GB2417050A

GB2417050A - Pulsation damper for pipe system

Info

Publication number: GB2417050A
Application number: GB0515933A
Authority: GB
Inventors: Luca Frediani
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-08-04
Filing date: 2005-08-03
Publication date: 2006-02-15
Also published as: AT500633B1; AT500633A3; DE102005036109A1; GB0515933D0; CH698080B1; AT500633A2

Abstract

A pulsation damper for damping fluid pressure vibrations in fluid pipes has at least two hermetically sealed damping elements 1a, 1b in the form of hollow bodies comprising a flexible and elastic membrane e.g. polypropylene, polyethylene containing a compressible medium e.g. air. The damped fluid can pass at least partially through the intermediate space between the elements which may be formed from tube welded into segments and with a fluid flow bore 4 formed in a connecting web. The damping elements can be arranged in a bypass arrangement in a housing communicating with the inside of the fluid pipe by an orifice which may be covered with a grid. The elements may be arranged in a cylindrical manner in a cage directly within the pipe. Used with eccentric, diaphragm or gear pumps in metering applications.

Description

24 1 7050

PULSATION DAMPER

Field of the invention

The invention relates to a pulsation damper according to the preamble of claim 1.

Background of the invention

Pulsation dampers are known to be used for damping liquid pressure variations in liquid pipes and fuel pipes.

Thus, DE 195 28 737 A1 describes a bypass pressure regulator for a fuel feed system, which regulator has a membrane arranged in a housing between a pressure- relieving first chamber and a second chamber containing liquid fuel. DE 41 43 507 C2 describes a pressure pulse damper in the form of a toroid which is shaped like a truncated cone, which pressure pulse damper is filled with compressed air and is arranged inside the pressure space of the fuel pump. DE 44 31 770 A1 discloses a pressure pulse damper for a fuel pump, which pressure pulse damper is produced from a thin-walled tube of flexible and resilient plastic. For reasons of operational safety, a plurality of gas-filled chambers is preferably provided. DE 44 43 623 provides a bellows-like pressure pulse modulator which is connected to the fuel duct so that existing pressure variations are substantially eliminated and the pump noise can be very greatly reduced.

Such arrangements which are intended for thefairly rough use in fuel pipes are, on the other hand, not suitable for damping high-frequency pulsations and/or pressure variations having small amplitudes. Pressure regulators which, as described above, provide membranes for pressure absorption with elasticity prove to be too sluggish for use in pumps which are used in coating technology or laboratory technology and cannot achieve the desired damping.

Brief description of the invention

Accordingly, it is the object of the invention to provide a pulsation damper which, for example, further improves the pressure constancy even in the case of the volumetric pumps, such as monoscrew pumps or eccentric screw pumps, which are considered to be substantially free of pulsation. The pulsation damper is also to be used in pipe and tube systems susceptible to vibration.

The vibrations occurring in such systems are substantially of a highfrequency nature, and the use of known pulsation dampers proves to be unsatisfactory owing to the inertia of the membranes used.

Pressure variations and hence variations of the delivery also occur in the case of the volumetric membrane or gear pumps used for conveying fluids; these vibrations can be minimized by using the pulsation damper according to the invention.

This object is achieved by realizing the defining features of claim 1. Alternative or preferred embodiments are described in the dependent claims.

The absorption of the pulsation energy is permitted virtually over the total surface of the damping element because the at least two hermetically sealed damping elements of the pulsation damper according to the invention, but in particular a plurality of said damping elements, which consist of a flexible and resilient membrane and which contain a compressible fluid medium, are separated from one another by means of an intermediate space through which passes the fluid whose pressure variations are to be damped. The pressure is not removed, as, for example, in the case of the known membrane damping members, but instead virtually the total surface of the damping elements is in contact with the fluid and the pressure on the membrane wall of the damping elements remains constant.

The pressure inside the damping element and the external pressure always remain substantially of the same magnitude. Even very thin and hence reactive membranes as wall material for the damping elements can thus be used without problems. Fatigue tears in the membrane surface can thus be substantially avoided.

The damping elements of the pulsation damper can be arranged in a housing, as a bypass arrangement, connected to the fluid pipe via an orifice through which the fluid can flow into the housing and emerge therefrom again substantially unhindered. In order to keep the damping elements positioned in the housing, a lattice-like cover of the orifice can additionally be provided.

Cage-like structures can also be coordinated directly with the inner wall of the fluid pipes, these structures then ensuring that fluid flows directly around the damping elements in the fluid pipe, for example said structures can be arranged in an annual manner on the inner wall.

