1. Field of the Invention
The present invention relates to a flow regulator for a water pump, particularly to a flow regulator for a water pump that maintains constant water pressure by a pressure driven switch.
2. Description of Related Art
For maintaining constant water pressure as well as ensuring suitable water pressure in modern high-rise buildings and public places, water pumps are often installed at supply pipes. In addition, a pressure control system is employed, having a pressure sensor and a frequency converter to drive a motor.
The motor has a speed varying according to an input frequency. The frequency converter is controlled by the pressure sensor, in turn varying the speed of the motor. If water pressure is low, the motor is driven up to high speed. When the water pressure is close to a maximum value, the motor speed is reduced. When the water pressure exceeds the maximum value, the motor is stopped. Thus, when a large flow of water is demanded, such that a large pressure difference along the supply pipe results, the frequency converter causes the motor to speed up, and the pumped water flow is increased. On the other hand, when just a small flow of water is demanded, such that a small pressure difference along the supply pipe results, the frequency converter causes the motor to slow down, and the pumped water flow is decreased, resulting in a rapid increase of the pressure difference along the supply pipe.
Using a frequency converter to control the motor for maintaining a constant water pressure has the advantage of rapid reaction to changes in demand and of precise control of pressure. Too steep a rise of water pressure after starting the motor and subsequent sudden stopping of the motor is avoided. Rather, smooth running of the motor is ensured, leading to efficient operation and saving of energy.
However, a frequency-regulated pump requires a motor that is controlled by a frequency converter, which is complicated and expensive to purchase and to maintain. Furthermore, the frequency converter generates heat, so a control box for housing thereof needs to be provided with a radiator, still the frequency converter often gets too hot during use and burns out For these reasons, frequency-regulated pumps are normally only installed in large supply systems.
Another type of flow-regulating system has a motor which is turned on and off by a pressure-sensitive switch. The motor operates at fixed speed. Upper and lower thresholds of water pressure are preset for the pressure-sensitive switch. When water pressure at a supply pipe falls below the lower threshold, the pressure-sensitive switch turns on the motor. When, on the other hand, the water pressure has risen above the upper threshold, the pressure-sensitive switch turns off the motor, until, due to increased demand, water pressure falls below the lower threshold, which causes the motor to be switched on again. Furthermore, to attenuate pressure rises and falls, a container is installed at an outlet of the flow-regulating system, using air or an elastic membrane to store water pressure. The container takes in water when the motor is turned on and releases water by pressure of air or the elastic membrane when the motor is turned off. Thus changes of the water pressure are smoothed out, and start-stop intervals of the motor are lengthened.
This type of flow-regulating system has a comparatively simple structure and is therefore less expensive and easier to maintain. However, the motor thereof runs at a fixed speed. Thus, after turning on the motor, a fixed maximum water flow is generated, independent of the water pressure.
In order to meet peak demand, the generated water flow is required to be sufficiently large. At times of lower demand, the motor, when running, still runs at full speed, so that excess water flow results and the water pressure rises quickly above the threshold, which in turn stops the motor. This leads to short start-stop cycles of the motor.
At the moment of starting the motor, electric power consumption has a peak value, so that starting and stopping the motor in short cycles results in high power consumption, even if demand for water is low. What is more, water supply in excess of demand leads to high counterpressure at the outlet and higher load as well as to increased power consumption.
It is the main object of the present invention to provide a flow regulator for a water pump which avoids short start-stop cycles of a motor, reducing power consumption.
Another object of the present invention is to provide a flow regulator for a water pump generating water output according to demand, avoiding excess flow of water and resulting waste of energy.
A further object of the present invention is to provide a flow regulator for a water pump which works in conjunction with a mechanical underpressure system, achieving the function of a frequency converter.
The present invention can be more fully understood by reference to the following description and accompanying drawings.