GB2134672A - Fluid pump control system - Google Patents

Abstract

A fluid pump control system Figure 1 is used to control a simple water supply system in which a header cistern is filled and kept topped-up by a pump which delivers water from a lower level. The control system has a control unit connected to fluid bleed lines both upstream T1 and downstream T2 of the pump, and pressure changes in the bleed lines control the pump by actuating a motor control switch D. The arrangement allows self priming of the pump by flow from T1 to T2 and also comprises an air bleed line T3 from the pump which vents air via free floating check valve H until closed by water. <IMAGE>

Description

SPECIFICATION Fluid pump control system This invention relates to a pump control system.

In a simple water supply system, a header cistern is filled and kept topped-up by a pump which delivers water from a lower level. In order to ensure a continuing supply, various systems, both mechanical and electro-mechanical, are known for monitoring the water level in the cistern and for switching the pump on and off 'according to need. These systems require a link, normally electrical control wires, from the cistern to the pump. The pump in addition needs a system to ensure priming, and cutout in the event of dry running.

The invention aims to provide a pump control system offering some or all of these facilities in one unit and without extensive control wiring.

The invention provides a fluid pump control system having a control unit connected by fluid bleed lines to the fluid flow both upstream and downstream of the pump, and in which switching of the pump is controlled by pressure changes transmitted by the bleed lines. Preferably, a further bleed line from the uppermost point of the pump casing controls the finish of pump priming.

In order that the invention shall be clearly understood, an exemplary embodiment thereof will now be described with reference to the accompanying drawings, in which: Figure 1 shows a pump control system according to the invention; Figure 2 shows a pump system to be controlled; Figure 3 shows the storage cistern of the pump system; Figure 4 shows an exploded, sectional view of a pressure stabiliser; Figure 5 shows an exploded, sectional view of a typical diaphragm valve as used in the control system; Figure 6 shows a typical one-way spring check valve as used in the control system; and Figure 7 shows a two-way check valve for use in the cistern.

The pump control system of this embodiment can be seen from Figs. 1 and 2 and comprises a single casting made from plastic or other suitable materials and with the required number of cavities formed for the described components, complete with its respective bolted on housing and covers; spring assemblies and flexible membranes. The components are: main priming unit A; auxiliary priming unit B; switch control unit C; pressure switch unit D; over-pressure control unit E; under-pressure control unit F; master control unit G; free floating ball check valve unit H; the one-way spring check valve units J, M 8 N; pressure stabilizer K; optional electronic control circuit unit L; small bore passages and special accessory of two-way free floating check valve unit P. The axes of the valves are all preferably horizontal.The exact configurations of the various components may be varied while fulfilling the same functions. Nevertheless, by way of example, the structure of the components will first be described in detail in turn.

(1) Main priming unit A: The function of this unit is to channel water from the pumping main into the suction pipeline of the pump concerned for priming purposes, exactly the same as when water is manually bypassed at a pump delivery check valve for the same purpose. The main priming unit A consists of four chambers, namely: (a) the innermost chamber Al, which is connected to the pumping main through a tubular passage Ti; (b) the inner chamber A2 which is connected to the suction pipeline through a tubular passage T2; (c) the outer chamber A3 which is connected to the oneway spring check valve J through small bore passage 10-7 and (d) the outermost chamber A4 which is the housing for the spring assembly SA.

In between the inner chamber A2 and the innermost chamber Al, a valve port VA is provided and completed with tapered female valve seat to receive a male valve pad for isolation purpose. The outer chamber A3 and the outermost chamber A4 are formed by a hatshaped casting serving as the spring housing as well as flanged cover to be fixed and secured in position by bolts and nuts to the cavity formed for the said main priming unit A. The innermost chamber Al and inner chamber A2 are separated from the outer chamber A3 and outermost chamber A4 by a flexible membrane suitably sized and make from selected material for such purpose as described hereunder.The flexible membrane serve as a spring rest with respect to its outer chamber A3 and outermost chamber A4 and it also serves a a valve stem with male valve pad fitted to its spindle extension with respect to its inner chamber A2 and its innermost chamber Al.

