GB2521464A

GB2521464A - Flow monitoring system

Info

Publication number: GB2521464A
Application number: GB1322760.8A
Authority: GB
Inventors: John Kosovich
Original assignee: Mincon International Ltd
Current assignee: Mincon International Ltd
Priority date: 2013-12-20
Filing date: 2013-12-20
Publication date: 2015-06-24
Also published as: GB201322760D0; WO2015091866A1

Abstract

A flow monitoring system for a hydraulic apparatus is provided. The flow monitoring system comprises means, in the form of a valve 10, for restricting the flow of hydraulic fluid to the apparatus if a difference between an outward flow rate of hydraulic fluid in pressure line 5 and a return flow rate of the hydraulic fluid in return line 8 exceeds a threshold.

Description

FLOW MONITORING SYSTEM

Field of the Invention

The present invention relates to measurement of flow rates of hydraulic fluid in hydraulic systems and in particular to the measurement of flow rates to detect leakages.

Background to the Invention

In hydraulic apparatus, the leaking of hydraulic fluid due to a component failure can lead to a number of problems such as damage to equipment, danger to equipment operators and pollution of the surrounding area. For example, in a hydraulic down the hole hammer drilling system there is a significant risk of hydraulic fluid being lost into a drilled hole in the event of a seal failure in the hammer or its ancillaries, In such cases, the hydraulic fluid, which is usually oil, is forced out of the hammer or drill string by the supply pressure, which is typically in the range t50 to 250 bar. In some cases seal failure may be obvious to the drilling rig operator, manifesting itself in reduced hammer performance and/or hydraulic fluid visibly ejected from the hole with the drill cuttings. In these situations, a competent and focused rig operator can quickly shut down the supply of hydraulic fluid to the hammer mechanism, limiting the fluid loss. However, in many cases, the failure will be less obvious to detect, such as where the fluid leak is not significant enough to influence hammer performance or where the fluid ejected from the hole is mixed, or otherwise confrised, with groundwater ejection. In these situations significant amounts of hydraulic fluid can be lost, even by competent operators, with significant cost arid/or environmental impact.

Conventional drilling rig design normally allows for a level switch, within the hydraulic fluid storage tank which will shut down all hydraulically operated rig functions when the level in the storage tank falls below a pre-set minimum. It is possible for these existing control systems to limit hydraulic fluid loss in the event of a down-hole seal failure. However these systems are, by necessity, a coarse control method, as they must allow for normal fluctuations of fluid level which occur when the rig's many hydraulic cylinders are extended or retracted, and so only act when there is a gross fluid level reduction. As a further limitation, such level switches are not sensitive to fluid loss from a specific part of the drilling rig and apply a blanket prevention of all rig functions. Often, in such level triggered shutdowns, many hydraulic functions could continue normally, and indeed may be needed to prevent, or recover from, an emergency situation.

It is therefore desirable to provide a system that simplifies and improves the sensitivity of leak detection within a hydraulic system, to assist in the reduction of hydraulic fluid loss through a variety of mechanisms. It is also desirable to provide a variety of loss prevention mechanisms appropriate to the various types of hydraulic drilling rig in common use.

Summary of the Invention

According to an aspect of the present invention, there is provided a flow monitoring system for a hydraulic apparatus comprising means for restricting (or preventing) the flow of hydraulic fluid to the apparatus if a difference between an outward flow rate of hydraulic fluid and a return flow rate of the hydraulic fluid exceeds a threshold.

The term "outward" is used herein to indicate a direction from a fluid reservoir to the hydraulic apparatus and the term "return" is used to indicate a direction from the hydraulic apparatus to the reservoir. Thus, the outward flow rate may he the flow rate of fluid from the reservoir to the apparatus (or between two intermediate points), that is, the flow rate of pressure fluid to the apparatus, and the return flow rate may be the flow rate of fluid from the apparatus to the reservoir (or between two intermediate points), that is, the flow rate of return fluid from the apparatus, An advantage of this arrangement is that the difference between the outward flow rate and the return flow rate can be used to make a determination as to whether there has been a sufficient decrease in the flow rate to indicate that an external leakage of hydraulic fluid has occurred at a point within the hydraulic apparatus. Some small variance in the volumetric flow rate between the pressure fluid and the return fluid may be expected in normal operation, due to compressibility and thermal expansion effects. To avoid the system signalling a fault erroneously in the event of these normal variations, a threshold may be set, corresponding to a predetermined proportion of the outward flow rate, which allows the system to act when fluid loss is apparent but also to avoid being overly sensitive. Thus, the flow of hydraulic fluid to the apparatus will only be restricted if the difference between the outward flow rate and return flow rate exceeds a predetermined threshold. This is a significant advantage as it provides a mechanism for indicating if a leakage has occurred and frirther limits the amount of fluid loss which would occur in the event of a leakage.

