JPH0545246A - Leakage sensing device for shaft sealing device - Google Patents

Abstract

PURPOSE:To predict possible generation of leakage in great quantity due to deterioration of the sealing function of a shaft sealing device. CONSTITUTION:A capacitance type leak sensor 10 consists of an electrode plate 10a where a shaft 2 or a rotating side component 6 is installed as the earth side electrode on a stationary side component 4 on the leak path 9 side including the sealed slide surfaces S. A leak sensing device concerned is equipped with this capacitance type leak sensor 10, a reference capacitance capacitor connected for the input in parallel with the leak sensor 10, and a differential amplifier which senses the capacitance difference between the leak sensor 10 and reference capacitance capacitor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leak detection device for detecting a leak of a fluid to be sealed in a shaft sealing device such as a mechanical seal.

[0002]

2. Description of the Related Art As a kind of shaft sealing device for sealing the shaft circumference of a rotating shaft, for example, a mating ring, which is a stationary part fixed airtight to the inner diameter of a housing, and an airtight seal to the outer circumference of the shaft. 2. Description of the Related Art A mechanical seal including a seal ring that is an axially movable component that is a rotating side component and a spring that urges the seal ring toward the mating ring is well known.

That is, in this mechanical seal, a seal ring that rotates integrally with the shaft is biased by a spring and slides closely against a non-rotating mating ring to form a sealing sliding surface, and this sealing is performed. This is to prevent the liquid to be sealed in the space inside the machine connected to the outer peripheral side of the sliding surface from flowing out of the machine from the circumference of the shaft.

In the shaft sealing device such as the mechanical seal, when the sealing performance is deteriorated due to wear or damage, it is necessary to replace or repair the sealing element such as the seal ring.
At present, the deterioration of the sealing performance is confirmed by the pressure drop of the fluid inside the machine due to leakage and the discovery of the leaked fluid flowing out of the machine. Therefore, at the time when the deterioration of the sealing function was confirmed, a large number of leakage accidents had already occurred.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. The problem is to prevent the occurrence of a large amount of leakage accidents due to deterioration of the sealing function of the shaft sealing device. It is an object of the present invention to provide a leak detection device for a shaft seal device that can be predicted.

[0006]

In order to solve the above-mentioned problems, a leak detection device for a shaft sealing device according to the present invention has a shaft around the shaft or a rotating side part provided on the shaft and a stationary side part. In a shaft sealing device that seals by closely sliding with, a capacitive leak including an electrode plate provided on a stationary side component on the leakage path side including a sealing sliding surface and using the shaft or rotating side component as a ground side electrode. A sensor,
A reference capacitance capacitor connected in parallel to the leak sensor with respect to the input, and a differential amplifier for detecting the capacitance difference between the leak sensor and the reference capacitance capacitor are adopted.

[0007]

In the leak detecting device for a shaft sealing device of the present invention, it can be considered that the shaft or the rotating side component is grounded to the main body of the device through the bearing or the like. A capacitive leak sensor is constructed by making the electrode plates provided on the side parts face each other along the leakage path.When the leakage liquid passes through the leakage path or the amount of passage of the leakage liquid changes, the permittivity or distance between both electrodes may change. Since the capacitance of the leak sensor changes, the capacitance difference between the leak sensor and the reference capacitance capacitor is detected and amplified by the differential amplifier and output.

[0008]

1 and 2 show a first embodiment of the present invention. First, in FIG. 1, 1 is a housing of an apparatus,
2 is a shaft that is inserted into the shaft hole of the housing 1,
The housing 1 and the shaft 2 are sealed with a mechanical seal, which is a kind of shaft sealing device.

The mechanical seal is a stationary mating ring 4 made of SiC or the like, which is loosely fitted to the outer periphery of the shaft 2 and hermetically fixed to the inner diameter of the housing 1 through an O-ring 3, and the shaft 2. A rotation side seal ring 6 made of carbon or the like is provided on the outer peripheral surface via an O ring 5 so as to be airtight and movable in the axial direction. The seal ring 6 rotating integrally with the shaft 2 is pressed against a spring 8 supported by a collar 7 fixed to the shaft 2, thereby forming a sealing sliding surface S between the seal ring 6 and the non-rotating mating ring 4. Then, the liquid L in the machine reaching the outer peripheral side is sealed.

Reference numeral 10 denotes a capacitance type leak sensor for detecting the leak of the liquid L from the sealing sliding surface S to the inner circumferential shaft gap 9 of the mating ring 4. The leak sensor 10 includes an electrode plate 10a embedded in the inner peripheral surface 41 of the mating ring 4 so as to face the axial clearance 9 which is the leakage path of the liquid L, that is, one electrode of the capacitor is mated. Since the shaft is embedded in the ring 4, it can be considered that the shaft is grounded through a bearing, a driving force transmitting portion, etc. (not shown). A capacitive relationship is established between the shaft 2 and the electrode plate 10a that faces the radial direction.

FIG. 2 shows a circuit diagram of a leak detecting device including the leak sensor 10, that is, 101 is a resistor R1 and the leak sensor 10 connected in series, and a first output terminal 101a is provided between them. The sensor unit 102 provided with
A resistor R2 having the same resistance value as the resistor R1 and a capacitor 11 having a reference capacitance are connected in series, and a second output terminal 1 is provided between them.
This is a reference sensor unit provided with 02a. The sensor unit 101 and the reference sensor unit 102 are connected in parallel to the positive electrode side input terminal 103 for inputting the constant voltage V. Further, as described above, the shaft 2 constituting one electrode of the leak sensor 10 is grounded via the bearing, the driving force transmitting portion, etc., and the negative electrode plate of the reference capacitance capacitor 11 is also grounded.