The valve port VA of this unit is normally kept in 'close' position except at the priming phase of the operation and remain open so long as starting and delivering water of the pumpset concerned is not successful.

(2) Auxiliary priming unit B: The structure of this unit is shown in Figure 5.

The function is to allow air, if any, trapped in the suction pipeline to escape into the atmosphere. It consists of four chambers, namely: (a) the innermost chamber B1 which is connected to the tubular passage T3; (b) the inner chamber B2 which is connected to a free floating ball check valve unit H through the tubular passage T4; (c) the outer chamber B3 which is connected to the one-way spring check valve J through a small bore passage 8-7; (d) the outermost chamber B4 which is the housing for the spring assembly SB.

In between the inner chamber B2 and the innermost chamber B1 a valve port VB is provided complete with tapered female valve seat to receive a male valve pad for isolation purpose.

The outer chamber B3 and outermost chamber B4 are formed by a hat-shaped casting serving as a spring housing and flanged cover to be fixed and secured in position by bolts and nuts to the cavity formed for the said auxiliary priming unit B. The innermost chamber B1 and inner chamber B2 are separated from the outer chamber B3 and outermost chamber B4 by a flexible membrane.

The flexible membrane supports a valve stem with male valve pad fitted to its spindle extension with respect to its inner chamber B2 and innermost chamber B1 and the said flexible membrane also serves as a spring rest for the spring assembly SB with respect to its outer chamber B3 and outermost chamber B4. Valve port VB is normally kept at 'close' position except during the priming phase of the operation and it will remain open so long as starting and delivering of the pumpset concerned is not successful.

(3) Switch control unit C: The function of this unit is to isolate the outer chamber D3 of the pressure switch unit D from the innermost chamber B1 during normal running stage of the operation. It consists of four chambers, namely: (a) the innermost chamber C1 which is connected to the inner chamber B2 of the auxiliary priming unit B through a small bore passage 16-16; (b) the inner chamber C2 which is connected to the outer chamber D3 of the pressure switch unit D through a small bore passage 15-15; (c) the outer chamber C3 which is connected to the one-way spring check valve J through a small bore passage 9-7; (d) the outermost chamber C4 which is the housing for the spring assembly SC.In between the inner chamber C2 and the innermost chamber C1, a valve port VC is provided complete with tapered female valve seat to receive the male valve pad for isolation purpose. The outer chamber C3 and the outermost chamber C4 are formed by a hatshaped casting serving as a spring housing as well as flanged cover to be fixed and secured in position by bolts and nuts to the cavity formed for the said switch control unit C. The inner chamber C2 and innermost chamber C1 are separated from its outer chamber C3 and outermost chamber C4 by a flexible membrane.The said flexible membrane supports a valve stem fitted with a male valve pad at its spindle extension with respect to the inner chamber C2 and innermost chamber C1 and the said flexible membrane also serve as a spring rest to the spring assembly SC with respect to its outer chamber C3 and outermost chamber C4. The valve port VC is normally kept at 'close' position except during the priming phase of the operation and will remain open so long as starting and pumping is not successful.

(4) Pressure switch unit D: The function of this unit is to provide the 'switch-on' and 'switch-off' signals to the electronic control circuit unit L. It consists of three chambers, namely: (a) the innermost chamber D1 which is the housing for two fixed contact pairs and one common movable contact or crosslinking conductor. One of the fixed contact pair is mounted at the inner part of this chamber whereas the other will be mounted at the outer part of the same chamber. Both of these contact pairs have its contact points extended with wires which in turn are connected to the respective terminals at the electronic control circuit unit L for the relevant switching functions.Besides the two fixed contact pairs, a third common and movable contact in the form of cross-linking conductor is provided which will travel within the space confined by the two fixed contact pairs according to the axial movement of the flexible membrane as described hereinunder; (b) the inner chamber D2 which serve as the housing for the spring assembly SD of the said pressure switch unit D; (c) the outer chamber D3 which is connected to the inner chamber C2 of the switch control unit C through a small bore passage 15-15. The said chamber also connected to the outermost chamber E4 of the over-pressure control unit E through a small bore passage 15-14.The said chamber is further connected to a one-way spring check valve unit M through a small bore passage 1 8-1 8. The outer chamber D3 is formed by a near-flat casting serving as a flanged cover to be fixed and secured in position by bolt and nuts to the cavity formed for the said pressure switch unit D. The inner chamber D2 and innermost chamber D1 are separated from the outer chamber D3 by a flexible membrane. The flexible membrane serve as a spring rest with respect to the inner chamber D2 and innermost chamber D1 and it also serves as a movable contact assembly consisting of a spindle and at the end of its extension is fitted with a cross-linking conductor complete with necessary damper springs.

