How to Choose the Right Regulating Valve? (Part 2)

Jul. 21, 2020

1.1.2 Straight-through double-seat control valve

The straight-through double-seat control valve has two valve cores and two valve seats. Since the upward thrust of the upper valve core and the downward thrust of the lower valve core is basically balanced, the unbalanced force of the entire valve core is small, allowing pressure The difference is large. For example, the DN100 double-seat control valve allows a pressure difference of 280kPa and has a large flow capacity. Compared with other control valves of the same diameter, the double-seat control valve can flow more fluid, and the flow capacity of the double-seat control valve of the same diameter is higher than that of a single-seat control valve. The flow capacity of the regulating valve is about 20% to 50% larger. For example, the DN100 double-seat regulating valve has a flow capacity of 160. Therefore, in order to obtain the same flow capacity, the double-seat regulating valve can choose a smaller thrust actuator. The double-seat regulating valve adopts top and bottom double guides. Therefore, the modification of the positive valve and the reverse valve is convenient, that is, the positive valve can be changed to the reverse valve or the reverse valve only by installing the valve core and valve seat in reverse. Change to a positive valve, without changing the type of positive or negative actuator. The upper and lower spools of the double-seat control valve cannot be guaranteed to be closed at the same time. The leakage is large. The standard leakage is 0.1%C (C is the rated flow coefficient); the flow path is complicated and it is not suitable for applications with a high-pressure difference. In this application, the valve is more severely eroded by high-pressure fluid, and it is prone to flash vaporization and cavitation, which will increase the scouring of the valve body. Similarly, it is not suitable for the control of fiber-containing media and high-viscosity fluids.

1.1.3 Sleeve control valve

A sleeve control valve is also called a cage valve. Its internal parts use valve core and cage (sleeve). The sleeve can be a straight-through single-seat control valve, a double-seat control valve or an angle control valve, etc.: Yes There are two structures of single seal and double seal. The former is equivalent to a single-seat regulating valve and is suitable for single-seat regulating valves; the latter is equivalent to a double-seat regulating valve and is suitable for double-seat regulating valves. In addition, it also has the characteristics of good stability, convenient loading, and unloading, convenient maintenance, reducing noise and reducing the influence of cavitation, but the price is 50% to 200% more expensive than single and double seat control valves, and special winding is required. Sealing gaskets are also widely used, second only to single-seat and double-seat control valves. However, this valve should not be used for dirty media and media that are easy to crystallize, stutter, and scale.

1.1.4 Angle control valve

The angle control valve is a single-seat control valve with a special valve body structure. It is suitable for specific piping and fluid applications. It changes the straight-through valve body to an angled (equivalent to an elbow) valve body, which throttles and receives force. The form is completely equivalent to the single-seat regulating valve. It retains the characteristics of small leakage and allowable pressure difference of the single-seat regulating valve. In addition, due to its simple flow path and "self-cleaning" performance, it can be applied to dirty media and can be further improved to an anti-blocking angle valve, which is suitable for working conditions containing suspended particles, especially in the installation space. It is especially suitable for restricted occasions.

1.1.5 Three-way control valve

The three-way control valve uses the spool itself to guide. The actuator must be replaced when replacing the air opening and air closing. It should be noted that the meaning of its air opening and air closing is different from other control valves. Its air opening and air closing must be It is clear which way, that is, the horizontal position or the vertical position. It has three channels, which can replace two straight-through single-seat control valves for splitting and merging two sets of streams and occasions where the temperature difference is less than or equal to 150°C. When DN is less than or equal to 80mm, the converging valve can be used for splitting.

 Eccentric Plug Valve

 Eccentric Plug Valve

1.1.6 Diaphragm regulating valve

The diaphragm regulating valve is composed of a corrosion-resistant diaphragm and a valve body lined with corrosion-resistant material. The flow path is simple, and it is suitable for two-position cut-off occasions for dirty media and weakly corrosive media. It is one of the earliest regulating valves. Due to its approximate quick-opening flow characteristics, the regulation quality is poor, and it is also affected by the material of the diaphragm and lining. It cannot be used in high temperature and high-pressure conditions. The general working pressure is ≤1.6MPa. Temperature ≤150℃, coupled with the shortcomings of easy damage to the diaphragm and short life, there are not many occasions for use now.

1.1.7 Butterfly valve

The butterfly valve is equivalent to a section of the pipeline as the valve body, with a valve plate throttling in the center. It is the most common rotary regulating valve used for control. It is suitable for low pressure, medium pressure, or occasions of high static pressure and large flow in rare cases, but the pressure difference is limited. It is small in size and light in weight, 4-10 times lighter than spherical control valves of the same caliber, and has a small ratio of caliber to price. It is especially suitable for large caliber occasions. The larger the caliber of the regulating valve, the more prominent this feature. Generally, when DN>300mm, it is usually completed by Plastic Lined Butterfly Valve.

1.1.8 Ball valve

The ball valve is a mature and old product, divided into "O" shape and "V" shape ball valve. The flow path is the simplest, the flow resistance is the smallest, the loss is the smallest, and the "self-cleaning" performance is the best. "O"-shaped ball valve is a kind of non-resistance regulating valve. Compared with the specifications, it has the largest rated flow coefficient. It is often used in large flow and dirty media. The v shaped Ball Valve provides approximate logarithmic flow. Features and large adjustable ratio, the "V"-shaped ball core and the valve seat produce a shearing effect when relative rotation, especially suitable for high viscosity, suspension flow, pulp, and other dirty, fiber-containing media adjustment and cutting. The price of the ball valve is more expensive.

1.1.9 Eccentric plug valve

Also known as the cam flex valve, it combines the advantages of ball valves and butterfly valves. It has a simple flow path, a good "self-cleaning" performance, and good adjustment performance. It is suitable for crystallization, stuttering, and dirty media. The valve body is small in size and light in weight. It can be assembled flexibly according to the site installation position without replacing any parts; the rated flow coefficient is large, 10% to 30% larger than the single-seat and double-seat control valves of the same caliber, and the adjustable ratio can reach 100:1; The seal is reliable. Due to the disturbing effect of the spool support arm and the eccentric rotation of the spool spherical surface, the required operating torque is reduced and some asymmetry is compensated. It can operate stably underflow opening, flow closing, and high pressure difference; When adjusting, a positioner is required, and the linear or equal percentage flow characteristics can be easily obtained by changing the position of the convex plate in the positioner.

1.2 Selection of special type regulating valve

For special applications, on the basis of the above-mentioned regulating valve, if the upper valve cover is lengthened and cooling fins are added, it can be used in low temperature and high-temperature occasions; the actuator with multiple springs can reduce the volume and weight of the entire regulating valve; to reduce noise A series of noise reduction measures can be designed to form a low noise control valve. In addition, there is also valve body separation regulating valves with a valve body separation structure for easy maintenance and cleaning; quick cut-off regulating valves for fast interlocking requirements; small flow regulating valves designed for small flow control requirements; used to prevent leakage The bellows seal regulating valve and so on.

These special types of regulating valves are all special valves used in the production process of special technology or a specific application, and they are non-standard. They have the characteristics of complex working conditions, high use requirements, and small production batches. These control valves are usually evolved and improved from standard types of products in response to use requirements. Therefore, the basic type should be determined first based on non-specialty, and then the corresponding deformation type and material should be determined for the particularity.