Low noise fluid control valve

#This invention relates generally to fluid control valves and, more particularly, to fluid control valve structures which suppress the noise normally generated by fluid flow through a control valve.

#One type of prior art fluid control valve includes a valve body having inlet and outlet ports, a sleeve-like cage, a valve plug that is slidable within the cage and a bonnet assembly which retains the cage and the valve plug in the valve body. The inlet port communicates with the outlet port through apertures, or windows, in the cage. Fluid flow through the valve is determined by the position of the valve plug relative to the windows of the cage. A valve stem attached to the valve plug extends through the bonnet assembly to an actuator for moving the valve plug relative to the cage. An example of a prior art fluid control valve is disclosed in U.S. Pat. No. 3,776,278, issued Dec. 4, 1973 to Allen. Additional fluid control valves are disclosed U.S. Pat. No. 5,769,122, issued Jun. 23, 1998 to Baumann et al; U.S. Pat. No. 5,941,281, issued Aug. 24, 1999 to Baumann et al; and U.S. Pat. No. 6,095,196, issued Aug. 1, 2000 to McCarty et al.

#Prior art fluid control valves have provided satisfactory performance but have certain drawbacks. The valve may generate undesirable noise under certain flow conditions, such as a high pressure drop through the valve. U.S. Pat. No. 3,776,278 discloses a valve structure for reducing noise in gas applications. In one embodiment, the cage is provided with slots having long dimensions parallel to the cage bore axis. The slots have their narrowest dimension intermediate their ends and taper or flare gradually to a wider dimension at the inner and outer surfaces. In another embodiment, the cage has closely-spaced, uniformly-distributed circular holes.

#For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:

#FIG. 1 is a cross-sectional view of a fluid control valve in accordance with a first embodiment of the invention, with the valve plug split along its axis such that the left half of the valve plug is shown in the closed position and the right half of the valve plug is shown in the open position;

#FIG. 2 is a cross-sectional view of a cage and a valve plug assembly in accordance with the first embodiment of the invention, with the valve plug assembly in a closed position, wherein the valve plug assembly is configured for operation with a gas;

#A fluid control valve in accordance with a first embodiment of the invention is shown in FIG. 1. A control valve 10 includes a valve body 12 having an inlet port 14 and an outlet port 16, a cage 20, a valve plug assembly 22 and a bonnet assembly 24. A major component of valve plug assembly 22 is a valve plug 26.

#The cage 20 is a sleeve-like structure having a generally cylindrical wall 30 which defines a cage bore 32 having an axis 34. Cage bore 32 has a lower section 32a with a first diameter, a middle section 32b with a second diameter that is larger than the first diameter and an upper section 32c with a third diameter that is larger than the first and second diameters. Cage 20 defines a valve seat 40 and one or more apertures, or windows 42. Windows 42 provide flow passages between cage bore 32 and the exterior of cage 20.

#A valve stem 44 attached to valve plug 26 extends through bonnet assembly 24 to an actuator (not shown). The valve plug assembly 22 is slidable along axis 34 within the middle section 32b of cage bore 32 between an open position, shown on the right of axis 34 in FIG. 1, and a closed position, shown on the left of axis 34 in FIG. 1. In the closed position, a seating surface 50 of valve plug 26 engages valve seat 40, thereby blocking fluid flow through the control valve. In the open position, valve plug assembly 22 is moved along axis 34 to a position above windows 42 in cage 20. In the open position, the inlet port 14 communicates with the outlet port 16 through cage bore 32 and windows 42. The valve plug assembly 22 may be located at any intermediate position between the open and closed positions to achieve a desired rate of flow.