In one embodiment, the system may comprise a first positive displacement hydraulic device coupled to a pressure line configured to cany fluid from the reservoir to the apparatus and a second positive displacement hydraulic device coupled to a return line configured to carry fluid from the apparatus to the reservoir.

This is advantageous as the positive displacement devices provide a simple mechanical means of assessing fluid flow in the pressure and return lines.

The first positive displacement device may be arranged to operate as a motor, and the motor speed may be proportional to the outward fluid flow rate through the motor.

The second positive displacement device may be arranged to operate as a pump, and the first positive displacement device and the second positive displacement device may be coupled such that the second device moves at the same speed as the first. The second displacement device may have a lesser displacement than the first displacement device. Because of this, the flow of hydraulic fluid through the second displacement device may cause a back pressure in the return line.

Coupling the first displacement device to the second displacement device means that the motor speed imparted to the first device by the outward flow of fluid through the pressure line is transferred to the second displacement device, which operates as a pump. Furthermore, if the second displacement device has a smaller displacement than the first displacement device, it follows that, if there is no significant reduction in the return fluid flow rate in the return line compared to the outward fluid flow rate in the pressure line, a back pressure will build at the second displacement device.

The means for restricting may comprise a valve moveable between an open position in which hydraulic fluid is permitted to flow from the reservoir to the apparatus and a closed position in which hydraulic fluid is prevented from flowing from the reservoir to the apparatus, and the back pressure in the return line may act upon the valve to maintain it in the open position. The restricting means may restrict the flow of hydraulic fluid by closing the valve when the pressure in the return line drops below a predetermined threshold. In normal operation, when no leak is present, the back pressure in the return line may act upon the valve in order to keep the valve in an open position and thus permit unrestricted fluid flow to the apparatus. However, if the S return fluid flow rate drops, due to a leakage, then the back pressure which occurs as a result of the normal return line flow rate will also drop.

In this embodiment, when the difference between the outward flow rate and the return flow rate exceeds a threshold, the back pressure acting upon the valve is insufficient to maintain the valve in the open position. Thus, the valve may close and restrict the flow of hydraulic fluid to the apparatus. This is advantageous as it allows the difference in flow rate between the pressure line and return line to be used to control whether hydraulic fluid should be allowed to continue flowing to the system or whether the hydraulic fluid flow should be restricted. In a preferred embodiment, the threshold is configured at about 95?/b of the outward flow rate.

In an alternate embodiment of the invention, the system comprises a first flow meter coupled to a pressure line configured to carry fluid from the reservoir to the apparatus; and a second flow meter coupled to a return line configured to carry fluid from the apparatus to the reservoir; wherein the first flow meter produces a first electrical output proportional to the outward flow rate and the second flow meter produces a second electrical output proportional to the return flow rate.

These electrical output flow meters can measure either volumetric or mass flow rates, to allow precise control. This embodiment provides an alternate means of determining the fluid flow rates in the pressure line and the return line.

In this embodiment, the first electrical output and the second electrical output are voltages. This provides a means of allowing the fluid flow rates in the pressure line and the return line to be translated into an electrical output.

The system may further comprise a voltage comparator. The first output and the second output are input to the voltage comparator to produce a comparator output.

Preferably, the comparator is configured such that when the difference between the first electrical output and the second electrical output exceeds the threshold, the comparator output is a first voltage (or logic) level, and otherwise, the comparator output is a second voltage (or logic) level. This provides an arrangement which allows for the flow rates in the pressure and return lines to be compared and for the comparison to produce a detectable output signal. The comparator output of the system may be coupled to the means for restricting the flow, The restricting means of the system restricts the flow of hydraulic fluid if the comparator output is the first voltage level. In one embodiment, a high comparator output is triggered if the difference in flow meter outputs exceeds the predetermined threshold, Alternatively, a low comparator output may be triggered if the difference in flow meter outputs exceeds the predetermined threshold. The means for restricting may comprise a circuit to operate a control valve between an open position in which hydraulic fluid is permitted to flow from the reservoir to the apparatus and a closed position in which hydraulic fluid is prevented from flowing from the reservoir to the apparatus, In an alternate embodiment of the invention, the first output and second output may comprise digital electronic outputs, The first output and second output may be input to a controller. The controller of the system may comprise a digital control system, This provides an advantage in that digital signals may be more easily transmitted to a range of devices meaning that control may be performed off site or over a network, Furthermore, digital signals allow for greater provision of command controls such as restart of the system after a failure or greater ease of data capture and archiving of historical flow rates and working conditions of the system, This is particularly advantageous for system optimisation and fault analysis, The controller may comprise a CAN controller module. This provides the advantage of an established set of control instmctions operating on a robust protocol. The controller may produce a controller output that corresponds to a difference between the outward flow rate and the return flow rate, The controller of the system may restrict the flow of hydraulic fluid, for example by activating a valve, if the difference between the inputs to the controller from the first flow meter and second flow meter indicates a fault condition. The system may be configured such that if the difference between the first and second outputs exceeds the threshold, a digital fault signal is output by the controller. The digital fault signal may be used to operate a valve which restricts hydraulic fluid to the apparatus.

