DEVICE AND METHOD FOR DETERMINING THE WEIGHT OF A HYDRAULIC ACCUMULATOR

Abstract

The invention relates to a device for determining the weight of a hydraulic accumulator (10) during the operation thereof in a hydraulic facility, where a pressurised liquid is introduced into a pressure vessel at least partially filled with a gas, said pressurised liquid compressing the gas and being stored in such a way that when it leaves the accumulator (10), hydraulic energy is emitted to the facility, and where the respective current weight of the hydraulic accumulator (10) is detected by means of a weighing device (14) applied to the hydraulic accumulator (10).

Claims

1. A device for determining the weight of a hydraulic accumulator (10) during operation within a hydraulic plant, in which a pressurized liquid is introduced into a pressure vessel that is at least partially filled with gas, in which the gas is compressed and the liquid is stored under pressure in such a way that, at its discharge from the accumulator (10), hydraulic energy is released to the plant, and in which the current weight of the hydraulic accumulator (10) is determined by a weighing device (14) that engages with the hydraulic accumulator (10).

2. The device according to claim 1, characterized in that the weighing device (14) is provided with a seat (18) that surrounds the housing (16) of the hydraulic accumulator (10) at least partially, or onto which the hydraulic accumulator (10) can be seated with its bottom end, and that the seat (18) interacts with a measuring facility for determining the weight of the hydraulic accumulator (10).

3. The device according to claim 1, characterized in that the measuring facility comprises at least one load cell (22) with a bending beam (24) and at least one strain gauge disposed thereon.

4. The device according to claim 1, characterized in that the measuring facility is connected to a signal amplifier for the purpose of visualizing its measuring result.

5. The device according to claim 1, characterized in that the load cell (22) is designed as double bending beam made from a metallic material of preferably rectangular cross-section.

6. The device according to claim 1, characterized in that disposed on the upper side of the respective load cell (22) is the collar together with the associated components for supporting the hydraulic accumulator (10).

7. The device according to claim 1, characterized in that the seat (18) takes the form of a support ring (28), on which the bottom end of the hydraulic accumulator (10) rests and at least partially engages with the opening of said support ring (28), and that the support ring (28) is supported by at least three sensing columns (34) that are disposed at a distance from each other, which stand on three associable load cells (22) that are braced at the bottom against an equipment ring (32), which is firmly attached to the load cells (22).

8. The device according to claim 1, characterized in that the respective support ring (28) surrounds a passage opening in such a way that liquid-conducting tube can be connected to the pressure vessel on the liquid side of the hydraulic accumulator (10).

9. A method for the implementation of a weight measurement on a hydraulic accumulator to determine the present gas volume at the gas side of the hydraulic accumulator (10), in which it is determined, based upon a reference value for the stored gas volume, how the said stored gas volume diminishes if, at a predeterminable operating state of the hydraulic accumulator (10) the volume of the liquid in the liquid side of the hydraulic accumulator (10) increases.

10. A method for the implementation of a piston position measurement in a piston accumulator (12) by means of a weight measurement for determining the respective current piston position wherein, based upon a reference value for a predetermined piston position, how said piston position changes if, at a predeterminable operating state of the piston accumulator (12) the gas volume in the gas side diminishes and the volume of the liquid in the liquid side of the piston accumulator (12) increases.

Description

[0014] The device according to the invention for determining the weight of a hydraulic accumulator will now be explained in greater detail by way of exemplary embodiments shown in the drawings. Shown are, in schematic form and not to scale, in

[0015] FIGS. 1 & 2 a perspective view of a piston accumulator or a bladder accumulator respectively including the associated weighing device;

[0016] FIGS. 3 & 4 once in perspective view and once in side elevation, the weighing device used for a bladder accumulator according to FIG. 2.

[0017] FIG. 1 depicts a device for determining the weight of a hydraulic accumulator 10 in form of a piston accumulator 12 in which the respective actual weight of the accumulator 10, 12 is ascertained by means of a weighing device 14 that engages with the hydraulic accumulator 10.