Particularly in the case of special applications of pumps which are used, for example, for exact metering of media, such as eccentric screw pumps, the accuracy of metering of said pumps can be substantially improved by the use of the pulsation damper according to the invention. The size and number of the damping element can be chosen as a function of the pressure conditions and pressure variations present in the fluid pipes. The shape of the hollow body - ideally spherical - is determined from the ratio of surface to volume, which ratio should be as large as possible in order to be able to react virtually without delay to pressure variations.

For relatively low pressures of a few bar, such as, for example, in pumps which are used in laboratory or coating technology, the damping elements simply for economic reasons - are preferably filled with air at atmospheric pressure, and polypropylene or high-density polyethylene has proven to be useful as a material for the damping element membranes. PTFE, for example, is preferably used when fluids to which aggressive media have been added are used.

In the case of larger machines from which pipes lead away and to which pipes lead, vibrations occur in the pipes or the pipes themselves vibrate, the resulting pressure variations can have an adverse effect on the accuracy and service lives of the systems, and premature wear and unnecessary repair costs can result.

The associated noise annoyance for personnel is also negative.

At relatively high pressures of about 10 bar, as occur, for example, also in water pipes, the damping elements are filled with compressed air in order to provide a sufficient initial tension.

The individual hollow bodies can be produced in a simple and economical manner from plastic tubes filled with the fluid medium, such as air or compressed air, by creating in each case cushion-like compartments by heat-sealing or adhesive bonding. The damping elements produced in this manner are preferably separated from one another or - if reliable relative positioning of the individual damping elements in the fluid pipe is required - the connecting parts between the damping elements are provided with orifices, for example in the form of perforations, in order to ensure that the fluid flows reliably around the damping elements.

Brief description of the drawings

The invention is described below purely by way of example with reference to drawings.

Fig. la and lb show the schematic diagram of the hollow body elements of a pulsation damper according to the invention; Fig. 2 shows bypass arrangements of the pulsation damper according to the invention in a fluid-conveying pipe and tube system; Fig. 3 shows a possible arrangement of the pulsation damper inside a fluid-conveying pipe and tube system; Fig. 4a and 4b show the pressure curve (p in bar) of a mixing component having transport in an eccentric screw pump, with and without the use of a pulsation damper according to the invention.

Detailed description of the invention

Figures la and lb show - in each case in cross-section - firstly an individual damping element la and secondly damping elements lb which are connected to one another via a connecting part. The damping elements la and lb are approximately spherical, lenticular or doughnut- shaped hollow bodies, and the enveloping surface is formed from resilient, flexible material, such as, for example, polypropylene or high-density polyethylene.

The interior 2 of the hollow bodies la, lb is - depending on the intended use - filled with a compressible, fluid medium, in practice air at atmospheric pressure for applications in fluid pipes in which pressures of a few bar prevail, or compressed air for applications in which pressures of about 10 bar or more occur. As is evident from Figure lb, the damping elements can be produced in a simple and economical manner from an elongated tube filled with the medium, by welding together said tube segment by segment.

Thereafter, the individual damping elements are separated from one another at the resulting connecting parts 3, or (and this can simplify, for example, an arrangement according to Figure 3), orifices 4 are arranged which are dimensioned so that virtually unhindered passage of the fluid is possible. As is evident in particular in Figure la, pressure variations which occur in the fluid surrounding the damping element la are taken up over the total surface of the damping element, substantially uniformly distributed on all sides. The pressure pulses are taken up as a whole by the damping element and absorbed by compression of the medium contained. Because of the geometry of the damping element, the membrane envelope is contacted in each case with the same pressure difference, signs of fatigue are minimized and the life of the pulsation damper is considerably increased.

Figure 2 shows arrangements of pulsation dampers 8 according to the invention on pipe and tube systems 6 and 7, respectively. The damping elements la introduced individually and loosely into a housing 10 are connected to the fluid pipe via a bypass connecting piece 11 through which the fluid flows unhindered into the housing and can flow around the damping elements on all sides. To ensure that the damping elements la - if the cross-section of the connecting piece 11 is chosen to be correspondingly large - are kept in the housing 10, the inlet orifice of connecting piece 11 into the housing 10 is covered with a grid which permits substantially unhindered passage of the fluid. It would also be possible to provide a plurality of connecting orifices between fluid pipe and housing, optionally in an upward and downward direction of the pipe, with the result that improved flow through the housing is possible.

As shown in Figure 2, the pulsation damper - independently of whether the fluid pipe is designed as a pipeline or tubing - can be arranged as close as possible to the pump 5, for example membrane, gear or eccentric pump or other pump types, or the consumer 9, for example a coating nozzle. For best results, pulsation dampers can be provided both close to the pump and close to the consumer. Consequently, on the one hand pressure pulses are reduced on the pump side and on the other hand variations of the amount of fluid delivered via the consumer, which arise as a result of pressure variations which are inherent in the pipe or tube system, are reduced.

