WO1989006765A1 - Volumetric, self-resetting, hydraulic fuse - Google Patents

Abstract

A hydraulic fuse or cut-off device divides fluid flow into: (i) a primary fluid stream; and (ii) a secondary fluid stream having a substantially constant, but small ratio of flow to said primary stream. The secondary stream exerts pressure on a timing piston (7) which thereby monitors the entire flow and causes the fuse to cut-off when a predetermined volume of fluid has passed through the device. The fuse includes a regulating piston (6) for building inlet pressure to a value sufficient to develop the power necessary to drive the timing piston. Greater simplicity of the component parts and decreased sensitivity to contamination results from the use of a small fluid orifice to control the secondary stream. This is achieved by fitting the regulating piston with an inwardly directed flange (9), just touching the peripheral surface of a slightly tapered, central pin (10) whereby the taper of the pin causes the orifice to be created as the regulating piston is caused to slide as a result of the primary fluid flow.

Description

VOLUMETRIC, SELF-RESETTING, HYDRAULIC FUSE

TECHNICAL FIELD This invention relates to a hydraulic fuse and more particularly concerns itself with an in-line hydraulic fuse or sensor that monitors the quantity of hydraulic fluid passing through the device and thereafter blocks the flow when a pre-selected quantity of fluid has passed through. BACKGROUND ART

Devices employed to monitor and interrupt fluid flow have generally employed buoyant pistons as the timing element to cut-off such flow after a predetermined volume of fluid has passed through the fuse. Examples of such buoyant piston devices are shown in U.S. Patents 2,512,190; 2,518,988; 2,592,486; and 2,554,390. Reliance on a buoyant piston configuration necessitates that a hydraulic fuse be constructed, utilizing very close tolerances and a large number of parts. Recently, a fuse has been described (U.S. 4,655,245) which employs a regulating element for building inlet pressure to a value sufficient to develop the power necessary to drive the timing element — eliminating the requirement for timing element buoyancy. The addition of a regulating element (a movable sleeve in the '245 patent) permits the fuse to function more accurately at lower flow conditions as compared with the predecessor, buoyant piston systems. Since the regulating element permits power to develop sufficient to actuate the timing element, the latter can more accurately measure the quantity of fluid as it passes through the valve, generally independent of the rate of flow, such that actuation of the shut- off mechanism is reliable both at high and low flow rates . The '245 patent employs a basic spool and sleeve mechanism for both the regulation and the timing elements. Thus, with respect to the regulating element, the metering slots are near the outer periphery of the cylinder — resulting in a large circumferential length (and therefore large surface area) which necessitates the use of tight tolerances to achieve accurate metering. Not only are tight tolerances disadvantageous in that they are more costly to produce, but they are also more sensitive to contamination and to variations in temperature. With respect to the timing element, since the spool and sleeve mechanism has to effect a fluid-tight seal between the outside diameter of the spool and the inside diameter of the sleeve, two additional disadvantages result: (i) concern with the concentricity of the spool; and (ii) the requirement to employ O-ring seals or the equivalent to prevent leakage — thereby incurring increased friction, which detracts from accuracy, particularly at low flow rates and temperatures. DISCLOSURE OF INVENTION

Rather than utilizing the relative movement between the regulating, sleeve element and a spool guide element to control both the timing stream (i.e., the fluid stream which controls the timing element) and the primary flow stream exiting the primary port; the instant invention utilizes relative movement between an inwardly directed flange of the regulating element and a centrally located pin, to form a comparatively small, surface area metering orifice — eliminating the need for tight tolerances or clearances. The instant device is therefore less costly to produce, less sensitive to contamination and temperature variations, and is easier to adjust. As a result, simplicity of the fuse's component parts not only drives down production costs, but also ensures both a lower failure rate on the assembly line and a higher reliability rate in actual use. These and other advantages of the instant invention will become more apparent from a reading of the following description, when read in conjunction with the appended claims and the following drawings.

BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a side elevation, partly in longitudinal section, of the inventive fuse, in its initial or open position. Figures 2 through 4 show analogous side elevations, partly in longitudinal section, illustrating the progression of both the regulating piston and the timing piston, at various stages of volumetric flow, whereby Figure 4 shows the "shut-off" position. Figure 5, likewise, is a partly sectioned longitudinal elevation, showing the elements in reverse or "free flow" position.

