METHOD AND VALVE FOR CONTROLLING LIQUID DRAINING

Abstract: A method for draining liquid from, for example, a liquid separator in a pressure-gas conduit, with the aid of a valve. The invention is based on the concept that when a fluid flows through two constrictions connected in series, the pressure between the constrictions will vary in dependence on whether the fluid is a gas or a liquid. In the former case the pressure will be higher, and can therewith be used to close the constrictions. The invention also relates to a valve for carrying out the method, the valve comprising an inlet (32), a first constriction (33) which opens into an intermediate pressure chamber (36), a second constriction (34) located between the intermediate pressure chamber (36) and an outlet (41). A valve body (35) located in the intermediate pressure chamber is arranged to be activated in a direction which closes the constrictions (33, 34) by the pressure prevailing in the intermediate pressure chamber (36) and in an opening direction by the pressures prevailing in the constrictions (33, 34), the pressure in the intermediate pressure chamber (36) being increased when gas appears in the first constriction (33) instead of liquid, and the pressure increase and the areas of the constrictions (33, 34) being adapted so that the valve will close in response to the aforesaid increase in pressure.

Description: METHOD AND VALVE FOR CONTROLLING LIQUID DRAINING The present invention relates to a method for controll¬ ing the drainage of liquid from a liquid-containing pres¬ sure-gas conduit, with the aid of a valve arranged in a drainage channel, and also to a drainage valve for carrying out the method. Pressure-gas systems that contain major or minor quanti¬ ties of liquid must, as a rule, be provided with liquid se¬ parators which in turn require the provision of devices for draining-off the liquid separated thereby. Large systems use float-controlled valves for this purpose. Such valves, however, are expensive and highly space consuming. The present invention is not concerned with devices of this kind, but relates more specifically to small, inexpen¬ sive devices which require only a small amount of space and which can be used, for instance, in conjunction with small compressors into which oil is injected. Compressors of this kind normally include a suitably located nozzle means which constantly drains-off gas and liquid. The smaller the comp¬ ressor the more sensitive it becomes to the loss of gas through drainage. Consequently, it is normal practice to instal a valve which will open periodically so as to drain off gas and liquid intermittently over a given active pe¬ riod, e.g. a period of 10 seconds duration. The active area of the nozzle or valve may not be made too small, however, since the flow of liquid separated may be quite large at times. Obviously, it is difficult to choose an optimum nozzle dimension which will satisfy at one and the same time both the requirement of economy and that of safety against overloads. The object of the present invention is to provide a so¬ lution which while overcoming the aforesaid problems will not be encumbered with the aforementioned drawbacks. This object is achieved with the method according to the present invention, in which the liquid to be drained from, for example, a liquid separator is enabled to flow through two constrictions which are coupled in series in a drainage channel and which can be closed with the aid of a valve bo¬ dy in response to a pressure increase that occurs there- between when gas instead of liquid passes through the first constriction as seen in the flow direction, this pressure increase being allowed to attenuate through a leakage passage, past the other constriction until the valve re¬ opens and detects either the presence of liquid or of gas at the first constriction, in which latter case the valve is again closed. Thus, the valve is opened periodically at a frequency which is dependent on the negligible leakage past the second constriction. However, in distinction to the known time-controlled valve, the valve according to the present invention is closed immediately the presence of gas instead of liquid is detected in the first constriction, therewith preventing gas from being lost from the system without restricting the drainage capacity thereof. A drainage valve for carrying out the method according to the invention has the features set forth in the charac¬ terizing clause of claim 2. The invention will now be described in more detail with reference to the accompanying drawing, in which - Figure 1 illustrates schematically a channel for