AU605184B2 - Liquid pressure system controller - Google Patents

Description

518 4 COMMONWEALTi

PATENTS

COMPLETE

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Int. Class Application Number: PH 08344 Lodged: 06.10.1986 Complete Specification Lodged: Accepted: Published: o00 0 0 P'iority: 0 00 0 SReated Art: 0 0 0 0 S0 U j

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0 0 Name of Applicant: DAVEY PRODUCTS PTY. LTD.

0 SAddress of Applicant 2- 2 2 Hargreaves Street, Huntingdale, Victoria 3166, Australia.

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Actual Inventor:

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0 Address for Service; TONY KLEIN and CHRISTOPHER GEORGE LACEY EDWD. WATERS SONS, 50 QUEEN STREET, MELBOURNE, AUSTRALIA, 3000.

Complete Specification for the invention entitled: LIQUID PRESSURE SYSTEM CONTROLLER The following statement is a full description of this inve 7 torincludino-thae.b s thp of performing it known to 'US SLODGED AT SUB-OFFICE S~ OCT 1987 Melboue ~ll~r~ 2 LIQUID PRESSURE SYSTEM CONTROLLER The present invention relates to apparatus for maintaining and controlling the pressure in a pressurized fluid system and for the protection of pump equipment used in the system against damage caused by loss of fluid flow.

The present invention is perceived to have a number of applications in pumping systems used to pressurize fluids and five of these are set out below: 1. Water Pressure Systems: Conventional water pressure systems using an accumulator (hydro pneumatic tank) employ a pressure switch to control a pump. The switch is set to operate the pump between two pressure values occurring in the hydro pneumatic o0o tank.

000. 15 For example, when water is being used and the oo a pressure in the tank drops below a preset minimum value the 00oo oo00 0 00 0 o pump switches on, pumping water into the tank and raising 0000 o0o0 the air pressure, until, at a set maximum value the pump o0 0 oo switches off (cut out).

oo If the amount of water being used is near to or exceeds the pumping rate (say 15 to 20 litres/minute) the 0 0 o0 pump will continue to operate for the duration of water use.

0 ooo oo00 If however, the amount of water being used is much c Go less than the pump is capable of delivering at the preset o o025 cut-out pressure for the system, over the period or duration ooo of water use the pump will cycle, i.e. constantly be 0-3000 0 0 switching itself off and on as the set value of the pressure

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GO in the tank is reduced by the user and quickly restored by a the pump.

Such a cycling situation occurs, for example, when a shower only is being used and in the event that the hot water is supplied at a constant pressure from an alternative system the shower will change temperature owing to pressure system cycling and consequent variations in cold water pressure.

OJ 0 030 03 0 00 00 0 t 0 0 0000 0 o

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00 C 00 0 C 0C 3 Furthermore, in the event that a conventional pressure system, as described above "runs out of water" the pump will continue to operate continuously until it is either manually switched off or fails because of damage.

Similarly in the event that the conventional water pressure system is prevented from reaching its "cut out" pressure the pump will again run continuously, either until it is manually switched off, or alternatively, it fails because of damage.

Accordingly, there is a need to maintain pump operation irrespective of the system pressure, while water is being used in order to provide a stable supply pressure and prevent cycling (switching on and switching off).

There is also the need to protect pressure systems 15 against operating when there is no water available at the system suction pipe and also to prevent units operating continuously when they are unable to achieve their normal preset "cut out" pressure. Circumstances that will prevent pumps reaching their normal preset cut out pressure are, '20 increases in suction lift, blockages or partial blockages within the system or pump and reductions in pump rotational speed caused by voltage fluctuations.

The present invention seeks to meet all the above needs by initiating operation of the pressure system pump when system pressure is reduced to a minimum preset figure and then to maintain system operation until sensing means o located in the unit discharge detects that demand flow has ceased or been reduced to a preset minimum and also that 0 pressure has been restored to a maximum level in the systems accumulator e.g. a hydropneumatic tank.

2. Protection of Electric Pumps against Operating when Fluid is not available at the Pumps Suction or when there is a Restriction in the Pumping System that Prevents Flow: Pumps used for both industrial and agricultural applications must run for extended periods unattended and under these circumstances there is the risk that an 00 o0 0 u0t: 0 00 0 C 0 0.

