FLUID FLOW CONTROL DEVICES

Abstract: A fluid flow control device having a sleeve and sleeve guide axially movable relative to each other but biassed by spring means in one direction, and control slots formed by the sleeve and sleeve guide to control flow to a piston and to a port, wherein at a threshold flow rate the piston is moved towards the port and at a flow rate above the threshold relative movement between the sleeve and the sleeve guide maintains substantially constant the fluid pressure drop across primary slot means of the control slots and also meters flow to the piston via metering slots of the control slots, whereby the piston closes the port after a required flow of fluid.

Description: Field of Invention This invention relates to fluid flow control devices and more particularly to resettable fuses (or sensors) which monitor the quantity of fluid flowing through the fuse, and then blocks the flow when a pre-selected quantity of fluid has passed through. The invention is particularly suitable for use with hydraulic fluids. Known control devices of this type have previously employed buoyant pistons or vane motors. Those employing buoyant pistons are commonly undesirably and inherently sensitive to changes in attitude of the fuse and also undesirably critical with respect to fit and clearances. A hydraulic fuse device is proposed in US 2592486 in which a proportion of the fluid flow is tapped to operate a primary piston which closes an outlet port to stop the fluid flow after a predetermined volume of fluid has flowed through the device. A second piston in the path of the fluid flow is responsive to said flow and controls movement of the primary piston so that it can only move to close the outlet port in response to said fluid flow. A hydraulic fluid flow control device is also proposed in US 4056133 which stops the fluid flow below a predetermined flow rate and comprises a poppet valve through which the fluid passes to an outlet port and which assumes a position below said predetermined flow rate which causes a metering valve to pass fluid to a primary piston to close the outlet port. The metering valve comprises a pin that cooperates with a central bore in the poppet valve. This device is used exclusively to prevent fluid flow below a predetermined flow rate. Fuses employing vane motors are undesirably expensive. The invention is concerned, therefore, with the provision of a fuse which, in general, is simple and effective in terms of construction, modes of operation and results and has few manufactured parts, relatively high force levels in sensing mechanism, and flow/volume characteristics which can be readily tailored, i.e. fitted, to many different design requirements. Disclosure of the Invention In accordance with the invention, there is provided a fluid flow control device characterised in that it comprises: a) a body defining a cavity, b) a primary piston in the cavity and movable endwise to control fluid flow through a first port, c) a sleeve, and a sleeve guide in the cavity and in the path of fluid flow toward the primary piston, d) the sleeve and guide being axially movable relative to each other, and there being spring means acting to urge one of the sleeve and guide in one axial direction, e) and control slots formed by the sleeve and sleeve guide to control flow both to the piston for controllably displacing the piston, and to the first port, wherein i) as the forward flow rate through the device reaches a threshold the piston begins said movement towards the first port, and ii) as the flow rate increases above the threshold, relative axial movement between the sleeve and guide acts: to maintain substantially constant the fluid pressure drop across primary slot means included within the control slots; and to meter fluid flow to the piston via metering slot means included within the control slots, for displacing the piston as aforesaid, whereby the piston is displaced to close the first port after a required quantity of fluid has passed through the device. The devices of the invention can usefully be referred to as fuses and typically can be reset by either flowing fluid through them in a reverse direction or by lowering the differential pressure across the fuse to a low limit. A threshold characteristic is provided which will not allow the fuse to close when the flow rate is less than a pre-set minimum. The moving components, i.e. the piston and the sleeve, are preferably positioned about a single element, i.e. the sleeve guide, and the majority of the static components are preferably also located by the sleeve guide. Preferably, the spring means urges the sleeve in a direction which reduces fluid flow through the primary slot means located in the sleeve and the sleeve guide. Advantageously the sleeve guide is hollow to allow