Ultrasound testing device for gas pressure accumulators

An ultrasound testing device for gas pressure accumulators is used to test a predeterminable set position that can be taken by a movable separating element inside an accumulator filled with gas and connected to a fluid circuit. The separating element has at least one testing body associated with a visible mark which indicates the set position of the separating element. An ultrasound testing device on a testing body can be set on the accumulator in alignment with the visible mark. This testing device allows a plurality of accumulators of the same type to be tested for their predeterminable gas pressure set value, which corresponds to the gas pre-filling pressure, by a single hand apparatus. This kind of test is economical and achieves reliable results.

FIELD OF THE INVENTION 
The present invention relates to a device to monitor or control a 
predetermined set position, which can be sensed, of a movable separating 
element within an accumulator. The accumulator can be filled with gas and 
can be connected to a fluid circuit. The separating element position in 
the accumulator can be sensed by an ultrasound testing device mountable on 
the accumulator. 
BACKGROUND OF THE INVENTION 
Such accumulators can be called gas pressure accumulators, piston 
accumulators, diaphragm accumulators and bubble accumulators. Each 
accumulator has a predetermined pressure set value on the gas side before 
connection thereof to the fluid circuit. This value can be indicated as 
the initial gas pressure of the accumulator. In such accumulators, it is 
necessary at certain time intervals to monitor and control the initial gas 
pressure required for precise and safe operation. Some gas leakage is to 
be dealt with dependent upon the manner of operation of the accumulator. 
Furthermore, in safety devices, the gas level or gas pressure may not drop 
below a minimum level in an accumulator to guarantee that the system 
continues to operate. 
German Patent No. 40 06 905 A1 (corresponding to U.S. patent application 
Ser. No. 07/664,285, entitled Method and Apparatus For Maintaining A 
Predetermined Theoretical Pressure Level and filed in the name of 
Karl-Eberhard Baldauf on Mar. 5, 1991, now abandoned, the subject matter 
of which is hereby incorporated by reference) discloses maintaining a 
predeterminable pressure set value in the accumulator by a measuring 
process in which at least at certain time intervals a connection for 
charging the gas is produced between the accumulator and a measuring 
chamber, having only a portion of the accumulator volume, while the 
measuring chamber is accessible through a suitable pressure measuring 
device. To maintain the predeterminable set pressure level when a pressure 
drop occurs, the connection is produced between the accumulator and a 
filling device through the measuring chamber. The measuring chamber then 
serves as a dosing chamber until the actual pressure level in the 
accumulator is again identical to the set value. High-cost and highly 
technical equipment is required for this known process for establishing 
gas pressure. Completely automatic operation is possible only with a 
control means of complicated construction. Thus, this known monitoring 
device is costly in construction and operation. 
To limit the technical equipment outlay, a bubble accumulator is disclosed 
in the subsequently published German Patent No. 41 16 482 (corresponding 
to U.S. patent application Ser. No. 08/119,147, entitled Method of 
Measuring The Pressure Of A Gas In A Gas Accumulator And Device For 
Carrying Out The Method, and filed on Sep. 22, 1993 in the names of 
Gunther Peter and Norbert Weber, now U.S. Pat. No. 5,445,034, the subject 
matter of which is hereby incorporated by reference), to measure the gas 
pressure set value associated with the separating element (bubble 
accumulator) in a predeterminable position by means of a pressure pickup 
on the fluid side. The control of the position of the separating element 
occurs through the contact/closing position of the poppet valve of the 
accumulator. The contact position is controllable by means of a control 
device. However, considerable technical outlay is required for each 
individual accumulator to be controlled. Furthermore, the measuring device 
required for processing of the position data of the poppet valve and to 
pick up the values from the pressure level pick-up on the fluid side is 
technically costly. Thus, this monitoring device is costly in production 
and operation. 
German Patent No. 26 49 049 A1 discloses a device for monitoring the 
position of a separating element movable within an accumulator in the form 
of a hydraulic cylinder. An ultrasound testing device is present in and 
arranged stationary on or near the bottom of the hydraulic cylinder. This 
known device detects movements and breakdown of the operation in 
underground mining operations, where the hydraulic cylinder being used 
must work safely and reliably for a long time under difficult working 
conditions. The measured path of movement of the separating element can 
also be detected from a remote station, so that central monitoring and 
control of an approximate point is possible. This device is costly and 
cost-intensive, since the controlled hydraulic cylinder is permanently 
provided with the ultrasound testing device to obtain monitoring or 
control. Additionally, the measuring and evaluating unit associated with 
the ultrasound testing device is correspondingly expensive, since the 
dynamic movements of the piston of the hydraulic cylinder are picked up by 
the monitoring system. 