flowing fluid; - Figure 2 is a longitudinal sectional view of a valve constructed to illustrate the inventive method; - Figure 3 is a longitudinal sectional view of a valve constructed in accordance with a preferred embodiment of the invention, said view being taken on the line III-III in Figure 4; - Figure 4 is a cross-sectional view taken on the line IV-IV in Figure 3; and - Figure 5 is an enlarged view of part of the valve illustrated in Figure 3. Referring to Figure 1 , where a liquid flows through a channel 1 that incorporates two identical and mutually sequential restrictions A and B, the drop in pressure across the two constrictions A and B will be the same, i.e. in the case of the indicated pressures p-,, P2, P3, p<| - p 2 will = 2 - P3- If, on the other hand, air flows through the channel, will equal 1.24 irrespective of P3, provided that the ratio P1/P3 is greater than 2.5. These circumstances can be utilized to drain, e.g. oil from an oil separator located at the outlet of an air compressor into which oil is injected, as illustrated schematically in Figure 2, with the aid of a theoretically suitable valve 2 connected to an oil separator 3. As with the illustrative channel of Figure 1 , the valve 2 also in- corporates a first constriction A and a second constriction B which is equally as large as the first constriction. Both of the constrictions have an active surface area A-, . The pressure between the constrictions is designated 2• The constrictions A and B can be closed by means of a common valve body 4, which presents a piston in the axial extension thereof. The piston extends into a cylindrical chamber 6 connected to the channel 1. The piston 5 has a larger active area than the constrictions A and B and is also provided with a pressure equalizing channel 7 which equalizes the pressure on both sides of the valve body 4. A leakage passage 8 extends from one of the spaces in which this pressure prevails, i.e. the pressure p , to the outlet at which pressure P3 prevails, e.g. between the peripheral surface of the piston 5 and the opposing cylinder wall of the chamber 6. When seen in the drawing, the pressure p-| acts downward¬ ly on the closed valve body 4, and the pressure P2 acts with an equal force in both an upward and a downward direc¬ tion. The constant outlet pressure P3 acts downwardly on an annular surface 9 on the piston 5, whereas the variable pressure P2 acts upwards on the undersurface of the piston 5, this undersurface having an area A2• If it is assumed that the pressure P3 is equal to the pressure 0.1 x p-j, it can readily be shown that when the ratio between the areas h- and 2 lies between 0.5 and 0.7, the pressure P2 will be sufficiently high to close the valve when air is present in the constriction A. When oil is present in the constriction A, the pressure P2 will fall sufficiently for the pressure P1 on the surface area A-] and pressure P3 on the annular surface 9 to overcome the pressure P2 on the surface area A2 and therewith hold the valve open until air begins to flow through the constriction A. When the valve is closed by the pressure P2 acting on the surface area 2., leakage occurs through the passage 8, so as to gradually attenuate the pressure P2- This leakage is negligible, but, however, as beforementioned, causes the valve to open at given time intervals, so as to be able to detect whether liquid or gas begins to flow through the constriction A. If gas is present in the constriction, the valve will close immediately. As beforementioned, the valve illustrated in Figure 2 is unsuitable both with regard to its manufacture and to its method of operation. A more practicable and more suitable valve arrangement is illustrated in Figures 3-5. The valve housing of this valve arrangement comprises an upper part 30 and a lower part 31. The inlet at which pressure <| pre¬ vails is designated 32 and the first constriction is de¬ fined by two axial bores 33. The other constriction is de¬ fined by three axial bores 34 which are finer than the bores 33. The mouths or outlet orifices of the two con¬ strictions are thus adjacent one another, instead of being located one behind the other as in the valve arrangement described with reference to Figure 2. This enables the valve body to have the form of a planar valve plate or disc 35 located in an intermediate chamber 36 in which the pres¬ sure P2 prevails. The outlet orifices of respective bores 5 33, 34 present a thin, forwardly projecting edge 37, 38 -which when ground flat will ensure that an effective seal is obtained between the mouths of the bores 33, 34 and the upper surface of the valve plate 35. In the