Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-08-23
2003-12-23
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S659000, C073S660000, C702S034000, C702S056000
Reexamination Certificate
active
06666093
ABSTRACT:
The present invention relates to a system for diagnosis of the state of wear of the delivery and suction valves of reciprocating compressors.
As is known, the term reciprocating volumetric compressors is used to indicate the thermal operating machines in which energy is transmitted by means of compressible fluids, substantially by varying their specific volume.
The variations of volume and the corresponding variations of pressure are obtained by the effect of the decrease of volume of the operating chamber of the machine, whereas the final variations are determined by the pressure conditions upstream and downstream from the operating machine itself.
In particular, the reciprocating compressors function with variations of volume of an operating chamber, which are obtained by straight displacement of a rigid body along the generatrices of a cylindrical cavity, and can be controlled by means of a crank mechanism, which permits transformation of motion from continuous circular, such as that which is generally supplied by electric and thermal motors, to reciprocating, as required in the specific case.
Like other reciprocating machines, for implementation of the different phases of the work cycle, the compressors of this type require an appropriate system of distribution, which is implemented almost exclusively by means of valves of two types: those of which the opening and closure is controlled, by means of a more or less complex kinematic chain, by the crankshaft of the compressor (controlled valves), and valves of the automatic type, which on the other hand are activated directly by the pressure differences between the interior and the exterior of the operating chamber.
At present, most compressors have automatic valves produced using different solutions, which are substantially derived from plate or cap valves.
Sealing is assured by the contact of various strips on a plate, which acts as a valve seat, and which contains numerous slits; the various strips are subjected to the action of return springs, which facilitate the closure and damp the opening.
In all cases, it is necessary to assure that the worn valves are replaced in time, since malfunctioning of the valves leads to decreases in the cross-sections of passage, and thus to reduced flow rates, with consequent unacceptable losses of load, which change the ideal work cycle into a significantly disadvantageous real cycle.
However, at present, replacement of the valves takes place after programmed maintenance has been carried out, i.e. when it is not yet strictly necessary, or after the valves have broken, resulting in undesirable stoppage of the compressor.
The disadvantages caused are apparent in both cases; in fact, these interventions give rise to interruption of production, whether the machine is stopped even if it is not necessary, or if the stoppage is unforeseen, owing to sudden breakage of one or more valves, or if the stoppage is longer than planned, because of any repairs of further components of the machine damaged by breakage of the valve(s).
As previously stated, the state of wear of a valve is indicated by various parameters, such as a decrease in delivery pressure, decrease in flow rate, increase in the temperature of the valve body, and noisiness of the valve in the field of audible frequencies.
Thus, by monitoring the undesirable variation of these parameters at each valve, it is possible to determine a valve which is malfunctioning, and to intervene mechanically in order to control the actual state of wear of that valve.
In all cases, periodic inspections of the state of wear are involved, which require stoppage of the compressor, with the same disadvantages as those previously described.
Alternatively, in order to evaluate the state of the valves during normal functioning of the compressor, it is known to make use of the phenomenon according to which the valves emit sound waves when they recirculate part of the compressed gas, after they have become worn.
In fact, the valves of the cylinders, both for suction and delivery, can undergo breakages of the rings, or they can function incorrectly owing to the presence of dirt or solid substances between the rings themselves and the corresponding stop seat.
In all these cases, there are conditions of reflux of the gas, which, as it heats up during the compression phase, gives rise to an increase in the temperature of the valve itself, the corresponding valve caps, and the body of the cylinder.
The progressive and physiological deterioration of the sealing surfaces, which come into contact between the valve and its seat, generate a phenomenon of recirculation of the gas, between the high-pressure side and the low-pressure side of the compressor, as a result of the irregularities which form on these surfaces over a period of time.
The recirculation of gas is caused by numerous small jets of gas, which escape through the irregularities of the contact surfaces, and give rise to emission of sound or ultrasound; measurement of this emission therefore provides an index of evaluation concerning the state of wear of the surfaces.
The object of the present invention is thus to indicate a system for diagnosis of the state of wear of the suction and delivery valves of reciprocating compressors, which makes it possible to monitor remotely the sound emissions produced by the malfunctioning valves, such as to be able to warn the operator during use, of the real need to stop the machine for maintenance on the valves.
This object and others according to the invention are achieved by a system for remote diagnosis of the state of wear of the suction and delivery valves of reciprocating compressors.
According to preferred, but non-limiting embodiments of the invention, in addition, the system for diagnosis uses a piezoelectric seismic sensor applied to each cylinder of the compressor at the valve to be monitored, which transforms the vibrations generated by the noise of the valves into a high-frequency electric signal, to be transmitted to a signal-amplifier device.
In addition, the electronic processing and control means comprise a signal-filtering device, which operates in the ultrasonic field of sound emission of the valves, an envelope detector, which determines the envelope of the input signal, with a resulting signal with a pass-band of 30 kHz, and a multiplexer for transmission of the data on a communication channel, such as a telephone line, a radio bridge, or satellite, or Internet/Intranet network. Advantageously, the system for diagnosis of the state of wear of the suction and delivery valves of reciprocating compressors according to the present invention, makes it possible to monitor remotely, from a remote seat, the sound emission produced by the valves in conditions of malfunctioning and imminent breakage of the latter, such as to warn the operator at the machine of the real need to stop the machine for maintenance or complete replacement of the valves.
By this means, it is no longer necessary for the operator to undertake periodic or planned stoppages of the compressor, or emergency interventions in order to repair any breakages of the valves; on the contrary, in the case of abnormalities of a valve, it is possible to detect and locate the occurrence of the degenerative phenomenon in good time.
In addition, the system for diagnosis which is the subject of the invention makes it possible to inform the operator of the machine accurately of the particular cylinder of the compressor which requires intervention, for maintenance on the valves.
Taking into consideration the fact that a reciprocating compressor may contain up to 12 cylinders with radial or axial valves, this possibility is extremely advantageous, since it prevents an entire series of dismantling operations, which would prove to be unnecessary once the malfunctioning valve(s) had been located.
Finally, the evaluation of the increase in noise over a period of time is an indication of the residual life of the valve, and makes it possible to stop the machine, for replacement of the valve, only when it is actually
Miller Rose M.
Nixon & Vanderhye
Nuovo Pignone Holding S.p.A.
Williams Hezron
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