GB2088025A - Device for Controlling the Passage of Liquid - Google Patents

Abstract

The device comprises a sleeve (1), an implosion member (2) extending into the sleeve and defining an implosion chamber (20) which provides a separated implosion zone and is interconnected by at least one row of entry channels (21) with a flow space (17) of variable volume defined between said member and said sleeve. A gate (3), having a tubular body closed at one end by a bottom (31), is slidably movable between said member and said sleeve into said flow space so as to vary its volume and to cover or uncover said entry channels. A cavity (30) of variable volume is defined in the gate between said bottom and said member. Radial channels (15) pass through the body of the gate to provide communication between said cavity and the outside of said gate. Resilient means (4) being situated in said cavity and bearing at one end against said member and at the opposite end against said bottom. <IMAGE>

Description

SPECIFICATION Device for Controlling the Passage of Liquid Having a Separated Implosion Zone The invention relates to a device for controlling the passage of liquid having a separated implosion zone. The device is especially suitable for controlling the passage of a condensate in a heat-regeneration system of a steam turbine.

When controlling passages of compressed liquids and especially compressed and hot liquids, there is a serious danger that in the outlets into the areas of valves, where the pressure is lowered below the pressure of saturation of the entering liquid, an erosive effect may be caused by the formed two-phase flow in its interaction with a solid wall. For instance a pressure drop behind a throttle edge of a cone of a control valve releases out of the liquid a steam component with a high velocity, which carries with it in the flow of the formed two-phase liquid a liquid in the shape of drops, which erodes the walls of throttle elements, of valve bodies, or of piping.

Many solutions are known for limiting or removing this effect which is very dangerous with respect to a function reliability and service life of control and recirculation valves. One of the known solutions, which considerably limits a creation of a two-phase mixture at a locally dynamic pressure drop, decreases step by step pressure differencies behind a throttle element of the valve by means of a system of suitable hydraulic resistances. A relatively new solution, which is very advantageous due to low requirements on the inner space of a control valve, is a method of collision of two-phase flows which resides in removing an axial momentum when two flows at least meet, the flows flowing one opposite the other towards the axis of the control valve.

Both mentioned solutions provide some drawbacks. As to the first solution it is a complicated production and space requirements of a system e.g. of labyrinth hydraulic resistors; as to the second solution there is a danger of remaining parasite forces caused by collided flows onto a movable throttle element together with a possibility of an errosive effect onto function surfaces of the valve if the implosition zone is shifted.

Some of the mentioned drawbacks may be limited considerably by the device for controlling a passage of liquids with a separated implosion zone, the principle of which resides in the fact that the implosion zone is situated in a cavity of a firm implosion chamber and is connected by means of radial channels to an outer surface of this chamber, on which a throttle element is slidingly seated.

In order that the invention may be clearly understood and readily carried into effect, a preferred embodiment thereof is, by way of example, hereinafter more fully described and illustrated in the accompanying diagrammatic drawing which shows a section of a device for a hydraulicly controlled control valve for relieving a hot condensate in a regeneration cascade of a steam turbine.

A device for controlling the passage of liquid having a separated implosion zone shown in the drawing comprises a sleeve 1 provided with a packing collar 10, firmly held between bearing surfaces of a body 7 of an action member and a body 8 of a control valve. A gate 3 is slidably mounted inside the sleeve 1. An implosion chamber 20 and several rows of flow channels 21 are provided in a body 2. On the outer surface of the body 2 is guided the gate 3 which has a tubular body closed at one end by a bottom 31.

The device is also provided with a compression spring 4.

The parts of the device are mutually so arranged, that a collar of the body 2 of the implosion chamber 20 bears against a packing 33 seated in the body 8 of the control valve above an outlet area 82. The implosion chamber 20, which is frusto-conically shaped, opens into this outlet area 82. The diameter of the outlet of the implosion chamber 20 is larger than the diameter of its bottom. A flow space 17, the volume of which is limited by the movement of the gate 3, is arranged between the outer surface of the body 2 of the implosion chamber 20 and the inner surface of the sleeve 1.The gate 3 covers or uncovers during its vertical movement, individual rows of the channels 21 which inter connect the implosion chamber 20 with the space 1 7. This space 1 7 is connected by means of connecting channels 16, formed in the sleeve 1, to the inlet area 80 of the body 8 of the control valve. The cavity in the gate 3 forms a variable equalizing space 30 which is connected by means of equalizing channels 15, formed in its wall, to the space 17. In the equalizing space 30 (into the described embodiment) is situated the spring 4, one end of which leans against the body 2 of the implosion chamber 20 and the other end leans against the bottom of the gate 3.A variable pressure space 23, which is connected to the outer source of the control liquid by means of the connecting piping 22, is limited inside the sleeve 1 by the outer surface of the bottom of the gate 3 and by the upper part of the body 7 of the action member.

