GB2122396A

GB2122396A - Monitoring system, for example for a pump or fluid mixer/agitator

Info

Publication number: GB2122396A
Application number: GB08217069A
Authority: GB
Inventors: Herbert Frank Ibbott
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1982-06-11
Filing date: 1982-06-11
Publication date: 1984-01-11
Also published as: GB2122396B

Abstract

The invention is concerned with a machine, such as a pump or fluid mixer 21, having a driven part 15 provided with one or more sealing members 19 for keeping to a low or zero value the leakage of fluid past the seal. In order to detect automatically the performance of the machine, a monitoring system is provided which comprises a fluid leakage detector 1 positioned alongside the last sealing member 19, a vibration detector 23 mounted on the machine body, and a circuit arrangement 24, 25 which produces an output alarm signal if the detected values of the leakage rate and vibration level are indicative of an abnormal operating condition. A preferred construction for the leakage detector 1 is also disclosed. <IMAGE>

Description

SPECIFICATION Monitoring system, for example for a pump or liquid mixer This invention relates to a monitoring system for a machine such as a pump or liquid mixer/agitator having a driven part provided with one or more sealing members for keeping to a low zero value the leakage of fluid passed the seal.

An example of such a machine is a mixer/ agitator which is secured to the side wall of a tank containing a liquid mixture. The mixer/ agitator is used for keeping the liquid mixture homogeneous. Such mixers/agitators are normally unmanned. Usually, to prevent as far as possible leakage of liquid from a tank, a first shaft seal is provided and any liquid leaking past the seal is collected in a chamber around the shaft and dumped. A further shaft seal at the other end of the collecting chamber is designed to prevent leakage of liquid into the gearbox or other internal equipment of the mixer/agitator. A problem which can arise, which is particularly serious with tanks containing valuable or portentially dangerous liquids, is that the first seal can start to leak significantly.The inventor has appreciated that this is due not only to prolonged usage but also to the fact that undue vibration levels caused by some mechanical malfunction can result in the condition of the sealing members rapidly deteriorating. In the absence of personnel present when a significant leakage occurs, the risk to the environment and safety and the expensive loss due to the dumping of large quantities of liquid can be very serious.

The invention provides a monitoring system for detecting an abnormal operating condition.

According to the invention there is provided a monitoring system for a machine, such as a pump or fluid mixer/agitator, having a driven part provided with an arrangement of one or more sealing for keeping to a low or zero value the leakage of fluid past the sealing arrangement, the monitoring system comprising a fluid leakage detector for positioning downstream of the sealing arrangement to detect the rate of any leakage, a vibration detector for mounting on the machine to detect its vibration level, and circuit means operative to produce an output indiciation if the detected values of leakage rate and vibration level are indicative of abnormal operation of the machine.

The fluid leakage detector can be a liquid detector or, especially for liquids which vaporise, a gas detector. To obtain high sensitivity to the vibration levels present, the vibration detector is preferably mounted on the machine in the vicinity of the driven shaft.

The vibration detector could take the form of a velocity type moving coil vibration pickup but, having moving parts, is liable to damage and malfunction. It is preferred, therefore, that the vibration detector be a piezoelectric accelerometer type vibration pickup.

Where, as is usually the case, the machine has a driven shaft, the vibration detector suitably is mounted on the bearing housing of the machine. When the machine additionally has a gearbox, the vibration detector can be mounted on the gearbox housing of the machine, or it could be mounted on the bearing housing.

In one envisaged application of the monitoring system, such as for monitoring the operation of a mixer/agitator mounted on a tank containing a voiatile product such as motor gasolene, a proportion of the product leaking past the last seal will generally vaporise. Accordingly, in a specially adapted monitoring system, a liquid leakage detector is located in a pipe leading downwardly from a location downstream of the sealing arrangement, a gas leakage detector is located in a vent pipe leading from said downstream location, and the circuit means is operative to produce said output indication only if the output values of the vibration, liquid leakage and gas leakage detectors are indicative of an abnormal operating condition.

In the case of a liquid leakage detector being used in the monitoring system the detector preferably comprises an orifice of restricted size for connection in the flow of leakage liquid, a reservoir upstream of the orifice for accumulating liquid in the event of the leakage rate through the sealing arrangement exceeding the flow rate determined by the orifice, and means operative to provide an indication upon detecting an accumulation of liquid in said reservoir.