Description of the Drawings

Figure 1 is a representation of a typical hydraulic down the hole hammer drilling rig; Figures 2 and 2A are schematic representations of a flow monitoring system for a hydraulically controlled drilling rig; Figures 3 and 3A are schematic representations of a flow monitoring system for an electrically controlled drilling rig; and Figure 4 is a schematic representation of a flow monitoring system for an electronically controlled drilling rig.

S Detailed Description of the Drawings

Figure 1 shows a hydraulic apparatus in the form of a typical hydraulic down the hole drilling rig. Hydraulic fluid is drawn from the reservoir 1 by percussion pump 2, pressurised, and then fed to the hammer 3 via the percussion control valve 4, pressure line 5, hydraulic swivel 6 and drill rod(s) 7, Once this hydraulic fluid has passed through the hammer's percussion mechanism it is returned, at low pressure, to the reservoir I via the drill rod(s) 7, hydraulic swivel 6, return line 8 and return filter 9.

During normal operation of the system the flow of fluid to the hammer through pressure line 5 will be fully returned to the reservoir 1 via return line 8. However, if there is an external leak from the system during operation, some of the pressurised fluid supplied via pressure line S will not be delivered back on return line 8.

The flow monitoring system of the invention allows the two flow rates to be compared such that they can be used to recognise fluid loss, for example such as that caused by a seal failure, and trigger a system which acts to prevents further fluid loss.

The flow monitoring system comprises means for restricting the flow of hydraulic fluid to the hammer 3 if a difference between an outward flow rate of hydraulic fluid from the reservoir I to the hammer and a return flow rate of the hydraulic fluid from the hammer to the reservoir I exceeds a threshold.

A first embodiment of the invention is shown in greater detail in Figures 2 and 2A, In this embodiment, the flow monitoring system for the hydraulic down-the-hole hammer 3 further comprises a comparator II comprising a first positive displacement hydraulic device or motor 1 1A coupled to the pressure line 5 from the reservoir 1 to S the drilling apparatus or hammer 3 and a second positive displacement hydraulic device or pump B coupled to a return line 8 from the hammer 3 to the reservoir I. In alternate embodiments, the comparator may be based on moveable spools, or a rotary valves.

The flow monitoring system also includes means for restricting the flow of hydraulic fluid comprising a valve 10 moveable between an open position in which hydraulic fluid is permitted to flow from the reservoir t to the hammer 3 and a closed position in which hydraulic fluid is prevented from flowing from the reservoir I to the hammer The valve lOis installed between the percussion control valve 4A and the hydraulic swivel 6. The percussion control valve 4A is a two position, open centre type control valve. However, the flow monitoring system of the invention is equally applicable to all hydraulic system control valve types, for example, open or closed centre, load sensing or otherwise. The valve lOis controlled by a pilot pressure from the flow comparator 1]. This embodiment is shown in greater detail in Figure 2A, Pressure fluid delivered from percussion pump 2 passes through the percussion control valve 4A to the valve to, and then on through side A of comparator t t, before being delivered to the apparatus or hammer 3 via the pressure line 5, The pressure fluid rotates the first motor 1 1A at a speed proportional to the outward fluid flow rate.

The motor I IA and the pump II B are coupled such that the pump I I B moves at the same speed as the motor I A. The motor I IA of the comparator II is connected to the pump 1 lB of the comparator 11 via a shaft. This causes the pump 1 lB on side B of the flow comparator t t to rotate at the same speed as motor t tA on side A of the flow comparator II. Hydraulic fluid being returned from the hammer 3 to the storage tank I via return line 8 passes through side B of the comparator II. The pump II B on side B of the comparator 11 has a smaller displacement (1-2% smaller) than the motor tA on side A, that is, pump t lB displaces 1-2% less fluid than motor I IA when rotating at the same speed. Thus, the flow of hydraulic fluid through the pump I B causes a back pressure in the return line 8. This smaller displacement, together with the volume difference created by the fluid's compressibility, means that a back pressure is created in the return line 8. This back pressure is applied to the valve 10 to pilot it into the open position, as shown in Figure 2A. A low pressure relief valve 12 keeps this back pressure within acceptable limits (approx. 5 bar) by passing the excess return fluid directly to the storage tank 1.

