Field of the Invention

The present invention relates to a gas displacement pump particularly, although not exclusively, for use in pumping liquids in flammable or otherwise hazardous environments. The invention also relates to a pumping system and to a method of pumping liquids.

Background of the Invention

A stripper well is an oil well that produces ten or less barrels of oil per day. There are approximately 400,000 stripper oil wells in the USA which together produce approximately 900,000 barrels of oil per day representing approximately 15% of US crude oil production.

One common pumping system for extracting oil from stripper wells is a sucker rod pumping system. This uses a sucker rod pump located at the bottom of a well, a surface pumping unit and a sucker rod string that runs between the surface pumping unit and the pump. The sucker rod pump comprises a stationary valve and a travelling valve which is coupled to the sucker rod string and moved up and down by the surface pumping unit. The travelling valve opens and the stationary valve closes during the downward stroke of the pumping system causing a flow of oil into a chamber in which the travelling valve is disposed and also displacing the oil from the top of the chamber into a well casing. An upward stroke of the pump closes the travelling valve and opens the stationary valve which allows a fresh charge of oil to flow into the casing as well as lifting a quantity of oil to the surface through a well head. A polished rod is used at the top of the sucker rod string and moves up and down through a stuffing box at the well head. A motor is provided at the surface pumping unit that rotates a crank which in turn is connected to one end of a walking beam, causing the walking beam to rise and fall. The polished rod is coupled to the opposite end of the walking beam and thus reciprocates the sucker rod string up and down within the well. The motor is often set on a timer to periodically turn the pumping system ON and OFF for the purposes of conserving power and preventing the pumping system from operating when there is insufficient oil in the well. Embodiments of the present invention were initially developed to provide alternate apparatus and systems for recovering oil from stripper wells. However embodiments of the invention are not limited to such use and may be applied to pumping of other liquids including liquid in flammable or otherwise hazardous environments.

Summary of the Invention

One aspect of the invention provides a gas displacement liquid pump comprising: a chamber having a liquid inlet and a liquid outlet; a liquid level sensing system arranged to sense liquid level within the chamber, the liquid level sensing system sensing liquid level independently of electrical properties of the liquid; and a port in selective communication between a vent and a supply of a compressed gas; wherein the liquid level sensing system is operable to: effect communication between the port and the vent to vent gas from the chamber and allow liquid to flow into the chamber through the inlet when the liquid level sensing system senses liquid within the chamber being below an upper threshold level; and, effect communication between the port and the supply of compressed gas to allow a volume of compressed gas to flow into the chamber and displace a quantity of liquid from the chamber through the outlet when the liquid level sensing system senses liquid within the chamber reaching the upper threshold level and until liquid within the chamber is sensed as dropping to a lower threshold level.

The liquid level sensing system may comprise a first sensor which senses when liquid within the chamber reaches the upper threshold level, and a second sensor which senses when liquid within the chamber reaches the lower threshold level.

One or both of the first and second sensors may comprise a tuning fork sensor.

The pump may comprise a submergible pump wherein the chamber is arranged for submersion into the liquid to be pumped. The pumping system may comprise one or more risers connectabie to the outlet and to each other, the risers supporting the chamber in the liquid and forming a conduit through which liquid displaced from the chamber through the outlet can flow to a remote location.

Each riser may have an outer diameter of less than 50mm.

Each riser has an outer diameter of less than 30mm.

The pump may comprise one or more couplings, each coupling configured to couple together two adjacent risers and further arrange to engage one or more conduits providing communication between the chamber and a distant controller.

The or each coupling may comprise respective channels for seating the or each conduit, and a wedge that wedges the or each conduit into each respective channels.

The or each coupling may comprise a body provided with the or each channel and an opening into which the wedge is received to wedge the or each conduit into each respective channel.

The inlet may comprises a one way check valve having a ball seat wherein one or both of the check ball and the ball seat is made of tungsten carbide.

The outlet may comprise a one way check valve having a check ball and a ball seat wherein one or both of the check ball and the ball seat is made of tungsten carbide.

