GB2513645A

GB2513645A - Improvements in liquid level gauges

Info

Publication number: GB2513645A
Application number: GB201307988A
Authority: GB
Inventors: Peter Cipriani; Otto Herman Varga
Original assignee: Seetru Ltd
Current assignee: Seetru Ltd
Priority date: 2013-05-02
Filing date: 2013-05-02
Publication date: 2014-11-05
Also published as: GB201307988D0

Abstract

A vented float 100 for a liquid level gauge with a hollow body has a top end, a bottom end and an internal cavity 103. A vent passage 114 is provided having an upper end open to the exterior of the body and a lower end opening into the internal cavity whereby liquid collecting in the bottom of the cavity can be forced up through the passage by a pressure difference between the interior and exterior. The body may comprise a tube and top 101 and bottom 109 end caps which define the internal cavity. The vent passage may comprise a bore in the top end cap joined to a vent tube which extends along the vent passage. The vent passage may comprise a capillary tube. The float may comprise a magnet 105a,b held centrally within the tube of the body by a holder 106a,b.

Description

IMPROVEMENTS IN LIQUID LEVEL GAUGES

This invention relates to a vented float for a magnetic liquid level gauge in which the float floats on liquid in a by-pass tube which is connected top and bottom to a vessel and the level of the liquid is indicated by a magnetic follower ring rising and falling on the outside of the by-pass tube in unison with the magnetic tloat inside the tube.

Background

Floats in magnetic by-pass type liquid level gauges are often sealed, in which case they risk being crushed if the pressure of the vessel is elevated. A vented float is insensitive to the pressure, but is then exposed to condensation forming in the float which may increase its weigh! to the extent that it can no longer float on the liquid to be indicated which may be of low specific gravity.

The present invention provides: a vented float arrangement in which any condensation trapped in it is expelled as the pressure in which it operates falls from a previous level; and a liquid level gauge comprising the vented float arrangement.

Statements of Invention

According to a first aspect the invention provides a vented float for a liquid level gauge which may comprise a hollow body having a top end, a bottom end and an internal cavity, wherein a vent passage may be provided having an upper end open to the exterior of the body and a lower end opening into the internal cavity whereby liquid collecting in the bottom of the cavity can be forced up through the passage by a pressure difference between the interior and exterior of the cavity.

The body may be elongate and cylindrical. The body may coniprise a tube and top and bottom end caps at the ends of the tube which define the internal cavity. The internal cavity may substantially fill the body volume. The internal cavity may be tapered towards the bottom, and the lower end of the vent passage is located towards the bottom of the taper.

The upper end of the vent passage may be formed in the side of the top end cap. The upper end of the vent passage may be located in the circumfcrcncc of the top end cap.

The end caps may be welded to the tube or fitted with a sealing means such as an 0-ring seal. The top surface of the top end cap may be tapper to prevent liquid resting on top of the float.

The vent passage may comprise a bore in the top end cap joined to a vent tube which cxtcnds the vcnt passage downwards from thc top end cap. Thc borc may cxtcnd from the side of the top end cap towards the centre of the body tube where it joins the vent tube. From the side of the top end cap to the centre of the tube the bore may extend at an inclined angle above horizontal. The vent tube may run down the centreline of the body tube. The vent passage may comprise a capillary tube. Capillary tube may be used to draw liquid out of the reservoir under capillary action.

The float may comprise a magnet held within the body of the float. The magnet may be a ring magnet. The magnet may be held centrally within the tube of the body by a holder. The holder may support the vent tube in the centre of the body tube.

According a second aspect the invcntion provides a liquid lcvcl indicator which may comprise a cylindrical bypass tube and the vented float according to the first aspect of the invention.

The bypass tube may be made of a non-magnetic material and may comprise a follower ring comprising a magnet arranged to slide over the external surface of the bypass tube. The bypass tube may comprise connectors at either end of the tube for connection to a vessel. Each connector may comprise an isolation valve for isolating the gauge from the vessel. The bypass tube may comprise a valve for depressurising the by-pass tube.

Specific Description

By way of example only, embodiments of the invention are described below with reference to the accompanying drawings in which: Figure I is a section drawing showing a view of a vented float according to an embodiment of the invention; Figure 2 is a section drawing showing a view of a level indicator including the float of Figure I; and Figure 3 is a schematic drawing showing a modification to the level indicator of Figure 2.

Referring to Figure 1, a vented float has a body 100 which comprises an elongated cylindrical tube 104 with a top end cap 101 and a bottom end cap 109. The end caps and the tube define an internal cavity 103 to the body which substantially fills the volume of the body.