The output terminal 101a of the sensor unit 101 has a differential amplifier OP via a first amplifier A1 and a resistor R3.
Is connected to the negative input terminal of. Further, the output terminal 102a of the reference sensor unit 102 is connected to the positive input terminal of the differential amplifier OP and the ground via the second amplifier A2 and the resistor R4. Part of the output of the differential amplifier OP is fed back to the negative input terminal of the differential amplifier OP via a feedback circuit having a resistor R5.

In the above configuration, the principle of leak detection by the leak sensor 10 is that, when a dielectric is interposed between the counter electrodes Ca and Cb of the capacitor as shown in FIG. 3, it depends on the size and material of the dielectric. This utilizes the fact that the capacitance C changes. That is, assuming that the distance between the electrodes Ca and Cb is d and the dielectric constant of the substance interposed between the electrodes Ca and Cb is ε, C = ε / d (1) When the liquid L flows between the electrodes Ca and Cb where only the intervening material is present, the capacitance C changes due to the change of the dielectric constant ε due to the change of the intervening substance.

That is, the above-mentioned leak detecting device compares the capacitance change of the leak sensor 10 which changes due to the liquid L leaking from the sealing sliding surface S to the shaft gap 9 flowing between the electrode plate 10a and the shaft 2. Is detected as a capacitance difference with the reference capacitance capacitor 11 provided as above. The difference in output voltage due to the capacitance difference between the leak sensor 10 and the reference capacitance capacitor 11 is amplified by the first and second amplifiers A1 and A2, The voltage difference is detected and amplified by the differential amplifier OP, and the voltage V ₀ is output to the output terminal 104.

By the way, as is apparent from the above equation (1), the capacitance C of the leak sensor 10 changes depending on the distance between the electrode plate 10a and the outer peripheral surface of the shaft 2,
When the electrode plate 10a is provided only at one position in the circumferential direction, vibration or radial displacement of the shaft 2 may cause unstable detection accuracy. For this reason, it is preferable that the electrode plate 10a be provided in a circumferentially equidistant shape or have a continuous annular shape.

Next, the second embodiment of the present invention shown in FIG.
A leak sensor 12 is provided instead of the leak sensor 10 in the first embodiment. The leak sensor 12 is embedded in the end surface 42 of the mating ring 4 so as to face the sealing sliding surface S which is a part of the leak path.
2a is included. That is, the carbon seal ring 6 which is a rotating side component includes the spring 8, the collar 7, and the shaft 2.
Also, since it can be considered that the liquid L is grounded via a bearing or a driving force transmission unit (not shown), the liquid L to be sealed is sealed.
A part of the above is a capacitive relationship between the seal ring 6 and the electrode plate 12a axially opposed to each other with a gap between the sealing sliding surfaces S interposed as a lubricating liquid film. Other configurations are similar to those of the first embodiment.

In this embodiment, in the normal state, the liquid L to be sealed is present on the sealing sliding surface S with a proper film thickness as a lubricating liquid film, but the sealing sliding surface S is worn or partially damaged. As a result, when the flow rate of the liquid L to be sealed leaking from the sealing sliding surface S toward the inner diameter side increases, the dielectric constant ε is constant,
Since the distance between the electrode plate 12a and the seal ring 6 increases, the capacitance C of the leak sensor 12 changes.

The present invention is not limited to the illustrated embodiment. For example, the circuit of FIG. 3 is direct current,
This may be replaced by an AC circuit, and the electrode plate of the leak sensor may be provided on the inner diameter of the housing 1 on the leak path side and closely face the outer peripheral surface of the shaft 2.
It is also possible to configure it for leak detection of shaft sealing devices other than mechanical seals.

[0019]

As is apparent from the above description, the leak detection device for a shaft sealing device according to the present invention is a capacitive leak sensor in which an electrode plate is provided on a stationary side and a shaft or a rotating side component is an earth side electrode. The differential amplifier detects and amplifies the capacity difference between the leak sensor capacity that changes when the leaked fluid passes and the reference capacitor of constant capacity. Also, the deterioration of the sealing function can be confirmed at an early stage without depending on the discovery of leaked fluid that has flowed out of the machine. Therefore, it is possible to predict in advance the occurrence of a large amount of leakage and to take appropriate measures such as replacement of the seal parts.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram of the same.

FIG. 3 is an explanatory diagram of a detection principle of the same.

FIG. 4 is a cross-sectional view of essential parts showing a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Shaft 4 Mating ring (stationary side part) 6 Seal ring (rotating side part) 9 Axial clearance (leakage path) 10,12 Leak sensor 10a, 12a Electrode plate 11 Reference capacity capacitor OP Differential amplifier S Sealing slide Surface

Claims (1)

[Claims] 1. A shaft sealing device for sealing the shaft circumference by close sliding between a shaft or a rotating side component provided on the shaft and a stationary side component, which is located on a leak path side including a sealing sliding surface. And a capacitance type leak sensor including an electrode plate provided on the stationary side component with the shaft or the rotary side component as an earth side electrode, a reference capacitance capacitor connected in parallel to the leak sensor for input, and the leak sensor. And a differential amplifier for detecting a capacitance difference between a reference capacitance capacitor and a leak detection device for a shaft sealing device.