A second aspect of the invention provides a submersible gas displacement stripper well pump comprising: a chamber having a liquid inlet and a liquid outlet; a liquid level sensing system arranged to sense liquid level within the chamber; and, a port in selective communication between a vent and a supply compressed gas, wherein the liquid level sensing system is operable to: effect - A - communication between the port and the vent to vent gas from the chamber to allow liquid to flow into the chamber through the inlet when the liquid level sensing system senses liquid within the chamber being below an upper threshold level; and, effect communication between the port and the supply of compressed gas to allow a volume of compress gas to flow into the chamber and displace a quantity of liquid from the chamber through the outlet when liquid within the chamber is sensed as reaching the upper threshold level and until the liquid is sensed as dropping to a lower threshold level; and, one or more risers coupled with the outlet, the risers supporting the chamber in the stripper well and providing fluid communication between the outlet and a remote location wherein oil pumped by the pump flows to the remote location via the one or more risers.

A third aspect of the invention provides a pumping system comprising: one or more gas displacement liquid pumps; a supply of compressed gas common to the one or more pumps; a pump controller for each pump; a conduit extending between each pump controller and its respective pump; a reticulation system providing fluid communication between the supply of compressed gas and each pump controller; each pump being provided with a liquid level sensing system in communication with its corresponding pump controller wherein the liquid level sensing system signals the pump controller to connect the conduit to either the supply of compressed gas or a vent depending on sensed liquid level within the chamber.

A fourth aspect of the invention provides a method of pumping liquid comprising: submerging a single stage gas displacement pump into the liquid; sensing a level of liquid inside the pump; and, sequentially switching the pump between a connection to: a vent when sensed liquid level in the pump is below a upper threshold level, wherein the liquid can flow into the pump; and, a supply of compressed gas when sensed liquid level in the pump reaches the upper threshold level to displace liquid from the pump until the liquid level is sensed as dropping to a lower threshold level. Submerging the chamber may comprise submerging the chamber in a stripper well.

The method may comprise supporting the pump submerged in the liquid by one or more risers, wherein the risers provide fluid communication between the pump and a remote liquid storage or processing facility.

The method may comprise connecting selected adjacent risers together with respective couplings, each coupling being provided with a clamp; and, providing at least a first conduit between the pump and remote location where the conduit can be connected to the supply of compressed gas, wherein the conduit is retained by the clamp.

A first aspect of the invention provides a method of recovering oil from one or more stripper wells comprising: supporting a single stage gas displacement pump in the or each stripper well; sensing a level of oil inside the or each pump; and, sequentially switching the or each pump between a connection to: a vent when sensed liquid level in the pump is below a upper threshold level, wherein the liquid can flow into the or each pump; and, a supply of compressed gas when sensed liquid level in the or each pump reaches the upper threshold level to displace liquid from the or each pump until the liquid level is sensed as dropping to a lower threshold level.

The method may comprise: providing a common supply of compressed gas; and providing a reticulation system to provide fluid communication between the or each pump and the common supply of compressed gas.

The method may comprise: providing a pump controller for each pump, connecting each pump controller to the common supply of compressed gas; and, coupling a conduit between each pump and its corresponding pump controller, wherein the pump controller selectively connects the conduit between the supply of compressed gas and the vent. Sensing the level of oil may comprise providing a sensing system which senses oil level on a basis other than electrical properties of the oil.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a pumping system in accordance with embodiments of the present invention;

Figure 2 is a schematic representation of an embodiment of a pump incorporated in the pumping system shown in Figure 1 where the pump is in a first operational state;

Figure 3 is a schematic representation of the pump shown in Figure 2 but in a second operational state;

Figure 4 is a plan view of the pump shown in Figures 2 and 3;

Figure 5a is a plan view of a body portion of a riser coupling incorporated in an embodiment of the present invention;

Figure 5b is a front view of the coupling shown in Figure 5a;

Figure 5c is a view of section A-A of the coupling shown in Figure 5b;

Figure 5d is a perspective view from one side of a wedge incorporated in the coupling;

