Flow meter with cleaning means

Abstract: A flow rate measuring apparatus includes a measuring pipe in which a fluid to be measured flows, a flowmeter (101) for measuring a flow rate of the fluid to be measured flowing in the measuring pipe (410a), and a cleaning flow generator (105) for removing an adhesive substance in the measuring pipe by using the fluid to be measured, thereby correctly performing flow rate measurement. When the flowmeter (101) is an electro­ magnetic flowmeter, the cleaning flow generator (105) prevents the adhesive substance from resistively connecting electrodes for induced electromotive force detection. When the flowmeter (101) is an ultrasonic flowmeter, the cleaning flow generator (105) prevents the adhesive substance from interfering with trans­ mission of an ultrasonic wave in the measuring pipe. The cleaning flow generator (105) removes the adhesive substance by performing at least one of inflating a balloon in the measuring pipe, turning the fluid to be measured, and charging a high-pressure gas into the flow path of the fluid to be measured.

Description: The present invention relates to a flow rate measuring apparatus suitable for measuring a flow rate of a fluid such as a sewage, a human waste, a sludge, or an organic drainage which tends to produce an adhesive substance on a pipe and, more particularly to a flow rate measuring apparatus capable of removing an adhesive substance on a measuring pipe without removing pipes. Various types of flow rate measuring apparatuses are used in various places. An example of the places in which the flow rate measuring apparatus is used is a sewage disposal plant. In the sewage disposal plant or the like, various types of substances adhere on the inner surface of the measuring pipe (if the measuring pipe has a lining, the inner surface of the lining) of a flowmeter due to properties of a fluid whose flow rate is to be measured. When the flowmeter is an electromagnetic flowmeter and an adhesive substance has high conductance, the adhesive substance resistively connects electrodes for detecting an induced electromotive force and decreases an indication value of the flowmeter. This adhesive substance deteriorates over time due to bacteria, microorganisms, or the like into a hard cement-like substance consisting of carbon, minerals, and the like in the adhesive substance. Layers of this cement-like substance strongly adhere on the inner surface of the measuring pipe and therefor cannot be easily removed. In addition, when an adhesive substance decays in summer time, the adhesive substance sometimes deteriorates into a bread-like substance due to a gas generated upon decay. This bread-like adhesive substance hardly transmits an ultrasonic wave. For this reason, when the flow rate measuring apparatus is an ultrasonic flowmeter, it is difficult to perform measurement, or a measurement error occurs. Such a bread-like substance also deteriorates into a hard substance over time and therefore cannot be easily removed. Such an adhesive substance also poses various problems in a flowmeter except for the electromagnetic flowmeter or the ultrasonic flowmeter. For example, an effective area of a measuring pipe is reduced, and a measurement value error occurs. These problems are not limited to a sewage but arise for any type of fluid although a degree of the problem differs. For this reason, this adhesive substance must be removed while it can be easily removed. Since, however, a measuring pipe is connected to a pipe system, it is difficult to clean the inner surface of the measuring pipe. Examples of a conventional technique of removing an adhesive substance in a measuring pipe without removing the measuring pipe from a pipe system are: (1) a method of blowing a cleaning solution against electrodes of an electromagnetic flowmeter and their peripheral portions to remove an adhesive substance (Japanese Utility Model Publication No. 57-59937); and (2) a method in which a porous substance is used as a lining material of a measuring pipe and a cleaning solution is injected to remove an adhesive substance (Japanese Utility Model Publication No. 57-49779). In these techniques, however, since electrodes and their peripheral portions of an electromagnetic flowmeter are mainly cleaned, only a part of an adhesive substance can be removed. Therefore, (1) a problem in which electrodes of an electromagnetic flowmeter are resistively connected, (2) a problem in which transmission of an ultrasonic wave is interfered, and (3) a problem in which an effective area of a measuring pipe is reduced are basically left unsolved. In addition, in the above cleaning methods, a measuring pipe must be emptied upon cleaning in order to achieve a sufficient cleaning effect, resulting in an inconvenient operation. To solve these problems, the inventor hereof developed an apparatus, wherein a vane is located within a pipe, thereby to discharges the fluid to be measured, into the measuring pipe, or a vane or the like is located within the path of the fluid, thus narrowing this path and making the fluid to flow through the path at a