fluid to flow via the primary slot means from the sleeve exterior to the guide interior and then towards the first port. The metering slot means can usefully communicate with an annular cavity within which the sleeve is axially movable. The control slots preferably include primary slot means extending radially through the sleeve to allow fluid to flow to the first port in full flow axial position of the sleeve. In addition, the control slots preferably also include threshold slot means associated with the primary slot means to initiate flow through the sleeve to the first port when the sleeve is substantially in a no flow position. The metering slot means can we axially spaced from the primary slot means to meter the flow to the piston. The control slots advantageously include reset slot means at the end of the sleeve to allow escape of fluid from the piston under conditions of no fluid flow to the first port. The sleeve preferably has axially opposed lost motion couplings to the spring means, whereby the sleeve may be oppositely displaced by fluid flow pressures in opposite directions corresponding to full forward flow through the device, and reverse flow through the device. Additionally, the sleeve can usefully have a reverse flow position in which the sleeve is displaced endwise relative to the guide by reverse flow pressure, the spring means acting yieldably to limit the extent of the endwise opposite sleeve displacement so that the reverse flow passes through the guide to exit the sleeve via the primary slot means included within the control slots. In general, the combination of the sleeve, the sleeve guide and a sleeve spring are used to translate fluid flow through the fuse into a proportional, smaller flow that is used to detect the total volume of fluid that has passed through the fuse. In this regard, the sleeve has multiple primary flow slots, a small slot for setting the threshold, a metering slot, and reset slots for resetting the fuse. Fluid flow through the primary slots creates a nearly constant differential pressure across the fuse through the combination of the sleeve area and the sleeve spring force. The small threshold slot is used to set the upper and lower threshold limits; the metering slot meters flow into the piston cavity and thereby shuts off the flow through the fuse; and the reset slots allow fluid to escape from the piston cavity when the sleeve is in the no-flow position. Description of the Drawings For a better understanding of the invention, reference is now made, by way of example only, to the accompanying drawings in which: Figure 1 is an external, side elevation, showing an hydraulic fuse of the invention; Figure 2 is an end view of the fuse shown in Figure 1 taken on the line 2-2 of Figure 1; Figure 3 is a sectional view of the fuse shown in Figures 1 and 2 taken on line 3-3 of Figure 2; and Figures 4-7 are fragmentary enlargements of the view shown in Figure 3 showing the fuse in zero flow condition (Figure 4); threshold flow condition (Figure 5); full flow condition (Figure 6); and reverse flow condition (Figure 7). Mode of Carrying Out the Invention Referring to the drawings, the fuse 10 is adapted to monitor a quantity of hydraulic fluid passing through it, for example in direction of arrows 11 and 12, and then block such flow when a selected quantity of fluid has passed through it. The fuse includes body 13 defining a cavity 14. The body comprises a forward cylinder 13 a , a rearward plug 13 b , and an assembly 13 d . The cylinder has an enlarged rearward section 15 telescopically receiving the plug 13 b , with threads interconnecting these elements at 16 and sealed by an O-ring seal 17. A sleeve guide 18 extends in the body cylinder, i.e. within the cavity 14, and has a flange 18 a that fits the bore 15 a of section 13 c . It is held in an axial position, against an internal tapered shoulder 19 of cylinder 13 a by the forward end 20 of the plug 13 b . An O-ring seal 21 seals the flange outer surface and the bore 15 a . A primary piston 22 is located in the cavity (within the cylinder), to move endwise for controlling fluid flow through first and second ports 23 and 24. As shown, the piston 22 is annular and is slidable along the tubular stem 18 b of the guide 18. As the piston moves to the right (as shown, for example, in Figure 3), its tubular stem 22 a closes four ports 23 in stem 18 b , to block forward flow of fluid via these ports and hence to exit points 24 in the tapered end piece 15 c of the cylinder 13 a . A compression spring 26 in the cavity 14 yieldably resists forward movement of the piston. Seals 27 and 28 respectively act between the piston bore 22 b and the guide stem 18 b , and between the piston outer surface 22 c and the bore 15 e of the cylinder section 13 a . The tapered end 15 g of the