(5) Over-pressure control unit E: The function of this unit is to check constantly the pumping main pressure so as to stop the pumpset concerned in case of the pumping main pressure is in excess of a predetermined value. It consists of three chambers, namely: (a) the inner chamber E2 which is connected to the inner chamber G2 of the master control unit G through a small bore passage 5-3; (b) the outer chamber E3 which is connected to the outer chamber G3 of the master control unit G via a one-way spring ball check valve unit N through a small bore passage 13-13 and 20-20; (c) the outermost chamber E4 which is connected to the outer chamber D3 of the pressure switch unit D through a small bore passage 14-15. In between the outer chamber E3 and the outermost chamber E4 a valve port VE is provided complete with tapered female valve seat to receive a male valve pad which is seated by spring force from its spring assembly SE for isolation purpose. The outer chamber E3 and outermost chamber E4 are formed by a hat-shaped casting serving as a spring housing as well as flanged cover to be fixed and secured in position by bolts and nuts to the cavity formed for the said over-pressure control unit E. the inner chamber E2 is separated from the outer chamber E3 and outer-most chamber E4 by a flexible membrane. The said flexible membrane will serve as a push-rod for the actuation of the said valve port VE by acting against the spring force from its spring assembly SE. Such valve port is normally kept in 'close' position until offbalanced due to excessive pumping main pressure.

(6) Under-pressure control unit F: The function of this unit is to check constantly the pumping main pressure so as to prime and start the pumpset in case of the dropping of pumping main pressure beyond the predetermined value. It consists of three chambers, namely: (a) the inner chamber F2 which is connected to the inner chamber G2 of the master control unit G through a small bore passage 4-3; (b) the outer chamber F3 which is connected to the tubular passage T5 through a small bore passage 12-12; (c) the outermost chamber F4 which is connected to the one-way spring check valve J via a small bore passage 11-7. In between the outer chamber F3 and the outermost chamber F4 of the said under-pressure control unit F a valve port VF is provided complete with tapered female valve seat for receiving the male valve pad to facilitate the required valve operation.The inner chamber F2 is separated from the outer chamber F3 and outermost chamber F4 by a flexible membrane. The said flexible membrane serve as a valve stem complete with the aforesaid male valve pad and further spindle extension beyond the latter for receiving the spring force from the spring assembly SF of the said underpressure control unit F. The outer chamber F3 and outermost chamber F4 are formed by hat-shaped casting which serves as spring housing as well as flanged cover to be fixed and secured in position by bolts and nuts to the cavity formed for the under-pressure control unit F. The valve port VF is normally kept in 'close' position until the pumping main pressure drop beyond the predetermined low value and will remain open until the pumpset concerned is operating.

