GB2397385A

GB2397385A - Apparatus for measuring the rate of flow of an unpressurised medium in a closed conduit

Info

Publication number: GB2397385A
Application number: GB0300366A
Authority: GB
Inventors: Bryan Frederick Davenport; Nigel James Davenport
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-01-08
Filing date: 2003-01-08
Publication date: 2004-07-21
Anticipated expiration: 2023-01-08
Also published as: GB2397385B; GB0300366D0

Abstract

A flow measuring apparatus for measuring the rate of flow of an unpressurised non-gaseous medium in a closed conduit comprises level coaxial pipework sections 2, 3, 4 for location in or as a section of the closed conduit. The sections comprise an approach section 2, an entry section 3 joined to a downstream end of the approach section 2, and an exit section 4 located downstream of the entry section 3. The entry section 3 converges uniformly along its length towards the exit section 4, and the exit section 4 diverges uniformly along its length away from the entry section 3. A level sensor 8 is mounted in an upper portion of the approach section 2. The apparatus may additionally comprise a further throat section 5 of pipework with uniform cross-sectional area located between the entry and exit sections 3, 4.

Description

A FLOW MEASURING APPARATUS

The present invention relates to a flow measuring apparatus for measuring the rate of flow of an unpressurized, non-gaseous medium in a closed conduit.

In the following description and in the claims, the term unpressurized flow' should be understood as meaning a flow which occurs solely under the influence of gravity without any additional motive force from a pump or similar device.

Similarly, the term 'closed conduit' should be understood as meaning a pipe, tube or other enclosed channel as opposed to an open-topped channel or gully.

It should be appreciated that unpressurized flow in a closed conduit does not preclude a surcharged flow wherein the non-gaseous medium completely fills the conduit as opposed to running along the bottom of the conduit provided that the surcharge occurs naturally and that a pressure recovery means, such as an expansion chamber or equivalent, is provided upstream of the apparatus to ensure that the non- gaseous medium can develop a natural head of pressure in an approach section of the apparatus as described below.

However, it is expected that under most normal conditions, the flow will not be surcharged and will only part-fill the conduit. Such flow typically occurs in pipes used within the water industry, for example in sewers, water treatment works and the like.

The rate of flow of a non-gaseous medium in an open channel or gully is dependent on the mean velocity of the medium and the cross-sectional area of the flow. Hence, the rate of flow is dependent on the depth of the flow.

Conventional flow measuring apparatus use this fact and operate by measuring the velocity of the flow and its depth - 2 in a channel of predetermined width so that the rate of flow can be to calculated.

A more sophisticated way of measuring the rate of flow is to use a flume, weir or other apparatus which incorporates a restricted channel, called a throat, that generates a predetermined, accurate cross-sectional area of flow which ensures that the mean velocity of the medium is solely dependent on the head created immediately upstream of the throat regardless of any downstream condition. It is then only necessary to measure a single variable, namely the depth of the head created immediately upstream of the throat.

Flumes are usually used in the water industry so that rates of water flow can be measured for various purposes including water supply, effluent control and the like.

Conventionally, flumes have been manufactured either by being cast in situ with a channel or more recently by using preformed cheeks or single- piece troughs which are positioned in a recess in a channel and backfilled with concrete. The level measuring instrument is separately supplied and once position, the flume is calibrated on site.

Similar apparatus to those used in open channels have also been used to measure the rate of unpressurized flow in closed conduits such as sewers and the like by installing them in a part of the system where there is an open channel, such as beneath a manhole or in an access chamber. However, there are several disadvantages with such arrangements, as follows.

1. The throat of the apparatus can severely limit the rate of flow able to pass through the apparatus.

2. The shape of the apparatus may require reconstruction of that part of a conduit approaching the apparatus. - 3

3. The accuracy of the results obtained from the apparatus is directly dependent on the accuracy of the on-site construction of the apparatus.

4. Calibration of the apparatus can be difficult and uncertainties in installation tolerances and flow patterns through the apparatus mean that the accuracy of the apparatus can only be guaranteed with a wide error margin.

The object of the present invention is to provide a flow measuring apparatus for measuring the rate of flow of an unpressurized, non-gaseous medium in a closed conduit which overcomes or substantially mitigates all of the aforementioned disadvantages.

According to the present invention there is provided flow measuring apparatus for measuring the rate of flow of an unpressurized, non-gaseous medium in a closed conduit comprising coaxial pipework for location in or as a section of the closed conduit with its longitudinal axis level and defining an approach section, a level sensor mounted in an upper portion of the approach section, an entry section joined to a downstream end of the approach section, and a exit section located downstream of the entry section, the entry section converging uniformly along its length towards the exit section and the exit section diverging uniformly along its length away from the entry section.

