Automatic Drain System for Compressed Air Systems and the Like

This invention is intended to improve the automatic drain system of U.S. Pat. No. 4,058,240 and application Ser. No. 249,030 by providing an air pressure chamber which assists in emptying the valve and maintaining the valve clean.

In a preferred form, the air chamber may take the form of a closed top standpipe connected to the valve body between the seals.

In the drawing,

FIG. 1 shows a draining system for compressed air dryers, aftercoolers and the like;

FIG. 2 is a section on line 2--2 of FIG. 1;

FIG. 3 is a section on line 3--3 of FIG. 1.

In the drawing, the numeral 1 indicates the sump of a compressed air dryer, aftercooler, separator or the like having a drain 2 in its lowermost part. During operation of the compressed air system, moisture is removed from the compressed air and settles into the sump. Heretofore excess accumulation of liquid in the sump has been prevented by periodically opening a drain valve and allowing the compressed air to force the liquid out through the drain 2. This has caused a substantial loss of compressed air, plus violent broadcast of accumulated liquids, solids, etc. This loss of compressed air is prevented by draining the sump through a rotary valve 3, such as a ball valve which is specially designed to block the flow of compressed air in all positions of the valve. The valve has a body 4 with an inlet 5 connected to the drain and an outlet 6 for connection to a suitable drain line or open bucket. The need for a drain line is eliminated as there is never any massive discharge of the combined compressed gas and accumulated liquid or slurry. In the body of the valve is a ball 7 rotatable by a spindle 8 having a tongue and slot driving connection 9 to the ball. Annular seals 10 and 11 prevent leakage between the ball and the body and a seal 12 prevents leakage around the stem. There is substantial clearance between the ball 7 and the body 4 as indicated at 10a and 11a. The seals 10, 11 accordingly are the supporting surfaces for the ball. The stem 8 is driven by a geared electric motor 14 providing a very slow and continuous rotation approximately one to ten R.P.M. An in line pressure switch starts the motor when the system is pressurized and stops the motor only when the system is depressurized. A compressed gas operated motor may be substituted for the electric motor. Automatic drain valves now on the market using floats or other controls for the liquid level in the sump are not reliable under the conditions which exist in compressed air and gas systems.

The ball has circumferentially extending slots 15 each having ends 16, 17 spaced on opposite sides of a plane through the axis of rotation of the ball. The slots are spaced on opposite sides of a plane through the center of the ball and normal to said axis. The bottoms of the slots are preferably semicircular as in a Woodruff key. The spacing between the slots is substantially the same as the width of the slots. The length of the slots is less than the inside diameter of the seals 10 and 11 and is also less than the spacing between the seals 10 and 11. The slots can therefore occupy four central positions with respect to the seals, one in each quadrant, in each of which both ends of the slots are spaced from the seals. When the slots are uppermost and centered as shown in full lines in FIGS. 1 and 2, the slots are open and presented to the liquid in the sump. When the stem 8 is rotated 180.degree. from the position shown, the slots will be inverted and the liquid contained in the slots emptied by gravity. In passing from the upright to the inverted positions, the slots pass through an intermediate position in which the open tops of the slots are between the seals 10 and 11 which prevent loss of compressed air and also hold all of the liquid within the slots. Seals 10 and 11 block the flow of compressed air in all positions of the ball. So long as any part of an open end of the slots is presented to the liquid in the sump, as shown in dotted lines at 18 in FIG. 2, the full pressure of the compressed air acting on the liquid forces the liquid into the slots so the slots are filled with liquid under pressure. There will usually be a small amount of compressed air above the surface of the liquid in the slots so long as both ends 16 and 17 of the slots are between the seals 10 and 11. As soon as the ball rotates enough so that end 16 of the slots is slightly beyond the seal 11, as shown at 19 in FIG. 2, the trapped compressed air in the slots forcibly expels the liquid into the outlet. The small amount of compressed air trapped in slots which are not completely filled with liquid is therefore advantageous in cleaning the slots of any residue and the loss of air is negligible.

As shown in FIGS. 1 and 3, there is a spherical surface 20 between the slots 15 and spherical surfaces 22 and 23 on opposite sides of the slots 15 so that the seals 10, 11 are well supported while the ball 3 is rotated about its axis and the slots 15 are progressively brought into and out of contact with the seals. This eliminates leakage through the seals.