(7) Master control unit G: The function of this unit is to check constantly both the suction line pressure and the pumping main pressure so as to 'channel' or 'isolate' the control pressure to the relevant chambers. It consists of four chambers, namely: (a) the innermost chamber G 1 which is connected to the one-way spring check valve J through a small bore passage 6-6 which in turn connected to relevant chambers as shown in Fig. 1; (b) the inner chamber G2 which is connected to the innermost chamber Al of the main priming unit A via the small bore passages 3-3 and 1-1 and pressure stabiliser K;The said chamber also connected to the inner chamber F2 of the underpressure control unit F via small bore passage 4-3 and also the inner chamber E2 of the overpressure control unit E via small bore passages 53; (c) the outer chamber G3 which is connected to the inner chamber A2 of the main priming unit A through a small bore passage 1 7-1 7. Connection via such small bore passage 17-17 can be direct or via another pressure stabilizer identical to the aforesaid pressure stabilizer K subject to further confirmation upon elaborated field and working testing; (d) the outermost chamber G4 which is merely a housing for its spring assembly SG. In between the inner chamber G2 and innermost chamber G 1 a valve port VG is provided complete with tapered female valve seat for receiving a male valve pad for isolation purpose.The inner chamber G2 and the innermost chamber G1 are separated from the outer chamber G3 and outermost chamber G4 by a flexible membrane.

The said flexible membrane serve as a spring rest to the spring assembly SG with respect to the outer chamber G3 and outermost chamber G4.

The same flexible membrane also serves, with respect to the inner chamber G2 and innermost chamber G1, as a valve stem fitted with male valve pad at its spindle extension for maintaining the valve port VG at either 'close' or 'open' position. Such valve action will in turn cut-off or introduce the control pressure to relevant chambers in a manner as described above. The balancing of forces at the flexible membrane will determine the position and hence the opening or closure of valve port VG.

(8) Free floating ball check valve unit H: The function of this unit is to prevent water from escaping into the amosphere and hence help to assist pressurising the pressure switch unit D to provide the 'switch-on' instruction to the electronic control circuit unit L. The said unit H will be physically the same as any of the one-way spring check valve unit J, M and N (Fig. 6) except that unit H is not provided with the spring assembly and it must be casted in the upright position with respect to the wail-mounted and finished unit of our invention. The inlet of this unit H is connected to the inner chamber B2 of the auxiliary priming unit B via tubular passage T4 whereas the outlet, i.e. the end furnished with the valve seat, will be connected to the common vent passage T5.

(9) Electronic control circuit unit L: The function of this unit is to provide a switching device for engaging the external electrical accessories for both 'starting' and 'stopping' the prime mover of the engine driven pumpset. This particular unit L is to be ignored and NOT included in the finished product IF our invention is used for controlling electrical driven pumpset. The said electronic control circuit unit L of our invention will serve nothing more than a power contactor which energise the relevant external electrical accessories for a predetermined time span and HENCE should not be pressumed to carry out the same duty, either in part or in full, as those transistorized level controller as described in Item C of page 2 in this write-up.For electrical driven pumpset, the contact pairs are provided at the innermost chamber D1 of the pressure switch unit D will be sufficient and it will serve as the remote push button unit for such switching purpose.

(10) One-way spring check value unity: The function of this unit is to direct the flow of control medium to only one-directional flow to prevent the flow from untimely operating of the related components. It will be formed by a tubular cavity, properly shaped and casted, in the main casting completed with suitably sized elastic spherical ball or cone shape valve pad made from selected material to act as a stopper and a spring unit further completed with an externally threaded end-plug as illustrated in Fig. 6.

(11) Pressure stabilizer unit K: The function of this unit (illustrated in Fig. 4) is to stabilize the pumping main pressure which is introduced from the innermost chamber Al at the main priming unit A into the inner chamber G2 at the master control unit G. Referring to Fig. 3 which show the isometric view for the parts required and full sectional view for the valve body of the said pressure stabiliser unit K. The complete unit K consists of a tubular cavity formed by the main casting to serve as the pressure stabilizer body; a free but snugly moving piston; two identical spring unit and externally threaded end-plug. The said piston will be suitably sized to move freely but snugly within the tubular cavity and will be provided with two circumferentially cut grooves the spacing of them will be exactly the same as the spring between the two connecting small bore passage 1-1 and 3-3.Between the two circumferentially cut grooves, a longitudinal groove will be cut to form as inter-connection for the aforesaid grooves. On the same piston, a central hole is provided by drilling axially and longitudinally through the said piston to act as pressure equalizer. One end of the said pressure stabilizer K will be joined to the tubular passage T1 via small bore passage 2-2 whereas the other end is fitted with an externally threaded end-plug for spring adjustment and piston position adjustment. When the pressure is stable, the piston will be equilibrium and hence the two circumferentially cut grooves will be facing its respective connecting small bore passages 1-1 and 3-3.In other words, the two small bore passages 1-1 and 3-3 will be interconnected with each other only when the piston is in equilibrium (or at its neutral and balanced position), otherwise the two aforesaid small bore passages will be isolated from each other by the piston. The central drilling in the piston will serve as pressure equalizer for equalizing the pressure on both sides of the piston. The disturbed piston will travel axially toward either direction which depends on the nature, i.e. whether it is positive or negative pressure, of the pressure fluctuation.