German Patent No. 37 32 219 A1 discloses a method in which 
electric-magnetic ultrasound conversion is used for control of filling 
level and bubble formation in enclosures (accumulators). The ultrasound 
testing device is mounted on the outside of the accumulator, and provides 
a coupling of the ultrasound test heads without liquid/fluid coupling 
medium and without special coupling foils. This known filling condition 
and bubble detection serves for monitoring/control of liquids in nuclear 
reactor pressure containers, especially those in the form of so-called 
boiling water reactors. 
SUMMARY OF THE INVENTION 
Objects of the invention involve providing a device for monitoring or 
controlling a gas pressure set value in an accumulator, which is low-cost 
in production and operation and which can monitor a plurality of 
accumulators without modification of accumulator construction. 
The foregoing objects are basically obtained by a device for monitoring a 
predetermined set position of a separating element which is movably 
mounted in an accumulator. The accumulator is filled with gas and coupled 
to a fluid circuit. The device comprises a plurality of testing bodies 
having mounting means for attaching the testing bodies on the separating 
element at a predetermined spacing from one another, visible marking means 
for mounting on an outside periphery of the accumulator and defining the 
predetermined set position of the separating element, and a manual element 
having ultrasound testing means alignable with the markings. The manual 
apparatus is accessible to each of the testing bodies through a testing 
head. 
The manual apparatus, with the ultra-sound testing means, can be brought 
into position in alignment with the markings such that every testing body 
has a testing head at its disposal. A single testing device can monitor a 
plurality of accumulators of a certain order of magnitude for gas and 
pressure leaks. The technical equipment outlay thereby is limited. 
Furthermore, the accumulators to be monitored need not be altered or 
modified, providing an operationally safe and low-cost operation of the 
accumulator, as well as the site provided with it. Ultrasound testing 
devices have been the state of the art for many years. Many users of gas 
pressure accumulators in other technical areas, such as material testing, 
are familiar with their use, so that technical problems in the 
introduction of the monitoring devices according to the present invention 
are not expected from the users. 
By using a plurality of testing bodies, the position of the separating 
element, and therewith, the presence of the predeterminable gas pressure 
set value in the accumulator can be established. With three or more 
testing bodies a redundant system is obtained. The breakdown of one 
testing body or testing head does not cause breakdown of the entire 
monitoring device as a result. The configuration of a part of the 
ultrasound testing device as a manual apparatus allows for user-friendly 
mobile use. 
For the markings on the outside periphery of the accumulator, the spacing 
of the markings is preferably selected to be identical or equal to the 
height/level of the separating element. The manual element outside contour 
can be brought into alignment with these markings. In this manner, a 
secure positioning of the manual device within the predeterminable 
markings, which are ascertained by the set position of the separating 
element, is guaranteed, so that errors in measurement are certain to be 
avoided. The marking can also be at some slightly divergent spacing 
therefrom, so that a sort of tolerance field/range is formed. Within that 
range, the piston can assume its set position in such a manner that the 
operability of the gas pressure accumulator according to the automatically 
set values is still assured. 
In one preferred embodiment of the device according to the present 
invention, the relevant testing body is formed of a control strip and/or 
of sealing gasket of the separating element. In this manner, control 
strips and sealing gaskets, which are already traditionally provided on a 
separating element, can be used as testing bodies. Constructive 
modifications of the separating element are a waste of time and effort 
with application of additional testing bodies. 
In another preferred embodiment of the device according to the present 
invention, the manual device has an interface for connecting the manual 
device to a measuring device of the ultrasound testing apparatus. For 
this, the measuring device of the ultrasound testing apparatus can be 
arranged stationary within a hydraulic assembly. The accumulator and the 
manual device need only be connected through its interface to an interface 
of the measuring device associated with the accumulator. In one preferred 
embodiment, the measuring device is located in the manual device and the 
operator receives an optical or acoustic signal as soon as the pairs of 
testing bodies and testing sensors associated with one another lie 
adjacent to one another. 
Other objects, advantages and salient features of the present invention 
will become apparent from the following detailed description, which, taken 
in conjunction with the annexed drawings, discloses preferred embodiments 
of the present invention.