[0018] Such hydraulic accumulators are also called hydropneumatic accumulators or simply accumulators in the industry. The basic purpose of such hydraulic accumulators is to store a liquid, in particular in form of a hydraulic medium, under pressure inside the accumulator. When discharging the liquid inside the accumulator under the pressure of the pre-loaded gas into the hydraulic circuit of a hydraulic plant, the stored hydraulic energy can be released. To this end the respective hydraulic accumulator 10 is usually connected at its lower end through tubes (not shown in detail in FIGS. 1 and 2) to a hydraulic circuit or a hydraulic plant (not shown). The pressure of the liquid in the accumulator compresses a gas, usually in form of nitrogen, inside the hydraulic accumulator. After the volume discharge described above the accumulator gas expands and the pressure at the gas side is reduced. The gas stored inside the hydraulic accumulator and the hydraulic liquid are usually separated from each other by a separating element, which is preferably sealed against media leakage. Different separating elements are used depending on the design of the accumulator. A membrane accumulator uses a membrane as separating element; a bladder accumulator an elastomer bladder, a piston accumulator a piston and a bellows-type accumulator a metal bellows as separating member or separating element. The object of the separating member or separating element is to provide a separation between gas and liquid over a prolonged operating period of the respective hydraulic accumulator, wherein the loss of gas via the separating element into the liquid side of the accumulator can basically not be avoided.

[0019] The actual loss of gas essentially depends on the type of elastomer used for the separating membrane or the accumulator bladder, as well as the liquid used and the molecule size of the accumulator gas. Further influencing variables are predetermined by the choice of material and the thickness of the separating element, but the pressure differences during operation of the hydraulic accumulator between gas and liquid side as well as the number of load cycles in operation and the operating temperature of the hydraulic accumulator also play a significant role. Piston accumulators can generally lose gas from the gas side of the piston accumulator to its liquid side via the sealing system of the separating piston, which is guided along the inner circumference of the accumulator housing or pressure housing. The above-mentioned metal bellows accumulators, which are another kind of hydraulic accumulators, are on the other hand virtually gas-tight and have no permeation since the bellows-like metal membranes commonly used in them do not let any gas through, even at high temperatures; only in the instance of failure, that is, when the metal bellows rips, the accumulator also loses its ability to function, which also applies for failures of the separating element of membrane accumulators, bladder accumulators and piston accumulators.

[0020] The equations for the change of state of gases are used for sizing of the respective hydraulic accumulator, wherein nitrogen is commonly used as accumulator gas for hydraulic accumulators. When calculating and sizing accumulators the ideal change of state in gases is often used, whereas at very high pressures the respective real gas characteristics must be taken into consideration. Moreover, iterative computations are used under consideration of measured values for pressure change, temperature change and volume change.

[0021] As already explained, the functionality of the respective hydraulic accumulator is diminished if, due to losses, there is insufficient accumulator gas present in the gas side that is under a predeterminable pressure inside the accumulator 10. In this instance the liquid side of the hydraulic accumulator 10 necessarily takes up more liquid, which can easily be measured via the weighing device 14 for the hydraulic accumulator 10.

[0022] It is therefore possible, for example, to determine the empty weight by means of the weighing device 14 prior to taking the hydraulic accumulator 10 into service and, based upon reference values of known, functional accumulators it is possible to set the ideal liquid filling volume inside the hydraulic accumulator 10, the weight of which is detected by the weighing device 14. It is therefore known very accurately what the weight of a hydraulic accumulator 10 of a certain type and size in service should be to be operational. In the instance that the gas volume in the gas side decreases unintentionally during operation of the accumulator, the volume of the liquid in the liquid side increases correspondingly, depending on the operating cycle, and the resulting increase in mass or weight is registered by the weighing device 14. As soon as any predeterminable limit values are exceeded, the hydraulic accumulator 10 is recognized as being diminished in functionality or as inoperative with the result that the gas in the gas side is replenished at a predeterminable pressure, or it is replaced by a new accumulator.

[0023] Since the weighing device 14 is permanently attached to the hydraulic accumulator 10 and takes measurements continuously, it is possible to register trends via an evaluation and diagnosis unit (not shown in detail) and so determine for how long the accumulator may be functionally reliable. If the respective separating element fails, in this instance in form of a separating piston for the piston accumulator 12, the weighing device 14 detects this immediately since the entire hydraulic accumulator 10 fills up rapidly with liquid, wherein the rapidly rising liquid inrush is interpreted by the weighing device 14 together with the connected electronic evaluation unit as a failure of the hydraulic accumulator 10, which makes it particularly sensible to use such weighing devices 14 for those hydraulic accumulators 10 in machine components that are used, for example, in the power generation sector, if they are to ensure their reliability in the instance of failure by providing their function also in a breakdown situation.