0000 o o 0 0 0O 00 -4unforeseen shortage of fluid or a blockage in the pump or pumping system may cause the pump to operate without water actually being pumped.

Pumps are dependent on water passing through the unit to provide cooling and lubrication of seals and "close running" parts and if such fluid flow is not present damage to ,the pump is inevitable.

The invention can be used as a part of a pressurized fluid system (either with a pump or without a pump included in the system) so as to automatically "shut down" the system in the event that fluid flow is interrupted, so as to protect the pump and prevent other mechanical or electrical equipment being damaged.

3. Maintaining Appropriate Pressure and Flows in 15 Pressure Boosting Systems.

0 4 00 Pressure boosting systems used for such 0 applications as supplying water in large buildings are 000 called on to provide various levels of flow depending on 0 building occupancy and water use at particular times.

This invention can be used to sense water demand in various sections of the building and to use the signals 0 provided by the invention to increase or decrease water flow 000O 0 by varying the output of a single pump or adding or deleting o oo pumps from a multiple pump system.

ooo0 25 4. Simple Pressure Boosting Applications: 8000 ooooIn instances where there is a fluid reticulation 80000 ooa 0 0 system that has some residual pressure that requires o0 boosting to a higher pressure the invention can be mounted in the piping being used to supply the discharge point and will provide a signal that will initiate the operation of a pressure boosting pump when a delivery valve is opened and flow commences. When flow is stopped by turning off a valve the invention will sense that water is no longer required and send an additional signal that will stop the pressure boosting pump.

Maintaining the Level in a Water Storage Container: The device according to the invention can be used to control the filling of a water storage container by controlling the pump forming part of a pressurized delivery system. In this application a "shut off" valve that will prevent water flow once the container is filled is mounted on .the end of the delivery pipe filling the container. The pump draws water from an available source and delivers it to the aforementioned delivery pipe. Tank filling is initiated by a programmable timer that initiates pump operation at regular appropriate intervals. The pump then discharges water into the storage container until such time as the "shut off" valve mounted on the end of the discharge pumps o senses that the container is full and shuts off the water delivery. Once the water delivery has ceased the sensor 0 which forms part of the invention senses that flow has ceased and "shuts off" the pump.

0 0o There are a number of known flow sensing devices 00 0 00 known to applicant, however, each suffers from a number of 0 a 0 oo undesirable problems when considered for the above proposed applications.

oo mechanical flow sensors require fine clearances, 0 ooo oo00 and too easily clog up with dirt and grit in the water o supply.

25 vortex flow sensors (including jet and venturi arrangements) require especially shaped elements that impede 0 o flow and are expensive, and often are not sensitive enough.

00 ultrasonic sensors are too expensive for standard 0004 water systems and more sensitive than required.

magnetic flow sensors are easily affected by other electromagnetic interference, and are of no value if water is pure or not conductive, they are also expensive.

The present invention seeks to meet the need for sensing flow to maintain regulation of fluid pressure or sense low levels of flow by electronic circuit means and in particular a circuit including the use of a thermistor to sense flow.

v -6 A water pressure system including a pump and pressure accumulator tank for supplying water under pressure for household, farm, commercial or industrial use including an electrical flow sensing control circuit and a water pressure switch, said flow sensing control circuit including a thermistor acting as a water flow sensing means and exhibiting first and second states of electrical conduction, said first state occurring in the presence of a water flow in a range above a predetermined minimum flow and said second state of non electrical conduction occurring when said water flow is below a predetermined minimum flow range, said pump being controlled in response to said first and second electrical conduction states wherein said pressure switch acts to energise said pump to supply water to the 0 1 accumulator tank when the water pressure falls below a 15 predetermined level in the system, said flow sensing control oo circuit acting to maintain said pump energised for as long o as there is a continued demand for water from the system o o'-0 above a predetermined said minimum flow rate.

