AU2005100918A4 - Stand alone in-line electrical monitoring device to provide protection for centrifugal pumps from dry running or low flow operating conditions - Google Patents

Description

AUSTRALIA

Patents Act 1990 INNOVATION PATENT SPECIFICATION STAND ALONE IN-LINE ELECTRICAL MONITORING DEVICE TO PROVIDE PROTECTION FOR

CENTRIFUGAL

FLOV

PUMPS FROM DRY RUNNING OR LOW V OPERATING CONDITIONS.

in November 1,2005 Perry, Andrew Joh PROVISIONAL PATENT APPLICATION TITLE: ELECTRICAL MONITORING AND CONTROL SYSTEM TO PROVIDE PROTECTION FOR CENTRIFUGAL PUMPS FROM DRY RUNNING OR LOW FLOW OPERATING CONDITIONS.

PROVISIONAL PATENT APPLICATION NO: 2004906246 PROVISIONAL PATENT DATE: NOVEMBER 1, 2004 Page 1 SDescription BACKGROUND OF THE INVENTION 0 Z This invention is intended to provide protection for centrifugal pumps from mechanical damage caused by operating under the following conditions.

Dry (or partially dry) running condition.

Flow rate below the design minimum for the pump 00 Centrifugal pumps are designed to operate above a certain minimum flow rate of liquid.

Damage to the pump can occur if liquid rate is diluted by the introduction of quantities of gas or air into the pump feed (dry or partially dry running), or if running for prolonged periods at liquid flow rate below minimum design SIntroduction of gas into the pump feed could be caused by: 0 Running out of liquid in the reservoir feed to the pump, and drawing air (or other gas into the suction.

Running devises such as automatic swimming pool cleaners.

Loss or reduction in liquid flow rate could be caused by: Closing on a valve in the feed or discharge system piping Filter or strainer blockage All of the above conditions are undesirable as they can cause local overheating of the pump shaft seals and permanent mechanical damage to the pump.

This invention is applicable to any centrifugal or similar pumping device operating under conditions where there is a risk of the pump operating under low or no flow conditions which might cause mechanical damage to the pump, for example: 1. Swimming pool pump operating an automatic pool cleaner which could allow air to be sucked into the pump suction, causing loss of adequate water flow.

2. Pump being left unattended to empty a reservoir of liquid from a system, drawing air into the system when the system becomes empty. This invention will automatically shutdown the pump once the reservoir is empty and air is drawn as part of the feed to the pump.

3. Pump being blocked in on suction or discharge system allowing no flow of the fluid, for example by a filter becoming fully blocked.

SUMMARY OF PRINCIPLE OF THIS INVENTION

O

oThe novel approach of this invention is to use provide a stand alone in-line unit which provides the mains power supply to the pump to infer acceptable pump operation without any intrusive physical fluid property measurement or internal intrusive physical measurement of the motor electrical characteristic.

The measurement is independent of the physical configuration of the liquid feed reservoir and the pump, and requires only simple calibration of the electrical measurement set point.

A centrifugal pump, typical of the kind used for filtration circulation of domestic swimming o pools, has certain flow rate, differential pressure (head of liquid) and power requirement characteristics.

oThe key characteristic that is utilised in this invention is the relationship between flow rate 0and head of the pump and the power consumed.

The relationship between centrifugal pump flow rate, power and head is given by the O following formula: Power Flow rate x Head x Fluid Density x g x Efficiency Where: Power is watts Flow rate is mA3/s Head is pressure head developed in meters of fluid m Fluid Density kg/mA3 g gravitational constant 9.81 m/sA2 Efficiency of pump and motor If air is entrained into the pump suction, the average fluid density falls in proportion to the amount of air in the water air mixture. For most systems, the variation in efficiency is small enough to allow a reasonably proportional relationship between power drawn and the fraction of air in the system and the power drawn by the by the pump correspondingly decreases as the air fraction in the feed increases. Thus a direct measure of power consumption can be used to infer either dry (or partially dry) running condition.

As the flow rate decreases to below a safe design minimum, the above formula shows that the power also decreases. Again the variation in efficiency is small enough to allow a reasonably proportional relationship between power drawn and the flow rate of liquid. Thus detecting the power can also be used as an indication of flow rate falling below the design minimum for the pump, either through low flow rate or dry or partially dry running.

For fixed speed electrically powered systems, power can be inferred for a measurement of the flowing electrical current (in Amps) by the following formula: Power Volts x Amps x Motor Efficiency Again, the variation in motor efficiency is small enough to allow a reasonably proportional relationship between power and current. Therefore a direct measurement of the pump motor's electrical current ampere requirement will give a direct indication of the flow condition of the pump itself.

This invention continuously measures the current, (and therefore inferring the power consumed by the pump), by a current detection relay, and automatically trips out the power supply as soon as the current drops below a certain predetermined acceptable level corresponding to acceptable fluid flow conditions.

DESCRIPTION OF PREFERRED EMBODIMENT For a typical 240 vac electric motor powered centrifugal pump, the invention is made up of 0 the following electrical components, as shown in figure 1.

Low Current Detection Relay Detector Coil and Power Supply (lA).

One Shot Timer Relay (timer set at 4 seconds) with Manual Override Button (non latching).

Delay On Timer Relay (timer set at 2 seconds).

Delay Off Timer Relay (timer set at 2 seconds).

240vac Power Supply Single Phase Active/Neutral (Earth not shown for clarity).

240vac Power Output to pump motor Single Phase Active/Neutral (Earth not shown _for clarity).

SFor a typical domestic swimming pool application, the following components are also shown to describe how the invention operates: Domestic Swimming Pool Pool Pump shown here elevated above normal water level.