The bottom end cap 109 has a sealing plug 107 which is received into the open end of the tube 104 which closes the end of the tube and supports an 0-ring seal 108 in a groove which forms a leak proof seal between the end cap 109 and the internal wall of the tube 104. The end cap also has a tapered recess 112 in the centre of the sealing plug 107 which tapers inwards towards its bottom and is open to the cavity 103 at its top end. The tapered recess 112 forms part of the boundary to the internal cavity 103 of the body when it is inserted into the tube 104. The end cap 109 also coniprises a rim 111 which is external to the tube and abuts the end of the tube. The rim has a diameter which is wider than the diameter of the tube and is sized so that it locates the bottom of the float centrally within the upright by-pass tube 204 (see Figure 2) without interference between the two allowing the float 100 to slide within the by-pass tube 204.

The top end cap 101 has a sealing plug 113 which is received within the open end of the tube which supports an 0-ring 114 around the internal circumference of the tube creating a leak proof seal between the end cap 101 and the tube 104. The top end cap 101 also has a rim 116 which is external to the tube. The rim 116 has a diameter which is wider than the diameter of the tube 104 and is sized so that it locates the top of the float centrally within the upright by-pass tube 204 (see Figure 2) without interference between the two allowing the float to slide within the by-pass tube 204.

Above the external rim 116 the top end cap is tapered to a central point 117. The top end cap 101 has a vent passage 115 extending through it. The vent passage comprises a small radial bore in the top end cap with an opening that lies on the circumference of the top end cap between the rim 115 and the end of the tube 104. The vent passage I 14 extends from the circumference of the end cap I 17 parallel to the taper above the external rim 116 until it reaches the centre the tube where it changes direction through an angle of approximately 110 degrees to join a small axial bore that follows the centre line of the tube out of the centre of the scaling plug in the top end cap and into the internal cavity. The vent passage is extended down to the base of the internal cavity by a vent tube 102. The vent tube 102 is supported at its top end in the axial bore in the centre of the sealing plug and extends down the centreline of the tube to the bottom end cap leaving a small clearance between the opening 110 in the bottom end of the vent tube and the bottom of the tapered reservoir fonned by the wall of the bottom end cap 109.

In this embodiment the end caps are removable plugs, however it will be appreciated that other arrangements are possible such as welded end caps which do not require an 0-ring seal.

Within the internal cavity of the body two magnet holders 106a, 106b are positioned separated apart from one another along the longitudinal axis of the tube 104. Each of the magnet holders has an 0-ring in its outer circumference which fits against the inner surfacc of the tube 104 to locate it in position. Each supports a single ring magnet 105a, 105b. The ring magnets allow the vent tube to pass through the centre of the tube. Each of the magnet holders I 06a and 1065 also has an aperture through its centre though which the tube 102 passes so that the tube 102 is supported on the axis of the tube 104 by the magnet holders.

Referring to Figure 2, a level gauge 200 comprises an upright non-magnetic by-pass tube 204 inside which the vented float 100 is free to slide up and down. The by-pass tube is connected by top 201 and bottom 203 connectors to a vessel containing liquid in which the level of liquid requires monitoring. A follower ring is free to slide up and down the external surface of the by-pass tube. The follower ring comprises a ring magnet 203.

Referring to Figure 3, a level gauge 300 comprises an upright by-pass tube 305 inside which the vented float 100 is free to slide up and down with the liquid level 303. The by-pass tube comprises top 301 and bottom 304 isolation valves which are arranged to isolate the by-pass tube from the vessel 302. Between the top isolation valve 301 and the upright by-pass tube 305 a pressure relief valve 306 is fitted which is arranged to release pressure in the by-pass tube to atmosphere.

In use when the level gauge is fitted to a vessel which is filled or partly filled with liquid, liquid will enter the bypass tube at the bottom connector 203 and will rise up the bypass tube 204 until it reaches the level of liquid in the vessel. Both the bypass tube and the vessel will maintain the same level of liquid because the top connector 201 allows the pressure in both to equalise. The float's large internal cavity 103 provides it with buoyancy. Providing the specific gravity of the float is lower than that of the liquid it will float on the liquid and rise and fall with the liquid level in the vessel. Movement of the float causes corresponding movement of the follower ring 202 on the external surface of the by-pass tube 204 which provides a clear indication of the liquid level in the vessel to an observer. The follower 202 follows the float because of the magnetic attraction between the two ring magnets 105a, 105b of the float and the ring magnet 203 on the follower 202.

In vessels which are kept under high pressure a non-vented float with an internal cavity sealed at atmospheric pressure can be crushed under the pressure of the system.

Providing a vent hole in the top of the float above the liquid level in the bypass tube can solve this problem. However, providing a vent hole in the float then creates the problem of the possibility of liquid collecting within the internal cavity of the float increasing the specific gravity of the float so that it floats at a different height relative to the surface of the liquid being measured. This obviously affects the accuracy of the gauge. The weight of liquid collected in the tloat can potentially get to the point where the float can no longer float on the surface of the liquid and provide an indication of the vessel's liquid level. Vaporised liquid may enter the float and then condense on the wall of the inner cavity where it will collect in the base of the cavity.