higher speed, so as to remove an adhesive substance from the inner surface of the measuring pipe. This apparatus is disclosed in Japanese Patent Disclosure No. hei 1-46615, published February 21, 1989. This apparatus cannot remove the adhesive substance to the desired extent when the water head is relatively small. There is a demand for flow rate measuring apparatuses which can remove the adhesive substance from a measuring pipe with high efficiency. FR-A-2592601 discloses a technique of cleaning a pipe by using a high pressure air jet. JP-U-57-59937, mentioned above, discloses a cleaning device comprising an insertable and retractable nozzle for providing a liquid jet. It is the object of the invention to provide a flow rate measuring apparatus which can remove an adhesive substance from a measuring pipe without removing the flow rate measuring apparatus from a pipe system and which has a higher efficiency than the prior art. This object is solved by a flow rate measuring apparatus as claimed in claim 1. Due to the fact that the flow path is closed off for a cleaning operation the flow rate measuring apparatus according to the present invention provides a better result with respect to the cleaning efficiency than the known devices where no valves are provided. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which Figs. 1 and 2 are views showing an arrangement of a flow rate measuring apparatus according to an embodiment of the present invention. A flow rate measuring apparatus according to an embodiment of the present invention will now be described with reference to Fig. 1. In Fig. 1, a gas injection device 503 is connected to an upstream side portion of a measuring pipe 510a (including a lining) of a flowmeter 510. The gas injection device 503 comprises a nozzle 505 for injecting gas into the measuring pipe 510a and a pushing/pulling device 507 for pushing/ pulling the nozzle 505 into/from the flow path. The pushing/pulling device 507 is connected to a gas controller 509. The gas control device 509 is connected to a high-pressure gas source through a pipe 511. The gas injection device 503 is provided with a gas extraction valve 513. Valves 515 and 517 are mounted on the gas injection device 503. The structural elements of the apparatus are controlled by a controller 519. The operation of the above apparatus will now be described. At the time of normal flow rate measurement, the valves 515 and 517 are opened by the controller 519, and the nozzle 505 is pulled in the pushing/pulling device 507. A signal produced from an electrode 521 is output through the controller 519. At the time of cleaning of the pipe, the valves 515 and 519 are closed by the controller 519, and the nozzle 505 is pushed out of the pushing/pulling device 507. Then, the controller 519 causes the gas controller 509 to inject gas into the pushing/pulling device 507. The injected gas is supplied into the measuring pipe 510a through the nozzle 505. The injected gas is caused to bubble in the fluid to be measured. The bubbling gas is escaped from the valve 513. The inner surface of the measuring pipe 510a is cleaned by the mixture of bubbling gas and the fluid. During the cleaning, the controller 519 does not output a flow rate signal. In a general sewage disposal plant, a pump is driven intermittently. In such a plant, the pipe can be cleaned while the pump is stopped. Alternatively, the pipe can be cleaned after the controller 519 detected that the flow rate of the fluid to be measured reached a predetermined value and the pump was stopped. Fig. 2 is a cross section showing an example of the structure of the valve 513. A float is normally located in the position A. When gas is injected into the measuring pipe 510a and the pressure within the measuring pipe rises, the float 530 is raised, and the gas within the measuring pipe 510a is escaped. On the other hand, when the liquid level rises and the float shifts to the position B, the liquid is sealed.

Claims: Flow rate measuring apparatus comprising: a flow meter having a measuring pipe (510a) through which passes a liquid the flow rate of which is to be measured and cleaning means, for removing substances adhering to the inside wall of said measuring pipe, and comprising a fluid injection device (503), connected to the measuring pipe, and comprising a nozzle (505) for injecting high pressure fluid onto the inside wall of the measuring pipe, and a device (507) for pushing the nozzle into and withdrawing it out of the flow path, characterized in that said high pressure fluid is a gas, and in that a gas extraction valve (513) is provided for allowing gas to escape from the flow path, and valves (515, 517) are provided respectively upstream and downstream of the measuring pipe, which are arranged to be closed to prevent flow of the liquid to be measured through the pipe during a cleaning operation performed using said fluid injection device.

Inventors: WADA ICHIRO C O INTELLECTUAL P, WADA, ICHIRO C/O INTELLECTUAL PROPERTY DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1989
Main classification: G01F15
IPC codes: G01F1, G01F15, B08B9