piston stem first seats against an O-ring seal 29 and then against a taper 30 of the cylinder at an extreme rightward position of the piston. Hydraulic fluid pressure to displace the piston to the right (as shown in Figure 3) passes via slot means (to be described) and ports 31 in the guide 18 to the chamber 32 adjacent the left end face of the piston. Also provided in the body cavity is a tubular control sleeve 35, which is axially movable along and upon the guide 18. The sleeve has a bore 35 a slidably closely fitting on the outer cylindrical surface 18 h of the guide stem 18 i , projecting to the left (as shown) from flanged portion 18 a of the guide. The sleeve 35 and guide 18 are in the path of fluid flow toward the primary piston, and they are axially movable relative to each other. A compression spring 36 acts to urge the sleeve in an axial direction, i.e. to the left, in the example. The spring is in a permanent state of compression between a tubular seat 37, and an annular retainer 38. The latter initially engages a plug shoulder 39 a to limit spring extension, but when sufficient force build-up occurs, the retainer 38 is displaced to the right (as shown) by the sleeve shoulder 35 b . The sleeve includes a cap 39 that fits over the left end of the guide 18, and forms therewith a primary flow slot 40. Extending the description to Figures 4 to 7, flow control slots are formed by the relatively movable sleeve and guide to control flow both to the piston and to the first port 23, and also port 24. These slots include the primary flow slot or slots 40, a small threshold slot 40 a at the forward end of slots 40 (these slots extending radially through the sleeve wall 41); a metering slot 42 through wall 41, spaced forwardly of slot 40 a ; and a reset slot or slots 43 through wall 41, at the forward end of the sleeve. In addition, there are recesses or grooves 44 and 45 sunk in the wall of stem 18 i , the recess 44 opening at 46 to the interior 47 of the guide in communication with port 23. Four primary slots 40 are provided about the sleeve axis. In operation of the fuse, fluid entering ports 50 and 51 in fittings 13 d passes to the interior 52 of the plug, externally of the cap 39. Under essentially zero condition, as represented in Figure 4, no fluid flows to the ports 23 and 24 via the primary slot 40 since the sleeve is positioned as shown, whereby the slot 40 is blanked by the exterior surface 56 of the guide. The threshold slot 40 a sets upper and lower threshold flow limits, such that when fluid pressure in 52 reaches an upper limit, the sleeve moves slightly to the right to a threshold flow condition, as seen in Figure 5, so that fluid now flows through slot 40 to port 23, via 46 and 47, and fluid also flows past the retainer 38 into cavity or space 58 exposed to metering slot 42. Thus, fluid flow is metered via slot 42 to groove 45 and via passage 31 to the piston, initiating its movement to the right (as shown). Such flows to 47 and to the piston are increased under full flow condition as represented in Figure 6; and when the predetermined quantity of fluid has passed through the fuse, (determined by the amount of metered fluid needed to drive piston 22 fully to the right), the outlet ports 23 and 24 are closed. Fluid flow through the primary slots creates a nearly constant differential pressure across the fuse through the combination of the sleeve area and the sleeve spring force. Since the pressure drop across the sleeve will never exceed 345 kN/m² (50 lb/in²), for example, even at extreme flow rate, the diametral clearance between the sleeve and sleeve guide can be quite large, say from 0.0025 to 0.0125mm (0.0001 to 0.0005 inches) which allows the components to be interchangeable with no matched sets. Under zero conditions as shown in Figure 4, the reset slots 43 allow fluid to escape from the piston chamber (at the left of the piston face) as indicated by arrows 70 and 71. At that time, spring 26 urges the piston to the left. The fuse construction also allows for reverse flow, as represented by arrows 80 and 81 in Figure 7. Under such conditions, the fluid pressure acting against the cap 39 displaces the sleeve to the left (as shown) so that fluid by-passes grooves 44 and 45, exits the left end 83 of the guide 18, and escapes the sleeve via slots 40. The spring 36 yieldably resists displacement to the left of the sleeve by virtue of the seating of the retainer 38 at 35 b , and leftward compression of the spring by the retainer 37 a . In Figure 6, the retainer 37 a seats at 27, and allows the sleeve to move to the right relative thereto. Such yieldably resisted movements of the sleeve are facilitated by "lost motion" couplings to the spring 36 as described. A spring 60 urges seat 37 leftwardly against body cylinder shoulder 61, in Figure 4.

