DE20002181U1 - Stop valve - Google Patents

Description

Hans Luette 3 February 2000

Seelhofstrasse 24
79539 Loerrach

Plant for compressing a gaseous medium

Description

The invention relates to a system for compressing a gaseous medium, consisting of a drive machine and a liquid-injection-cooled compressor stage connected thereto via a coupling according to the preamble of patent claim 1.

In some compressor systems, a dryer is connected downstream of the compressor stage, depending on the requirements of the gaseous medium to be compressed. The dryer is usually a 2-chamber dryer with two dryer elements in the form of cartridges. The 2-chamber dryer offers the option of switching to the second cartridge after one dryer element has been saturated and dewatering the first. To do this, a switching element is activated that diverts the compressed, moisture-laden gas flow from one cartridge to the adjacent one and back again. During these switching processes, the pressure in the compressor to the dryer outlet drops within one second by up to 5 bar from the operating pressure, depending on the length of the line acting as a buffer. In a 2-chamber dryer, these sudden reliefs can occur every 30 seconds or every few minutes. The resulting disadvantages can be described as follows.

a) The separator arranged between the compressor stage and the dryer in the pressure line is loaded by the switching operations, whereby the differential pressures at the separator (dirty side / clean side) can reach up to 5 bar

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The dynamic increase in load leads over time (number of switching operations) to the destruction of the separator.

b) The manufacturer of the separators has great difficulty in producing separators that are statically strong enough to withstand the pressure surges over the long term without damage. Since the flow through the separator is from the inside to the outside, the separators must be wound tightly against the outer casing. As a preventive measure, the replacement intervals for separators are currently limited to 400 operating hours, although even this cannot be 100% guaranteed. However, the majority of customers want a time interval of at least 1500 operating hours, which is equivalent to an annual replacement.

c) The separator works in such a way that the gas flows through it from the inside to the outside or from the outside to the inside, whereby the moisture contained in the compressed gas coagulates as it flows through the separator and falls as drops on the outer or inner casing of the separator via gravity down to a collecting pocket, from where it is fed back into the process.

If an explosive discharge occurs when the dryer is switched on, the resulting increase in flow speed entrains the liquid droplets and leads them to the dryer. Since oil is usually used as a coolant and lubricant for the compressor stage, the entrained oil in the dryer contaminates the granulate, which leads to a reduction in drying performance. With a pressure ratio of 2, the flow speed increases in the order of the speed of sound.

d) During the unloading process, heat is removed from the compressor stage, which results in the formation of condensate if the compressor stage is switched on for a short time, particularly in the area of the separator.

The object of the invention is to provide a system for compressing a gaseous medium, consisting of a drive machine and a liquid-injection-cooled compressor stage connected to it via a coupling, with which the

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The time interval for replacing the separator can be significantly increased, the residual liquid content, in particular the residual oil content in the compressed gas can be reduced and the risk of condensate formation in the system can be reduced.

This object is achieved on the basis of the generic term with the features specified in the characterizing part of patent claim 1. Advantageous further developments are part of the subclaims.

The core of the invention is the arrangement of a valve between the compressor stage and the dryer that throttles the volume flow in the direction of the pressure gradient. The valve is preferably arranged on the inlet side of the dryer in order to be able to use the line between the compressor stage and the dryer as a buffer volume.

The valve has a spring-loaded control piston which interacts with a seat arranged in a housing and which is provided with a bypass opening on the front side and with overflow channels in the jacket area.

If there is a sudden drop in pressure as a result of the dryer being switched on, the control piston closes against the spring force in the direction of the pressure drop. The compressed gaseous medium conveyed by the compressor stage now only passes through the valve via the bypass opening arranged in the control piston. This opening is dimensioned so that the control piston maintains a dynamic pressure equal to the compressor pressure. After the switching process in the dryer, the system downstream of the valve is refilled via the bypass opening. If the pressure behind the valve reaches the operating pressure, the compression spring opens the valve and the compressed gaseous medium passes through the valve via the overflow channels arranged in the jacket area. These are dimensioned so large that the pressure loss that occurs there is negligible. The closing path of the control piston is preferably selected to be < 2 mm, so that the closing time is short and the pressure drop that has occurred up to that point in the downstream system is small and does not stress the sensitive parts. The small closing stroke also has the advantage that only small acceleration forces are effective during closing, which in turn has a positive effect on the material stress on the control piston.

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The inventive arrangement of a valve in the pressure line between the compressor stage and the dryer results in the following advantages.

The liquid separator is not subjected to any dynamic swelling stress even during frequent switching changes of the dryer.

No liquid breakthroughs are to be expected in the separator. The replacement interval for the separator can be increased.

