GB2122356A

GB2122356A - Flow rate detector

Info

Publication number: GB2122356A
Application number: GB08217070A
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: GB2122356B

Abstract

A flow rate detector 1 that is simple in construction and effective in operation comprises an orifice 7 of restricted size for connection in a flow of liquid to be monitored. A container 2 with an inlet 3 is located upstream of the orifice 7 and accumulates liquid in the event of the flow rate upstream of the orifice 7 exceeding the flow rate determined by the orifice size. A level detector 6 detects the level of liquid in the container 2 and its output voltage can be used for giving a warning in the event of a predetermined liquid level being reached. In a system monitoring the performance of a machine such as a pump or side entry mixer/agitator the detector senses leakage. The system includes a vibration detector and, if the fluid is volatile, a vapor detector. <IMAGE>

Description

SPECIFICATION Flow rate detector This invention relates to a flow rate detector which will provide an indication when a monitored liquid flow rate exceeds a preset value.

According to the invention there is provided a flow rate detector comprising an orifice of restricted size for connection in a flow of liquid to be monitored, a reservoir upstream of the orifice for accumulating liquid in the event of the flow rate upstream of the orifice 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 flow rate detector for detecting 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 quickly 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 inward pipe for admitting the liquid flow and also a vertical outward pipe incorporating said orifice.

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

A preferred or intended use of the flow rate detector involves 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 or zero value the leakage of fluid past 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 mixer/agitators ae normally unmanned. Usually, to pevent as far as possible leakage of liquid from a tank, a first shaft seal is provided and any liquid leaking passed 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 gear box or other internal equipment of the mixer/agitator. A problem which can arise, which is particularly serious with tanks containing valuable or potentially dangerous liquids, is that the first seal can startto 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.

In order to provide a monitoring system for detecting an abnormal operating condition of a machine, such as a pumporfluid mixer/agitator, having a driven part provided with an arrangement of one or more sealing members for keeping to a low or zero value the leakage of fluid into past the sealing arrangement, a monitoring system comprises a flow rate detector as described above 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.

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 pick-up but, having moving parts, is liable to damage and malfunction. It is preferred, therefore, that the vibration detector be a piezoelectric accelerometer type vibration pick-up.

Where, as is usally 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 sytem, such as for monitoring the operation of a mixer/agitator pump mounted on a tank containing a volatile 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, in addition tousing the liquid leakage detector, which is located in a pipe 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 three vibration, flow rate and gas leakage detectors are indicative of an abnormal operating condition.

The circuit means can take on various forms. An especially preferred form is where it comprises an adder circuit, connected to receive the output 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.

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 and3 are, respectively, a plan view, a rear elevation and a side elevation of a preferred embodiment of the invention, Figure 4 indicates diagrammatically a preferred application of the flow rate detector in which it forms part of a monitoring system for monitoring the operation of a side entry tank mixer, FigureS shows a modification to the circuitry of Figure 4, and Figure 6 shows diagramatically a modification to the collecting chamber of the side entry mixer shown in Figure 1, in which the collecting chamber is additionally provided with a gas vent pipe.

Referring to Figures 1 to 3, there is shown a 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 Figures, 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 flow rate 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 restriction 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 the pot 2. This in turn decreases the capacitance of the probe whose output voltage accordingly 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 Figure 4 which illustrates diagrammatically a preferred use of the flow rate detector of Figures 1 to 3, there is shown a side entry tank mixer/(or agitator) 21 which is bolted in an aperture in an upright side wall 12 of a mixer tank containing a liquid mixture (e.g. crude oil). The tank mixer 21 comprises essentially an electric motor 13 whose shaft 14 drives an output shaft 15, projecting through into the inside of the tank, by way of a gearbox 16. A mixing propeller or blade 17 is mounted on the free end of the projecting shaft 15.

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 15 and the inside of the housing 18, of the tank mixer, is provided.

The sealing arrangement is deliberately designed to seal completely, but with prolonged used 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 19, and to dump the drained off liquid. Afurther seal 29 prevents leakage of any liquid in the collecting chamber 21 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 Figures 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 printout 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 Figure 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 1 and associated monitoring system shown in Figure 1 is for mixing a volatile product, such as motor gasolene, in a tank. In that case, as illustrated diagrammatically in Figure 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 homogenous, 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.

The monitoring system described herein with reference to Figures 4 and 5 forms the subject of our co-pending UK patent application 82 (UK patent ), to which attention is directed.

Claims

1. A flow rate detector comprising an orifice of restricted size for connection in a flow of liquid to be monitored, a reservoir upstream of the orifice for accumulating liquid in the event of the flow rate upsteam of the orifice 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.

2. Aflow rate detector according to claim 1, wherein the orifice size is adjustable for adapting the flow rate detector for detecting different flow rates.

3. A flow rate detector according to claim 1 or 2, wherein the liquid accumulation detecting means comprises a level detector inside the reservoir.

4. Aflow rate detector according to claim 1,2 or 3, wherein the level detector comprises a capacitance probe.

5. A flow rate detector according to any preceding claim, wherein the level detector is screwed into the top of, and extends downwardly inside, the reservoir.

6. A flow rate detector according to any preceding claim, wherein the reservoir has, at a lower end, a horizontal inlet pipe for admitting the liquid flow and also a vertical outlet pipe incorporating said orifice.

7. A flow rate detector according to any preceding claim, wherein an overflow pipe connects an upper region of the reservoir to a location in the liquid flow downstream of said orifice.

8. 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 the leakage of fluid past the sealing arrangement, the monitoring system comprising a flow rate detector according to any preceding claim for positioning downstream of the sealing arrangement to detect the rate of any leakage, a vibration detectorfor mounting on the machine to detect its vibration level, and circuit means operative to produce an output indication if the detector values of leakage rate and vibration level are indicative of abnormal operation of the machine.

9. A monitoring system according to claim 8 and in operative asociation with a machine having a driven shaft, wherein the vibration detector is mounted on the machine in the vicinity of the driven shaft.

10. A monitoring system according to claim 8 or 9, wherein the vibration detector is a piezoelectric accelerometer type vibration pick-up

11. A monitoring system according to claim 8,9 or 10 and in operative association with a machine having a driven shaft, wherein the vibration detector is mounted on the bearing housing of the machine.

12. A monitoring system according to claim 8,9 or 10 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.

13. A monitoring system according to any one of claims 8 to 12 and in operative association with a machine having a driven shaft, wherein the flow rate 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, flow rate and gas leakage detectors are indicative of an abnormal operating condition.

14. A monitoring system according to any one of claims 8 to 13, 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.

15. A monitoring system according to any one of claims 8 to 13, 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.

16. A flow rate detector substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

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

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