Expansible chamber devices – With inspection window in expansible chamber wall portion – With lock
Reexamination Certificate
2001-05-17
2003-02-25
Look, Edward K. (Department: 3745)
Expansible chamber devices
With inspection window in expansible chamber wall portion
With lock
C092S1030SD
Reexamination Certificate
active
06523454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a device for monitoring the integrity of a diaphragm in a diaphragm transport unit made of one or a plurality of layers, having a resistance device connected to one layer and having a measuring device interconnected to a current source via a link.
2. Background Information
In the chemical and pharmaceutical industries diaphragm pumps are in widespread use for delivering and metering liquids. The pump action is achieved by a periodic deflection of a diaphragm. In the following, by the word diaphragm is to be understood a flexible layer which, by itself or in connection with other layers, separates a transport chamber from a drive chamber in a diaphragm transport unit. The deflection of the diaphragm can be effected mechanically, e.g. by a moved metal flange, pneumatically or by hydraulic fluid. Thus one surface of the diaphragm is in direct contact with the transport medium. Depending on the area of application, the transport medium may be poisonous, toxic and also inflammable. For safety reasons and so as largely to rule out injury to people and damage to the environment and plant components, one endeavors to prevent the escape of transport medium by regular maintenance of the transport device and by monitoring the process. The diaphragm itself is subject to great alternating stress, and is mostly the component having the greatest rate of failure in these installations. The alternating stress is predefined by operating parameters such as pumping capacity, chemical composition and the temperature of the transport medium. In order to be sure to avoid the escape of critical liquids, the pump diaphragm is replaced after a certain operating time, within the scope of maintenance work. However, in doing so, one often replaces an intact diaphragm which still has a relatively high remaining service life. For reasons of safety, and so as to be able to conduct this maintenance work as efficiently as possible, an attempt is made to detect ahead of time impending damage by measurement technology, using suitable measuring devices. One should be able to ascertain a diaphragm rupture as far ahead of time as possible. The diaphragm should be changed safely before its failure, but with only a short service life remaining. In any case, an incipient rupture of the diaphragm, or a leak which has appeared, have to be detectable by the process control system.
Various devices are known for making damage in an agitated diaphragm technically measurable.
In German Laid-Open Document 37 29 726 a diaphragm having a plurality of layers is proposed, in which a membrane gap is furnished with a detector and monitors the gap. If one of the layers is destroyed, the fluid penetrates the gap and the leak detector recognizes what the trouble is. However, the detector records the leak only when enough liquid has leaked out. Only when the two layers of the diaphragm have been pushed sufficiently far apart, and liquid has reached the detector, is the damage recognized.
In German DE 40 27 027 C2, for the purpose of recognizing a location of rupture in a diaphragm made of a plurality of layers, monitoring the space between two layers is also proposed. The pump is driven hydraulically. The space between the two layers is set up in such a way that underpressure prevails compared to the atmosphere. The space is originally free of liquid. When one of the outer diaphragms is damaged, either hydraulic fluid or transport fluid penetrate into the space between the diaphragm layers. As a result, the pressure in this space changes. (It changes) either toward the discharge pressure or toward the working pressure. The pressure change is measured by a measuring transducer in a measuring chamber connected to this space. A pressure change always occurs when one of the two layers of the diaphragm pair ruptures. However, it can happen that the connecting duct to the measuring chamber does not open, and a status signal is released too late or not at all. Because of that, damage cannot be reliably prevented, because the remaining layer of the diaphragm pair, can, for a limited duration to be sure, still safeguard the pumping function, but it should not be excluded that it might come to a leak in the second diaphragm in rapd succession. In a hydraulically driven pump hydraulic fluid can get into the transport chamber. This is always a disadvantage if high purity of the delivered fluid is important.
In WO 95/06205, for predicting a fault of a pump diaphragm, using an electrically conductive fiber made of polytetrafluoroethylene is proposed. This conductive fiber is embedded in a diaphragm layer of the same material. The fiber is dimensioned in such a way that it essentially covers the entire area of the diaphragm in the form of a spiral or double spiral, or in zigzag shape. The ends of the fiber are brought out at the edge, and can be connected to an electrical measuring device. The resistance of the fiber in ohms is measured. As soon as the diaphragm layer shows signs of fatigue or rupture, these are transferred to the fiber. Since the fiber is made of the same or very similar material as the diaphragm itself, the sagging life of the diaphragm is just about the same as that of the fiber. As a result of the signs of fatigue or the fissures of the diaphragm, the conductivity of the fiber changes, and thereby a fissure or beginning rupture can be detected with measuring technology and can be signaled. A disadvantage is the very expensive production of the conductive plastic fiber and its embedding into the diaphragm. A further disadvantage is the dependence of the quantity to be measured on the temperature of the transport medium. The post-connected electronic signal enhancer has to distinguish between a change of resistance, caused by a sign of fatigue, an extension on account of pump lift and a temperature-dependent change of resistance.
SUMMARY OF THE INVENTION
The object of the present invention is based on creating a device with the aid of which the integrity of a diaphragm in a diaphragm transport unit can reliably be monitored in a simple manner. The device should be refined in such a way that the monitoring is as independent as possible of the temperature and flow of the transport fluid in the transport chamber, and independent of a long-term deviation of the measuring device itself.
The object is attained by a device in which at least one layer of a multi-layer diaphragm is interconnected to a resistance device and to a measuring device having a current source, according to the present invention, by the measuring device's working in the manner of a Wheatstone bridge in which the resistance device forms a bridge resistance in at least one bridge arm and an incipient rupture of a layer of the diaphragm effects a change in the galvanometer arm voltage.
On account of the change in the electrical resistance of a resistive sensor, connected to a diaphragm layer, which is positioned in at least one bridge arm of a resistance measuring bridge, the integrity of a diaphragm in a transport unit can be monitored in a technically simple manner. The sensitivity of the measuring bridge makes it possible reliably to detect an incipient rupture, spreading in one of the layers of the diaphragm, already in the preliminary stages. Wheatstone bridges are precision measuring devices for measuring resistances by comparison with built-in resistances of known values. In the present case, the bridge resistances of the measuring device can be advantageously integrated in a technically simple way with the diaphragm transport unit. This circuit arrangement of the kind of the Wheatstone bridge leads to a simple and space saving construction of the monitoring unit. In an advantageous further refinement, the bridge circuit makes possible the positioning of the bridge resistances in such a way that the disturbing influence of the temperature of the transport fluid and also the long-term drift of the resistive sensor can be eliminated.
The resistance device can be formed from vario
Leslie Michael
Look Edward K.
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