(12) One-way spring check valve unit M: The function of this unit is to regulate the pressure within the outer chamber D3 at the pressure switch unit D to or near its minimum pressure requirement. It generally is similar to the aforesaid unit J except that this unit serves as a pressure regulator rather than a non-return check valve. Fig. 6 illustrates it generally in configurarion.

(13) One-way spring check valve unit N: The function of this unit is to prevent the outer chamber E3 at the over-pressure control unit E from being unduly pressurised during transient condition. This unit is physically the same as the aforesaid unit J and Fig. 6 illustrates its general configuration.

(14) Two-way free floating check valve unit P: This item is not shown and hence not included in both Fig. 1 and Fig. 2 but is to be considered fitted at the discharge end of the pumping main as indicated in Fig. 3 in order to form a complete automatic pumping control system. The function of this unit is to, when pressure at Q is greater than that at R, prevent water from discharging through this unit P. However, its further function is to, when pressure at R is greater than that at Q, prevent water from discharging back into the pumping main. When pressures are equal at both Q and R, the said check valve unit P will provide a means to check the water level constantly, and hence its pressure, so as to activate the pump controller of our invention accordingly.The said unit P consists of a tubular enclosure, to be sized and shaped accordingly, with both ends completed with female tapered valve seats.

Within the space confined by the two valve seats.

a spherical ball will be enclosed and allow to travel freely to act as the male valve pad. One end of the tubular enclosure will be jointed to the pumping main as shown in Fig. 6 whereas the other end will be exposed to the water.

With the control system properly installed and connected with relevant external pipework, the pump and other components of the pump system as illustrated in Figs. 2 and 3 and as described herein, the operation will now be described.

The pumpset concerned is assumed to have stopped running for at least a short while prior to re-starting to allow pressure within the said control system to stabiliser. The pumping main pressure is then assumed to be under static delivery head pressure only. When such pressure is further reduced, because of further lowering in water level at the discharge container, to less than the pressure setting of the spring assembly SF at the under-pressure control unit F, the force exerted by the spring assembly SF will be greater than the pressure force from its inner chamber F2 due to the reduced pumping main pressure. Such off-balanced force will then cause the valve stem to move toward the direction of inner chamber F2 and hence crack open its valve port VF, thus bypassing the outer chamber F3 and the outermost chamber F4 of the under-pressure control unit F.

The opening of valve port VF then leads to release of pressure to atmosphere at the outermost chamber A3, outer chamber B3, outer chamber C3 and innermost chamber G1 of the relevant control components.

As a result of pressure release to atmosphere, all the aforesaid chambers are now subjected to atmospheric pressure and their valve ports will be held in position by such pressure and its spring force only. In this instance, valve port VA of the main priming unit A will be crack-open and eventually fully open by the pumping main pressure. The opening of valve port VA thus allows water from the pumping main to flow into the suction pipe via tubular passage T1 and tubular passage T2. While the suction pipeline is being filled up in such manner, air initially trapped inside the suction pipeline will be expelled by displacement effect of the filling water and collected at the highest point, i.e. the vent cock of the pump casing.This phenomenon continues until the whole of the suction pipeline, the pump casing and those portions of the pumping main between the pump and delivery check valve are fully filled up with water.

