Continuous Positive and Negative Pressure Control in Online Medical Ventilation Valve Inspection Device

Continuous Positive and Negative Pressure Control in Online Medical Ventilation Valve Inspection Device

Abstract: Poor automation ability of continuous calibration of positive and negative pressure in the current domestic breathing valve online inspection device, this article introduces the solution of continuous precision control of positive and negative pressure in the process of breathing valve inspection in detail, and introduces various electronic flow regulator in detail. We introduce controller configuration, which can reach fully automatic inspection of breathing valves of various sizes under continuous positive and negative pressure conditions.

1. Question

A breathing valve refers to a valve that not only ensures the airtight container and the space of storage tank are isolated from the atmosphere within a certain pressure range, but also breathes with the atmosphere when it exceeds or falls below this pressure range. Its function is to prevent the damage of containers and storage tanks due to overpressure or vacuum, and at the same time, it can reduce the evaporation loss of storage liquid.

As an important accessory of atmospheric storage tanks in the petroleum, chemical and gas industries, breathing valves play a vital role in safety production and environmental protection. The inspection of breathing valves in the annual inspection of tank vehicles for transporting dangerous goods is also important. An important part of it is that higher requirements are put forward for the online detection device and method of breathing valve with a large number of people. The various breathing valve inspection devices currently in use still have the following problems:

(1) In the existing method, a pressure gauge is generally installed on site, which can only measure the sealing performance and positive pressure opening of valve under positive pressure conditions, and it is impossible to determine whether the negative pressure opening function of valve is in good condition. This operation is a security risk.

(2) For the sake of safety, the breathing and discharge pressure range of breathing valve is small, such as -30.0Kpa to +50Kpa, and it is difficult for conventional testing devices to complete inspection and calibration under high-precision conditions.

(3) There are many types of breathing valves with different calibers, and the passage range is generally DN20~DN300mm. It is difficult for the existing breathing valve detection and calibration device to cover such a wide breathing valve.

(4) The automation level of the existing breathing valve calibration devices is low, and the positive and negative pressures cannot be controlled automatically and precisely. Many devices rely on human experience for on-site pressure regulation, which is prone to over-pressure and damage to equipment. In severe cases, it would damage to the oil tank. In addition, many test records rely on manual filling, which is prone to errors and is not conducive to archival preservation.

In view of the above-mentioned problems existing in the current domestic breathing valve online inspection devices, this article will introduce the solutions for continuous and precise control of positive and negative pressure in the breathing valve inspection process, and introduce in detail about the various regulating valves including the electronic flow regulator and controller configurations, which can reach various fully automated inspection of breathing valves of specifications and sizes under continuous positive and negative pressure conditions.

2. Solution

The inspection and calibration principle of the breathing valve is to completely simulate the vacuum pressure working condition of breathing valve, accurately simulate the corresponding positive pressure and negative pressure at the measurement port of breathing valve, and monitor the vacuum pressure value when the breathing valve is in action. Repeating this test procedure several times to verify and calibrate the breathing valve.

In order to reach the fully automatic inspection of breathing valve, it is best to make the simulation change of positive and negative pressure a continuous precise and controllable round-trip process, such as in the vacuum pressure range of -30.0Kpa to +50Kpa. From positive pressure to negative pressure, the cycle repeats automatically so that the repeatability test result of breathing valve can be obtained. In addition, the inspection device of breathing valve can meet the inspection needs and accuracy requirements of breathing valves of various sizes. According to this design requirement, the basic principle of the solution proposed in this article is shown in Figure 1.

The basic principle of precise continuous control of positive and negative pressure of breathing valve is as follows:

(1) The control principle is based on the dynamic balance method of air inlet and outlet of airtight container, which is a typical closed-loop control loop. The PID controller collects the vacuum pressure sensor signal and sets it with comparing the values and adjusting the opening of intake electronic flow regulator and exhaust electronic flow regulator, and finally make the sensor measurement value equal to the set value to achieve accurate control of the vacuum pressure.