MODES FOR CARRYING OUT THE INVENTION Figure 1 is a partial section, showing the essential components of the fuse in its initial or open position. The fuse consists of cylindrical housing 1_, having a bore or cavity which includes inlet port 2_ and outlet port 3_. As illustrated, the primary fluid flow ("fused flow direction") is from left to right. The housing includes guide tube 4_ and stop 5_. Stop 5_ divides the interior volume of tube 4_ into what may be considered two chambers — the upstream chamber, which houses regulating piston 6_, and the downstream chamber, which houses timing piston 7_ — each of such pistons being biased in the reverse flow direction by respective springs 8_r and 8_t. Desirably, the combination of stop 5_ and guide element 4_ will be constructed as an integral member. If should be apparent, however, that the combination may be formed by joining two or more pieces. Affixed to piston 6 is flange 9, the inside diameter of which abuts the peripheral surface of pin ljj. At least a portion of the peripheral surface of 1 is tapered in the direction of fused flow. (The sharpness of the taper is exaggerated in the figures for purposes of illustration, but would normally be about 1°.) Thus, as fluid pressure increases above the threshold established by spring 8_r, flange 9_ moves axially (to the right in the figures) , resulting in an increased clearance between the edge or inside diameter of 9_ and the peripheral surface of 1 — thereby increasing the orifice which is created as a result of such movement. While flange 9_ may be integral with piston 6_, it is preferably affixed thereto by nut 11, permitting ready replacement or adjustment of the flange. In the construction illustrated, the various parts (some of which will be described later) are inserted into housing 1_ and held in place by end cap 12_, leakage around the peripheral surface of which can be prevented by resilient rings, e.g., rubber O-ring 13_ and back-up, Teflon ring 14. End cap 12 may carry shoulder 1_5 which serves to form a seat for poppet lι5 located at the downstream end of piston l__t such that travel of piston 7_ to its downstream limit will result in poppet 1_ forming a positive closure of the primary fluid path (shown by the arrows in Figures 2-4) .

The operation of the fuse and the function of the various elements not yet described can better be understood by referring to Figures 2 through 5. As shown by the arrows, fluid -enters the fuse through inlet port 2_. The fluid works across shoulder 17_, located at the upstream end of regulating piston 6_. In the initial ("at rest") position shown in Figure 1, piston 6_ bottoms against stop 18_ and poppet 19_. However, as illustrated in Figure 2, reverse flow poppet 1_9_ and piston 6_ are moved slightly away by the fluid pressure (when sufficient to overcome the bias of spring 8_r) , allowing flow to begin, both through a portion of slot 2 and through central port 2_1 — protected against contamination by screen filter 2_2. As a result of the opening of outlet slot 2_0, flow enters the annular region 2_3 formed between the outer surface of guide 4_ and the inner surface of the housing. Thereafter, this primary fluid stream travels through inlet slot 2_4_, re-enters the interior of guide 4_, and exits the fuse through outlet port 3_. In the embodiment illustrated, fluid must first pass through holes in spring retainer 2_5 prior to exiting outlet port 3_. It should be apparent that the spring retainer could be otherwise supported — permitting flow to pass directly from slot 24_ to port 3_. As noted above, when flow through the primary fluid path becomes possible, a second stream of flow is initiated through central port 21 and then through the orifice created (as a result of the movement of piston 6 ) between flange 9_ and pin 1£ — developing enough pressure to overcome the bias of spring 8_t and move timing piston 7_. Thus, the rate of flow of this second stream and, concomitantly, the timing of shut-off piston 7_ are controlled by the orifice formed between self-cleaning, tapered pin 1 and the inside diameter of the flange 9_. As illustrated, pin 1£ is comprised of integral, cylindrical portions, in which the smaller diameter cylindrical portion is tapered toward the fused flow direction to provide an increase in the orifice so-formed, as regulating piston 6_ and therefore flange 9_ moves in the fused direction.