Figure 5e is an isometric view of the wedge shown in Figure 5d from an alternate angle;

Figure 6 is a schematic block representation of a pump controller incorporated in an embodiment of the pumping system; and, Figure 7 is a schematic representation of a second embodiment of the present invention

Detailed Description of the Preferred Embodiments

Figure 1 illustrates an embodiment of a pumping system 10 incorporating an embodiment of a gas displacement liquid pump 12. To provide context, the pumping system 10 will be described in relation to the recovery of oil 14 from a stripper well 16. However, it is to be understood that the system 10 and the pump 12 may be used to pump liquids other than oil, and in particular as explained in greater detail below, flammable liquids or liquids in flammable or otherwise hazardous environments. For example, the system 10 and pump 12 may be used for coal bed methane dewatering in which the pump 12 extracts water from methane producing underground carbon reservoirs.

In broad terms, the illustrated pumping system 10 comprises a supply 18 of compressed gas, such as but not limited to, air, the pump 12, and a pump controller 20. While the system 10 in Figure 1 is illustrated as comprising only a single pump 12 and corresponding pump controller 20, it is envisaged that the system 10 may comprise multiple pumps 12 with multiple corresponding controllers 20. The supply 18 is a common supply to each of the pumps 12 in the system 10. A reticulation system 22 comprising one or more air hoses 24 provides fluid communication between the supply 18 and each of the pump controllers 20. A conduit 26 provides fluid communication between the pump 12 and its corresponding controller 20. The conduit 26 can be selectively coupled to either (a) the supply 18 which results in compressed air being injected into the pump 12 displacing oil from the pump; or (b) a vent 25 which vents the pump 12 to allow oil to flow into the pump 12. The connection of the conduit 26 to either the supply 18 or the vent is determined by the level of oil sensed within the pump 12 by a liquid level sensing system 28. When the liquid level sensing system 28 senses liquid level within the pump 12 as being below an upper threshold level, it signals the controller 20 to connect the conduit 26 to the vent 25 which vents the interior of the pump 12 to atmosphere and allows oil to flow into the pump 12. When the liquid level sensing system 28 senses that the level of liquid within the pump 12 reaches an upper threshold level, it signals the pump controller 20 to connect the conduit 26 to the supply 18 so that compressed air is injected into the pump 12. The compressed air displaces the oil within the pump 12 so as to flow through a plurality of risers 30 and a connected pipe 32 to a remote storage tank 34. The injection of compressed gas into the pump 12 continues until the liquid level sensing system 28 senses the liquid level within the pump 12 dropping to a lower threshold level. At that time, the liquid level sensing system 28 signals the pump controller 20 to connect the conduit 26 to the vent. This cycle continues ad infinitum to recover the oil 14 from the well 16.

The components and features of the pumping system 10 and pump 12 will now be described in greater detail.

Figures 2 - 4 depict in greater detail the structure and components of the pump 12. Figure 2 depicts the pump 12 at the commencement of a gas displacement cycle where compressed air is being injected into the pump 12 to displace oil 14 from the pump 12 and thus cause the flow of oil to the tank 34. Figure 3 depicts the pump 12 at the commencement of a fill cycle where the pump 12 is vented to allow a fresh charge of oil 14 to flow into the pump 12.

The pump 12 comprises a cylindrical housing or chamber 36 fitted at a down hole end 38 with a one way inlet valve 40. An opposite up hole end 42 of the pump 12 is provided with a one way outlet valve 44. An internal pipe 46 extends from the outlet valve 44 to a location near the down hole end 38 adjacent the inlet valve 40. In order to facilitate safe operation of the pump 12 within flammable or hazardous environments, the liquid level sensing system 28 is arranged to sense liquid level on a basis independent of electrical properties of the liquid (in this case, oil) in which it operates. The liquid level sensing system 28 comprises a first sensor 48 which senses when oil 14 reaches an upper threshold level 50, and a second sensor 52 which senses when oil 14 within the chamber 36/pump 12 is at or below a lower threshold level 54.

