SECTION VALVE COUNTERACTING PRESSURE TRANSIENTS IN PIPE SYSTEMS

Abstract: During the sectioning of pipe systems for liquids pressure transients occur, which often overload the pipe and which can give cause to serious damages to pipes and plants. In particular pipe systems with long pipelines are sensitive to pressure transients. The specially shaped section valve counteracts pressure transients by means of cutouts or the like in the valve housing or in the movable valve body (plug, ball, disk) or in both. By a specially matched actuator the movable valve body is moved at low speed during the sensitive part (sensitive with respect to pressure transients) of the valve manoeuvre.

Description: Description Title Section valve counteracting pressure transients in pipe systems. 5-!2iS2£2-*._2-_-. Pipe systems must have valves for sectioning purposes. Section valves are typically used to shut off pipelines, to isolate components in the system or to create alter¬ native ways for the flow through the pipe network. The reasons for sectioning are several: Shutting off for maintenance or removal, sectioning for improved flow distribution, adjustments due to load changes, on/off flow control etc. Examples of pipe systems, where sec- tioning is a common event are: Networks for district heating, distribution systems for drinking water*, pipe¬ lines for raw water and sewerage, industrial pipe sys¬ tems for cooling water and process liquids, pipelines for irrigation and fire-fighting and the like. During a valve manoeuvre pressure fluctuations occur (pressure transients, hydraulic transients, pressure surges, water hammer ...) , which often overload the pipe and have given cause to pipe ruptures or to other serious damages to plants. Pressure transients occur during valve closures as well as during valve openings. The invented section valve counteracts pressure trans¬ ients and reduces the pressure fluctuations during a valve manoeuvre to acceptable strength with reference to the pressure load, of the pipe system. The only method, which up to now has been available for sectioning long pipelines 'with credit' , is that of combining two valves. The main valve is of a dimension similar to the pipe and has a low pressure loss. The by-pass-valve is considerably smaller and connected to the pipe in parallell with the main valv.e. The shut off process starts with the closure of the main valve, while the by-pass-valve is still in open position. Then the by-pass-valve is closed slowly. The procedure of a valve opening is carried out in reversed order. ■ §_ϊi§_;_§§§2ϊiEέi2ϋ_2-;_-=^-!_ ε§ϊi-!2-! The invention enables the same effect, i.e. reduction of the strength of the pressure transients, to be ob¬ tained by means of specially shaped flow channels with¬ in the valve with or without the assistance of a match¬ ing actuator. A conventional valve closure can be described by means of four more or less clearly defined positions (figure 1). a) Completely opened valve i.e. the least possible (figure 1a) pressure loss b) Throttling position i.e. when sufficiently (figure 1b) large pressure drop initiates a notice¬ able flow reduction c) Hydraulic closed i.e. when there is no flow position (figure 1c) through the valve, except for possible leakage d) Completely closed i.e. when the valve must valve (figure 1d) be completely tight The far too rapid deceleration of the flow between OMPI "throttling position" and "hydraulic closed position" during a conventional valve closure is the principal cause for strong pressure transients. The corresponding positions for the invented section valve counteracting pressure transients are illustrated in figure 2. During a valve closure the plug (2) moves at high speed from "completely opened position" (figure 2a) to "thrott¬ ling position" (figure 2b) . Closed to (at, slightly be¬ fore or slightly after) "throttling position" low speed is applied. After "hydraulic closed position" (figure 2c) high speed can again be applied for the transport to "completely closed position" (figure 2d) . "Throttling position" is characterized by the fact that cutouts or the like in the valve housing (seat, ...) or in the plug (ball, disk, sector, ...) or in both create a through-flow channel of suitable size. The size of the through-flow area is chosen with re¬ spect to the acceptable pressure change, which depends on the flow velocity in the connected pipe, the press¬ ure waves propagation speed and the detailed design of the valve. The through-flow area in "throttling posi¬ tion" is in the order of 2-20% of the cross-section area of the connected pipe with 5% as a typical value. The change of the through-flow area with the valve stroke is illustrated in figure 3 a-d. The shape of the through-flow area in "throttling posi¬ tion" is characterized by the fact that the change of the area ratio (through-flow area/cross-section area of connected pipe) with the valve stroke becomes consider¬ ably less at valve strokes less than in "throttling position". In this way the change of flow rate per unit time is reduced. Figure 4 a-d illustrates an example of how the section valve counteracting pressure transients can be designed in case of a gate valve. In some applications the valve manoeuvre can be per¬ formed with one and the same speed. The reduction of pressure transients will, however, be most effective with a matching actuator with variable speed. Such an actuator must have at least one high and one low speed. Low speed is applied at, slightly before or slightly after "throttling position". Correspondingly, low speed is applied from "hydraulic closed position" to "thrott¬ ling position" during a valve opening. High speed can be used for the transport from "completely opened valve" to "throttling position", and from "hydraulic closed position" to "completely closed valve" or between the mentioned positions in reversed order. Typical for the invention with reference to theactuator is that low speed is applied between "throttling posi¬ tion" and "hydraulic closed position" or between the same positions in reversed order. The time for the manoeuvre from "throttling position" to "hydraulic closed position" is determined due to acceptable strength of the pressure transients, which depend on the length of the pipe system connected to the valve, the propagation speed of the pressure waves in the pipes and the stationary flow velocity. The manoeuvre time, therefore, has to be selected from case to case. Typical values, however, are in the order of 10-300 sees, The valve opening process is performed in a similar way but in reversed order with respect to time.