[0024] By determining the state of the liquid and gas volumes through the weighing device 14, it is indirectly also possible to establish the piston position inside the accumulator housing of the piston accumulator 12, which in turn gives an indication regarding the desired unrestricted movement of the piston as separating element inside the accumulator housing 16.

[0025] The tube connections (not shown) of the hydraulic plant to which the hydraulic accumulators 10 with their liquid side are commonly connected at their bottom end have only a very indirect negative effect on the weight measurement by means of the weighing device 14 since the tubing is necessarily flexible and their influence on the weight can be compensated for by the electronic evaluation unit to which the weighing device 14 is connected. Erroneous measurements due to respective operating conditions of the hydraulic accumulator 10 are therefore excluded.

[0026] According to the representation in FIG. 1 the weighing device 14 is provided with a circular seat 18, which tightly encloses the bottom end 20 of the housing 16 of the hydraulic accumulator 10 so that the pressure vessel of the hydraulic accumulator 10 can be placed with its bottom end onto the seat 18 and is retained there. The seat 18 therefore supports the piston accumulator 12 in the manner of a weighing pan. The seat 18 is part of the weighing device 14, and the associated measuring facility comprises a load cell 22 with a bending beam 24 and at least one strain gauge (not shown) that is attached thereto. Load cells 22 of this kind are also called platform load cells in the industry. They may, for example, be purchased under the trading name PW12C . . . from the German company Hottinger Baldwin Messtechnik GmbH. The respective load cell 22 may also be designed as a double bending beam made from a metallic material, such as aluminum, with a preferably rectangular cross-section. Moreover, said measuring facility may also be connected to a signal amplifier of the electronic evaluation unit in order to visualize the measuring results. A suitable signal amplifier, for example DAD141.1, may be purchased from the company Soemer.

[0027] The annular seat 18 consists of a solid metal ring, which makes it possible for the tube connections (not shown) at the liquid side of the piston accumulator 12 to pass through the ring. According to the representation in FIG. 1, moreover, the respective collar in form of the seat 18 is, together with the associated components for mounting the piston accumulator 12, mounted to the seat 18 at the upper end of the respective load cell 22.

[0028] A weight measurement for a bladder accumulator 26 of a commonly used design is depicted in the embodiment according to FIG. 2. Through consideration of reference values for comparable bladder accumulators, and preferably based upon the determination of the weight when empty by means of the weighing device 14, it is now for the first time possible for a bladder accumulator 26 to ascertain a value for the fill level of the accumulator on the gas side in order to obtain an indication concerning the functionality and functional reliability of the bladder accumulator 26.

[0029] To this end the bladder accumulator 26 is inserted with its bottom end into a support ring 28, which is part of the already described seat 18. As is shown in particular in FIG. 3, the depicted support ring 28 is closed and is disposed at the upper side onto a slotted attachment ring 30, which is also part of the seat 18 and thus part of the weighing device 14. An equipment ring 32, which has a slot that corresponds to the attachment ring 30, extends coaxial to the support ring 28 and the attachment ring 30 below both said rings. The equipment ring 32 is also part of the weighing device 14 as a whole, and with it the weighing device 14 can be stood on a floor or other surface together with the bladder accumulator 26. Three load cells 22 are disposed and firmly attached on the upper annular ring surface of the equipment ring 32, wherein said load cells 22 carry at their top side a sensing column 34 each, which engage with their free upper end with the underside of the attachment ring 30.

[0030] The load cell 22 according to the embodiment in FIGS. 2 to 4 may be purchased under the product name K2A at the German company Wgetechnik Kohn GmbH. Said load cell K2A is part of the series of so-called double bending beam load cells that have an aluminum housing of a rectangular cross-section. The above-mentioned strain gauges are disposed on the upper and lower side. To this extent the sensing columns 34 are in operative connection with the upper strain gauge DMS of the load cell K2A.

[0031] Thus, with the combination of components depicted in FIGS. 3 and 4 a weighing device 14 has been provided as a measuring facility, which permits the acquisition of measurements concerning weight or mass respectively at any stage of fill level of hydraulic accumulators 10, such as, for example, the bladder accumulator 26 shown in FIG. 2. The load cells 22 described above have proven to be particularly suitable so that conclusions may be drawn, indirectly via the weight measurement of the hydraulic accumulator 10, to its current gas charging state. This has no equivalent in the prior art.