One sensing system that may be used in flammable or hazardous environments comprises one or more tuning fork sensors. The present embodiment illustrates the first sensor 48 and a second sensor 52 as each comprising a tuning fork sensor. Each of the sensors comprises respective processing units 48a and 52a, and corresponding tuning forks 48b and 52b. The processing units 48a and 52a cause vibration of the respective forks 48b and 52b at predetermined frequencies, and detect changes in the frequencies of vibration. Changes in frequency of vibration are due to physical contact of the respective forks 48b, 52b with the oil 14.

A socket 56 is provided near the uphole end 42 of the chamber 36 to enable a cable 58 (shown in Figure 1) to connect the liquid level sensing system 28, and in particular, the sensors 48 and 52 to the pump controller 20. The cable 58 enables electrical power to be delivered to the sensors 48 from the pump controller 20, as well as providing signal communication between the liquid level sensing system 28 and the pump controller 20. A cable 60 extends internally of the chamber 36 between the second sensor 52 and the socket 56 to enable electrical power to be delivered to the second sensor 52 and signal communication between the sensor 52 and the pump controller 20. A support plate 62 is provided intermediate the sensors 48 and 52 and extends transversely inside the chamber 36 to provide support to both the cable 62 and the internal pipe 46.

The inlet valve 40 is in the form of a one way check valve comprising a check ball 64 and a valve seat 66. This valve allows flow of oil into the chamber 36 but prevents a back flow of oil from the chamber through the seat 66 back to the well 16. A cage 68 extends from the seat 66 and provides a limit to the motion of the ball 64, allowing it to lift a predetermined distance off the seat 66 by action of the pressure of oil 14 within the well 16 below the valve 40. In one embodiment, the valve 64 and the valve seat 66 may be made from a metal or metal allow such as tungsten carbide. The cage 68 comprises a plurality of fingers 70 that extend from the seat 66 and curve over the ball 64 forming an opening between the tips of the fingers 70 having a diameter less than that of the ball 64. A hole 72 may be formed in each finger 70 adjacent the seat 66 so that when the ball 64 is lifted from the seat 66 oil 14 can flow from the seat 66 through the hole 72 into the chamber 36.

The outlet valve 44 is provided in an extension 74 extending axially from the up hole end 42 of the chamber 36. The extension 74 axially displaces the valve 44 from the socket 56 to provide sufficient room for coupling of the risers 30 and the cable 58 to the pump 12.

The valve 44 is also a one way ball check valve which allows flow of oil 14 out of the chamber 36/pump 12 via a riser adapter 76 but prevents a back flow of oil from the risers 30 into the chamber 36. The outlet valve 44 comprises a valve ball 78 and valve seat 80. Both the valve ball 78 and the seat 80 may be made from a hard wearing metal or metal alloy such as tungsten carbide.

A port 82 (see Figure 4) is formed on an end wall 84 at the up hole end 42 of the pump 12. The port 82 is coupled with the conduit 26 (shown in Figure 1) and selectively provides fluid communication between the chamber 36/pump 12 and, either the supply of compressed gas 18, or the vent 25. Thus the port 82 and the conduit 26 enable both the injection of compressed gas into the chamber 36/pump 12, and the venting of the chamber 36. When the chamber 36 is vented via the port 82 and conduit 26, and the pressure of the oil 14 within the well 16 is greater than atmospheric pressure the inlet valve 40 opens and oil flows into the chamber 36. As the chamber 36 fills with oil, air and/or the other gasses within the chamber 36 are displaced and vented to atmosphere via the port 82. During this process, the valve 44 is closed by combined action of gravity acting on the valve ball 78 holding it onto the seat 80, as well as the hydrostatic pressure of the column of oil 14 within the riser 30.

