Achieving a long service life and an extended maintenance-free period depends on the following factors: normal operating conditions, maintaining a harmonious temperature-pressure ratio, and appropriate consideration of corrosion data.
Even when the ball valve is in the closed position, pressurized fluid remains present within the valve body.
Prior to maintenance: Relieve the line pressure and place the valve in the open position; disconnect the power supply or pneumatic source; and detach the actuator from its mounting bracket.
Disassembly and breakdown operations must not commence until it has been verified that the upstream and downstream pipelines connected to the ball valve have been completely depressurized.
During disassembly and reassembly, extreme care must be taken to prevent damage to the sealing surfaces of the components-particularly non-metallic parts. Specialized tools should be used when removing O-rings.
During assembly, the bolts on the flanges must be tightened symmetrically, gradually, and uniformly.
The cleaning agent used must be compatible with the rubber, plastic, and metal components of the ball valve, as well as with the working medium (e.g., natural gas). If the working medium is natural gas, gasoline (per standard GB484-89) may be used to clean the metal components; non-metallic components should be cleaned using pure water or alcohol.
Non-metallic components must be removed from the cleaning agent immediately after washing and should not be allowed to soak for extended periods.
After cleaning, assembly should proceed only after the cleaning agent has fully evaporated from the cleaned surfaces (this process can be accelerated by wiping with a silk cloth that has not been dipped in the cleaning agent). However, the cleaned parts should not be left exposed for too long, as this may lead to rusting or contamination by dust.
New components must also be thoroughly cleaned prior to assembly.
During assembly, care must be taken to ensure that no metal shavings, fibers, grease (other than specified lubricants), dust, or other impurities or foreign objects contaminate, adhere to, or remain on component surfaces, or enter the internal cavities. If minor leakage occurs at the packing gland, the valve stem nut must be retightened.
Note: Do not overtighten. Typically, an additional tightening of 1/4 to 1 full turn is sufficient to stop the leakage.
A) Disassembly
Place the valve in the semi-open position, then flush and purge the interior and exterior of the valve body to remove any potentially hazardous substances.
Close the ball valve, remove the connecting bolts and nuts from the flanges on both sides, and then completely remove the valve from the pipeline. Sequentially disassemble the drive unit/actuator, mounting bracket, anti-loosening washer, stem nut, Belleville spring, gland nut, wear plate, and stem packing.
Remove the body-cover connection bolts and nuts, separate the valve cover from the valve body, and remove the valve cover gasket.
Verify that the valve ball is in the "closed" position; this facilitates its easy removal from the valve body. Subsequently, remove the valve seats.
Gently push the valve stem downward through the central bore of the valve body until it is completely removed; then, remove the O-ring and the lower stem packing.
Note: Exercise caution during this process to avoid scratching the surface of the valve stem or the sealing surfaces within the valve body's stuffing box.
B) Reassembly
Clean and inspect all disassembled parts. It is strongly recommended to replace sealing components-such as the valve seats and valve cover gasket-using a spare parts kit.
Reassemble the valve by reversing the disassembly sequence.
Tighten the flange connection bolts using the specified torque values and a cross-tightening pattern.
Tighten the stem nut to the specified torque value.
After installing the actuator, apply the appropriate control signal to rotate the valve stem, thereby rotating the valve ball to cycle the valve between its fully open and fully closed positions.
If feasible, perform pressure seal tests and functional performance tests on the valve-in accordance with relevant standards-prior to reinstalling it into the pipeline.
1. Principle of Operation
The opening and closing element of a ball valve is a spherical ball. The valve operates by rotating this ball around the central axis of the valve body to achieve the opening or closing of the flow path.
2. Applicable Applications
Typically used in low-pressure, small-bore pipelines to cut off fluid flow, to divert or distribute fluid flow, or in applications requiring rapid opening and closing capabilities.
3. Key Features
1) Low flow resistance.
2) Simple structural design.
3) Compact size and lightweight construction.
4) The sealing surfaces of the ball valve are typically constructed from plastic materials, ensuring excellent sealing performance.
5) Convenient operation; offers rapid opening and closing speeds, facilitating remote control capabilities.
6) Easy maintenance; the sealing rings are generally movable components, making them easy to disassemble and replace.
7) When the valve is either fully open or fully closed, the sealing surfaces of the ball and valve seats are isolated from the flowing medium, thereby preventing erosion of the valve's sealing surfaces by the fluid flow.
4. Classification
1) Commonly used ball valves are classified-based on their operating principles-into floating ball valves, trunnion-mounted ball valves, lift-stem ball valves, etc.
2) Based on their flow path configuration, ball valves can be classified into straight-through, three-way, and angle types. The latter two types are used to distribute the medium or to divert the direction of flow.
5. Key Points for Construction and Installation
1) The installation location, height, and inlet/outlet orientation must comply with design requirements; connections must be secure and tight.
2) For all types of manually operated valves installed on insulated pipelines, the operating handles must not be positioned facing downward.
3) Prior to installation, valves must undergo a visual inspection; the valve nameplate must comply with the provisions of the current national standard *General Valves Marking* (GB 12220). For valves with a working pressure exceeding 1.0 MPa, as well as those serving as shut-off valves on main pipelines, strength and tightness tests must be conducted prior to installation; they may be put into service only after passing these tests. During the strength test, the test pressure shall be 1.5 times the nominal pressure and maintained for a duration of no less than 5 minutes; the valve body and packing are deemed to pass if no leakage is observed. During the tightness test, the test pressure shall be 1.1 times the nominal pressure; the duration for which the test pressure is maintained must comply with the requirements of standard GB 50243, and the valve is deemed to pass if no leakage is observed at the valve disc sealing surface.
4) A gasket shall be installed between the valve flange and the pipeline flange in accordance with the pipeline design requirements.
5) Ball valves equipped with actuation mechanisms shall be installed in accordance with the instructions provided in the product's user manual. 6. Applicable Standards
1) Product Standards
GB/T 12237-2007: *Steel Ball Valves for Petroleum, Petrochemical and Allied Industries* (Superseded and Repealed)
GB/T 12224-2005: *Steel Valves - General Requirements*
GB/T 17219-1998: *Standard for Safety Evaluation of Equipment and Protective Materials in Drinking Water Supply and Distribution Systems*
2) Engineering Standards
GB 50242-2002: *Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Works*
GB 50243-2002: *Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works*
