tools. It is therefore common practice to provide a filter in a compressed air line. These filters collect water which must be drained regularly. The present invention seeks to provide an automatic drain valve for a compressed air filter, which is inexpensive to manufacture and reliable. According to the present invention, there is provided an automatic drain valve for a compressed air filter, comprising a valve body having first and second fluid inlets and a fluid outlet, a first valve member for opening and closing a fluid communication path between the first fluid inlet and the fluid outlet, . a second valve member for opening and closing the second fluid inlet, and a float operable in use as water collects in the filter to move the second valve member from a first position in which it closes the second fluid inlet to a second position in which it opens the second fluid inlet, the first valve member being responsive in use to compressed air entering the second fluid inlet, when the second valve member moves to its second position, ' to open the fluid communication path between the first fluid inlet and the fluid outlet to allow water to drain away from the filter and being responsive to the pressure at the first fluid inlet, when the second fluid inlet closes as the water level in the filter falls, to close the fluid communication path between the first fluid inlet and the fluid outlet. Preferably, the valve body defines therein a chamber and the first valve member includes a piston movable in the chamber between a first position in which the first valve member closes the fluid communication path between the first fluid inlet and the fluid outlet and a second position in which the first valve member opens the fluid communication path between the first fluid inlet and the fluid outlet, the first fluid inlet communicating with the chamber on one side of the piston and the second fluid inlet communicating with the chamber on the other side of the piston and there being an air bleed between said other side of the piston and the fluid outlet so that air can escape from said other side of the piston when the second valve member closes the second fluid inlet. The air bleed conveniently comprises a bleed jet provided in a secondary piston which is urged into contact with the first mentioned piston by spring means and a through passage in the first mentioned piston for exhausting air which bleeds through the bleed jet to the fluid outlet. In this case, the bleed jet may be a small nick formed in the edge of an annular seat of the secondary piston, and the first mentioned piston may have a recess for receiving the secondary piston. Preferably, the first fluid inlet is in use below the float and the second fluid inlet is in use above the float. Preferably, the second valve member comprises a sealing element supported by a lever which is pivotally connected at one end to the valve body and at the other end to the float. In this case, means are preferably provided for adjusting the position of the float relative to the lever. Advantageously, a strainer is provided for filtering fluid entering the first fluid inlet. Preferably, the valve body comprises two parts which may be snap-fittable together and, where a strainer is provided, the strainer may be held between the two parts of the valve body. The invention will now be more particularly described by way of example with reference to the accompanying drawing which is a vertical section through one embodiment of an automatic drain valve according to the present invention. Referring to the drawing, the automatic drain valve is shown fitted to a filter housing 10. The housing has a . compressed air inlet (not shown) , a compressed air outlet (not shown) and a filter element (not shown) , which is typically of sintered bronze, between the compressed air inlet and the compressed air outlet. The air inlet side of the filter element communicates directly with the lower end of the housing 10 where the drain valve is located. The drain valve comprises a valve body 11 formed of two parts 11a and lib snap-fitted together. The valve body 11 defines therein a cylindrical chamber 12 and has a first fluid inlet provided by an annular array of slots 13 in the upper body part 11a. where the latter joins the lower body part lib, and a second fluid inlet in the form of a single, vertically extending orifice 14 at the upper end of the upper body part 11a. The lower body part lib defines a fluid outlet 15 and extends through an aperture in the wall of the housing 10. The lower body part lib is fixed to the housing 10 by a nut 16 which also serves as a connector for a drain hose (not shown) and an O-ring seal 17 is provided between housing 10 and the lower body part lib. The drain valve includes a first valve member 18 which is slidable within the valve body 11 and a second valve member 19 operable by a float 20. The first valve member 18 comprises a piston 21 which is free to move within the chamber 12 and a stem 22 integral with the piston 21. The piston 21 has a peripheral groove 23 in which an annular seal 24 is located and a central recess 25 in its upper face. The stem 22 projects from the lower face of the piston 21 and into the fluid outlet 15. A passage 26 extends through the piston 21 and the stem 22 and communicates the base of the recess 25 with the fluid outlet 15. The lower end of the stem 22 is of enlarged diameter and has an annular groove locating an O-ring seal 27. The upper end of the fluid outlet 15 is of reduced diameter and co-operates with the seal 27 when the piston 21 is at an uppermost position within the chamber 12 to seal the outlet 15 from the chamber 12. However, when the piston is at a lowermost position within the chamber 12, the seal 27 no longer co-operates with the reduced diameter portion of the fluid outlet and fluid in the chamber 12 below the piston 21 can discharge through the outlet 15. The float 20 is mounted about the upper body part 11a and is guided by the upper body part 11a for generally vertical movement relative thereto. The second valve member 19, which is operable by the float 20, comprises a lever arm 28 pivotally connected at one end to the body part 11a by a hinge 29 and at the other end to a set screw 30 which is threadably engaged with a hole in the float 20, and a sealing element 31 which is supported by the arm 28 and which closes the orifice 14 when the float 20 is in a lower position. The pivotal connection between the arm 28 and the screw 30 is formed by a pair of opposed pegs 32 which are provided on a bifurcated end portion 33 of the arm 28 and which are located in an annular groove 34 in the screw 30. The screw 30 provides for slight