In the position shown in FIG. 1, seals 10 and 11 make contact with the upper and lower surfaces of the ball 3 in the regions defined by dotted line 24 and solid line 25 (FIG. 3). The seals 10 and 11 are the same size and are centered on the axis of the inlet and outlet 5 and 6. In this position the surface of the ball 7 presented to the inlet 5 is subject to the compressed air system pressure and the portion of the ball 7 presented to the outlet 6 is subject to atmospheric pressure. The regions between the seals 10 and 11 are subject to a positive pressure above atmospheric pressure. As the ball 7 is rotated about the axis of spindle 8, liquid under system pressure is forced into the slots 15 until the ball reaches the position indicated by numeral 18. The liquid forced into the slots is drained to atmospheric pressure when the ball reaches the position indicated by the numeral 19. The slots 15 are effective in draining liquid from the compressed air system without appreciable loss of compressed air, but the capacity of the slots is limited, and the rate of drainage of liquid is therefore low or small.

To increase the capacity of the drain valve, holes 26 were drilled on opposite sides of the ball 7 through the bottoms of the slots 15. These holes were centered on the axis of rotation of the ball and were slightly inclined to the axis so that the inner ends of the holes intersected (FIG. 1). The median spherical surface 20 and the spherical surfaces 22, 23 outside the holes 26 provide adequate support for the seals 10, 11 in all positions of the ball. The addition of the holes 26 to the slots 15 made a large increase in the volume available to receive liquid, but it did not make a large increase of the capacity of the valve because the liquid did not drain quickly from the valve. A large proportion of the liquid remained in the holes 26 and did not empty into the outlet. This defect was overcome by drilling an axially extending hole 27 through the lower ends of the cylindrical holes 26. The hole 27 is in a portion of the ball which is always between the upper and lower seals 10, 11 and therefore at the time the cylindrical holes 26 are being filled with liquid, the axial hole is subject to the full compressed air system pressure and is likewise filled with liquid. As the cylindrical holes move to the drainage position, the pressure in the axial hole 27 acts initially to force the liquid out of the holes 26 and 27 and slots 15. The speed of drainage is increased by a pressure chamber which in a preferred form consists of a street elbow 29 with one end 30 screwed or otherwise fixed in a hole 30a in body 4 coaxial with the hole 27 in ball 7 and the other end closed by a plug 32. The pressure chamber plus the clearance 10a, 11a is under full inlet pressure until the slots 15 pass seal 10 as shown by dotted lines 18 in FIG. 2. Air will collect in the upright area 33 of the elbow. The balance of the elbow will be filled with liquid. When the slots reach the position shown by dotted lines 19 in FIG. 3, the air pressure in the chamber acts on the liquid in the elbow and forces it into the outer end of the passage 27 and out the passage and through the holes 26 and slots 15 into the drain 6. This discharge keeps the passages clean. The air drives a solid slug of liquid in front of it.

The shape of the liquid receiving cavities 26, 27 is not critical. In the structure shown, these cavities were formed as drilled holes. If the cavities had been formed by some other process, for example, by cores in a casting, other cross-sectional shapes could be used. The holes 26 could occupy the entire area between the medial spherical surface 20 and the inner diameter of the seal 10 without changing the function and mode of operation of the cavities. When viewed from the top as in FIG. 6, the holes 26 would then be generally semicylindrical in appearance on opposite sides of the medial spherical surface 20. A further modification would be to omit the slots 15 entirely and to rely solely on the cavities 26 and 27 for condensate collection. This would make only a very slight reduction in capacity and would not change the mode of operation. The omitted portions of the slots 15 would have very small fluid capacity as is evident from FIGS. 2, 3. The supporting action of the spherical strip 20 would be retained so that the seals 10, 11 would be adequately supported in the liquid receiving and liquid delivery positions of the ball.

In operation, the motor 14 is started when the compressed air system is pressurized and runs continuously at a slow rate so long as the system is under pressure. During each revolution of the motor, the ball is rotated from a liquid collecting position to a liquid emptying position and back to the liquid collecting position. While the amount of liquid removed during each revolution of the shaft may be small, the cumulative results are emough to take care of any compressed air system. The amount of compressed air lost with this system is so small as to be negligible.