The orifice size can be fixed or, for adapting the liquid leakage detector for detecting different flow rates, the orifice size can be adjustable.

The liquid accumulation detecting means may comprise a level detector inside the reservoir. Suitably the level detector may comprise a capacitance probe. Conveniently, the level detector is screwed into the top of, and extends downwardly inside, the reservoir. This arrangement is particularly advantageous for permitting quick replacement of the level detector in the event of malfunction and also rapid access to the inside of the container for inspection and servicing. A particularly advantageous arrangement is one in which the reservoir has, at a lower end, a horizontal inlet pipe for admitting leakage flow and also a vertical outlet pipe incorporating said orifice.

The circuit means can take on various forms. An especially preferred form is where it comprises an adder circuit, connected to receive the outputs of the detectors, and a comparator arranged to produce an output alarm signal if the output level of the adder circuit exceeds a preset threshold This circuit means is to be preferred for two reasons.

Firstly, it is very simple to realise in practice.

Secondly, if for example the vibration level is abnormally high, then even if the leakage rate is quite normal, an alarm signal will nevertheless be generated to indicate that attention is required. This is advantageous in that a high vibration level will normally lead in due course to rapid deterioration of the sealing properties of the sealing members and therefore needs to be detected at its onset. Another possible arrangement for the circuit means, which again is simple to realise, comprises a plurality of comparators, each being arranged to compare the output level of a respective detector with a preset threshold level, and AND means arranged to produce an output alarm signal if the levels of the output signals from the detectors exceed their respective preset threshold levels.

In order to cope with a very large accumulation of liquid filling the container to the top, an overflow pipe can be provided which connects the top of the container to a location in the leakage liquid flow downstream of said orifice.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of Example, to the accompanying drawings, in which: Figures 1, 2 and 3 are respectively a plan view, a rear elevation and a side elevation of a leakage rate detector which is particularly suitable for use in the monitoring system of Fig.

4, Figure 4 is a diagrammatic vertical sectional view through a first embodiment of the invention having a side entry mixer installed in a tank containing a liquid mixture, such as crude oil, and provided with a malfunction monitoring system.

Figure 5 shows a alternative form for the circuitry for generating an alarm signal in the event of abnormal operation, and Figure 6 shows diagrammatically a modification to the collecting chamber of the side entry mixer shown in Fig. 1, in which the collecting chamber is additionally provided with a gas vent pipe.

Referring to Figs. 1 to 3, there is shown a leakage or flow rate detector 1 which is intended for detecting the flow rate of a liquid which is greater than a preset flow rate.

The detector 1 comprises essentially a reservoir in the form of an upright cylindrical container or pot 2 having a horizontal inlet pipe 3 in its lower region and an outlet pipe 4 extending vertically downwards from its bottom end face. The top end of the pot 2 is formed with a central screw-threaded bore into which a capacitance probe 5 is screwed with its sensitive part extending vertically downwardly inside the pot along its axis and terminating just above the bottom face of the pot 2. As diagrammatically illustrated in the Figs. the capacitance probe 5 can incorporate an integrated circuit 6, including an amplifier circuit, for producing an output voltage which increases with decreasing effective capacitance of the probe.

Connected in the outlet pipe 4 is a restriction orifice 7 which can either be fixed, or adjustable for determining a pre-selected flow rate through the orifice. An overflow pipe 8 connects the top of the pot 2 to the outlet pipe 4 at a location downstream of the restriction orifice 7.

The flowrate detector 1 is connected in a pipeline, through which flows a liquid (e.g. a hydrocarbon liquid such as crude oil) whose flow rate is to be monitored by means of its inlet and outlet pipes 3, 4. For low flow rates, that is to say for flow rates which are less than the flow rate determined by the size of the restricted orifice 7, the liquid enters into the pot from the inlet pipe 3 and straight out again through the outlet pipe 4. The liquid level in the reservoir is very low. If, however, the flow rate increases to above that determined by the orifice 7, an accumulation of liquid will start to build-up upstream of the orifice, causing a rise in liquid level in a pot 2. This in turn decreases the capacitance of the probe whose output voltage increases to provide an indication that the flow rate value determined by the orifice size has been exceeded.The output voltage can be compared with a threshold value for generating an alarm signal when the threshold is exceeded.

