RU2436003C2 - Throttle-control valve - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: throttle-control valve consists of case, of hollow slide with perforations and of diffuser seat. Perforation holes create an internal cavity of the slide with external streamlined surface. Perforation holes are arranged only on a section of streamlined surface below seating diametre D₁ not less, than on three diametres (D₁>D₂>D₃)<D_n. Diametres of perforation holes on this diametres d₁,d₂,d₃ are decreased downstream.

EFFECT: reduced negative effects of secondary flows, facilitation of stable flow and smooth flow rate characteristic of valve at all positions of slide.

5 dwg

Description

The invention relates to the field of power valve engineering and, in particular, to throttle control valves.

Known control valves, for example, a steam turbine containing a valve box (housing), a spool with a rod and a discharge diffuser. The streamlined surface of the spool can have a wide variety of shapes from a spherical surface to a complex profiled surface (Zaryankin A.E., Simonov B.P. Regulating and stop-regulating valves of steam turbines. MPEI. 2005, p. 289). The main drawback of existing throttle control valves is their increased vibration, which in some modes reaches unacceptably large values, which most often leads to the destruction of the stem.

This drawback is almost absent in perforated valves, where the spool is made with an internal cavity that connects to the space behind the spool using perforation holes uniformly distributed over the entire surface located below the bore diameter (SU 399671 A1, 03/10/1973 - prototype).

However, with continuous perforation of the streamlined surface on a number of modes, a complex secondary flow arises in the valve channel, due to the fact that behind the seating diameter along the surface of the valve, there is a fairly intense increase in pressure on the valve with a spherical shape of the valve (partial opening of the valve). The specified pressure difference leads to the flow of part of the working fluid through the perforation holes from the bottom of the spool to the low-pressure region located immediately behind the bore diameter. This secondary (transverse) flow disrupts the flow characteristics of the valve and, in some modes, raising the spool does not lead to an adequate increase in flow, since the transverse discharge of the working fluid from the internal cavity of the spool makes the main flow more difficult and generates additional pressure pulsations in the flow in such modes.

In profiled valves (Fig. 2), where the valve channel at a partial rise of the spools is an axisymmetric annular Laval nozzle, the flow pattern is even more complicated, since here at a considerable distance after the bore diameter there is a confuser flow with a decrease in pressure in the stream, followed by its increase in the remainder of the channel. In this case, at partial openings of the valve and large pressure drops in such a channel, supersonic flow regimes with a shock wave inside the channel are realized. In the case of continuous perforation of the streamlined surface of the spool, this leads to intensification of the transverse flow of the working fluid in the zone of confusional flow.

The present invention is intended to reduce the negative effects of these secondary flows and to ensure a stable flow and smooth flow characteristics of the valves in question at all positions of the spool.

To achieve this goal, continuous perforation of the streamlined spool surface is proposed to be replaced by perforation of only part of the surface, with a decrease in the diameter of the perforation holes along the flow.

Figure 1 shows a valve with partial perforation of the spherical surface of the spool. Figure 2 shows a profiled valve with partial perforation of the streamlined profiled part of the spool.

Both for the spherical (Fig. 1) and profiled (Fig. 2) spools, their internal cavity 1 is connected to the space of the diffuser seat 2 using three rows of perforation holes 3, 4, 5, which are located on a part of the streamlined surface below the bore diameter D _p , and the diameters of the perforation holes d ₁ , d ₂ , d ₃ decrease along the flow.

The appropriateness of such an arrangement of the perforation holes is determined by the fact that with small valve openings only at the inlet part of the streamlined spool surface, the confuser nature of the flow is maintained with pressure decreasing along the flow, and then, at supercritical flow velocities, subsequent pressure surges cause a sharp increase in pressure even with a continuous perforated surface intense secondary flows occur through the internal cavity of the valve. The negative consequences of such currents were considered above.

The marked shock waves are located approximately half the length of the generatrix that delineates the spool profile. It follows that the region of partial perforation on the streamlined surface of the spool should be located in the upper part of this surface, occupying no more than half the length of the generatrix that defines this surface.

(

, где h - подъем клапана, a D₁ - диаметр узкого сечения диффузорного седла). Для иллюстрации сказанного на фиг.3 приведена осциллограмма усилий на штоке модельного профилированного клапана при его открытии, равном

, и непрерывном увеличении относительного давления ∈₂ (∈₂=P₂/P₀, где P₀ - начальное давление рабочей среды в клапанной коробке, а Р₂ - давление за клапаном) от докритических к сверхкритическим значениям (∈₂<0,5). Указанная осциллограмма была получена при одном поясе перфорации, расположенном вблизи посадочного диаметра D_p.The need to use at least three perforation belts follows from the need to exclude a crisis reduction in the efforts on the valve stem, followed by a sharp increase in the dynamic loads on the rod during the transition from subsonic to supersonic flows in the valve flow section. On control valves of energy steam turbines, such modes occur in the area of small valve openings

(

where h is the valve lift, and D ₁ is the diameter of the narrow section of the diffuser seat). To illustrate the foregoing, Fig. 3 shows the oscillogram of the forces on the stem of a profiled model valve when it is opened, equal to

, and a continuous increase in relative pressure ∈ ₂ (∈ ₂ = P ₂ / P ₀ , where P ₀ is the initial pressure of the working medium in the valve box, and P ₂ is the pressure behind the valve) from subcritical to supercritical values (∈ ₂ <0.5 ) The indicated waveform was obtained with one perforation belt located near the bore diameter D _p .

It can be seen that with c ∈ ₂ = 0.46, a sharp decrease in the force on the rod followed by the development of very large pulsations of the axial force.

With two perforation belts, a crisis drop in the forces on the rod occurred at ∈ ₂ = 0.521 and the ripple of forces on the rod sharply decreased with a decrease in the value of ∈ ₂ to 0.403 (Fig. 4).

The transition to three zones of perforation (Fig. 5) will provide an almost crisis-free reduction of efforts on the rod during the transition to the region of supercritical pressure drops (∈ ₂ <0.5).

At the same time, a further decrease in the amplitude of pressure pulsations occurred.

до

.The feasibility of reducing the diameters of the perforation holes along the flow is determined by the fact that all control valves operate in an extremely wide range of pressure drops and can occupy any position within the range of changes in the relative height of the spool from

before

.

As a result, even with partial perforation, one or even two of the latter along the flow of the perforation belt may be in the region of increased pressure relative to the first belt. In this case, with reduced diameters of the perforation holes of subsequent perforation belts, the intensity of the flow of the working medium through the internal cavity of the spool turns out to be low, unable to violate the smoothness of the flow rate characteristic of the valve.

Thus, the use of partial perforation of the streamlined surface of the spool, together with a decrease in the diameters of the perforation holes along the stream, can drastically reduce the intensity of the secondary flows through the internal cavity of the spool, and with an increased diameter of the holes of the first row relative to the perforations of the subsequent rows due to a decrease in the velocity normal to the surface of the spool almost no longer can affect the flow characteristics of the valve, since the first row of perforations as even and on profiled valves it is always in the zone of confusional flow, where external disturbances decay very quickly.

Claims (1)

A throttle control valve containing a housing, a hollow spool with perforation holes connecting the internal cavity to the external streamlined surface, and a diffuser seat, characterized in that the perforation holes are located only on a part of the streamlined surface below the bore diameter D _{1 of} at least three diameters ( D ₁ > D ₂ > D ₃ ) <D _p , and the diameters of the perforation holes at these diameters d ₁ , d ₂ , d ₃ decrease along the flow.

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