Conveniently the thermistor is independently or indirectly heated by a separate heating element. In such a o form a thermistor exhibiting a negative temperature 0,o coefficient is utilized such that upon heating to a predetermined temperature, consistent with a low liquid flow 0° P rate, the resistance of the thermistor decreases sharply V 0° which is sensed by an electronic control circuit in order to control the operation of said pump.

The thermistor resistance characteristic may be such as to provide a sharp change in resistance for a small 30 increase in temperature so that when a critical temperature 3O is reached the control circuit is activated by the thermistor.

In a further form of the invention a positive thermal coefficient (PTC) thermistor is preferably -6apositioned in the cold water line of the standard (domestic) water pressure system and has applied to it a low voltage at a predetermined rate sufficient to cause the temperature of the thermistor to rise. When the temperature of the thermistor rises above a pre-set threshold, a large increase in resistance occurs across the thermistor. This increase in resistance is transformed, electronically, into a signal, to allow the pump unit to switch off.

When fluid passes over the thermistor, its temperature rise whether directly or indirectly heated can be restricted, keeping the device below the pre-set 3a 0 03 3 o 0 3 (~o3 00 3 0 03 0 O 3 3 33 3 33 33 0 4 03 A.l j 7 threshold. This prevents the generation of the signal that would normally switch the pump unit off, and allows the pump to continue operating above its normal cut-out pressure and to switch off only when the flow stops or reaches a minimum which does not prevent the temperature rise of the thermistor above the pre-set threshold value.

It can be seen from the above that the use of the invention will minimize water pressure system cycling and other applications discussed earlier, eliminating the need for any external flow control devices, and minimizing the number of motor starts of a pump. Minimized cycling will also allow a much smaller hydropneumatic tank to be used.

With pump cut-out being flow dependant, a wider pressure ooo range can be used giving a larger draw-off from the pressure 00 15 tank.

00 The invention is applicable to most modern pumps Sand, in particular, centrifugal pumps having a pressure head 000.., characteristic that prevents a pressure build up or only o 2 allows a limited build up.

o 0' 20 For example, modern pumps running within 70 kPa of top pressure will not have a substantial pressure build up oO in a low flow situation and can be used with the invention.

The invention will be further described with 0 reference to the accompanying figures: o oo 25 Figure 1 is a block diagram of a control circuit for use in the fluid pressure regulation system.

00 o0 Figure 2 is a sectional view of an indirectly heated thermistor element.

Soo o.co Figure 3 is a typical electronic control circuit utilising a negative resistance coefficient thermistor.

Figure 4 is a typical control circuit for a positive resistance coefficient thermistor.

With reference to Figures 1 and 3 there is schematically shown a motor, pump and accumalator arrangement. Such water pressure arrangement is of

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-8conventional type for use in improving water pressure reticulation from rain water tanks, dams or like low pressure supplies as is commonly encountered in rural areas.

The accumulator includes a pressure switch for switching power to the motor/pump upon a pressure drop in the accumalator. The control circuit includes a motor relay RL1 and, control relay RL2 which are adapted to latch in upon energisation of the pressure switch.

The relays will maintain the motor/pump in operation when the pressure switch contacts open due to an increase of liquid pressure. The control circuit also controls heating of the heating element of the temperature sensing N.T.C. thermistor (labelled sensor assembly).

oa.. Thus if there is a significant liquid flow to the o 015 consumer the thermistor temperature will stabilise and 0" remain at a low level. However, if there is low or no o o liquid flow, the N.T.C. thermistor will heat and at a predetermined temperature its resistance will show a marked oo fall thereby activating the latching comparator to switch 0 0 0 20 the voltage regulator off.

The pump will therefore stop when low or no flow to 00 the consumer is detected.

0o 0o An additional feature of the present invention S° provides that if the pressure switch closes again within one 25 half a second of the pump stopping the system will revert to a fault condition due to the power up delay built into the Ouoo control circuit. In this instance the power up delay will 0 00 be one half a second.

o0 The pump will also stop if the pressure switch is faulty, causing the contacts to remain closed. In this event the pulmp will remain "off" unless the system is reset by manual resetting and switching of the power supply.

If the system is in a fault condition it will not operate normally until the pressure switch is repaired.

