Valve selection principle

Valve selection principle

The correct choice of the meaning of the valve

Proper selection of valves is essential for ensuring safe production of the unit, increasing valve life and meeting long-term operation of the unit. The main reason for many valve accidents is improper valve selection. For example, cast iron valves are used in cold regions. Because the water in the oil accumulates in the valve body, it is easy to freeze the valve during winter freezing. In some pump outlet valves, for some reasons, where the required flow is low and the pump power is large, the small gate valve is often used to adjust the flow rate. Because the gate valve plate is partially opened, vibration is generated and the brake is accelerated. The wear of the sealing surfaces of the plates and the seat can easily cause leakage of the valve. In addition, the quality of the valve also has a great impact on production and use.

 

For example, if a chemical fertilizer plant has a major explosion accident, the cause of the accident is identified as a liability accident caused by serious quality problems in the valve. The reason for the explosion was that the second-stage outlet valve could not withstand the normal working pressure and suddenly burst, and the check valve failed. The semi-aqueous gas of 0.75 MPa in the system quickly overflowed, mixed with the surrounding air to form an explosive gas space, and a chemical explosion occurred. According to the test, the valve has a number of indicators that do not meet the relevant national standards. In addition, these two are valves made of water, steam and oil as the medium, non-combustible gas special valves , and the selection of the design department is also wrong. Therefore, the correct selection of the valve is very important for the production, safety, long-term operation of the device and improvement of efficiency.

 

Principle of valve selection

Valves for petrochemical production equipment should meet the following basic principles

â—† Reliability

Petrochemical production requires continuous, stable, long-term operation. Therefore, the required valve should have high reliability, large safety factor, and can not cause major production safety and casualty accidents due to valve failure; meet the requirements of long-term operation of the device, long-cycle continuous production is the benefit; in addition, reduce or avoid The “ run, run, drip, leak ” caused by the valve creates a clean, civilized factory and implements HSE management.

 

â—† Meet the process production requirements

The valve should meet the requirements of operating medium, pressure temperature and application, which is also the most basic requirement for valve selection. For example, if the valve needs to protect against overpressure, the safety valve and the relief valve should be used for discharging excess medium ; if it is necessary to prevent the medium from returning during operation, a check valve should be used ; the steam pipe and the continuously generated condensation in the equipment need to be automatically discharged. Water, air and other non-condensable gases, while preventing steam from escaping, should use a trap. In addition, for corrosive media, corrosion resistant material valve body should be used.

 

â—† Easy operation, installation, maintenance and repair

After the valve is safe, the operator should correctly identify the valve direction, opening degree mark and indication signal, so as to facilitate timely and decisive handling of various emergency faults. At the same time, the selected valve type structure should be as simple as possible, easy to install and repair.

 

â—† economy

Pay attention to saving investment and reducing equipment costs. Today's investment is the cost of tomorrow. For general occasions, domestic production can meet the requirements of use, domestic valves should be selected; several different valve types can meet the requirements of use, and low-cost, simple structure valves should be used; universal materials can meet the requirements of use, should not be used Higher grade materials such as Cr-Mo steel, stainless steel, babbitt, etc.

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