Pool Pump 240vac Motor Pump suction pipe from pool (11) Pool filter on discharge of pump (12) Water return pipe to pool.

The system operates as follows: 1. On initial power supply to the unit, the One Shot Timer Relay closes to bypass power supply around the Low Current Detection Relay Detector Coil for the high surge current the pump motor requires on initial start up, and the pump motor will start and run the pump 2. The One Shot Timer Relay 2nd contacts also close to supply a start timer signal to the Delay Off Timer Relay which in term closes to supply a start timer signal to the Delay On Timer Relay 3. Once the pump has started and initial start up surge current has fallen to normal running current, the Delay On Timer Relay activates, allowing running current to flow simultaneously through the start up bypass contacts of the One Shot Timer Relay (2) AND through the Low Current Detection Relay Detector Coil 4. Once the One Shot Timer Relay times out, it opens the bypass supply contacts, and the signal contacts to the Delay Off Timer Relay which starts it's timer cycle. This allows time for the full normal running current to be established through the Low Current Detection Relay Detector Coil after the One Shot Timer Relay has isolated the start-up bypass supply.

If acceptable pump fluid flow rate is established during the start up period (approximately seconds, adjustable), normal running current will be detected before the Delay Off Timer Relay timer runs down and the Low Current Detection Relay contacts close, providing a new start timer signal to the Delay Off Timer Relay The Delay Off Timer Relay timer is reset to restart by this signal, which in turn holds on power supply to the already active Delay On Timer Relay which in turn hold on power supply through the Low Current Detection Relay Detector Coil to supply power to the pump motor.

6. Thus the pump continues to operate.

7. If acceptable pump fluid flow rate is not established during the start up period O (approximately 5 seconds, adjustable), due to for example too low a level on the oswimming pool causing air ingress to the pump inlet or a fully blocked filter or if this occurs at any time after normal operation is established, a low running current detected will not enable the Low Current Detection Relay Detector Coil (1) 0 z contacts to close to reset the timer on the Delay Off Timer Relay Once this timer runs down (2 seconds, adjustable), it will isolate the supply to the On Delay Timer Relay, which will open, isolating power supply to the pump motor and stopping the pump running under the unacceptable flow conditions.

8. Once the pump/motor has tripped out in this way, the pool operator should determine the o cause of the running problem and rectify the problem.

9. If it is required to run the pump for a short period partially dry to prime the pump, this can 0be achieved by pressing the manual override button on the One Shot Timer Relay oThis will provide power via the Low Current Detection Relay Detector Coil bypass to run 0the pump motor for as long as the button is held in, to prime the pump with fluid.

tl 10. Once acceptable flow rate is established, the manual push button can be released and the Odevise will go through the normal timer cycle described previously.

11. If mains power supply is isolated and restarted without rectifying the cause of the dry running condition, the system will go through one timer cycle trial to try to re-start the pump. However if acceptable operating conditions are still not available the unit will trip thus providing continued protection against the unacceptable operating condition.

A demonstration device operating 240v/1.2 kW pump operating a domestic swimming pool filtration system has been build, installed and successfully tested.

ALTERNATIVE APPLICATION OF THIS INVENTION Although the described embodiment of this invention is as a separate electrical device installed in the active power supply circuit to a pump motor, it can be appreciated that it would be possible to engineer the described current detection relay and trip relay into the local pump motor control circuitry. In other words, to incorporate this invention into the complete motor/pump package to provide in-built low flow protection.

POSSIBLE OTHER APPLICATIONS OF THIS INVENTION TO TYPES OF EQUIPMENT OTHER THAN MOTOR POWERED CENTRIFUGAL PUMPS This invention has a number of other possible manifestations to types of equipment other than electrical powered centrifugal pumps. For example, with variations in embodiment methodology, this invention is applicable to the following systems: 1. The invention is applicable to power souses other than electrical. For example, a petrol engine power pump could be configured to be controlled by a variation of this invention.

By inferring the engine power from the fuel regulator valve position (on a speed governor output signal for example) it would be possible to install a spring loaded trip system which trips fuel supply to the pump engine if the fuel flow throttle valve (ie inferred power supply) closes to a certain pre-determined point.

2. Positive displacement pumps. The invention is applicable for protection of positive displacements, or any other type of pump which show a similar characteristic reduction in power requirement on dry or partially dry running. For positive displacement pumps a blockage or closure of the pump outlet causes an increase in power requirement.

Therefore this system would not protect a positive displacement pump from protection of low flow due to blocking in the discharge system. However a suction system blockage, or t dry or partially dry running would be equally be protected by this system as for a centrifugal pump. Therefore this invention would be applicable to protect high pressure Spositive displacement booster pumps from dry running, i.e. without an adequate water supply to the pump.

3. Compressors. Although not applicable for protection from dry running, this methodology z can be used to protect gas or air compressors from damage caused by low flow due to restricting the inlet flow (centrifugal and reciprocating machines) or restricting the discharge (centrifugal machines only).

00 tt

Claims (3)

1. 2. A device according to claim 1, wherein the pump is a centrifugal pump and the sensor detects low current flow in the circuit.
2. 3. A device according to claim 1 wherein the switch includes an override by which a user can prevent action of the switch.
3. 4. A device according to claim 1 wherein the switch includes a bypass for pump startup operation. A method of protecting a pump from dry running, including: connecting a sensor and a switch to an existing circuit which provides power to the pump, determining a level of current flow in the circuit which indicates dry running of the pump, operating the pump while sensing current flow in the circuit, and operating the switch to open the circuit and stop the pump when dry running is sensed.