Claims: A fluid flow control device comprising: a) a body (13) defining a cavity (14), b) a primary piston (22) in the cavity (14) and movable endwise to control fluid flow through a first port (23), characterised in that it further comprises: c) a sleeve (35), and a sleeve guide (18) in the cavity (14) and in the path of fluid flow toward the primary piston (22), d) the sleeve (35) and guide (18) being axially movable relative to each other, and there being spring means (36) acting to urge one of the sleeve (35) and guide (18) in one axial direction, e) and control slots (40, 42, 44, 45) formed by the sleeve (35) and sleeve guide (18) to control flow both to the piston (22) for controllably displacing the piston, and to the first port (23), wherein i) as the forward flow rate through the device reaches a threshold the piston (22) begins said movement towards the first port (23), and ii) as the flow rate increases above the threshold, relative axial movement between the sleeve (35) and guide (18) acts: to maintain substantially constant the fluid pressure drop across primary slot means (40, 44) included within the control slots; and to meter fluid flow to the piston (22) via metering slot means (42, 45) included within the control slots, for displacing the piston (22) as aforesaid, whereby the piston (22) is displaced to close the first port (23) after a required quantity of fluid has passed through the device. A device according to claim 1 in which the piston (22) and the sleeve (35) are positioned about a single element (18). A device according to claim 1 or claim 2 in which the spring means (36) urges the sleeve (35) in a direction which reduces fluid flow through the primary slot means (40, 44) located in the sleeve (35) and the sleeve guide (18). A device according to any preceding claim in which the sleeve guide (18) is hollow to allow fluid to flow via the primary slot means (40, 44) from the sleeve exterior to the guide interior and then towards the first port (23). A device according to any preceding claim in which the metering slot means (42, 45) communicate with an annular cavity (58) within which the sleeve (35) is axially movable. A device according to any preceding claim in which the control slots include primary slot means (40) extending radially through the sleeve (35) to allow fluid to flow to the first port (23) in full flow axial position of the sleeve (35). A device according to any preceding claim in which the control slots also include threshold slot means (40a) associated with the primary slot means (40) to initiate flow through the sleeve (35) to the first port (23) when the sleeve (35) is substantially in a no flow position. A device according to any preceding claim in which the control slots include metering slot means (44) axially spaced from the primary slot means to meter the flow to the piston. A device according to any preceding claim in which the control slots include reset slot means (43) at the end of the sleeve (35) to allow escape of fluid from the piston (22) under conditions of no fluid flow to the first port (23). A device according to any preceding claim in which the sleeve (35) has axially opposed lost motion couplings (38, 37a) to the spring means (36), whereby the sleeve (35) may be oppositely displaced by fluid flow pressures in opposite directions corresponding to full forward flow through the device, and reverse flow through the device. A device according to any preceding claim in which the sleeve (35) has a reverse flow position in which the sleeve (35) is displaced endwise relative to the guide (18) by reverse flow pressure, the spring means (36) acting yieldably to limit the extent of the endwise opposite sleeve displacement so that the reverse flow passes through the guide (18) to exit the sleeve (35) via the primary slot means (40, 44) included within the control slots.

Inventors: GELLERSON, WALTER G.
Applicants: DOWTY DECOTO INC.
Application year: 1987
Main classification: G05D7
IPC codes: F16K17, G05D7, F16K21, F16K31