What Are the Operational Risks of Pneumatic Actuators and Corresponding Countermeasures?

Continuous industrial production has a high degree of automation. Correct distribution and stable control of the flow medium are very important for stable production. The control of energy exchange, flow rate, liquid level and other process parameters is usually completed by applying actuators. At the production site, the working conditions of many actuators, such as temperature, pressure, corrosion, and pollution, are harsh environments with high temperature, high pressure, corrosion, and crystallization. This is very easy to cause the actuator to fail or malfunction, which will increase the difficulty of adjusting the process parameters, which will affect the quality of the product and even cause serious safety accidents.

 

According to their energy form, actuators can be divided into three categories: pneumatic air actuator, hydraulic actuator, and electric motor actuator.

 

Compact pneumatic actuator uses compressed air as energy source, so it is widely used in the production process of chemical industry, papermaking, oil refining, etc. It can be conveniently used with passive instruments. Its characteristics are simple structure, reliable action, stable operation, large output thrust, convenient maintenance, fire and explosion prevention, and low price. Electric actuators have convenient energy access and rapid signal transmission, but they have complex structures and poor explosion-proof performance. The hydraulic actuator is basically not used in the production process of chemical industry, oil refining, etc. It is characterized by a large output thrust.

 

This article mainly introduces the operational risks and corresponding countermeasures of pneumatic actuators.

 

As one of the important control instruments, compressed air actuator is the most widely used in petroleum, chemical, electric power, metallurgy and other industrial enterprises.

 

The pneumatic actuator uses compressed air as a power source, converts the input control signal into a pneumatic signal and adds it to the pneumatic actuation system to drive the valve to achieve continuous adjustment or switching action. This can be equipped with accessories such as electrical converters, valve positioners, solenoid valves, and retaining valves. The solenoid valve pneumatic actuator is a notable example.

 

There are two types of pneumatic actuators: diaphragm type and piston type. Common pneumatic actuators are mostly membrane type, which are characterized by simple structure, low price, but small output stroke. Membrane pneumatic actuators are divided into two types: spring and non-spring. When the force of the spring is balanced with the thrust generated by the signal pressure on the diaphragm, the push rod is stabilized at a corresponding position. The displacement of the push rod is the output of the actuator, also called the stroke.

 

Operational Risk Analysis

 

In the chemical production process, due to the long-term high temperature and high pressure environment of the pneumatic actuator, and the relatively frequent action, the failure rate is relatively high. It is prone to leakage of valve stem packing, disconnection of connectors, and loose gas pipeline.

 

Pneumatic actuators with solenoid valves are likely to cause abnormal actions of the pneumatic actuators due to solenoid valve failure, which brings great hidden dangers to normal production. In view of the problems encountered in practical applications, the sources of operational risks of pneumatic actuators should be analyzed, so as to formulate corresponding measures to minimize operational risks.

1. Common risks such as packing leakage

 

Spot inspection and regular repair is a method of equipment management that inspects the specified parts of the equipment in accordance with certain standards and certain cycles, so as to discover hidden troubles of equipment early, repair and adjust in time, and make the equipment maintain its specified functions.

 

2. The actuator is disconnected from the electrical components

 

Due to the particularity of chemical production, the actuator may disconnect from the positioner due to vibration.

 

3. Solenoid valve failure

 

In order to prevent the operation risk of the pneumatic actuator caused by the failure of the solenoid valve, the solenoid valve single configuration is transformed into a dual configuration, DCS digital output dual point setting, forming a dual insurance with the valve control relationship.