The function of the device according to the invention may be described by its function in the range of two limit regimes, which are shown in the drawing such that in its left-hand half the device is shown in the condition when the passage of liquid is limited to maximum, and in the right-hand half in the condition, when the device provides a minimum hydraulic resistance to the passing liquid, and in this way it allows a maximum passage through this system. A passage of liquid, which is enabled by a pressure drop between the inlet area 80 and outlet area 82, is controlled by the position of the gate 3 that covers or uncovers the mouths of the channels 21 on the outer surface of the body 2 of the implosion chamber 20.The pressure level of the liquid is transported from the inlet area 80 by means of the connecting channels 16 into the space 17; the pressure difference between the pressure of the liquid in the space 1 7 and pressure in the implosion chamber 20 affects the passage of the liquid in the channels 21 which are not covered by the gate 3. Jets of liquid, which flow opposite to each other from the coaxial channels 21, collide in each row in the centre of the implosion chamber 20, and the homogenized liquid then flows out, at a considerably decreased velocity, through the outlet of the implosion chamber 20 into the outlet area in the body 8 of the control valve.

An integral embodiment of the device according to the invention, realized by a fixed connection of the control valve to its hydraulic drive, aims to increase the accuracy of the passage control of liquids by limiting parasite forces affecting the gate 3 which is the only moving part of the device. The controlling pressure liquid creates a hydraulic signal, which is transported into the pressure space 23 of this device through the connecting piping 22 and affects the upper part of the bottom 31 of the gate 3. The position of the gate 3, with respect to the body 2 of the implosion chamber 20, which determines the number of open or closed channels 21, depends upon a resultant of forces between forces acting on both sides of the bottom 31 of the gate 3.These forces are created by pressure relations in the pressure space 23, in the equalizing space 30, by pressing the spring 4 and by parasite forces, which may be of a stationary or dynamic character. The effect of parasite forces on the position of the gate 3 when pressure and flow conditions in the device according to the invention change may be limited to a minimum in case of stationary parasite forces - by straight surfaces of the bottom 31 of the gate 3, on which act pressures in the pressure space 23 and equalizing space 30, and possibly in the space 17, into which the lower throttle edge 300 of the gate protrudes.

The gate design of the device according to the invention avoids the existence of dynamic parasite forces caused by the passage of liquid, because the process of acceleration and interaction of masses of the passing liquid, created by a pressure drop into the space of the implosion chamber 20 is separated. If a quick closing of other piping sections, through which liquid flows, is required, which is always a process involving the danger of a hydraulic shock by immediate stopping of the liquid column in the inlet piping section, the safe speed of closing of the throughflow area of the device according to the invention is determined by an auxiliary controlled quantity. This quantity is created by transferring the pressure increase at the beginning of the hydraulic shock from the space 17 through the equalizing channels 1 5 into the equalizing space 30. A dynamic change of the resultant of forces which affects the gate 3, limits the closing speed at this transition effect, and in this way a dangerous increase of pressure in the body 8 of the control valve.

The device according to the invention may be used for controlling the passage of liquids anywhere, where a suitable source of a controlling hydraulic medium is at hand and where a quick and explicit response to an inlet hydraulic signal is required.

Although the invention is illustrated and described with reference to one preferred embodiment thereof, it is expressly understood, that it is in no way limited to the disclosure of such a preferred embodiment, but is capabie of numerous modifications within the scope of the appended claims.

Claims (3)

Claims

1. A device for controlling the passage of liquid, comprising a sleeve, an implosion member extending into the sleeve and defining at least one implosion chamber which provides a separated implosion zone and is interconnected by at least one row of entry channels with a flow space of variable volume defined between said member and said sleeve, a gate having a tubular body closed at one end by a bottom being arranged to be slidably movable between said member and said sleeve into said flow space so as to vary its volume and to cover or uncover said entry channels, a cavity of variable volume being defined in the gate between said bottom and said member, radial channels passing through the body of the gate to provide communication between said cavity and the outside of said gate, resilient means being situated in said cavity and bearing at one end against said member and at the opposite end against said bottom.

2. A device according to Claim 1 wherein the member is substantially cylindrical and defines a single said implosion chamber which is substantially frusto-conical and closed at its narrow end by a bottom, several said rows of entry channels providing communication between the implosion chamber and the outside of the member, the channel in each row being substantially radial and opening into the implosion chamber at the narrow part thereof.

3. A device for controlling the passage of liquid substantially as herein described with reference to, and as shown in, the accompanying diagrammatic drawing.