Air escaping from the pump vent will then enter the auxiliary priming unit B through tubular passage T3. Such air inflow will then cause valve port VB to open and allow air to escape through the free floating ball check valve H via the tubular passage T5 and thus to the atmosphere. This process continues until water instead of air enters the auxiliary priming unit B. Water then fills up the innermost chamber B1 and inner chamber B2 and also innermost chamber C1 of the switch control unit C, thus forcing the valve port VC to open. The opening of valve port VC will then fill up the inner chamber C2 with water and further fill up the outer chamber D3 of the pressure switch unit D and the outermost chamber E4 of the overpressure control unit E through its small bore passage inter-connections.When all such chambers have been fully filled up. the vertically positioned, free-floating ball check valve unit H will also fill. Under such circumstances, the ball float within the unit H will float by the buoyant force and flow pressure and hence act against the tapered female valve seat to prevent further flow of water into the tubular passage T5.

The prevention of flow at unit H will then gradually pressurise the innermost chamber B1, the inner chamber B2, the innermost chamber C1, the inner chamber C2, the outer chamber D3, and the outermost chamber E4. When all these chambers have been pressurised to its minimum steady pressure, such pressure will force the flexible membrane in the pressure switch unit D to move in the direction toward the innermost chamber D1 and hence cause the moving contact attached to the spindle extension of the flexible membrane to reach the inner contact pair fitted within the innermost chamber D1 of the pressure switch unit D.Such action will then actuate the 'pump start' circuitry at the electronic control circuit unit L via its wires extended to such terminals and thus in turn energise the external electrical accessory at the prime mover and hence 'start' the pump accordingly.

While the pump is picking up speed and begins to deliver liquid, pressure in the pump will gradually build up. Such pressure build-up will be experienced by all the above-mentioned chambers particularly the outer chamber D3 at unit D. Due to the provision of one-way spring check valve unit M connected to the said chamber D3, excess pressure greater than its spring setting will be bled-off and hence maintain the pressure within the said chambers at approximately the startic delivery pressure.

In the event that priming of the pumpset concerned fails, the above-mentioned pressure build-up will not occur but instead will drop rapidly. Such drop in pressure will then be experienced by the abovementioned chambers which subsequently reduce the force exerted in the outer chamber D3 and hence allowing its flexible membrane to return to its previous position by the spring force from its spring assembly SD. Such flexible membrane movement will cause its moving contact attachment on the stem to move toward and eventually into contact with its outer fixed contact pair mounted in innermost chamber D1 and hence activate the 'pump stop' circuitry at the electronic control circuit unit L. The latter will in turn energise the external electrical accessory at the prime mover and eventually bring the pumpset concerned to halt.After the pumpset has been brought to stand-still and the system return to its steady or stagnant condition, the whole operating cycle as described above will be repeated automatically until the pump concerned eventually starts and delivers liquid as required.

When the pump concerned is delivering liquid properly, the pumping main pressure and the suction pipe pressure will soon reach their dynamic delivery pressure. These two pressure signals eventually reach, respectively, the inner chamber G2 and outer chamber G3 at the master control unit G subjecting the flexible membrane of unit G to the total dynamic pressure of which the pump concerned can generated under rated running condition.The said flexible membrane will then act against and further overcome its spring force causing its valve port VG crack-open by moving in a direction away from the innermost chamber G1. Such valve port action therefore allow the dynamic delivery pressure which has been maintained in the inner chamber G2 to be channelled to the following chamber, namely: the outermost chamber F4, the outer chamber A3, the outer chamber C3 and the outer chamber 83.

The introduction of the dynamic delivery pressure to the aforesaid chambers will thus act against static delivery pressure which is exerted on the other side of their flexible membranes and maintain the relevant valve ports in 'closed' position with the help from their respective spring assembly.