In the event of a large increase in the upstream flow rate, the liquid level in the pot 2 will rise until it reaches the inlet to the overflow pipe 8, whereupon it will run down that pipe and into the inlet pipe 4, downstream of the orifice 7.

It will be appreciated that the described flow rate detector is simple in construction, cheap to manufacture and can be designed to operate at low input voltages, which is desirable for safety reasons.

Referring now to Fig. 4 which illustrates diagrammatically a first embodiment of the invention, there is shown a side entry tank mixer (or agitator) 21 which is bolted in an aperture in an upright side wall 1 2 of a mixer tank containing a liquid mixture (e.g. crude oil). The tank mixer 21 comprises essentially an electric motor 1 3 whose shaft 14 drives an output shaft 15, projecting through into the inside of the tank, by way of a gearbox 1 6. A mixing propeller or blade 1 7 is mounted on the free end of the projecting shaft 1 5.

In order to prevent or keep to a minimum leakage of liquid from the tank, a sealing arrangement 19, consisting of one or more shaft seals between the surface of the shaft 1 5 and the inside of the housing 1 8 of the tank mixer, is provided. The sealing arrange ment is deliberately designed to seal completely, but with prolonged use a small quantity of leakage is accepted. For this reason, a downwardly extending drain pipe 20 serves to conduct leakage liquid from a collecting chamber 21 around the shaft 5 and downstream of the last seal 1 9 and to dump the drained of liquid. A further seal 29 prevents leakage of any liquid in the collecting chamber 2 into the gearbox of the tank mixer.

The leakage flow through the drain pipe 10 is monitored by a leakage detector 1 as described above and illustrated in Figs. 1 to 3.

The leakage detector 1 produces an output voltage which increases in dependence upon increases in the leakage rate. Additionally, the vibration level of the tank mixer is monitored by a vibration detector 23 mounted at the front end of the bearing housing of the machine and this produces an output voltage which is proportional to the vibration levels. It could alternatively be mounted on the gearbox casing of the tank mixer. The output voltages of the leakage and vibration detectors are combined in an adder circuit 24 whose output voltage is compared, in a comparator 25, with a reference voltage. If the output voltage of the adder circuit 24 exceeds the threshold voltage, an output signal is produced by the comparator 25 which can be used to operate a remote alarm and/or a printed device at a central monitoring station.

The circuitry for generating the alarm can take on various alternative forms. For example, the adder circuit 24 could be a multiplier circuit. Another possible arrangement is shown in Fig. 5. Here, the output voltages from the leakage detector 1 and vibration detector 23 are received as first inputs to respective comparators 26, 27 and if, in each case, the output voltage from the associated detector exceeds a reference voltage (V1, V2) applied to the non-inverting input of the comparator, an output voltage is produced and supplied to a respective input of an AND gate 28. Therefore, in the event that both threshold levels of the comparators 26, 27 are exceeded, the AND gate 28 produces an output alarm signal.

One envisaged application of the side entry tank mixer and associated monitoring system is for mixing a volatile product, such as motor gasolene, in a tank. In that case, as illustrated diagrammatically in Fig. 6, in addition to the drain pipe 20, a vent pipe 30 is also provided communicating with the collecting chamber 21, the vent pipe having a gas leakage detector therein 31 producing an output voltage dependent on the gas flow rate which would be supplied as a third input to the adder circuit 24. It is also envisaged that the tank mixer might be used for keeping a separable gas mixture homogeneous, in which case only a vent pipe with a gas flow detector therein would be required.

The sealing arrangement 19, as mentioned above, is intended to seal as completely as possible. There are, however, other possible applications of the monitoring system where the associated machine has a sealing arrangement which is deliberately designed to allow a certain leakage under normal operation but will respond to abnormally high leakage rates.

It will be appreciated that the described monitoring system is simple to make and therefore likely to be reliable in operation. It can serve to avoid environmental and safety hazards resulting from leakage through the sealing arrangement and also avoid the loss of valuable liquid or gas. Additionally, existing tank mixers can easily be adapted by merely fitting them with vibration and leakage detectors.

