Anti-cavitation system in pipelines which avoids that the fluid reaches its vapour pressure at the output of a given contraction using a device that connects the output section of the contraction with its downstream pressure

Abstract

A anticavitation system that has a pipeline piece (1) that has a contraction (3), as an example a valve. Upstream of the contraction (3) the fluid moves in a direction (2) with a P1, and downstream of the contraction (3) with a pressure P2. To avoid that the fluid pressure reached the Pv, exiting the contraction (3), the system has cavities and holes (4) located downstream of the contraction, where the pressure is stable and reaches a value P2. The system has a second set of cavities (5) located just outside the contraction (3). Using a connection media (6) the system feeds back the stable prssure P2, to the area outside the contraction (3) where the pressure reaches Pv and can produce the undesirable cavitation. For this, as it feeds back the pressure P2 using the connection media (6) to the cavity (5), the pressure exiting the contraction (3) reaches a value P3 that is higher than Pv. The connection media (6) can have a chamber-chamber (9) that has a surrounding (7) and the external wall of the pipeline (1)

Description

FIELD OF APPLICATION OF THE INVENTION

The invention mentioned in this document refers to a new device that allows to suppress the phenomenon called cavitation that affects control valves in industrial processes with a higher efficiency than with the current systems and mechanisms and from a different approach.

CAVITATION DESCRIPTION

Cavitation is a multi-step phenomenon that occurs in a liquid flow stream. First, due to some changes in flow geometry (such as a valve), the fluid falls below its vapour pressure, which creates some vapour in the liquid.

Next, the fluid returns to a pressure that is greater than its vapour pressure, causing the vapour bubbles to collapse. The formation and collapse of vapour bubbles is referred as cavitation.

To better understand the phenomenon of cavitation, one can start by analyzing the velocity and pressure profiles of a fluid as it passes through a restriction.

The important point to note is that at the smallest cross-sectional flow area of the fluid stream (referred to as the Vena Contracta), fluid velocity increases and the fluid pressure decreases. This relationship between fluid velocity and fluid pressure is known as Bernouilli's Law.

1. As fluid flows through a restriction, fluid velocity increases

2. Bernouilli's Las: If velocity increases, pressure will decrease.

3. The Vena Contracta, downstream of the restriction, is the point of smallest flow area, highest velocity, and lowest pressure.

If the pressure of a liquid falls below its vapour pressure, the liquid will begin to vapourize. If the vena contracta pressure (Pvc) falls below the vapour pressure (Pv) of the fluid, then fluid vapourization will occur.

If the downstream pressure P2 increases to a value that is greater than the fluid's vapour pressure, the bubbles collapse and the fluid is cavitating.

If the vapour bubbles that are formed during the cavitation cycle implode on or near fluid boundaries such as valve components and pipe walls, high velocity microjets and sonic waves can result in rapid and serious damage to the components of the valve and pipeline.

COMMENTS REGARDING PRIOR ART

Document U.S. Pat. No. 3,946,562 (Ross) of Mar. 30^th, 1976 shows a cavitation suppressor to be used on hydraulic systems. The Cavitation Suppressor is useful to prevent the excessive pressure using a hydraulic fluid bypass around a mix section to reduce the use of additional fluid aspiration from a reservoir.

The Cavitation Suppressor prevents the incorporation of air within the system from the added solution. It includes and input, a mixer and output sections, additionally to the bypass media which communicates the input and output sections.

Document U.S. Pat. No. 4,016,898 (Tokarchuk et al.) of Apr. 12^th, 1977 show a cavitation and bubble suppressor in a fluid passing through a high pressure relief valve, where that fluid is coming from a valve with high counter pressure on the discharge line of the relief valve. The high-pressure valve has pistons with differential area which keeps the counter pressure on a fixed rate with respect to the high pressure until reaching the relief valve's input. This rate is at least 1:3.

Document U.S. Pat. No. 4,739,794 (Ballum) of Apr. 26^th, 1988 show an anticavitation configuration for a rotary valve that includes a bypass conduit on the flow passage that connects the upstream and downstream terminals of the valve's passage. A manual valve is placed in the conduit and it is open to measure a vacuum over the flux terminal downstream of the valve or by manual mechanisms to allow the process fluid to freely flow to the vacuum and, by that way, prevent cavitation.

Many documents about the previous art are using a bypass which communicates the fluid's pressure downstream and upstream of the contraction or valve, where additional devices or connections are needed to avoid cavitation, increasing the total cost of the solution.

BRIEF SUMMARY OF THE DRAWINGS

The attached drawings, that are included in order to provide a better understanding of the invention, illustrate part of the previous art and an execution of the invention, along with the description, allows to explain the principles of the invention.

FIG. 1 shows the cavitation effect, that is produced at the exit of a contraction of the pipeline, when the fluid gets to a value below Pv.

FIG. 2 shows the schematic of the theory of the solution proposed by the invention, that also comes with a pressure graph.

FIG. 3 shows the product.