As is evident from Figure 2, the pulsation dampers 8 contain a plurality of damping elements la. The individual elements act in their totality but, as described above, are elements independent of one another. Even if one element was to be faulty or a few of these elements were to be faulty, this would have virtually no adverse effect on the mode of action of the pulsation damper Figure 3 shows a further possibility for arranging the pulsation damper. Here, the damping elements la are kept directly in the fluid flow, for example coordinated with the inner surface of the pipe 6. The individual damping elements la can be arranged loosely in one layer or a plurality of layers in a substantially cylindrical manner, and a cage-like structure lla ensures unhindered flow of the fluid through this structure and around the damping elements la. Alternatively, damping elements lb (corresponding l to Figure lb) connected to one another via connecting parts 3 provided with orifices 4 could also be arranged in an annular manner on the inner surface. Optionally, a retaining structure could then be dispensed with.

Below, an exemplary use of the pulsation damper according to the invention is described with reference to Figures 4a and 4b. Figure 4a shows the pressure curve of a component of a component mixture transported in an eccentric screw pump, at measuring intervals of in each case 5 sec. As is evident, pressure variations have a high frequency in the region of 100 Hz and are on average 1%. Pumps having such characteristics are considered to be virtually pulsation-free and are used for exact metering in mixing systems. However, for special applications, such as, for example, the use as a metering pump in coating technology, even such small pressure variations no longer result in tolerable metering variations. It has been found that, when a pulsation damper according to the invention is arranged close to the pump, the pressure variations can be reduced by about 80%, to 0.2%. In the case considered a four-speed eccentric screw pump was used for metering a dispersion. The damping elements - in this case in a bypass arrangement in a housing close to the pump - were produced from a thin, commercial high density polyethylene layer and filled with air at atmospheric pressure and were approximately spherical, having a diameter of about 5 cm.

Claims

PATENT CLAIMS

1. Pulsation damper for damping fluid pressure vibrations in fluid pipes, comprising at least two hermetically sealed damping elements (la, lb) in the form of substantially spherical hollow bodies comprising a flexible and resilient membrane, which hollow bodies contain a compressible fluid medium, characterized in that the fluid can pass at least partly through the intermediate space between the at least two damping elements.

2. Pulsation damper according to Patent Claim 1 as a bypass arrangement of the fluid pipe, characterized in that the at least two damping elements are arranged in a housing connected to the interior of the fluid pipe via at least one connecting orifice, in particular the at least one connecting orifice between fluid pipe and housing being covered by a grid- like structure which does not inhibit the fluid flow.

3. Pulsation damper according to Patent Claim l, characterized in that the at least two damping elements are arranged in the region of the inner surface of the fluid pipe, in particular in an annular manner, in particular means for keeping the at least two damping elements positioned in this region being provided.

4. Pulsation damper according to Patent Claim 3, characterized in that the means for positioning are provided as a grid-like structure which does not inhibit the fluid flow.

5. Pulsation damper according to any of the preceding Claims, characterized in that the material of the membrane consists of polypropylene (PP) or high density polyethylene (HDPE).

6. Pulsation damper according to any of the preceding Claims, characterized in that the fluid medium is air.

7. Pulsation damper according to any of the preceding Claims, characterized in that the at least two damping elements are connected to one another via a web provided with at least one orifice, in particular with a plurality of perforations.

8. Pulsation damper according to any of the preceding Claims for use in eccentric pumps, in particular for suppressing metering variations.

9. Pulsation damper according to, any of the preceding Claims for use in diaphragm or gear pumps.

9. Pulsation damper according to any of the preceding Claims for use in diaphragm or gear pumps.

Amendments to the claims have been filed as follows

PATENT CLAIMS lid

1. Pulsation damper for damping fluid pressure vibrations of high frequency in the region of about 100 Hz in fluid pipes of eccentric screw pumps, volumetric membrane or gear pumps, having relatively low pressures of a few bars, comprising at least two hermetically sealed damping elements (la, lb) in the form of substantially spherical hollow bodies comprising a flexible and resilient membrane, which hollow bodies contain a compressible fluid medium, characterized in that the fluid can pass at least partly through the intermediate space between the at least two damping elements.

3. Pulsation damper according to Patent Claim 1, characterized in that the at least two damping elements are arranged in the region of the inner surface of the fluid pipe, in particular in an annular manner, in particular means for keeping the at least two damping elements positioned in this region being provided.

5. Pulsation damper according to any of the preceding Claims, characterized in that the material of the membrane consists of polypropylene (PP) or high density polyethylene (HOPE).

6. Pulsation damper according to any of the preceding Claims, characterized in that the fluid medium is alr.