No liquid, especially oil, is entrained because there is no significant increase in flow velocity.

The residual liquid content, especially the residual oil content, is reduced.

The compressor stage can heat up more quickly. The risk of condensation forming is reduced.

The drawing explains the compressor system designed according to the invention in more detail using an exemplary embodiment. It shows:

Figure 1 is a schematic diagram of a system designed according to the invention

Figure 2 shows a longitudinal section of the valve designed according to the invention

Figure 3 a section in direction A-A in Figure 2

Figure 1 shows a schematic diagram of a system designed according to the invention for compressing a gaseous medium. It consists of a drive machine 1, preferably an Egr; motor, and a liquid-injection-cooled compressor stage 3 connected to it via a coupling 2. A separator 5 and a check valve 6 are arranged in the pressure line 4. The liquid separated in the separator 5 is returned via a line 7 of the compressor stage 3. If special requirements are placed on the compressed gaseous medium, a dryer 8 is usually arranged in the pressure line. This has two dryer elements 9, 9' designed as cartridges with a housing 10 connected to it, in which the switching element (not shown here) is located.

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This switching element makes it possible to pass the compressed gaseous medium once through the first dryer element 9 and, after saturation, to switch over to the second dryer element 9'. The drainage takes place via a line 12 provided with a shut-off valve 11. After the dryer 8, the cleaned and dried gaseous medium leaves the system via a check valve 13 and is fed to a consumer not shown here.

According to the invention, a valve 14 which throttles the volume flow in the direction of the pressure gradient is arranged in the pressure line 4 between the compressor stage 3 and the dryer 8. It can be installed either after the check valve 6 in the compressor housing or directly at the outlet area of the compressor stage 3 (dashed lines) or preferably in the inlet area of the dryer 8.

The individual parts of the valve 14 are shown in Figures 2 and 3. The valve 14 has a cylindrical housing 15 in which an axially movable control piston 18 is arranged, which is spring-loaded via a compression spring 17, and is aligned with the housing axis 16. In this exemplary embodiment, the control piston 18 is designed as a hollow body. The conical head region 20 of the control piston 18, which faces the outlet side 19, interacts with a seat surface 21 arranged in the housing 15 in a complementary manner. A bypass opening 22 is arranged in the front face of the head region 20 of the control piston 18, which is preferably designed as a bore here. In the jacket region of the control piston 18, overflow channels 23, 23' extending through the wall are provided. On the back, the control piston 18 is supported against a snap ring 24 arranged in the housing 15.

The operation of the valve 14 is described below. If the pressure on the outlet side 19 drops suddenly as a result of a switching process in the dryer 8 (Figure 1), the pressure acting on the inlet side 25 pushes the control piston 18 to the right against the force of the compression spring 17, so that the conical head area 20 comes to rest on the seat surface 21. A further flow of the gaseous medium from the hollow central area via the overflow channels 23, 23' is therefore no longer possible. The gaseous medium can

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the valve 14 can only be left via the bypass opening 22. This opening 22 acts like a throttle point, so that a corresponding back pressure builds up at the rear. During the switching process of the dryer 8, gaseous medium continues to be supplied to the subsequent system via the bypass opening 22 until operating pressure prevails in this area again. As soon as this state is reached, the compression spring 17 presses the control piston 18 back to the left into the starting position, so that the compressed gaseous medium can leave the valve 14 via the overflow channels 23, 23' with almost no pressure loss.

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Claims (7)

1. Installation for compressing a gaseous medium comprising a drive machine and a liquid-injection-cooled compressor stage connected thereto via a coupling, a liquid separator arranged in the pressure line and a dryer connected downstream of the separator, which is provided with a switching element and a drainage system, characterized in that a valve throttling the volume flow in the direction of the pressure gradient is arranged in the pressure line between the compressor stage and the dryer. 2. System according to claim 1, characterized in that the valve is arranged in the pressure-side outlet bore of the compressor stage. 3. Plant according to claim 1, characterized in that the valve is arranged at the pressure-side inlet of the dryer. 4. System according to one of claims 1-3, characterized in that the valve is designed as a self-switching throttle valve. 5. System according to claim 4, characterized in that the valve has a housing in which a spring-loaded, axially movable control piston is arranged coaxially with the housing axis, the head region of which facing the outlet side interacts with a seat surface arranged in the housing and which is provided with a bypass opening on the front side and with overflow channels in the jacket region. 6. System according to claim 5, characterized in that the bypass opening is dimensioned such that the control piston maintains a back pressure equal to the compressor pressure. 7. System according to claims 5 and 6, characterized in that the closing travel of the control piston is ≤ 5 mm.