adjustment of the position of the float 20 relative to the valve body 11. The slots 13 forming the first fluid inlet are below the float 20 and communicate with the chamber 12 on the underside of the piston 21. The orifice 14, on the other hand, is above the float 20 and communicates with the chamber 12 on the top side of the piston 21. Thus, water collecting in the filter will enter the chamber 12 via the slots 13 before the float 20 begins to rise, whilst the orifice 14, when open, will always be exposed to compressed air in the filter housing 10. As the water level in the housing 10 rises, it will reach a level which will cause the float 20 to rise and this in turn will open the orifice 14. Compressed air will pass through the orifice 14 and the differential pressure applied to the piston 21 will move the piston downwards in the chamber 12 with the result that the seal 27 will move out of contact with the wall of the outlet 15 and the slots 13 will communicate with the outlet 15 to discharge water from the filter. A secondary piston 35 made of plastics material is loosely mounted in the recess 25 in the upper face of the piston 21. The lower end of the piston 35 has a thin annular seat 36 which is urged into contact with the base of the recess 25 by a coiled compression spring 37. A small nick 38 provided by a knife cut is formed in the seat 36 to bleed air from the top side of the piston 21 to the outlet 15 via the passage 26 in the stem 22. Thus, when the float 20 falls as water is discharged from the filter and the valve member 19 closes the orifice 14, the air pressure acting on the top side of the piston 21 will fall as a result of air being exhausted via the outlet 15 and the fluid pressure on the underside of the piston 21 will cause the latter to move upwards in the chamber 12 so that the chamber 12 is again sealed from the outlet 15. In addition to urging the seat 36 of the secondary piston 35 into contact with the base of the recess 25, the compression spring 37 also serves to move the piston 21 downwards and open the outlet 15 when the supply of compressed air to the filter is shut off. A strainer 39 is provided for filtering water entering the chamber 12 via the slots 13. The strainer 39 surrounds the slots 13 and is held in place between the two parts of the valve body 11. The embodiment described above is given by way of example only and various modifications will be apparent to persons skilled in the art without departing from the scope of the invention. For example, in the embodiment shown, the float will not rise until slots 13 are fully submerged in water collecting in the filter. However, the float could be arranged to rise so as to open the orifice 14 when the slots 13 are only partly submerged in water.

Claims: C L A I M S 1. An automatic drain valve for a compressed air filter, comprising a valve body having first and second fluid inlets and a fluid outlet, a first valve member for opening and closing a fluid communication path between the first fluid inlet and the fluid outlet, a second valve member for opening and closing the second fluid inlet, and a float operable in use as water collects in the filter to move the second valve member from a first position in which it closes the second fluid inlet to a second position in which it opens the second fluid inlet, the first valve member being responsive in use to compressed air entering the second fluid inlet, when the second valve member moves to its second position, to open the fluid communication path between the first fluid inlet and the fluid outlet to allow water to drain away from the filter and being responsive in use to the pressure at the first fluid inlet, when the second fluid inlet closes as the water level in the filter falls, to close the fluid communication path between the first fluid inlet and the fluid outlet. 2. An automatic drain valve as claimed in claim 1, wherein the valve body defines therein a chamber and the first valve member includes a piston movable in the chamber between a first position in which the first valve member closes the fluid communication path between the first fluid inlet and the fluid outlet and a second position in which the first valve member opens the fluid communication path between the first fluid inlet and the fluid outlet, the first fluid inlet communicating with the chamber on one . side of the piston and the second fluid inlet communicating with the chamber on the other side of the piston and there being an air bleed between said other side . of the piston and the fluid outlet so that air can escape from said other side of the piston when the second valve member closes the second fluid in'let. 3. An automatic drain valve as claimed in claim 2, wherein the air bleed comprises a bleed jet provided in a secondary piston which is urged into contact with the first mentioned piston by spring means and a through passage in the first mentioned piston for exhausting air, which bleeds through the bleed jet, to the fluid outlet. 4. . An automatic drain valve as claimed in claim 3, wherein the bleed jet is a small nick formed in an annular seat of the secondary piston. 5. An automatic drain valve as claimed in claim 3 or claim 4, wherein the first mentioned piston has a recess for receiving the secondary piston. SUBSTI 6. An automatic drain valve as claimed in any one of the preceding claims, wherein the first fluid inlet is in use below the float and the second fluid inlet is in use above the float. 7. An automatic drain valve as claimed in any one of the preceding claims, wherein the second valve member comprises a sealing element supported by a lever which is pivotally connected at one end to the valve body and at the other end to the float. 8. An automatic drain valve as claimed in claim 7, wherein means are provided for adjusting the position of the float relative to the lever. 9. An automatic drain valve as claimed in any one of the preceding claims, wherein a strainer is provided for filtering fluid entering the first fluid inlet. 10. An automatic drain valve as claimed in any one of the preceding claims, wherein the valve body comprises two parts. 11. An automatic drain valve as claimed in claim 10, wherein the two parts of the valve body are snap- fitted together. 12. An automatic drawing valve as claimed in claim 10 or claim 11 when dependant on claim 9, wherein the strainer is held between the two parts of the valve body. 13. A compressed air. filter equipped with an automatic drain valve according to any one of the preceding claims.

Inventors: CLARKE DOUGLAS CECIL, CLARKE, DOUGLAS, CECIL
Applicants: CLARKE AUTOMATION LIMITED
Application year: 1992
Main classification: F16K31
IPC codes: F16T1