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Pump system

Pump system description/claims

The present patent application claims priority from United Kindgom Patent Application No. 0715947.8 filed on Aug. 15, 2007.

The present invention relates to a pump system for use in a pressure sewer system.

Pressure sewer systems are an alternative to a traditional gravity feed sewers and are particularly useful in areas where it is difficult and/or expensive to install a traditional gravity sewer mains, such as areas that are hilly, extremely flat, of environmental significance, built up or where minimum disruption is required. In such a system, each home may be provided with a sealed sewage collection tank into which waste from the home is passed. Periodically, the waste is pumped from the sewage collection tank under pressure through relatively small-bore pipes to a processing station. The pipes may follow the natural contour of the ground, resulting in considerable cost savings in installation and maintenance.

A problem with pressure sewer systems is that it is reliant on the correct functioning of the pumps provided for each sewage collection tank. Accordingly, reliability of the pumps is essential. However, the pumps may become damaged, for example if they attempt to operate when the pressure in the waste pipe leading to the processing station is too high. The pressure in these pipes may vary depending on, for example, the number of pumps operating at a given instant to pump waste into the pipe. Therefore, there have previously been suggested ways of avoiding damage to the pump due to operation against too high a pressure. For example it has been known to monitor the temperature of the pump and to stop the pump if the temperature exceeds a given point because the temperature may damage the pump and may indicate an elevated pressure within the waste pipe. Alternatively, it has been proposed to monitor the pressure of the waste in the pipe leading to the processing station such that the pump may be controlled not to activate if the pressure is too high.

However, both these proposals have disadvantages. For example, there can be a significant delay between a pump experiencing a high pressure and the temperature of the pump rising significantly at the point at which the temperature is measured. Accordingly, damage may be caused to the pump during such periods of delay. Likewise monitoring the pressure of the waste in the discharge pipe may be unreliable because it involves the provision of pressure switches within the discharge pipe. Such switches may not be reliable because they are in contact with the sewage which can partially or fully block them.

Accordingly, it is an object of the present invention to provide an improved pump system for use in a pressure sewer system and an improved method of controlling such a pump system.

The present invention provides a pump system for use in a pressure sewer system, comprising:

a pump;

a cutter; and

an electric motor configured to drive the pump and the cutter;

wherein the pump system further comprises:

a current sensor configured to measure the electric current provided to the motor; and

a controller that is configured to monitor the electric current measured by the current sensor during operation of the pump system and, if the measured electric current exceeds a predetermined threshold, stop the operation of the motor.

The present invention also provides a method of controlling a pump system for use in a pressure sewer system, said pump system comprising a pump, a cutter and an electric motor configured to drive the pump and the cutter; and the method comprising:

measuring the electric current provided to the motor during operation of the pump system and, if the measured electric current exceeds a predetermined threshold, stopping the operation of the motor.

Systems according to the present invention do not suffer from the drawbacks of the previously proposed arrangements. In particular, controlling the operation of the pump system based on the electric current provided to the electric motor advantageously provides a quick response to any increase in pressure in the discharge pipe. In particular, the electric current drawn by the motor may be directly proportional to the pressure against which the pump is acting. Accordingly, the measurement of the electric current may provide an immediate measurement of the pressure within the discharge pipe. Furthermore, the electric current sensor is not in contact with the sewage and accordingly, may be extremely reliable, requiring little or no routine maintenance.

Furthermore, if the pump or cutter becomes blocked, the electric current drawn by the motor may increase considerably. Accordingly, the system of the present invention may detect such a blockage by monitoring the electric current. Accordingly, the system may be arranged such that if the electric current exceeds a given level, the motor is reversed by a given amount, such as a quarter turn, in order to unblock the cutter and/or pump.

The system of the present invention may also be arranged to delay the re-start of the motor for a given period of time after the measured electric current has exceeded the threshold. In the case of the excess current being caused by an elevated pressure in the discharge pipe, for example, one may expect that when the pump system is re-started, other pump systems connected to the discharge pipe may have ceased operation and, accordingly, the pressure in the discharge pipe may have lowered sufficiently that the current drawn by the electric motor in order to pump waste into the discharge pipe will have fallen below the threshold.

The electric motor may be a single-phase motor with capacitor-start. In this case the provision of a delay between re-start of the pump system may be beneficial because the capacitors used in a single phase motor with capacitor-start may be damaged if there is not a sufficient time delay between successive starts of the motor and/or if there are too many re-starts in a given period of time.

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