In a first embodiment, the exit section is joined directly to the downstream end of the entry section.

Alternatively, in a second embodiment a throat section with a uniform cross-sectional area is located between the downstream end of the entry section and the upstream end of the exit section. - 4 -

Preferably also, the throat section has a uniform circular crosssectional area.

Preferably also, the approach section defines a uniform cross-sectional area along its length.

Preferably also, the approach section, the entry section and the exit section all define circular cross-sectional areas at all points along their length.

Preferably also, the level sensor is located in a housing which is located above and communicates with the interior of the approach section.

Preferably also, the level sensor comprises a means enabling readings to be taken remotely.

Preferably also, the pipework is fabricated from metal pipework sections which are joined together.

Preferably also the metal pipework sections are made of stainless steel.

Preferably also, the metal pipework sections are joined together by welded joints. Alternatively, the pipework sections are joined together using clamping fasteners.

Preferably also, the pipework is prefabricated and calibrated prior to being located in situ.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: - 5 Figs. 1, 2 and 3 are schematic side, end and plan elevations respectively of a flow measuring apparatus according to the invention; and Fig. 4 is a side elevation of a modified apparatus.

With reference to Figs. 1 to 3, a flow measuring apparatus 1 for measuring the rate of flow of an unpressurized, non-gaseous medium in a closed conduit comprises pipework which defines at least an approach section 2, an entry section 3 and an exit section 4. In a first embodiment, as shown in Figs 1 to 3, a throat section 5 can be interposed between the entry section 3 and the exit section 4. However, in a modified arrangement, as shown in Fig. 4, the throat section 5 is omitted.

The pipework sections 2, 3, 4 and 5, if present, are all coaxial and preferably define circular cross-sectional areas at all points along their length. In additional, the apparatus is designed to be located within or form a part of a closed conduit with its longitudinal axis 6 horizontal so that flow through the apparatus is not influenced by gravity.

The entry section 3 is joined to a downstream end of the approach section 2 and converges uniformly along its length towards the exit section 4. Similarly, the exit section 4 is located downstream of the entry section 3 and diverges uniformly along its length away from the entry section 3. If a throat section 5 is interposed between the entry section 3 and the exit section 4 then it has a uniform, cross-sectional area and it is important that the longitudinal axis through this section 5 is kept level. It will be appreciated that in the modified embodiment shown in Fig. 4, a notional throat section occurs at the joint 7 between the entry section 3 and the exit section 4 where the cross-sectional area of the apparatus is at its smallest. - 6 -

As in a flume, the predetermined convergent and divergent shapes of the entry and exit sections 3 and 4 with the throat 5 or notional throat 7 therebetween creates a restriction in the flow. This means that the mean velocity of the non-gaseous medium flowing through the apparatus 1 is solely dependent on the head created in the approach section 2 immediately upstream of the throat. It is then only necessary to measure a single variable, namely the depth of the head created in the approach section. To this end, a level sensor 8 is located in an upper portion of the approach section 2, preferably by being attached to a bracket (not shown) in a housing 9 that is mounted above and that communicates with the interior of the approach section 2. The housing 9 may comprise a pipe that can be accessed, for example, via a manhole 10 which is normally closed by a cover (not shown). Alternatively and preferably in many applications, the level sensor 8 comprises a transducer enabling readings to be taken remotely, for example by the provision of a radio link, or similar, to external apparatus.

Once installed, therefore, the apparatus never needs to be accessed directly except for maintenance purposes.

Conveniently, the manhole 10 can be made suitable for this purpose but in all cases it is important to ensure that the sensor 8 is not disturbed otherwise the apparatus may require recalibrating.

Although the pipework sections 2, 3, 4 and 5 could be manufactured by being cast from a mouldable material such as plastics or concrete, preferably the apparatus is fabricated from metal pipework sections which are joined together. The joints may be formed using clamping fasteners but preferably the joints are welded. Also, the sections 2, 3, 4 and 5, if present, are preferably made from stainless steel to obviate corrosion occurring, which over time will affect the accuracy of the measurements taken by the sensor 8. - 7 -

While the apparatus 1 could be manufactured totally in situ, preferably the apparatus 1 is prefabricated and calibrated prior to being installed. The dimensions of the apparatus 1, in particular the cross-sectional area of the various pipework sections 2, 3, 4 and 5 can be predetermined in accordance with the dimensions of the conduit in which the apparatus 1 is to be installed. Accurate measurements must be made of the interior dimensions of the pipework sections after fabrication for use in calibration of the apparatus 1.

