What type of control valve is suitable for steam at pressures above 4 MPa?

Selection of control valves – Characteristics of control valves. Control valves, also known as regulating valves, receive control signals from a control unit and use power to adjust the flow rate of fluids. A control valve generally consists of an actuator and a valve. Based on the power source used by their associated actuators, control valves can be divided into three types: pneumatic control valves, which use compressed air as a power source; electric control valves, which use electricity as a power source; and electro-hydraulic control valves, which use the pressure of a liquid medium such as oil as a power source. Additionally, depending on their functions and characteristics, there are also hydraulic control valves, solenoid valves, electronic control valves, intelligent control valves, and fieldbus-type control valves. Selection of the valve body type for control valves: There are many types of valve bodies available for control valves; common ones include straight-through single-seat, straight-through double-seat, angle-type, diaphragm-type, low-flow, three-way, eccentric rotating, butterfly, sleeve-type, and ball-type. When making a specific selection, the following factors can be taken into consideration: (1) The shape and structure of the valve core are mainly determined by factors such as the desired flow characteristics and unbalanced forces. (2) Wear resistance: When the fluid medium is a suspension containing high concentrations of abrasive particles, the internal materials of the valve must be hard. (3) Corrosion resistance: Since the medium is corrosive, valves with a simple structure should be preferred. (4) Temperature and pressure of the medium: When the temperature and pressure of the medium are high and subject to significant fluctuations, valves should be selected whose valve core and seat materials are less affected by such temperature and pressure changes. (5) Preventing flashing and cavitation: Flashing and cavitation occur only in liquid media. In actual production processes, flashing and cavitation can cause vibrations and noise, reducing the service life of valves; therefore, when selecting valves, it is necessary to prevent flashing and cavitation from occurring. Selection of the control valve actuator: For the control valve to function properly, the actuator used must be capable of generating sufficient output force to ensure a tight seal and the proper opening of the valve. Double-acting pneumatic, hydraulic, and electric actuators generally do not have a return spring. The magnitude of the acting force is independent of its direction of movement; therefore, the key to selecting an actuator lies in determining the maximum output force and the rotational torque of the motor. For single-acting pneumatic actuators, the output force is related to the valve opening, and the force acting on the control valve also affects its operating characteristics; therefore, it is necessary to establish a force balance across the entire range of valve openings. Determination of actuator type: After determining the output force of the actuator, the appropriate actuator is selected based on the requirements of the operating environment. When explosion protection is required on-site, pneumatic actuators should be selected. From an energy-saving perspective, electric actuators should be preferred as much as possible. If high adjustment accuracy is required, a hydraulic actuator can be selected. Such as the speed control of transparent machines in power plants, and the temperature control of catalyst reactors in refineries. Selection of the operating mode of the control valve: The operating mode of a control valve is a consideration only when selecting a pneumatic actuator; it is determined by the combination of the forward and reverse actions of the actuator along with those of the valve itself. There are 4 combination types: positive-positive (air-shut type), positive-negative (air-open type), negative-positive (air-open type), and negative-negative (air-shut type). The operation modes of the control valves resulting from these four combinations are air-open and air-shut. When selecting the operating mode of a control valve, three main factors are considered: a) process production safety ； b) Characteristics of the medium ； c) Ensure product quality and minimize economic losses.

Empirical criteria are adopted, with specific considerations in the following aspects: ① Analysis and selection based on the regulation quality of the control system； ②Considering the process piping layout ； ③Analysis based on load changes.

Is 4MPa a pressure difference? If so, a multi-stage pressure reduction control valve is required, as well as consideration of flow rate and temperature. Overall, single-seat control valves are not suitable; due to the special properties of steam, it causes severe erosion of the valve components. It is necessary to use materials with higher hardness for these components, or to apply surface hardening treatments to them. Multi-stage labyrinth control valves are a good choice; they can generally operate online for 5 years, and with the right selection, the internal components suffer little to no wear even after 20 years of online operation.

What was said upstairs is correct, but I’m not sure what a multi-stage labyrinth control valve is like; please explain in detail.

If the pressure difference is indeed 4 MPa, I agree with the view from the 4th floor. Additional note: The multi-stage pressure-reducing sleeve control valve features a balanced sleeve guidance structure. The sleeve utilizes a labyrinth-type multi-stage pressure reduction principle based on stacked disc layers, ensuring stable and accurate operation. It is a control valve suitable for fluid conditions involving high temperatures and large pressure differences. It can be made in an extended version or with fins. The standard actuation devices include multi-spring pneumatic actuators and electronic electric actuators. It features a labyrinth-type multi-stage pressure-reducing sleeve: this reduces the flow velocity of the fluid passing through the valve components, prevents cavitation in the liquid, lowers the noise generated by fluids under high pressure differences, and extends the service life of the valve components. It can meet ANSI B16.104 Class IV shutdown requirements under high temperature and pressure conditions, and can be used at temperatures above 230°C. Operates and maintains cost-effectiveness, with standard stainless steel valve internals that enhance wear resistance. Valve type: Straight-through sleeve-type cast ball valve. Valve core type: Sleeve-type plunger valve core

For example, with 4.2MP high-pressure steam, we choose gate valves: lol

It’s the first time I’ve heard of it; I’ve never seen one. Could you please explain in detail what kind of gate valve it is?

I fully agree with Student Sugai’s argument!