DETAILED DESCRIPTION OF THE INVENTION 
A piston 10 is used as an accumulator. Such piston accumulators are 
conventional, and thus, need not be described in detail. The piston 
accumulator cooperates with an ultrasound testing device according to the 
present invention. 
Piston accumulator 10 comprises breechblock mechanisms or closures 12 and 
14 on both ends. The closures have connector boreholes 16 and 18 passing 
through them. Connector boreholes 16 and 18 connect the accumulator to a 
nitrogen source or to a fluid circuit (both not shown). 
Within piston accumulator 10, a piston 20 is longitudinally slidably 
arranged. Piston 20 forms the separating element of accumulator 10 and 
separates a gas chamber 22 from a fluid or liquid chamber 24 in a sealed 
manner. Piston 20 has a sealing gasket 26 around its periphery, and 
control strips 28 and 30 adjacent its ends. The control strips 28 and 30 
can be of plastic materials and can protect against friction and wear 
during movement of piston 20 along the cylindrical peripheral housing 32 
of accumulator 10. 
Before its first use in a hydraulic system, the gas-pressure or 
hydraulic-accumulator is filled with a predeterminable gas volume in gas 
chamber 22, so that a gas pressure set value is present in gas chamber 22. 
According to the predetermined gas pre-filling pressure, the separating 
element (piston 20) assumes a set position, for instance, the position 
shown in the drawing. The set position of piston 20 can be determined 
beforehand and indicated by two markings 34 on the outside periphery of 
housing 32. In the illustrated embodiment, the spacing of the two markings 
34 from one another corresponds to the direction of movement of piston 20 
viewed along its piston length or piston height. To determine the set 
position of piston 20 for the gas pressure set level, an ultrasound 
testing device according to the present invention is used. 
The ultrasound testing device is accessible through a manual apparatus 36 
having a strap-like handle 38. Handle 38 is engaged on a plate-like front 
part 40 of manual apparatus 36. In the front of part 40, three testing 
heads 42 are embedded, open to the outside, and fit in tightly with the 
front of the front part 40. Testing heads 42 are conventional, 
commercially available ultrasound sensors. Each testing head 42 can 
transmit and receive ultrasound waves. 
As shown in FIG. 1, manual apparatus 36 is mounted in alignment with and 
between the two markings 34 on the outside periphery of piston accumulator 
10. If piston 20 is in its set position, shown in the drawing, each 
testing head 42 is arranged facing a testing body, formed by control strip 
28 or 30 or sealing gasket 26. The sound waves radiated from testing heads 
42 are reflected in the area of sealing gasket 26, as well as control 
strips 28 and 30, differently from transmission through the steel of 
housing 32 and piston 20. By linking of the reflected signals in testing 
heads 42, then, only with simultaneous multiple echos is an optical or 
acoustic signal indicated to the operator, so that the piston position and 
the gas pressure can be determined unambiguously. 
If piston 20 does not then assume its set position shown in the drawing, 
then this other position is determined through the ultrasound testing 
device. The gas disappearing is replaced/compensated through connector 
borehole 16 until the piston reaches its set position again. In this 
manner, safety devices assure that the gas pressure accumulator will not 
go below a minimum pressure, which could negatively influence or even 
totally abolish its operability. 
The monitoring/control device according to the present invention can also 
operate without further problems, with two pairs of testing heads and 
testing bodies. It would also be conceivable to read one single testing 
body by means of only one testing head, which in turn would be associated 
with one marking. This testing body would have to transmit a 
characteristic measuring image in the case of ultrasound testing, and the 
ultrasound testing device would likewise have to calibrate this special 
type of a signal. The ultrasound behavior of this testing body at any rate 
may not be comparable to the behavior of sealing gaskets or operating 
strips, which generally are required for the operation of the piston. 
The manual apparatus has an interface 44 for connection to the actual 
measuring device (not shown) of the ultrasound testing apparatus. That 
apparatus will process the reflected ultrasound signals which have been 
detected. Such testing apparatus or testing devices are known from 
material testing and belong to the state of the art. With suitable 
modification, the testing device according to the present invention can 
also be used with weight, spring and diaphragm accumulators. 
While various embodiments have been chosen to illustrate the invention, it 
will be understood by those skilled in the art that various changes and 
modifications can be made therein without departing from the scope of the 
invention as defined in the appended claims.