The disclosed system also finds application to other kinds of machine such as a pump or gas or liquid turbine where leakage occurs from the inside of the machine through to the exterior.

Finally, it is pointed out that the leakage detector described herein with reference to Figs. 1 to 3 forms the subject of our copending UK patent application 82 (UK patent ), to which attention is directed.

Claims

1. A monitoring system for a machine, such as a pump or fluid mixer/agitator, having a driven part provided with an arrangement of one or more sealing members for keeping to a low or zero value leakage of fluid past the sealing arrangement, the monitoring system comprising a fluid leakage detector for positioning downstream of the sealing arrangement to detect the rate of any leakage, a vibration detector for mounting on the machine to detect its vibration level, and circuit means operative to produce an output indication if the detected values of leakage rate and vibration level are indicative of abnormal operation of the machine.

2. A monitoring system according to claim 1 and in operative association with a machine having a driven shaft, wherein the vibration detector is mounted on the machine in the vicinity of the driven shaft.

3. A monitoring system according to claim 1 or 2, wherein the vibration detector is a piezoelectric accelerometer type vibration pickup.

4. A monitoring system according to claim 1, 2 or 3 and in operative association with a machine having a driven shaft, wherein the vibration detector is mounted on the bearing housing of the machine.

5. A monitoring system according to claim 1, 2 or 3 and in operative association with a machine having a driven shaft and a gearbox, wherein the vibration detector is mounted on the gearbox housing of the machine.

6. A monitoring system according to any preceding claim and in operative association with a machine having a driven shaft, wherein a liquid leakage detector is located in a pipe leading downwardly from a location downstream of the sealing arrangement, a gas leakage detector is located in a vent pipe leading from said downstream location, and the circuit means is operative to produce said output indication only if the output values of the vibration, liquid leakage and gas leakage detectors are indicative of an abnormal operating condition.

7. A monitoring system according to any preceding claim, wherein the circuit means comprises an adder circuit, connected to receive the outputs of the detectors, and a comparator arranged to produce an output alarm signal if the output level of the adder circuit exceeds a preset threshold.

8. A monitoring system according to any one of claims 1 to 6, wherein the circuit means comprises a plurality of comparators, each being arranged to compare the output level of a respective detector with a preset threshold level, and AND means arranged to produce an output alarm signal if the levels of the output signals from the detectors exceed their respective preset threshold levels.

9. A monitoring system according to any preceding claim and where a liquid leakage detector is used, wherein the liquid leakage detector comprises an orifice of restricted size for connection in the flow of leakage liquid, a reservoir upstream of the orifice for accumulating liquid in the event of the leakage rate through the sealing arrangement exceeding the flow rate determined by the orifice size, and means operative to provide an indication upon detecting an accumulation of liquid in said reservoir.

10. A monitoring system according to claim 9, wherein the orifice size is adjustable for adapting the liquid leakage detector for detecting different flow rates.

11. A monitoring system according to claim 9 or 10, wherein the liquid accumulation detecting means comprises a level detector inside the reservoir.

1 2. A monitoring system according to claim 9, 10 or 11, wherein the level detector comprises a capacitance probe.

1 3. A monitoring system according to claim 9, 10 or 11, wherein the level-detector is screwed into the top of, and extends downwardly inside, the reservoir.

14. A monitoring system according to any one of claims 9 to 13, wherein the reservoir has, at a lower end, a horizontal inlet pipe for admitting the leakage flow and also a vertical outlet for incorporating said orifice.

1 5. A monitoring system according to any one of claims 9 to 14, wherein an overflow pipe connects an upper region of the reservoir to a location in the leakage liquid flow downstream of said orifice.

16. A monitoring system for a machine, substantially as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.

1 7. A monitoring system for a machine, substantially as hereinbefore described with reference to Figs. 1 to 3 and 4 as modified by Fig. 5 of the accompanying drawings.

1 8. A monitoring system for a machine, substantially as hereinbefore described with reference to Fig. 4 of the accompanying drawings.

1 9. A monitoring system for a machine, substantially as hereinbefore described with reference to Fig. 4 as modified by Fig. 5 of the accompanying drawings.