Figure 3 shows the position of piston 7_ while the fuse is permitting full flow, such that the piston is timing the volume of fluid passed through the fuse before it reaches the fused position illustrated in Figure 4. As shown in Figure 4, poppet 16 is seated against shoulder 1_5 — shutting-off the primary flow path. Under this fused condition, fluid pressure is no longer working against regulating piston 6_, such that spring 8_r will therefore urge regulating piston 6_ back to the initial, closed position.

The reverse, essentially free-flow condition, permitted by the design of the fuse, is shown in Figure 5. Since timing piston 7_ is unrestrained (until it meets stop 5) in the reverse flow direction, fluid acting against piston _ 1 forces it to the left, opening slot 24_, permitting reverse flow through annular region 23 and through slot 20_ and port 2_6_, urging poppet 1_9 in the reverse direction, i.e., to the left in Figure 5. In this reverse direction, poppet 1_9_^ is restrained only by check return spring 21_, which desirably is provided with a low spring rate. It is therefore seen that reverse flow can be essentially "free", e.g., of the order of about 3 psi, since such flow has only to overcome the rather minimal spring bias. The regulating piston limits the amount of pressure rise, which would otherwise occur at high flow rates, e.g., to 15 to 17 psi. The regulated pressure works across the self-cleaning orifice (created between flange 9_ and taper-pin 10_) to effect closure of shut- off poppet 16_ more rapidly at high flow rates, thereby maintaining the same pre-selected volume capacity. As temperature variation affects fluid characteristics (e.g., as temperature increases, viscosity decreases, and fluid passes more easily through the orifice) the regulating piston moves more or less to compensate and limit the pre-selected volume capacity, so as to minimize variation resulting from such temperature differences.

Claims

1. A hydraulic fuse comprised of, an encircling housing having a bore, a tubular guide element mounted and axially aligned within said housing bore, said tubular guide element having outlet and inlet slots formed in its wall, such that fluid may travel into the interior of the tubular element, and thereafter outwardly through the outlet slot, located in an upstream portion of the guide element, to an annular-like region formed between the outer surface of the guide element and the inner surface of the housing bore, and then re-enter the interior of the tubular element through the inlet slot, located in a downstream portion of the guide element, and from said interior, pass through an exit port in the fuse — the fluid path so-formed being the primary fluid path; a regulating piston, slidably supported for axial movement within an upstream portion of the guide element, and a timing piston, slidably supported for axial movement within a downstream portion of the guide element, the pistons being reciprocated within the guide element — in one direction by fluid pressure and in the opposite direction by respective biasing springs; a cylindrical pin axially mounted within an upstream portion of the guide element, at least a portion of the pin having a peripheral surface tapering slightly in the primary direction of fluid flow; the regulating piston having: (i) a port formed within its wall, said port being at least partially matable with the outlet slot of the guide element; (ii) a shoulder at the upstream end thereof, the clearance between the shoulder and the outlet slot controlling the fluid flow to said primary fluid path; and (iii) a flange facing toward the tapered, peripheral surface of the pin, such that the peripheral pin surface confronts the innermost flange surface, whereby the taper of the pin causes an orifice to be created and to increase as the regulating piston slides in the primary flow direction, the resulting orifice permitting fluid to flow from the upstream portion of the guide element, thereby to act against the face of the timing piston and cause it, likewise, to travel in the primary flow direction; the timing piston having a poppet, at the downstream end thereof, such that travel of the timing piston downstream will control the fluid flow from the inlet slot of the guide element, by closing the primary flow path at the downstream limit of the timing piston.

2. The fuse of Claim 1, including a reverse flow poppet, slidably supported for axial movement upstream of the regulating piston, and a check spring urging the reverse flow poppet against the shoulder of the regulating piston, whereby fluid may travel in a direction "reverse" to said primary direction; by traveling first into said exit port, and thereafter through said inlet slot, said annular-like region, said outlet slot, and said port in the regulation piston, so as to exert fluid pressure on said reverse-flow poppet sufficient to overcome the bias of said check spring — thereby creating a clearance for the egress of the fluid through an inlet in said housing.

3. The fuse of Claim 2, wherein the check spring has a low spring rate, permitting reverse flow to occur at fluid pressures in excess of about 3 psi.