The flow monitoring system is configured with a threshold flow rate for the return line 8, as a percentage of the pressure line flow rate, so that during operation, if there is an external leak from the hammer 3 or drill string, such that, if the difference in the flow rates exceeds the threshold, the system restricts the flow of hydraulic fluid supply.

When the difference between the outward flow rate and the return flow rate exceeds a threshold, the back pressure acting upon the valve lOis insufficient to maintain the valve 10 in the open position. If the threshold is exceeded, the back pressure in return line 8 drops and thus the force piloting the valve 10 to the open position (as shown) reduces accordingly. At the point where the pilot pressure force reduces below the force of the return spring 13, the valve 10 will move to the closed position. A detent 16 on this valve will hold it in this position until a reset occurs, To reset the valve 10 after a fault, it may be manually moved via a lever 14 or via a pilot pressure signal on a line 15. A reset signal may also be used for initial start-up of the system. A small accumulator 17 and drain orifice 18 connected to the pilot line ensures that the shutoff valve 10 is not activated by short term transients in the return flow.

A second embodiment of the invention is shown in Figure 3. In this embodiment, the flow monitoring system comprises a first flow meter 20 coupled to a pressure line 5 that carries fluid from the reservoir 1 to the hammer 3 and a second flow meter 21 coupled to a return line 8 that carries fluid from the hammer to the reservoir 1. The first flow meter 20 produces a first electrical output proportional to the outward flow rate and the second flow meter 21 produces a second electrical output proportional to the return flow rate.

The flow meters 20,21 produce electrical outputs which are proportional to the fluid flow in the pressure 5 and return lines 8 respectively. These flow meters can measure either volumetric or mass flow rates. In the embodiment shown in Figure 3, the electrical outputs are voltage outputs. In alternate embodiments, the outputs may be current outputs. In the embodiment of Figure 3, the flow meter 20,21 outputs are used as inputs into a voltage comparator 22 to produce a comparator output. In the embodiment of Figure 3, if the return flow rate is equal to or above a predetermined percentage of the outward flow rate, the comparator output is a logical low, and, if the return flow rate falls below the predetermined percentage of the outward flow rate, the comparator output switches to a logical high. In an alternate embodiment, the comparator may be configured such that if the return flow rate is equal to or above a predetermined percentage of the outward flow rate the comparator output is a logical high and, if the return flow rate falls below the predetermined percentage, the comparator output switches to a logical low. The comparator output is used for control of the flow monitoring system.

The flow monitoring system of Figure 3 also includes means for restricting the flow of hydraulic fluid to the hammer, which comprises a circuit to operate the control valve 4B between an open position in which hydraulic fluid is permitted to flow from the reservoir to the hammer and a closed position in which hydraulic fluid is prevented from flowing from the reservoir to the hammer.

In the embodiment of Figure 3, the circuit acts to close the control valve 4B and thus restricts the flow of hydraulic fluid if the comparator 22 output is high. The circuit comprises a relay 23 which intemipts power supply to a solenoid 19 when a pre-set threshold flow differential is reached. Once power supply to the solenoid is interrupted, the control valve 4B closes and restricts further supply of hydraulic fluid to the hammer.

This embodiment is shown in greater detail in Figure 3A. The relay is a normally closed circuit design with an adjustable time delay on activation. The time delay ensures that the pressure fluid supply is not interrupted by transient variations to the return flow or during initial start-up. The relay is wired to provide a hold-in or latching feature once activated. A restart of the system requires either that the percussion ON signal is removed and reapplied or the reset switch 24 is activated.

Warning lights, audible alarms or other features can also be operated by the relay 23 once a fault condition occurs.

S A third embodiment of the invention is shown in Figure 4. The embodiment shown in Figure 4 comprises a first flow meter 25 on the pressure line 5 producing a first output and a second flow meter 26 on the return line 8 producing a second output. The first output and second output are digital electronic outputs. These flow meters can measure either volumetric flow rates or mass flow rates. The first output and the second output are input to a controller 27 comprising a digital control system to produce a controller output which corresponds to a difference between the outward flow rate and the return flow rate.

