The invention relates to a degasifying apparatus for eliminating gases such as ambient air from fluids such as oil.
Air may be present in dissolved and in undissolved form in pressure fluids such as hydraulic fluids. Although dissolved air is not visible in the fluid or oil, it is always present to a certain extent. Undissolved air is not always present in the fluid or oil, but when it is, it is visible as a second phase. Although the properties of pressure fluids, such as viscosity, compression modulus, and lubricating capacity, are substantially impaired by undissolved air, dissolved air in also affects certain properties of the pressure fluid, for example ageing behavior and cavitation tendency.
The maximum amount of air that can be dissolved in the fluid concerned is determined by the saturation curve of the fluid concerned. However, in principle, solubility increases with increasing pressure and to a lesser extent is also dependent on temperature. Because pressures and temperatures in hydraulic systems vary over time as well as according to location, a drop in pressure and consequent lowering of the solubility limit can result in air dissolving out during operation. As a result, the formation of a second phase (bubbles) and thus damage, for example by flow cavitation, can be expected, especially in areas of low static pressure, such as control cross sections of valves. Because the outgassing rate is greater than the dissolution rate, resulting air bubbles remain even when the pressure in the fluid increases again, thereby altering the properties of the pressure fluid on the one hand and possibly resulting in damages due to cavitation erosion upon a subsequent pressure increase on the other hand. In order to ensure reliable operation of hydraulic systems, it is therefore necessary to take measures for degasifying the pressure fluid. Vacuum evaporation is the process currently employed for achieving a particularly effective degasification, in which the degassed fluid contains only a small residual contamination. Although this has the advantage that water is simultaneously eliminated, the very high energy requirement and the elaborate construction of the apparatus are disadvantageous. In addition there is usually an undesired heating of the fluid, and it is not possible to integrate the degasifying apparatus in a main fluid flow of the fluid system.
In view of these problems, the object of the invention is that of providing a simple and cost-effectively operable degasifying apparatus for fluids such as hydraulic fluid.
According to the invention, this object is achieved by a degasifying apparatus having the features of claim 1 in its entirety.
Accordingly, the invention provides a permeation process for desgasifying, which takes place through a membrane. For separation, use is made of a dense membrane without pores, through which a diffusion process takes place. In comparison to other desgasifying techniques such as vacuum evaporation, the diffusion process can be carried out with very little energy use, as only a partial pressure gradient at the membrane is needed as a driving force. For desgasifying pressure fluids such as hydraulic fluid in hydraulic systems, the available pressure in the system can be used to increase the partial pressure differential. By means of the apparatus according to the invention, in which the degasifying is effected by allowing the fluid to flow over a membrane, the degasifying process can be advantageously carried out within the system, namely in a bypass of the pressure system as well as in a main volume flow of the system.
The permeable membrane used in the apparatus according to the invention can comprise a silicone material, and can preferably be composed entirely of silicone.
In particularly advantageous exemplary embodiments, a support body composed of a wire gauze, a sintered metal, a ceramic, or other structure, each having passages or pores, of which the free cross sections permit a gas passage, is provided for supporting the permeable membrane.
The permeable membrane with its support body can separate a fluid side from a gas side in a container, or the membrane can comprise a fluid guide. In this manner, the degasifying process can take place on a volume flow of a hydraulic system, flowing through a conduit encased by the tubular support body, against the inside of which the permeable membrane that separates the free cross section of the conduit from the exterior support body in a fluid-tight manner rests.
In advantageous exemplary embodiments, the permeation coefficient Q of the silicone membrane is 200 to 600×10−17 m2/s/Pa, preferably in the range of values from 300 to 400×10−17 m2/s/Pa, and particularly preferably in the range of values from 370 to 380×10−17 m2/s/Pa. Silopren®LSR 2640 is a commercially available silicone rubber that can be advantageously used as a silicone membrane.
With particular advantage, the degasifying apparatus can be integrated in a hydraulic system comprising a low pressure and a high pressure hydraulic accumulator, which are hooked up as an energy recovery device on the gas side to a hydrostatic drive, which preferably enables a four quadrant mode of operation, wherein the permeable membrane degasifies the fluid on the low pressure side of the energy recovery device.
With particular advantage it can be arranged such that the low pressure side of the energy recovery device is hooked up to the container with the permeable membrane, on the fluid inlet side of said container, and that the fluid outlet side of the container is hooked up to a transport device in the form of a spring-loaded differential piston pump or a Venturi nozzle. The degasifying apparatus thus forms a bypass to the low-pressure side of the energy recovery device.
In order to actuate the spring-loaded differential pressure pump, the larger piston face thereof can be subjected to the pressure of the low-pressure side of the low-pressure accumulator. The system pressure of the low-pressure side thus supplies the drive for the transport device.
The gas side of the container can have ambient pressure or it can be hooked up to a suction device, which increases the partial pressure differential on the membrane.
In particularly advantageous fashion, this suction device can have another spring-loaded differential piston pump, the larger piston face of which can be subjected to the pressure of the low pressure side of the low pressure accumulator for actuation and the movement of which is pressure-synchronized with the first differential piston pump. The system pressure of the low-pressure side thus also supplies the drive for the suction device.
The invention is explained in detail below, with reference to exemplary embodiments illustrated in the drawings, wherein:
With reference to
In these exemplary embodiments, the associated degasifying apparatus according to the invention has a container 14, to which the fluid 22 to be degasified can be conducted from the low pressure side 16 of the energy recovery device via a line 18, which opens into the bottom of the container 14 via a pressure relief valve 20. From the container 14, the fluid 22 can be returned to the low-pressure side 16 via another line 24. In this arrangement, the degasifying apparatus forms a bypass to the low-pressure side 16 of the associated system.
In the container 14, a membrane 26 separates the chamber containing the fluid 22 to be degasified from a chamber 28 that receives the gaseous phase that has passed through the membrane 26 by diffusion. From the top side of the chamber 28, this air that has been degassed from the fluid 22 passes to the surroundings 32 via a line 29 and via a venting filter 30. The pressure relief valve 20 is set to a value at which the acting pressure of the low-pressure side 16 is reduced to a value that corresponds to the partial pressure gradient at the membrane 26 desired for the diffusion process, in other words the pressure gradient relative to the ambient pressure prevailing in the chamber 28.
A transport device 34 is situated in the line 24 that is provided for the return flow of the fluid 22 from the container 14 to the low-pressure side. In the example of
The exemplary embodiment of
Besides the differential piston pump 36 that forms the transport device 34, a second differential piston pump 70 is provided as a suction device 68 in the exemplary embodiment of
The exemplary embodiment of
As in the examples described above, the membrane 26 can advantageously be made of a silicone material having a thickness of 1 mm to 2 mm, for example Silopren®LSR 2640, wherein the thickness of the material is selected such that the permeation coefficient Q lies in an advantageous range of values, preferably in the range of between 370 and 380×10−17 m2/s/Pa.
Number | Date | Country | Kind |
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10 2015 014 496.0 | Nov 2015 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2016/001595 | 9/23/2016 | WO | 00 |