Also, after fabrication of the pipework of the apparatus 1, the level sensor 8 is mounted in place and the distance between the operative face of the sensor and the opposing surface of the approach section 3 accurately measured and recorded. This distance measurement is also used as part of the calibration data for the apparatus.

The apparatus is now ready for shipment and location in the conduit where it is to be used. It is expected that the apparatus could be used either to replace a portion of an existing conduit or fit inside an existing conduit which is modified to ensure all flow occurs through the apparatus. It will also be appreciated that the apparatus can be built-in to form a portion a newly constructed conduit.

Once the apparatus has been located in the correct position on site with its longitudinal axis 6 horizontal, the apparatus 1 should be held rigidly in place, for example by backfilled around the exterior of the pipework with a construction material such as concrete. To assist in the retention of the axis 6 in a horizontal position, the apparatus may be provided with adjustable feet (not shown) or a base frame (not shown) which enables the position of the assembly 1 to be finely adjusted during positioning in its location. Such feet can comprise simple screw mounted feet so - 8 that the level of the assembly 1 can be altered to that required.

The detailed measurements taken after fabrication and prior to installation of the apparatus are used to produce accurate calibration data for the apparatus 1 without any need for a further visit to its location after installation.

Hence, the calibration data or precalibrated instrumentation can be provided along with the assembly 1 as a complete package. However, the apparatus 1 can be independently calibrated using known volumetric or gravimetric techniques Thus the invention provides a flow measuring apparatus which substantially overcomes the problems described above.

It can be prefabricated in a factory or workshop and may be shipped to site with full calibration data because when fitted with reasonable care the dimensions and tolerances of the apparatus will not vary.

Once set up and calibrated, the pipework sections 2, 3, 4 and 5, if present, generate a predetermined, accurate cross-sectional area of flow which ensures that the mean velocity of the unpressurized, non-gaseous medium is solely dependent on the upstream head created within the approach section 2. It is then only necessary to measure the depth of the head by means of the level sensor 8 to be able to calculate the rate of flow of the medium. Such measurements will be accurate regardless of whether the flow is above or below the top of the throat section 5 or the joint 7. - 9 -

Claims

1. A flow measuring apparatus for measuring the rate of flow of an unpressurized, non-gaseous medium in a closed conduit comprising prefabricated, coaxial pipework for location in or as a section of the closed conduit with its longitudinal axis level and defining an approach section, a level sensor mounted in an upper portion of the approach section, an entry section joined to a downstream end of the approach section, and a exit section located downstream of the entry section, the entry section converging uniformly along its length towards the exit section and the exit section diverging uniformly along its length away from the entry section.

2. An apparatus as claimed in Claim 1, wherein the exit section is joined directly to the downstream end of the entry section.

3. An apparatus as claimed in Claim 1, wherein a throat section with a uniform cross-sectional area is located between the downstream end of the entry section and the upstream end of the exit section.

4. An apparatus as claimed in Claim 3, wherein the throat section has a uniform circular cross-sectional area.

5. An apparatus as claimed in any of Claims 1 to 4, wherein the approach section defines a uniform cross-sectional area along its length.

6. An apparatus as claimed in any of Claims 1 to 5, wherein the approach section, the entry section and the exit section all define circular crosssectional areas at all points along their length. -

7. An apparatus as claimed in any of Claims 1 to 6, wherein the level sensor is located in a housing which is located above and communicates with the interior of the approach section.

8. An apparatus as claimed in any of Claims 1 to 7, wherein the level sensor comprises a means enabling readings to be taken remotely.

9. An apparatus as claimed in any of Claims 1 to 8, wherein the pipework is fabricated from metal pipework sections which are joined together.

10. An apparatus as claimed in Claim 9, wherein the metal pipework sections are made of stainless steel.

11. An apparatus as claimed in Claim 9 or Claim 10, wherein the metal pipework sections are joined together by welded joints.

12. An apparatus as claimed in Claim 9 or Claim 10, wherein the pipework sections are joined together using clamping fasteners.

13. An apparatus as claimed in any of Claims 1 to 12, wherein the pipework is prefabricated and calibrated prior to being located in situ.

A flow measuring apparatus for measuring the rate of flow of an unpressurized, non-gaseous medium in a closed conduit substantially as described herein with reference to Figs. 1 to 3, or Fig. 4 of the accompanying drawings.