Claims: Claims 1. A section valve counteracting pressure transients in pipe systems for liquids preferably with dimensions greater than DN 100 mm and with total pipelength greater than 100 , said valve equipped with an outer not manually driven actuator for the manoeuvring of the movable valve body c h a r a c t e r i z e d b y the fact that the valve housing (1) and the movable valve body (2) form a through-flow channel with an un¬ broken cross-section area, i.e. the cross-section area of the through-flow channel is everywhere delimited by one single continuous boundary line, and that said valve housing and said movable -valve body or both are so shap¬ ed that the change of area ratio (through-flow area of the valve/cross-section area of connected pipe) with the valve stroke obviously is given another character at "throttling position" (figure 2b, 3b, 4b) , i.e. when the area ratio is in the order of 2-20%, and that the change of area ratio with valve stroke is made considerably less at valve strokes less than in the neighbourhood of the "throttling position". 2. A section valve counteracting pressure transients according to claim 1 c h a r a c t e r i z e d b y the fact that the movable valve body (2) is a plug or a ball and that cutouts or filling ups in the valve hous¬ ing (1) or in the movable valve body (2) or in both con- tribute to form the through-flow channel with unbroken cross-section area so that the change of the area ratio with valve stroke becomes considerably less at valve strokes less than in the neighbourhood of "throttling position". 3. . A section valve counteracting pressure transients according to claim 1 c h a r a c t e r i z e d b y the fact that the movable valve body (3) is a not necessarily circular sliding disk and that cutouts or filling ups in valve housing (4) or in movable valve body (3) or in both contribute to form the through-flow channel with unbroken cross-section area so that the change of the area ratio with valve stroke becomes con¬ siderably less at valve strokes less than in the neigh¬ bourhood of "throttling position". A section valve counteracting pressure transients according to claim 1 , claim 2 or claim 3 c h a r a c t e r i z e d b y the fact that the manoeuvre speed of the not manually driven actuator is variable with at least one high and one low operational speed and that during a valve clos¬ ure the movable valve body is manoeuvred with high speed to a position in the neighbourhood of "thrott¬ ling position" and with low speed from the position in the neighbourhood of "throttling position" to "hydraul¬ ic closed position" and eventually again with high OM speed from "hydraulic closed position" to "completely closed position". 5. A section valve counteracting pressure transients according to claim 1 , claim 2 or claim 3 c h a r a c t e r i z e d b y the fact that the manoeuvre speed of the not manually driven actuator is variable with at least one high and one low operational speed and that during a valve open¬ ing the movable valve body is manoeuvred eventuallywith high speed from "completely closed position" to "hydraul¬ ic closed position", with low speed from "hydraulic closed position" to a position in the neighbourhood of "throttling position" and with high speed from the posi- tion in the neighbourhood of "throttling position" to completely open position". _OMPI ~ 7ipδ

Inventors: GUSTAFSON BROR-ARNE, GUSTAFSON, BROR-ARNE
Applicants: FLUDEX AB
Application year: 1984
Main classification: F16K47
IPC codes: F16K47, F17D1