FIG. 4 shows the product in a different angle

FIG. 5 shows the product from a different angle

FIG. 6 shows the pipeline without the invention

FIG. 7 shows the pipeline with the invented product.

DESCRIPTION OF THE INVENTION

The anticavitation system consists of a piece of pipeline (1) of a compatible material to the fluid to handle corrosion, erosion, pressure, or temperature; This material can be Carbon Steel, Stainless steel 316 SST, 304 SST, 321 SST, Hastelloy C275, Avesta 254 smo, plastics HDPE, CPVC, etc

The schedule can vary from SCH 40 to SCH 160. The length of the pipeline (1) is designed case by case to be adopt the existing pipeline or in projects that have specific operating process conditions of flow and pressure.

The anticativation system consists also of a series of cavities (5) between the pipeline (1) that are connected using feedback of the same process fluid that is located downstream of the valve (3) in an area where P2 has stabilized, in order to provide pressure to the vena contracta to a value Pv.

The anticavitation system has a pipeline (1) that has a contraction (3), for example a control valve. Upstream of the contraction (3) a fluid that moves in a direction (2) that has a pressure P1, and downstream of the contraction (3), the fluid has a pressure P2. To avoid that the fluid pressure decreases to its steam pressure Pv, immediately after contraction (3), the system has a cavity (4) that is located downstream of the contraction, where the pressure is stable and gets to a value P2. The system has a second cavity (5) located immediately downstream of the contraction (3). Through a connection (6) the system feeds back with the stable pressure P2 to the area immediately downstream of the contraction (3) where the pressure can decrease to Pv producing a potential cavitation. Therefore, with the connection (6), the output pressure of the contraction (3) increases to a value P3, where this value P3 is higher than the steam pressure Pv and less than P2.

FIG. 3 shows the preferred model for this invention, where the product has a pipeline piece (1). In this case, te contraction (3) is not shown in FIG. 3, but it can be any type of valve, and therefore this product can be connected downstream of the valve. In the preferred model of this invention, teh cavity (4) that is downstream of the valve (3), has holes where the pressure is stable and takes a value P2. The product has a second group of cavities (5) could be also holes, that are located immediately in the exit of the contraction or vlave (3). The connection piece (6) that feed the pressure stable P2, to the area exiting the valve (3) where the pressure can reach Pv, is a space (9) composed of a surrounding (7) and the external wall of the pipeline (1), that allows the communication of the holes (4,5). This way this space allowing that the pressure that is above the holes (4), can be feeded to the exit of the valve (3), and this way allowing to reach a value P3, where this value P3 is higher than the Pv and lower than P2 downstream of the valve 93). This product can be attached to any kind of pipeline configuration, where the preferred connection (8).

FIGS. 6 and 7 shows the invention product, that can be built with a pipeline piece (1) that can be made holes in its ends, to get the cavities (4,5), and then is mounted to the surrounding (7) to make the chamber space (9)—connection (6)—where the ends can be added end connections (8) to simplify the mounting at the exit of the valve (3).

This system allows the following advantages:

• • The current systems of the previous art, such as cavitation attenuators, produce high additional pressure losses, reducing the flow capacity of the valve. This invention product shall be minimal, as it does not consider additional pieces inside the valve that could be in contact with the fluid.
  • Aspiration tubes present limitations to work with corrosive, toxic, or explosive fluids, as there are always probabilities to spill the product through the check valves. Our system considers using the same proces fluid to pressurize the vena contracta area, therefore it does not need to inject or add external fluids that need check or cut valves to control the fluid that pressurizes the vena contracts.
  • Additionally this system does not have fluid losses or spills.

Claims

1. An anticavitation system for a pipeline having a contraction, where upstream of the contraction the fluid has a pressure P1, and downstream a pressure P2, comprising:

a first cavity downstream of the contraction where the pressure is stable and has a value P2;

a second cavity located immediately downstream of the contraction;

a connection device connecting the first cavity with the second cavity and feeds back the stable pressure P2, to the contraction area.

2. A system; according to claim 1, characterized in that the pressure outside the contraction reaches a value P3 that is less than P2.

3. A system according to claim 1, characterized in that contraction is a valve.

4. A system, according to claim 1 characterized in that the first cavity is a group of holes.

5. A system according to claim 1 characterized in that the second cavity is a group of holes.

6. A system according to claim 1 characterized in that the connection media comprises a chamber having a surrounding and the external wall of the pipeline.

7. A system according to claim 1 characterized in that the system has in its extremes flanges for connection to any kind of pipeline installation that has fluid.

8. A system according to claim 1 characterized in that the pipeline material is compatible with the characteristics of the fluid.

9. A system according claim 1, characterized in that the pressure exiting the contraction reaches a value P3, where this value P3 is higher than Pv.

10. A system according to claim 1 wherein the characteristics of the fluid is at least one selected from corrosion, erosion, pressure, and temperature,

11. A system according to claim 1 wherein the pipeline material comprises Carbon Steel, Stainless Steel 316 SST, 304 SST, 321 SST, Hastelloy C275, Avesta 254 smo, plastics HDPE, or CPVC.