In order to deliver a volume of oil through the riser 30 to the tank 34, a volume of compressed gas is injected into the chamber 36 through the port 82 when the level of oil 14 within the chamber 36 reaches the upper threshold level 50. This is detected by the tuning fork sensor 48 which sends a signal to the pump controller 20 to connect the conduit 26 to the supply of compressed gas 18. The compressed gas 18 pressurises the chamber 36 which shuts the inlet valve 40, opens the outlet valve 44 and displaces a quantity of oil 14 which flows through the internal pipe 46, the outlet valve 44, riser adapter 76 through the risers 30 and subsequently to the tank 34. The injection of pressurised gas continues until the level of oil 14 within the chamber 36 drops to the lower threshold level 54 as shown in Figure 3. At this time, the sensor 52 signals the pump controller 20 of the level of oil 14 within the chamber 36 causing the pump controller 20 to disconnect the conduit 26 from the supply of compressed gas 18, and reconnecting the conduit 26 to the vent 25. This results in a depressurisation of the chamber 36 which enables the inlet valve 40 to open by virtue of the pressure of oil 14 within the well 16. This represents one pumping cycle. The pumping cycles continue ad infinitum with the pumping controlled by the detected level of oil 14 within the chamber 36/pump 12. The pump 12 is submerged in the oil 14 and supported in the well 16 via the risers 30. Each riser 30 comprises steel pipe typically of a length of either 6m or 9m and may for example have an internal diameter of %" (19mm) and an outer diameter of less than 50mm, for example 1.050" (26.7mm) with a non- upset thread at opposite ends. A riser 30 of such diameter may have a weight in the order of 1.14 Ib/ft (170kg/m). By comparison, a typical sucker rod pipe has an outer diameter of 2 ³ / ₈ " (50.8mm). The difference in size between the risers 30 incorporated in the present embodiment of the system 10 and sucker rod pipes enables the system 10 and in particular the pump 12 to be deployed more quickly and using smaller and less expensive equipment and lifting apparatus due to the substantially lower mass of the risers 30. Further, the risers 30 are only required to support the pump 12 and provide a fluid flow path to the remote tank 34. The risers do not accommodate any moving parts that require sealing, such as a polished rod in a sucker rod pump. Accordingly the risers 30 are much less susceptible to leakage. Although in the above example the risers 30 are described as having non-upset thread, in an alternate embodiment risers 30 with upset thread may be used.

Adjacent risers 30 may be coupled together with either simple internally threaded collars 86 (shown in Figure 1) or, a coupling 88 shown in Figures 5A - 5E. The coupling 88 comprises two main components, a body 90 (shown in Figures 5A - 5C), and a wedge 92 (shown in Figures 5D and 5E). The coupling 88 couples two adjacent risers 30 together, and also clamps and supports the conduit 26 and the cable 58. The body 90 is provided with a central through hole 94 provided with internal threads at opposite ends 96 and 98 for threadingly engaging adjacent risers 30. The body 90 is also formed with two parallel longitudinal channels 100a and 102a for seating the cable 58 and conduit 26 respectively.

The body 90 is also provided with a pair of laterally extending and mutually facing side walls 104 provided with inwardly directed protrusions 106. The walls 104 and protrusions 106 define a recess 108 in which the wedge 92 can be received and locked. Channels 100a and 102a open onto the recess 108. A hole 110 extends transversely through each of the walls 104. The hole 110 receives a pin or tie wire (not shown) for locking the wedge 92 in the recess 108. Referring to Figures 5D and 5E, the wedge 92 comprises an elongated tapered body 112 which is provided at its wide end 114 with a rearwardly extending lip 116. The lip 116 assist in removing the wedge 92 from the body 90. A pair of channels 100b and 102b is formed along a face of the wedge 92. When the wedge 92 is located in the recess 108, the channels 100a and 100b are mutually opposed as are the channels 102a and 102b. The opposed channels form cylindrical or near cylindrical passages through which the cable 58 and conduit 26 extend. The coupling 88 is dimensioned relative to the cable 58 and conduit 26 so that when the wedge 92 is seated in the recess 108, the cable 58 and conduit 26 can be seated in the channels 100 and 102 and are gripped or clamped by the coupling 28 between the body 90 and the wedge 92. The wedge 92 is locked in place by a pin or tie wire passing through the hole 110.