As the pump keeps on pumping and building up the liquid level in the cistern or storage container, it will soon reach its top liquid level whence the delivery of liquid will be prevented by flow blocking device such as ball float valve or the like fitted at the liquid exit. The prevention of liquid flow in such a manner will then cause the pumping main to be further pressurised and it will eventually reach the predetermined magnitude or maximum pumping pressure when flow is further reduced. Such pressurisation effect will be faithfully reflected at the pumpset and hence at its inter-connected chambers, namely: the innermost chamber Al, the inner chamber E2, the inner chamber F2 and inner chamber G2.When this pressure goes beyond the pre-set spring force of spring assembly SE, such off-balance will then force the valve port VE to 'open' by force transmitted through the push rod attached to its flexible membrane. The opening of valve port VE will then introduce the suction line pressure through its inter-connection at outer chamber G3 and outer chamber E3. This suction line pressure will then be further chanelled to the inner chamber C2 and outer chamber D3. Under such circumstance the spring assembly SD at the pressure switch unit D will force its flexible membrane to return to its previous position and hence bring its moving contact or its cross-linking conductor to reach the outer contact pair provided in the innermost chamber D1.Such 'closing' contact of this outer contact pair will then lead to activating the 'pump stop' circuitry at the electronic control circuit unit L which in turn will energise the relevant external electrical accessory to bring the pumpset concerned to halt.

When the pumpset concerned has come to standstill, the pumping main pressure will return to its stagnant stage pressure at static delivery pressure and those in the suction pipeline will be at that of the static suction pressure. Valve port VG under such condition will therefore be maintained 'closed by its spring force from spring assembly SG. Whereas, valve ports VA, VB, and VC will be closed by the dynamic delivery pressure and their respective spring assembly SA, SB and SC. Pressure stabilizer similar to pressure stabilizer K might be required on small bore passages 17-17 and tubular passage T3 to give a better stabilization effect.

The pumping main at its stagnant stage is subject to only the static delivery pressure the full magnitude of which will be reflected in the innermost chamber Al and hence the inner chamber F2 of the under-pressure control unit F.

Should liquid level in the discharge storage container be reduced such drop in pressure will also be reflected accordingly at the above-mentioned chambers. If the drop in pressure go beyond the preset spring force from its spring assembly SF, valve port VF will be forced to open and therefore release the pressure which remained in the outermost chamber F4 through the outer chamber F3. Under such circumstance, pressure within the outer chamber A3, outer chamber B3 and outer chamber C3 will be reduced to atmospheric and the whole cycle of operation as described above will be repeated.

The unit L is to provide switching for the external electrical accessories for a pre-set period.

It uses a thyristor and triac circuit for switching power to its respective loads, and uni-junction for providing the time delay function.

It can be seen that a pump system using a pump control system as described can operate fully automatically once switched on, and has major advantages over systems available previously.

Claims (11)

Claims

1. A fluid pump control system having a control unit connected by fluid bleed lines to the fluid flow both upstream and downstream of the pump, and in which switching of the pump is controlled by pressure changes transmitted by the bleed lines.

2. A system as claimed in Claim 1, wherein a further bleed line is connected to a vent in the uppermost part of the pump casing, whereby priming of the pump can be monitored.

3. A system as claimed in Claim 1 or 2, wherein priming of the pump is achieved by fluid flow along said fluid bleed lines from upstream to downstream, said flow passing through the control unit.

4. A system as claimed in Claims 2 and 3, wherein priming stops and the pump is switched on when water rather than air reaches the control unit through the further bleed line.

5. A system as claimed in any preceding claim wherein the pump is switched off upon detection of an increased pressure upstream of the pump, caused by closing of a discharge orifice.

6. A system as claimed in any preceding claim wherein the pump is switched on upon detection of a reduced pressure upstream of the pump caused by fluid usage.

7. A system as claimed in any preceding claim wherein the control unit employs at least one diaphragm valve for registering the pressure changes.

8. A system as claimed in Claim 7, wherein said control unit embodies a plurality of diaphragm valves moulded into a single block and embodying necessary communication channels therebetween.

9. A system as claimed in any preceding claim, wherein switching of the pump is electrically effected under control of said pressure changes.

10. A pump control system substantially as herein described with reference to the accompanying drawings.

11. A pump system with a control system substantially as herein described with reference to the accompanying drawings.