Coolmay Inverters for Constant Pressure Water Supply Application

Release date:2020-06-19

1. Industry Overview
With the improvement of people's living standards, there are higher expectations for the water supply, and the traditional water supply method has been unable to meet people's requirements. Constant pressure water supply has become the main part of domestic water supply. 
In the water supply system, the constant pressure water supply refers to the control method of controlling the outlet pressure to keep the set value unchanged when the water consumption in the water supply network system changes by detecting the pressure of the pipe network. When using water pumps, the rated flow rate of the selected equipment usually exceeds the actual required flow rate, and the flow rate required during the actual water use process will change. For example, in the water supply of buildings, the water consumption during the day and night varies greatly, and it is more common to use valves to adjust the flow rate. Although the method is simple, this method actually achieves the adjustment purpose by artificially increasing resistance. This throttling adjustment method wastes a lot of electrical energy and increases the use and maintenance costs of the equipment.

2. Process requirements and processes
The constant pressure water supply system detects the pressure of the pipe network through the pressure sensor, and feeds it back to the inverter in the form of voltage or current (0-10V or 4-20mA). Its built-in PID adjusts the output speed of the motor by comparing the pressure set by the user with the feedback pressure to achieve the effect of constant pressure. When there is very little water consumption at night but the user’s life is not affected by the water pressure, the entire system enters a sleep state, and can automatically wake up the system after the water pressure drops to a certain value and maintains the pressure for more than a certain time.
 Constant Pressure Water Supply Application
(Frequency conversion constant pressure water supply system diagram)

3. Program advantages
1. The built-in PID function can automatically detect the water pressure according to the actual water consumption of the user to achieve constant pressure water supply.
2. Built-in sleep function. Under the condition that the water consumption is small and does not affect the normal use of the user, the frequency conversion water supply system can automatically enter the sleep state, and the water pump can automatically wake up when the water pressure drops to a certain value to meet the requirements of energy saving and consumption reduction.
3. The pressure of the pipe network can be constant, and the phenomenon of pipe network rupture and faucet resonance caused by excessive pressure in the traditional water supply is avoided.
4. No water supply tank is required, space-saving and low investment cost, and the secondary pollution of water quality is avoided.
5. The starting is smooth with small impact on the power grid and the motor pump, avoiding the water hammer phenomenon, and the service life of the pump is greatly increased.

4. Parameter settings

Coolmay CM540 series parameter settings (10 kg pressure gauge)




External terminal control start (DI1 and COM terminals)


Frequency given PID


(set as customer’s requirements)

Set pressure (percentage of the maximum range of the remote transmission pressure gauge), such as the remote transmission pressure gauge with a range of 1.0Mpa, requires 0.3Mpa (3 kg) pressure, 1.0Mpa×30%=0.3Mpa (3 kg)


PID feedback channel: AI1


Set to 0 or the pressure will reverse


Wake pressure deviation (set according to user needs, this value is after the pump reaches the pressure dormancy, the user uses water, the pressure setting value *70%=2.1 kg. That is, P8.49=70. When the pressure is less than this value, the pump starts again .)


The sleep frequency depends on the parameters set on site. During the operation of the inverter, the set pressure is reached. When the set frequency is less than or equal to the sleep frequency, the inverter enters the sleep state and automatically stops.

5. Cautions
1. If the pressure transmitter signal is 4-20mA, the J4 jumper on the control board needs to be adjusted to "I", and the PID feedback source is selected to be AI3 (PA-02=2);
2. 4-20mA is the linear input analog signal of AI3, and the corresponding relationship needs to be set in P4-23-P4-26. The parameters are marked with voltage values, for example, 2.00V represents 4MA (P4-23=2V);
3. The pressure transmitter is usually a two-wire system, that is, one is connected to the positive pole of 24V, and the other is connected to the AI3 signal input. COM and GND need to be shorted. Remote pressure gauge wiring: the initial range is connected to GND, the middle tap is connected to AI1, and the maximum range is connected to 10V.
4. The set pressure is the digital setting of PA-01, expressed as a percentage, where 100% corresponds to the 20mA signal which is the pressure of 10 kg.
5. The action direction of PID is set correctly according to the motor operation requirements, generally the positive action direction;
6. PID parameters generally only need to debug two parameters, KP and TI.
7. If the pressure does not reach the required pressure after running at 50Hz for a time, the total jump fault or the pressure is much different from the power frequency, it is generally caused by the motor reversing, and the motor steering needs to be changed.
8. If the water consumption is large, it is best not to use the sleep standby function.
9. After connecting the pressure gauge and setting the parameters, enter the monitoring group parameter U0-16, which is the PID feedback value. It should be very small when it is not running. If there is no or large value, that is, the pressure gauge is connected incorrectly, the resistance of the pressure gauge ground and the power supply should be about 400 ohms (maximum), the ground and center taps should be about 4-20 ohms, the power supply terminal and the center tap should be about 10 ohms smaller than the maximum value of the pressure gauge.
10. Pay attention to the correct wiring, the power supply is connected to R, S, T, and the motor is connected to U, V, W. The power switch cannot be used with leakage protection. If possible, lightning protection measures should be taken at the pressure gauge.
11. If the system pressure is unstable and easy to oscillate, there are several reasons:
A. There is a problem with the position of the pressure sensor collection system. The pressure collection point is too close to the water pump outlet, and the pipeline pressure is greatly affected by the water outlet speed. Thus, the pressure value feedback to the controller suddenly increases and decreases, causing system oscillation.
B. In addition, if the system uses an air pressure tank, and the pressure collection point is selected on the air pressure tank, it may also cause the system to oscillate. Because the air itself has a certain degree of elasticity, and the solubility of the gas in the water changes with the pressure, there is a certain time difference between the water pumped out and the pressure transmitted by the gas, which causes the system to oscillate.
12. When the pump is stopped, there is usually water in the water pipe, and the torque boost should be at least 5%. If you want to recover faster after changing the pressure, increase P slightly or decrease I.

● On-site pictures

Constant Pressure Water Supply Application

Constant Pressure Water Supply Application