Patent GB-774262-A (GB)
Title: Filter by-pass control
IPC: B01D35/147
Filed: 1955-08-26
Abstract: 774,262. Filters for liquids. JAY, K. W. Aug. 26, 1955, No. 24577/55. Class 46. A control for automatically by-passing a clogged filter comprises an inlet to the control, connection means between the control and the filter intake and normally communicating with the inlet whereby fluid is normally delivered from the inlet to the filter intake, a by-pass connection for flow of fluid from the control to a filter by-pass, and valve means normally obstructing the by-pass connection from communication with the inlet, the valve means being operated by piston means which in its normal position has a working face in communication with the filter connection means, the piston means being movable to another position in response to predetermined pressure ou the piston face due to clogging of the filter, and the valve means being operable by such piston movement to open the by-pass connection to the inlet and by-pass the filter, the movement of the valve means obstructing the filter connection from communication with the inlet to isolate the filter intake from the inlet to the control. The casing 20 of the control is bored to provide three coaxial stepped cylinders 22, 24, the smallest housing a piston valve 29 connected rigidly to a larger piston valve 32 which normally blocks a by-pass port 27 and is solid with a piston 33 sliding in the chamber 23 with its face 33a open to an inlet port 25 : the port 25 is normally open to a port 26 leading to the inlet port 18 of a filter 10. Normally the piston valve 32 is pressed against a shoulder 35, formed between the chambers 24, 23, by a spring 38 housed in the end cap 21 of the casing 20. The filter comprises a cylindrical screen 16 carried by the end cap 14 of the filter casing 12 with its outlet 19 in the end cap whence the filtered liquid flows through a delivery line 42 to join the corresponding line 43 from the bypass port 27 of the control. When the filter becomes clogged, back pressure displaces the piston 33 in the chamber 23 moving the piston valve 32 to uncover the by-pass port 27. Movement of the piston 33 also draws the piston valve 29 across the outlet 26, isolating the filter from the supply and the movement speeds up when the piston 33 clears the chamber 23 exposing the whole area of the piston valve 32 to the pressure, the pressure on the piston and valve 32, 33 being sufficient to keep the spring 38 compressed. In a modification adapted to reconnect the filter when the clogging is relieved, the casing 45, Fig. 2, comprises two chambers 49, 50 separated fluid-tightly by a collar 45a through which passes the rod 64 connecting the small and large pistons 62, 63. From an inlet 51, liquid enters the chamber 50 and flows out through a port 52 to the filter 10s. The piston valve 62 covers the by-pass outlet 53 in which there is a construction 54. Pressure at the inlet side of the filter 10<SP>1</SP> is communicated through a line 58 to the left hand side of the large piston 63 and pressure at the outlet side to the other face of the piston through a line 59. Pressure build up at the filter inlet displaces the piston against the action of a spring 67 moving the small piston 62 to cover the outlet 52, cutting off the filter supply and opening the by-pass 53 where the constriction 54 maintains sufficient pressure difference across the piston 63 to keep the spring 67 compressed. When the clogging is cleared, reduced pressure at the filter inlet is communicated through the line 58 to the left hand face of the piston 63 permitting the spring 67 to restore it to its normal position.