(2) The control loop is equipped with vacuum pump (negative pressure source) and air source (positive pressure source) to provide sufficient low pressure and high pressure capability.

(3) In order to cover the entire vacuum pressure range from negative pressure to positive pressure (such as -30.0Kpa to +50Kpa), a high-precision absolute pressure sensor with a test range within the required range can be configured, and the absolute pressure sensor outputs corresponding to the above vacuum pressure range. A DC analog signal with values ​​ranging from small to large (such as 0~10VDC). This analog signal is input to the PID controller, and the PID controller adjusts the opening of the intake valve and the exhaust valve to achieve precise pressure control. The advantage of using an absolute pressure sensor is that it is not affected by changes in local atmospheric pressure, and does not need to be corrected for pressure, which can better ensure the accuracy of the test.

(4) When the control changes from negative pressure to positive pressure, the opening of the intake electronic flow regulator (intake flow) at the beginning is much smaller than the opening of the exhaust electronic flow regulator (extraction flow), and by automatically adjusting the intake and exhaust air. The flow reaches different equilibrium states to reach different negative pressure control. Finally, the opening of intake electronic flow regulator is gradually much larger than the opening of exhaust electronic flow regulator, thereby reaching a series of set points or continuous slashes in the range of negative pressure to positive pressure of precise control. For the change control from positive pressure to negative pressure, the above process is reversed.

3. The specific content

The specific implementation content of this scheme is shown in Figure 2, which mainly includes high-pressure gas source, electronic flow regulator, closed container or pipeline, pressure sensor, high-precision PID controller and vacuum pump or vacuum generator.

The closed container or pipeline can directly adopt the on-site container and management, or can use the independent airtight container or pipeline and install the tested breathing valve. The size of independent airtight container is subject to the maximum diameter breathing valve, which can be used for the inspection and calibration of other small diameter breathing valves at the same time.

Using many breathing valves, the working pressure is basically around a standard atmospheric pressure. For precise control of vacuum pressure near standard atmospheric pressure, if the control accuracy is ±1% or less, it is generally necessary to use a two-way dynamic mode that adjusts the air extraction valve, that is, through a dual-channel PID controller, one channel is used for constant air inlet. The opening of electronic flow regulator at the outlet is basically unchanged, and the other channel adjusts the opening of the electronic flow regulator at the exhaust port according to the PID algorithm.

The positive and negative pressure control accuracy during the calibration process of the breathing valve is mainly determined by the accuracy of the pressure sensor, PID controller and electric needle valve. The PID controller uses 24-bit AD and 16-bit DA, and the electronic flow regulator is a high-precision stepper motor, so the test accuracy of this solution mainly depends on the pressure sensor accuracy. The pressure sensor can be selected according to the requirements of the breathing valve inspection and calibration.

For the inspection and calibration of the breathing valve, to achieve multiple reciprocating changes in the range of positive and negative pressure in the closed container, the program can be set in the PID controller. The setting degree is a line from positive pressure to negative pressure (or negative pressure to positive pressure) and the number of repetitions, so that the automatic control of the reciprocating change of positive and negative pressure can be reached.

4. Conclusion

The solution described in this article can fully realize the continuous control of vacuum pressure in the positive and negative pressure range during the inspection and calibration of the breathing valve using duet electronic flow regulator, and can achieve high control accuracy and speed, and the whole process is fully automated.

In addition to the automatic and precise control of positive and negative pressure, another feature of this solution is that it can meet the inspection and calibration of breathing valves of various sizes, and the vacuum pressure range is also relatively wide. The whole system is compact and integrated, which is convenient to form a portable online inspection device.

The solutions described in this article can also be applied to various types of breathing valves and safety valves, such as various end-of-pipe breathing valves, pipeline breathing valves, single-breathing valves and single-suction valves.

For further information on the electronic flow regulator, please visit:
https://www.genndih.com/proportional-flow-control-valve.htm