valve arrange¬ ment illustrated in Figure 3, the pressure equalizing chan- 0 nel 7 of the Figure 2 embodiment has the form of a clearan¬ ce 7' around the periphery of the valve plate 35. A plura¬ lity of low shoulders 39 provided on the undersurface of the plate 35 ensure that there is obtained beneath the plate 35 a clearance in which the pressure 2 can propa- 5 gate. The leakage passage 8 referred to in the description of the Figure 2 embodiment has correspondence in the Figure 3 embodiment in the form of a fine groove or like recess 40 in the forwardly projecting edge 38 of the exit orifices or 0 mouths of the bdres 34. When the valve is closed, leakage occurs from the chamber 36 via the bores 34 to an outlet 41 at which the pressure P3 prevails, as does also the drain¬ age of oil when the valve is closed, analogously with the described performance of the Figure 1-2 embodiment. 5 When the valve plate 35 occupies its closed position, the plate is subjected to the downwardly acting force of the pressure p- | across the total area of the bores 33 and the pressure P3 across the total area of the bores 34, and also to the upwardly acting force of the pressure P2 over a 0 corresponding area on the undersurface of the valve plate 35. When the pressure p decreases slightly as a result of ■-* * the leakage that takes place through the grooves 40 or be¬ cause of the presence of oil in the bores 33, the upwardly * acting force is not sufficient to hold the valve plate 35 5 in its closed position and hence the valve will open. When air subsequently appears in the bores 33, the pressure p 2 in the chamber 36 will rise, therewith initiating the aforedescribed sequence. If, for example, the total area of the bores 33 is assumed to be equal to the total area of the bores 34 and p- j and P3 are assumed to be equal to 8 bars and 1 bar re¬ spectively, P2 will alternate between a value of 4.5 bars when oil is present in the bores 33 and a value of 6.45 bars when air is present in said bores. The dimensioning is adapted so that the upwardly acting force which has a value corresponding to P2 = 4.5 bars is insufficient to hold the valve plate 35 in its closed position, whereas the pressure 2 which is equal to 6.45 bars is sufficient to cause the valve plate 35 to move to its closed positon.

Claims: CLAIMS 1. A method for controlling the drainage of fluid from a pressure gas conduit that contains gas and liquid, with the aid of a valve located in a drainage channel, characterized by enabling the liquid to flow through two constrictions which are connected in series in the drainage channel and which can be closed by a valve body in response to an in¬ crease in pressure occurring between the constrictions when pressure gas instead of liquid enters through a first of the two constrictions, this increase in pressure being allowed to attenuate through a leakage passage past the se¬ cond of said constrictions until the valve re-opens and de¬ tects the presence of liquid or of gas in the first const¬ riction in which latter case the valve is again closed. 2. A drainage valve for carrying out the method of claim 1, characterized in that the valve includes a valve housing having located therein at least one channel (33) which forms a first constriction (A) and which leads to a pres¬ sure chamber (36), and at least one further channel (34) which forms a second constriction (B) and which leads from the pressure chamber (36) to an outlet (41); in that the exit orifices or mouths of the channels in the pressure chamber (36) are located at right angles to and adjacent to one side of a valve plate (35) which incorporates a pres- sure equalizing channel (7') that leads to the other side of said valve plate; and in that the valve plate is ar¬ ranged to close sealingly the first constriction (A) when a high pressure acts on said other side of the valve plate (35), and with a small leakage to close the second const- riction (B) until the pressure increase has been reduced to a value which corresponds to the force required to open the valve. 3. A drainage valve according to claim 2, characterized in that the exit orifice of the two constrictions (33, 34) lo¬ cated in the pressure chamber are of circular configuration (37, 38) and are located in mutually the same plane; and in that said leakage through the second constriction (B) is effected through a groove or like recess (40) in the cy¬ lindrical defining wall of the outlet orifice (38) of said constriction.

Inventors: OLOFSSON HANS, OLOFSSON, HANS
Applicants: SVENSKA ROTOR MASKINER AB
Application year: 1986
Main classification: F16K24
IPC codes: F16K24, F16T1, F17D3