Because the base of the cavity is sealed the condensed liquid has no means of escape.

The vented float of Figure I can expel any liquid which has condensed within its internal cavity by providing a vent passage which is directed towards where the liquid collects in the reservoir at the base of the internal cavity. By depressurising the vessel, higher pressure gas within the internal cavity tries to escape from the float sucking any liquid which has collected in the base of the cavity out with it. Because the float is vented the pressure of the internal cavity will always seek to equalisc with the pressure of the vessel. Therefore in a system with fluctuating system pressure the float will automatically expel any liquid in the float when the system depressuriscs.

In systems which operate at constant pressure for long periods of time, the system can be slightly depressurised either manually or automatically for a short period while observing the follower ring, if the ring does not move then there is no condensation within the float, if the ring starts to risc then depressurisation should continue until the float rises no further meaning the liquid has all been expelled.

Alternatively the vent passage may comprise one or more capillary tubes which draw out liquid that collects in the internal cavity of the float by capillary action.

It will be appreciated that an automatic depressurisation cycle may be designed into the pressure control system for the vessel in order to provide automatic expulsion of condensate from the float as required.

Referring to Figure 3, the isolation valves 301 and 304 allow the upright by-pass tube to be isolated from the vessel 302 by closing both valves. Once isolated, the by-pass tube can be depressurised, in order to vent the float, by opening the depressurising valve 306. In this method, the main vessel 302 can be kept pressurised while the by-pass tube is depressurised. The float is fully vented once it can be observed that depressurising is not affecting the buoyancy for the float and therefore all fluid has been forced out of the float. Once vented, the pressurising valve can be closed and the isolation valves opened to rcturn the by-pass tube to opcration.

In order to optiniise the expulsion of liquid from the float, the tapered cavity of the bottom end cap gathers the liquid around the base of the vent tube which has a narrow clearance between the end of the vent tube and the wall of the end cap. Therefore any liquid which fills this clearance will be sucked out before any gas can escape via the vent passage. The vent passage in the top end cap 101 is first directed upwards from the vent hole in order to prevent drips of condensation landing on the vent hole and running down the vent passage into the internal cavity 103. The tapper point 117 above the external rim 116 of the top end cap prevents condensation sitting on top of the float affecting its specific gravity and also directing it away from the vent hole.

Claims

SCLAIMS1. A vented float for a liquid level gauge comprising a hollow body having a top end, a bottom end and an internal cavity, wherein a vent passage is provided having an upper end open to the exterior of the body and a lower end opening into the internal cavity whereby liquid collecting in the bottom of the cavity can be forced up through the passage by a pressure difference between the interior and exterior of the cavity.
2. A vented float according to claim 1 wherein the body comprises a tube and top and bottom end caps at the ends of the tube which define the internal cavity.
3. A vented float according to any preceding claim wherein the internal cavity is tapered towards the bottom, and the lower end of the vent passage is located towards the bottom of the taper.
4. A vented float according to claim 2 wherein the upper end of the vent passage is formed in the side of the top end cap.
5. A vcntcd float according to any of claims 2 to 4 whcrcin the vent passage comprises a bore in the top end cap joined to a vent tube which extends the vent passage downwards from the top end cap.
6. A vented float according to claim S wherein the bore extends from the side of the top end cap towards the centre of the body tube where it joins the vent tube.
7. A vented float according to claim 6 wherein the bore extends from the side of the top end cap towards the centre of the body tube at an inclined angle.
A vented float according to any of claims 5 to 7 wherein the vent tube runs down the centreline of the body tube.
9. A vented float according to any preceding claim wherein the vent passage comprises a capillary tube.
10. A vented float according to any preceding claim wherein the float comprises a magnet held within the body of the float.
11. A vented float according to claim 10 wherein the magnet is a ring magnet.
12. A vented float according to claim 10 or 11, when dependent on claim 2, wherein the magnet is held centrally within the tube of the body by a holder.
13. A vented float according to claim 12, when dependent on claim 5, wherein the holder supports the vent tube in the centre of the body tube.
14. A liquid level indicator comprising a cylindrical bypass tube and the vented float according to any of claims I to 13.
15. A liquid level indicator according to claim 14 wherein the bypass tube is made of a non-magnetic material and a follower ring comprising a magnet is arranged to slide over the external surface of the bypass tube.
16. A liquid lcvcl indicator according to claim 15 wherein the bypass tube comprises connectors at either end of the tube for connection to a vessel.
17. A liquid level indicator according to claims 16 wherein each connector comprises an isolation valve for isolating the gauge from the vessel.
18. A liquid level indicator according to claim 17 wherein the bypass tube comprises a valve for depressurising the by-pass tube when the isolation valves are closed.
19. A vented float or liquid level indicator substantially as described herein with reference to the accompanying drawings.