Thus the pump will not be exposed to so called cycling damage and operation when there is little or no liquid flow.

9 With reference to Figure 2 this shows a thermistor incorporated according to the present invention for application as an indirectly heated unit. The thermistor 11 is mounted in a housing 12 and includes an electric heating element 10 surrounding thermistor 11. The thermistor is connected to the control circuit by lead 13. The heating element 10 may be of any desired power according to the application to which the unit is to be put. Thus the control is sensitive to reduced flow rates and will react relatively quickly to prevent possible damage to the pump.

Furthermore the thermistor is not exposed to high current flows as would occur with a directly heated unit and accordingly there is little danger of any damage to the thermistor and it should be assured of a relatively long 15 life.

Referring to the Figure 4, mains power is connected 4o 44 across the terminals A and N and a control relay or switch "o device is connected across the terminals C1 and C2.

o In the first circumstance of a high flow through the fluid system, the P.T.C. thermistor 1 will have a low resistance, and the voltage across the resistor 2 will be Oao high. This circumstance will cause the threshold on the ao negative input of the comparator 3 to be exceeded making the output of the comparator 4 high. A high output from the o.o 25 comparator will turn the transistor 5 on which will prevent drive to the optically isolated triac 6, keeping it off, but O allowing the main triac 7 to fire which energizes the control relay, which is connected to the pump and keeps the pump on.

In the circumstance of no flow or less than the minimum required flow to keep the thermistor cool, the thermistor 1 is hot and the resistance of the thermistor is j; high. The voltage across the resistance 2 is accordingly low and the threshold of the negative input on the comparator 3 is not exceeded. The output of the comparator I i 10 is therefore low which turns off the transistor 5 and allows drive to turns on) the optically isolated triac 6.

This prevents the switching on of the main triac 7 and means the control relay is de-energized. Accordingly, no power will proceed to the pump connected thereto and the pump will switch off.

The transformer 8 is part of the power supply feeding into the comparator 3 via the logic circuitry therebetween.

The circuit is further designed to accommodate additional sensors to provide for control of other system functions.

The invention may also have application in swimming pools and spa bath systems where filters are backwashed for cleaning purposes, and flow sensing means can be used to oov ensure that waste water is not incorrectly fed into the spa S or pool.

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Claims (6)

1. A water pressure system including a pump and I pressure accumulator tank for supplying water under pressure for household, farm, commercial or industrial use including an electrical flow sensing control circuit and a water pressure switch, said flow sensing control circuit including a thermistor acting as a water flow sensing means and exhibiting first and second states of electrical conduction, said first state occurring in the presence of a water flow in a range above a predetermined minimum flow and said second state of non electrical conduction occurring when said water flow is below a predetermined minimum flow range, .0 said pump being controlled in response to said first and second electrical conduction states wherein said pressure ooo 01 switch acts to energise said pump to supply water to the 0o accumulator tank when the water pressure falls below a predetermined level in the system, said flow sensing control circuit acting to maintain said pump energised for as long as there is a continued demand for water from the system o 0 00 above a predetermined said minimum flow rate. 00ooo00 e o

2. A water pressure system as claimed in claim 1 ^o^o wherein the pump is of a centrifugal type and is maintained o in operation when at or near maximum pressure calpac 000000 0 4 water demand continues above said predetermined mini, T 0 rate.

3. A water pressure system as claimed in claims I or 2, said flow sensing control circuit being adapted to de-energise said pump irrespective of the conditioun of said pressure switch, in the event of lack of supply watet, pump shut down or other no water flow condition. It Y.J -12-

4. A liquid pressure system claimed in any precdeing claim wherein the thermistor is indirectly heated by a heating element.

A liquid pressure system as claimed in any preceding claim wherein the thermistor is of negative temperature co-efficient.

6. A liquid pressure system substantially as hereinbefore described having reference to the accompanying drawings. DATED this 18th day of September, 1990. DAVEY PRODUCTS PTY. LTD. WATERMARK PATENT TRADEMARK ATTORNEYS, 290 Burwood Road, HAWTHORN. VIC. 3122 AUSTRALIA LJD:jl(2.18 t W, L