Fluid flow throttle valve

Abstract

A fluid flow throttle valve that keeps the pressure of a fluid flow pumped into a system by a high-pressure pump constant and that is particularly suitable as a reject valve for maintaining the system pressure of a reverse osmosis device at a pressure level of <20 bar. The flow pressure is regulated by a spring-actuated cone that is partially within the outflow channel of the throttle valve at any given time. A motion restrictor is supported to the wider end of the cone such that in its lowest position, the cone permits a bypass flow of a predetermined volume up to the target pressure of the system. As the flow volume increases further and the cone rises as a result, the force exerted on the restrictor member by the flow pressure contributes to preventing the valve from closing.

Claims

1. A fluid flow throttle valve that keeps the pressure of a fluid flow pumped into a system by a high-pressure pump constant and that is particularly suitable as a reject valve for maintaining the system pressure of a reverse osmosis device at a pressure level of <20 bar, wherein the valve comprises a tubular body, where flow enters from one end thereof, and the body is provided with a central outflow channel with a circular cross-section, having a cone arranged therein with its narrower end on the inflow side and being axially supported on a stem to which a support plate movable along with the stem is supported on the inflow side, wherein the outer edge of the support plate is closely tangential to the inner surface of the body and wherein the support plate is provided with channels for flow therethrough, and wherein a loaded compression spring surrounding the stem is provided between the outflow channel and the support plate, the compression spring being supported to the support plate from its one end and to the body from its other end, wherein a motion restrictor is supported to the larger diameter end of the cone, the motion restrictor consisting of a restrictor member and restrictor legs supported to the restrictor member and extending from the restrictor member to a planar surface surrounding the outflow end of the outflow channel, wherein the restrictor legs are adapted to restrict the motion of the cone such that the cone is prevented from being pressed against the circumference of the outflow end of the outflow channel by the force generated by the spring, as a result of which the cone always permits an evenly surrounding bypass flow permitted to flow between the restrictor legs and further through a flow-permitting channel between the restrictor member and the body.

2. The valve according to claim 1, wherein the position of the support plate on the stem is adjustable in the axial direction of the stem.

3. The valve according to claim 1, wherein the stem passes through the cone and the restrictor member is releasably supported to the stem.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Next, the structure and operation of the throttle valve according to the invention is described in more detail with reference to FIGS. 1 to 3.

(2) FIG. 1 shows a check valve of the prior art in which the valve cone is supported on a conical seat.

(3) FIG. 2 shows a structure of the throttle valve according to the invention in longitudinal cross-section with the cone 3 in its lowest position.

(4) FIG. 3 shows the operation of the valve according to the invention.

DETAILED DESCRIPTION

(5) In FIG. 2: The throttle valve comprises a tubular body 1 where flow enters from one end thereof and wherein the body 1 is provided with an outflow channel 2 with a circular cross-section. A cone 3 is arranged in the outflow channel 2 such that the narrower end of the cone is on the inflow side and the cone is axially supported on a stem 4 passing through the cone 3. A support plate 5 is supported to the stem 4 on the inflow side, wherein the support plate 5 is movable along with the stem 4 and closely tangential to the inner surface of the body 1. A loaded compression spring 6 surrounding the stem 4 is provided between the outflow channel 2 and the support plate 5, which compression spring 6 is supported to the support plate 5 from its one end and to the body 1 from its other end. The support plate 5 is provided with one or more flow-permitting channels 10. A motion restrictor is supported to the larger diameter end of the cone 3, the motion restrictor consisting of a restrictor member 7 releasably supported to the stem 4 passing through the cone 3, having restrictor legs 8 supported thereto extending from the restrictor member 7 to a planar surface 9 surrounding the outflow end of the outflow channel 2. A flow-permitting channel 11 is formed between the restrictor member 7 and the body 1. The restrictor legs 8 restrict the motion of the cone 3 such that it is prevented from being pressed against the circumference of the end of the outflow channel 2 by the force exerted thereon by the spring 6. Owing to the restrictor legs 8, the cone 3 always permits an evenly surrounding bypass flow when the cone 3 is in its lowest position, whereby the flow can pass between the restrictor legs 8 and further through the channel 11. The volume of the bypass flow can be adjusted by adjusting the length of the restrictor legs 8.

(6) In FIG. 3: The pressure generated by the throttle valve is p1. The pressure between the outflow end of the outflow channel 2 and the restrictor member 7 is p2. The pressure difference across the outflow channel 2 is (p1p2). The pressure difference across the restrictor member 7 is (p2p0) and it as well as the magnitude of the force exerted by it on the restrictor member 7 can be adjusted by adjusting the size of the cross-sectional area of the restrictor member 7 perpendicular to the flow. The magnitude of the force exerted on the support plate 5 by the flow can be adjusted by adjusting the cross-sectional area of the channel 10 perpendicular to the flow.

(7) The flow pressure in the outflow channel 2 converts primarily to velocity (Bernoulli's principle). The flow velocity at the end of the outflow channel 2 is obtained from the equation v=C.sub.D(2gH).sup.1/2. The pressure head H corresponds to the pressure difference across the channel throttling the flow.