The coupling 88 transfers the weight of the conduit 26 and cable 58 onto the riser 30, and protects the conduit 26 and cable 58 from damage by maintaining them close but slightly spaced from the risers 30. The couplings 88 may be incorporated at every join between adjacent risers 30, or alternately at greater spaced locations such as every second or third coupling between risers 30.

Figure 6 illustrates the pump controller 20 in a block diagram form. The pump controller 20 comprises the following interconnected components or systems: a radio 118 with antenna 119, power unit 120, processor 122, and valve 124. The radio 118 enables communications with a central controller 126 (shown in Figure 1). The radio 118 provides operational information regarding the controller 20 and pump 12 to the central controller 126 and also enables receipt of control signals from a central controller 126 to control the controller 20 and its associated pump 12. The power unit 120 may typically comprise an electrical power storage unit such as a battery, and a recharging facility such as a solar panel 128. The power unit 120 provides sufficient power to operate the controller 20 and the pump 12. The power unit provides electrical power to the radio 118, processor 122, and valve 124 via cables 130a, 130b and 130c.

The processor 122 receives and processes signals from the liquid level sensing system 28 via the cable 58; and, provides signals via signal line 132 to the valve 124. The valve 124 is provided with: a port 134 which couples with the conduit 26; a port 136 that couples with the air hose 24 providing fluid communication with the compressed gas supply 18; and a port 138 which is coupled to the atmospheric vent 25. The valve 124 is operated by the processor 122 on the basis of the signals received from the liquid level sensing system 28 to selectively connect the port 134 and thus the conduit 26 and pump 12 to either the port 136, which then provides fluid communication to the compressed supply 18 via the air hose 24; or, the port 138 which provides communication to the atmospheric vent 25.

When the processor 122 receives signals from the liquid level sensing system 28 communicating that the level of oil 14 within the pump 12 is between the lower and upper threshold levels 54 and 50, the processor 122 controls the valve 124 so as to connect the conduit 26 to the vent 25. When the processor 122 receives a signal from the liquid level sensing system 28, and in particular, the upper sensor 48 that the oil 14 has reached the upper level 50, the processor 122 disconnects the conduit 26 from communication with the vent 25 and subsequently connects the conduit 26 to the air hose 24 and thus the supply of compressed air. The compressed air flows through the conduit 26 into the port 82 displacing oil from the pump 12 through the outlet valve 44 and risers 30 to the tank 34 The injection of compressed air continues until the lower sensor 52 senses that the oil within the chamber 36 has dropped to the lower threshold level 54 at which time the sensor 52 sends a signal to the processor 122 via the cable 158. Upon receipt of this signal, the processor 122 disconnects the conduit 26 from the supply of compressed gas 18, and reconnects it to the air vent 25.

A level sensor 142 (see Figure 1) may be provided in the tank 34 to provide a signal to the processor 122 via a signal line 144 when the level of oil within the tank 34 reaches a maximum level. The process 122 may at that time, disable the pump 12 to the extent that it will no longer discharge oil, and signal the central controller 120 via the radio 118 of the status of the storage tank 34. The central controller 126 may inturn signal a remote operation centre of the state of the tank 34 enabling the dispatch of one or more persons for emptying the tank 34.

Referring to Figure 1 , the compressed gas supply 18 may comprise a compressor 146 and an accumulator 148. The accumulator 148 is of a volume to store sufficient compressed air to enable operation of each pump 12 which is in fluid communication with the supply 18 via the reticulation system 22. The compressor 146 may be operated to recharge the accumulator 148 when air pressure within the accumulator 148 drops to a predetermined level.

The central controller 126 comprises a radio 150, processor 152, and power management unit 154. The radio 150 enables communication with the pump controller 20 as well as a remote operating centre (not shown). The processor 152 performs a range of functions including: provide signals to control the compressor 146, via communications line 147 receiving and processing signals from the remote operating centre, receiving and processing signals from the pump controller, calculating volume of oil displaced by the pump or pumps 12 in the pumping system 10, and provides operational data and status in relation to the system 10 to the remote operating centre.

