I. Core Explanation of Valve Ball Body 

The ball valve controls the flow of fluid by rotating the ball (with a circular hole). It has the following characteristics: 

1. Structural Type 

Floating ball valve: The ball body can freely float. It relies on the medium pressure to compress the outlet sealing surface. It is suitable for medium and low pressure conditions (such as DN6-DN1200, pressure ≤ PN40). 

Fixed ball valve: The ball is fixed while the valve seat is floating. The use of bearings reduces the operating torque. It is suitable for high pressure and large diameter applications (such as DN50-DN2000, with a pressure rating up to PN420). 

Flexible ball valve: The ball body has an elastic groove, and the seal is achieved through external force (such as a wedge-shaped head). It is suitable for high-temperature and high-pressure media (such as in conditions above 600℃). 

V-type ball valve: The ball has a V-shaped notch, which has a cutting function. It is suitable for media containing fibers/solid particles (such as pulp, chemical processes). 

2. Sealing Performance 

Soft seal: Made of materials such as PTFE and RPTFE, with a sealing grade of VI level (in accordance with GB/T 13927), suitable for clean media. 

Metal hard seal: Through hardening treatments such as spraying nickel-based alloys, it combines sealing performance with wear resistance, and is suitable for media containing particles. 

Double-sealing structure: Main seal (metal/soft seal) + auxiliary seal (fireproof graphite ring), in compliance with API 6FA fire protection standards. 

3. Driving Method 

Manual: Suitable for small-diameter valves with diameters of DN50 or less, with low cost. 

Pneumatic/Electrical: The pneumatic actuator responds quickly (0.05 - 0.1 seconds), and the electric actuator supports precise control (such as V-type ball valves with positioners). 

Worm gear transmission: Suitable for large-diameter valves with a diameter of 300mm or above. It is easy to operate. 

II. Key Steps for Installation Selection 

1. Matching of medium characteristics 

Corrosive medium: 316L stainless steel sphere + PTFE seal (for chemical processes). 

High-temperature medium: F51 duplex steel sphere (below 600℃) or Hastelloy C-276 (in highly corrosive environment). 

Particle-containing medium: V-type ball valve + metal hard seal (such as for pulp and slurry transportation). 

Low-temperature medium: Austenitic stainless steel cryogenic treatment (-196℃ and below). 

2. Calculation of Operating Conditions Parameters 

Pressure grade: Select PN or Class grade based on pipeline pressure (for example, choose the fixed ball structure for high-pressure conditions). 

Pathway selection: 

- DN ≤ 50: Threaded connection, floating ball structure. 

- DN65-200: Flanged connection, either floating ball or fixed ball is acceptable. 

- DN ≥ 250: Flange/welded connection. A fixed ball (with lower operating torque) must be selected. 

Temperature range: The sealing material must be compatible (for example, PTFE is applicable from -30 to 180℃, PPL is applicable from -30 to 250℃). 

3. Confirmation of Functional Requirements 

Switch control: O-type ball valve (full diameter, low flow resistance). 

Flow regulation: V-type ball valve (equal percentage flow characteristic, with a regulation ratio of 100:1). 

Medium diversion: Three-way ball valve (T-type split/merge, L-type distribution). 

4. Configuration of Actuators and Accessories 

Actuator selection: 

- Single-acting pneumatic: Automatic reset when air is lost (fully open/fully closed), suitable for hazardous media. 

- Double-acting pneumatic: Bidirectional air pressure drive, retains current position when air supply is lost, suitable for conventional control. 

- Torque accounting: actuator output torque ≥ valve operating torque ×1.5~2 times. 

Required attachments: Filter pressure reducer (to stabilize the air source), solenoid valve (for controlling the switching), limit switch (for status feedback). 

Optional accessories: Positioner (for precise adjustment), Handwheel mechanism (for emergency operation in case of gas cut-off), Air storage tank (for short-term gas cut-off protection). 

III. Installation and Maintenance Key Points 

1. Pre-installation Preparation 

Check the valve labels to ensure they are intact. Open and close the valve several times to verify its operational flexibility. 

Clean the debris (such as welding slag and oil stains) at the pipe interface to avoid damaging the sealing surface. 

Check the direction of the valve body to ensure it is consistent with the flow direction of the medium. 

2. Installation Procedure 

- Horizontal/Vertical installation: Ball valves can be installed at any position, but those with gearboxes or pneumatic drives must be installed vertically (the drive unit is located above the pipeline). 

- Flange connection: The sealing gasket is installed in accordance with the pipeline design requirements. The bolts are tightened symmetrically, sequentially and evenly (alternating tightening). 

- Threaded connection: Wrap raw material tape (clockwise, 15-20 turns), and avoid excessive force to prevent thread damage. 

3. Post-installation testing 

Slowly open the main valve and check if there is any leakage from the ball valve and its connections (using non-destructive testing methods such as magnetic particle testing and radiographic testing). 

Operate the drive unit to open and close the ball valve several times to ensure there is no sticking or sluggishness and the movement is smooth. 

4. Maintenance Suggestions 

Regularly clean the sealing system and valve chambers to prevent the accumulation of impurities. 

Check the limit positions and sealing conditions, and replace the damaged sealing components in time (for example, the PTFE sealing ring has a lifespan of approximately 2-3 years). 

Valves that have been out of use for a long time need to be operated by opening and closing them regularly to prevent them from seizing or losing their sealing function. 

IV. Selection Avoidance Pitfall Guide 

1. Ignoring the influence of temperature: Using cast iron valve bodies in high-temperature conditions resulted in deformation and failure. 

2. Incorrect medium identification: For media containing particles, a regular O-type ball valve was selected, which leads to rapid sealing wear. 

3. Insufficient torque calculation: The torque of the large-diameter valve actuator is insufficient, resulting in failure to open or close. 

4. Excessive selection: Ordinary water systems blindly choose 316L stainless steel, resulting in an increase of 30% in cost.