(8) The volume of the through-flow of the outflow channel 2 is obtained approximately from the formula Q=C.sub.0.Math.A.Math.(2g.Math.H).sup.1/2, where Q is [m.sup.3/s]; C.sub.0 a constant depending on the shape of the channel; A [m.sup.2] is the cross-sectional area of the channel; g is 9.81 m/s.sup.2, and H [m] is the pressure head, i.e. the pressure difference (p1p2) across the outflow channel 2.

(9) The same formula is also used to obtain the flow pressure difference across the restrictor member 7 and the support plate 5.

(10) Next, an exemplary embodiment of the valve according to the invention is described. The problem solved in the exemplary embodiment: In a case where the cone 3 closes the outflow channel 2 completely, the pressure generated by the high-pressure pump exerts a force on the cone 3 tending to open the valve. In order for the cone 3 to start rising only when the target pressure of the system has been reached, the preloaded spring 6 must cause a counterforce of equal magnitude. When the valve opens, the cross-sectional area of the cone 3 onto which the flow pressure is exerted decreases while the force generated by the spring 6 tending to close the valve increases. In the absence of other forces acting on the cone 3, the valve closes abruptly only to reopen immediately thereafter (hunting phenomenon). The solution: The forces parallel to the direction of the flow exerted on the restrictor member 7 and, where needed, on the support plate 5 of the throttle valve of the invention counteract the relative increase in the force tending to close the valve.

(11) In this exemplary embodiment, the volume pumped by the high-pressure pump ranges between 5 and 8 m.sup.3/h. The target pressure of the system is from 10.5 to 11 bar. The flow continues from the throttle valve to an ambient pressure of 0 barg. The dimensions of the throttle valve: The inner diameter of the body 1 is 30 mm The outflow channel 2 has a diameter of 16 mm and a cross-sectional area of 2 cm.sup.2 The cone angle of the cone 3 is 34 degrees The compression spring 6 has a free length of 185 mm, a wire thickness of 3.76 mm, a spring constant of 3.55 N/mm The cross-sectional area of the restrictor member 7 perpendicular to the flow is 3.7 cm.sup.2 The cross-sectional area of the channel 11 between the restrictor member 7 and the body 1 is 1.5 cm.sup.2 The length of the restrictor legs 8 of the motion restrictor is defined such that when the cone 3 is in its lowest position and p1p2=10 bar, a flow of m.sup.3/h can flow past the cone 3, FIG. 2. In this case, the cross-sectional area of the cone 3 at the outflow end of the outflow channel 2 is 1.7 cm.sup.2, and, correspondingly, the cross-sectional area of the annular flow opening permitting flow past the cone 3 is 0.3 cm.sup.2. The flow exerts a force of 170 N on the cone 3 in the direction of the flow. The pressure difference across the restrictor member 7 (p2p0=0.4 bar) exerts a force of 15N on the restrictor member 7. In order for the cone 3 to remain in place, the force generated by the spring 6 must be equal to the sum of the above-mentioned forces, i.e. 185N, which means that the spring 6 is preloaded to a length of 133 mm. The inflow side end of the stem 4 of the cone 3 is subjected to the same pressure as the cone 3, thus the cross-section of the cone 3 at the outflow end of the outflow channel 2 has been used in the calculations. At a volume of 5.5 m.sup.3/h, i.e. immediately after the valve has opened, the cross-sectional area 2 of the cone 3 at the outflow end is 1.67 cm.sup.2, in which case it is subjected to a force of 167 N generated by the flow pressure. The pressure difference across the restrictor member 7 is 0.5 bar, thus, the restrictor member 7 is subjected to a force of 19N. The spring 3 has been compressed by a further 0.25 mm, so the force generated by it has increased by 1 N, i.e. to 186N. Since 167 N+19 N=186 N, the valve remains open, particularly since the restrictor member 7 is additionally subjected to the dynamic pressure of the flow. At a maximum volume of 8 m.sup.3/h and a pressure difference of 10 bar across the outflow channel 2, the cone 3 has risen by 1.5 mm and the cross-sectional area of the annular flow opening surrounding it has increased to 0.5 cm.sup.2. The cross-sectional area of the cone 3 at the outflow end of the outflow channel 2 has correspondingly decreased to 1.50 cm.sup.2, whereby the force generated by the flow pressure and exerted on the cone 3 is 150 N. The force generated by the spring 3 has increased by 5 N, i.e. to 189 N. A flow of 8 m.sup.3/h causes a pressure difference of more than 1.1 bar across the restrictor member 7 of the motion restrictor. In this case, the force exerted on the restrictor member 7 by the flow is 41 N. Since 150 N+41 N>189 N, the valve does not close, particularly since the restrictor member 7 is also subjected to the dynamic pressure of the flow, causing an additional force parallel to the direction of the flow. Since at a flow volume of 8 m.sup.3/h, the pressure difference across the restrictor member is 1.1 bar, the pressure on the inflow side of the outflow channel 2 must be 11.1 bar in order for the pressure difference across the outflow channel 2 to be 10 bar. The size of the channel 10 in the support plate 5 may be used to influence the pressure difference across the support plate 5. Since the support plate 5 is supported on the stem 4 of the cone 3, the magnitude of the force exerted on the support plate 5 in the direction of the flow can be used to counteract the force exerted on the cone 3 by the spring 6, if necessary.

(12) As a result of the above-mentioned forces, the cone 3 automatically enters the equilibrium state at different flow volumes and the throttle valve according to the invention keeps the system pressure at the desired level.