The radio 118 in the pump controller 20, and the radio 150 in the central controller 126 together form a radio telemetry unit. The radios 118 and 150 may be of identical construction but switchable between either a master or slave configuration. In one embodiment the radios 110 in the pump controllers 20 are in the slave configuration, while the radio 150 at the central controller 126 is in the master configuration and communicates with each slave radio. In this embodiment the radios 118 may be provided with on board processing functionality in which event the separate processor 122 may not be required.

The master radio 150 with antenna 151 may be configured to communicate to the slave radios 118 via two channels, and the slave radios 118 may also be configured to communicate via two channels back to the master radio 150.

Further, the radios 118 may be provided with two outputs connected to an "Impulse Latching Relay". One output may be used to latch the relay and the other output used to un-latch this relay. When a relay is latched the corresponding pump 12 unit is "Enabled" and can therefore operate.

Each radio 118 may also be provided with two inputs one of each connected to the "Cycle Count" and "Tank Full" functions of an on board processor. Every time the pump 12 unit goes onto "Pressure Cycle" a coded signal pulse is sent to the central controller 126 by the radio 118 and received by the radio 150. When the cycle is complete and the pump reverts back to "Fill Cycle" a different coded pulse is sent back using the same input. The "Tank Full" input works the same way using the other Slave input and the second channel.

All inputs and outputs that are communicated between Master and Slave radios are verified back to the sending unit to ensure that all signals are correctly received. Multiple attempts, for example fifteen, may be made to send a signal before comms is considered lost.

In the event that a slave radio 118 unit looses communications with the master radio 150 for more than 2 minutes, the slave radio 118 will disable that pump until communications are restored.

The master radio 150 stores a register of all the slave pump numbers with which it communicates. In the event that the register of communicating pumps does not match up with the register of pumps that should be on line, which is stored in the processor 152, then a lost comms alarm is raised by the processor 152. This is a latching alarm which must be cleared manually. That means that if comms is lost for any reason it will be recorded.

The master and slave radios regularly poll each other to confirm comms status even if there is no comms traffic.

Figure 7 depicts a further embodiment of the system 10a in accordance with the present invention. The system 10a is substantially the same as the system 10 depicted in Figure 1 and the same reference numbers are used to denote like features. The substantive difference between the systems 10 and 10a resides in the source of gas for the supply 18. In the system 10 depicted in Figure 1 , the source of gas is the atmosphere surrounding the supply 18. However in the system 10a shown in Figure 7, gas from the well 16 is used as the source of gas for the supply 18. Gas from the well 16 is supplied to the supply 18 via a conduit 160 and hose 162. The pump 146 compresses the well gas which is stored in the accumulator 148 and can then be distributed to the pump controllers 20 and pumps 12 in the same way as described above in relation to the system 10. When the pump 12 is vented during a pumping cycle, the vented gas is directed through port 25 to a conduit 164 to return to the well 16. In all other aspects, the system 10a operates in the same manner as the system 10.

Now that embodiments of the present invention have been described in detail, it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the pump 12 is illustrated as comprising two tuning fork sensors 48, and 54. However in alternate embodiments, different types of sensors may be used that do not rely upon electrical properties of the liquid being pumped. For example, float or ultrasonic sensors may be used. When the system 10 and pump 12 are used for pumping the liquids which are either themselves flammable, or are extracted from flammable or hazardous environments, intrinsic safe systems normally deployed in such environments may be incorporated. This may include for example: the cable 58 being in the form of or comprising at least one two wire NAMUR intrinsic safe system; and, an intrinsic safe valve 124. The valve 124 may be controlled by a latching solenoid valve 125which does not require constant power to maintain its state and is activated by signals from the processor 122. In addition, one or more filters may be placed in the reticulation system 22 and/or the valves 124 to filter the moisture and/or foreign particles from the compressed air. The central controller 126 may communicate with a remote operation centre via a modem such as a GSM modem allowing control of the system 10 via a computer over a telecommunications network.

All such modifications and variations together with others that would be obvious to persons of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description and the appended claims.