The controller 27 is a controller area network (CAN) module. The digital outputs from the flow meters 25, 26 are broadcast over a CAN bus. The controller restricts the flow of hydraulic fluid to the hammer 3 if the difference between the inputs to the controller 27 from the first flow meter 25 and second flow meter 26 indicates a fault condition. The system is configured such that a detection of a flow rate differential between flow meter 25 and flow meter 26 greater than a threshold would lead to a digital fault signal being output by the controller 27. In the event of a fault condition being detected, the controller 27 output activates the control valve 4C which moves to a closed position to prevent hydraulic fluid from flowing from the reservoir to the apparatus. In addition to the function of shutting down fluid supply, other features such as; start-up override and reset after fault can be handled by a controller 27 program.

While the above embodiments are described in relation to hydraulic down the hole hammer drilling, it should be appreciated that the system has many applications and can be used on a wide variety of hydraulic equipment. It is particularly applicable to any remotely operated actuator where the return flow is always a fixed percentage of the supply flow, especially one where manual control is not possible or desirable.

The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof It is appreciated that certain features of the invention, which are, for clarity, described S in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination,

Claims

Claims 1. A flow monitoring system for a hydraulic apparatus comprising: means for restricting the flow of hydraulic fluid to the apparatus if a difference between an outward flow rate of hydraulic fluid and a return flow rate of the hydraulic S fluid exceeds a threshold.
2. The system of claim 1 wherein the outward flow rate is the flow rate from a reservoir to the apparatus and the return flow rate is the flow rate from the apparatus to the reservoir.
3. The system of claim I or 2 further comprising: a first positive displacement hydraulic device coupled to a pressure line configured to carry fluid from the reservoir to the apparatus; and a second positive displacement hydraulic device coupled to a return line configured to carry fluid from the apparatus to the reservoir.
4. The system of claim 3 wherein the first positive displacement device is arranged to operate as a motor that moves at a speed proportional to the outward flow rate and the second positive displacement device is arranged to operate as a pump and the first device and the second device are coupled such that the second device moves at the same speed as the first device.
5. The system of claim 4 wherein the second device has a smaller displacement than the first device such that the flow of hydraulic fluid through the second device causes a back pressure in the return line.
6. The system of claim 5 wherein the means for restricting comprises a valve moveable between an open position in which hydraulic fluid is permitted to flow from the reservoir to the apparatus and a closed position in which hydraulic fluid is prevented from flowing from the reservoir to the apparatus, and wherein the back pressure in the return line acts upon the valve to maintain it in the open position. in 1-,
7. The system of claim 6 wherein when the difference between the outward flow rate and the return flow rate exceeds the threshold, the back pressure acting upon the valve is insufficient to maintain the valve in the open position
8. The system of claim 1 further comprising: a first flow meter coupled to a pressure line configured to carry fluid from the reservoir to the apparatus; and a second flow meter coupled to a return line configured to carry fluid from the apparatus to the reservoir; wherein the first flow meter produces a first electrical output proportional to the outward flow rate arid the second flow meter produces a second electrical output proportional to the return flow rate.
9. The system of claim 8 wherein the first electrical output and the second electrical output are voltages.tO. The system of claim 8 or claim 9 wherein the system further comprises a voltage comparator.t t. The system of claim 10 wherein the first output and the second output are input to the voltage comparator to produce a comparator output, wherein when the difference between the first electrical output and the second electrical output exceeds a threshold, the comparator output is a first voltage level and otherwise the comparator output is a second voltage level.t2. The system of claim 11 wherein the means for restricting restricts the flow of hydraulic fluid if the comparator output is the first voltage level.13. The system of claim 11 wherein the means for restricting permits the flow of hydraulic fluid if the comparator output is the second logic level.14. The system of claim 12 or claim H wherein the means forrestricting comprises a circuit to operate a control valve between an open position in which hydraulic fluid is permitted to flow from the reservoir to the apparatus and a closed position in which hydraulic fluid is restricted from flowing from the reservoir to the apparatus.15. The system of claim 8 wherein the first output and second output comprise digital outputs.16. The system of claim 15 wherein the first output and second output are input to a controller.17. The system of claim 16 wherein the controller comprises a digital control system.18. The system of claim 16 or claim 7 wherein the controller comprises a CAN controller module.19. The system of any of claims 16 to 18 wherein the controller outputs a digital fault signal if a difference between the first 2md second outputs exceeds the threshold.20. The system of claim 19, wherein the digital fault signal operates a valve that restricts the flow of hydraulic fluid to the apparatus.21. The system of any preceding claim wherein the hydraulic apparatus comprises a hydraulic down the hole hammer.