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The core function of a control valve is to precisely regulate process parameters such as fluid flow rate, pressure, level, or temperature within a pipeline. It achieves this by altering the size of the internal flow passage cross-sectional area. Imagine a water faucet on a pipe: opening it wider increases the water flow, while closing it reduces the flow. A control valve operates similarly, but its control is far more precise and is typically operated remotely by an automated system.

The classification of ductile iron pipes first depends on their joint connection types, which directly determine installation methods and engineering adaptability. The most common flexible push-on joints (such as Tyton joints) utilize compressed rubber gaskets to achieve self-sealing, allowing post-installation angular deflection (typically 3-5 degrees) to accommodate ground settlement or thermal movement. Another type, mechanical joints (like K-type or Fastite joints), employ bolted gland rings to compress wedge-shaped gaskets, providing higher sealing integrity suitable for pump station valve connections requiring frequent maintenance. Flanged joints feature steel flanges cast or welded to pipe ends, creating rigid connections via high-strength bolts, specifically designed to withstand high-pressure thrust or interface with industrial equipment.

Visualize a gate valve as a vertical plate sliding across a straight pipe: when raised, flow is unobstructed; when lowered, the pipe is severed. Its structure prioritizes minimal flow resistance when open and bidirectional shutoff, resulting in a straight flow path and symmetrical body. A globe valve acts like a plug at a pipe bend: inserted downward to block the turn. Its design emphasizes sealing reliability and flow control, necessitating a tortuous flow path, asymmetrical body, and mandatory flow direction. These inherent structural contrasts define their divergent functionalities and applications.

The internal anti-corrosion lining is fundamental to ductile iron pipe's performance and longevity in water systems. It provides essential protection against corrosion and erosion caused by the conveyed fluid, safeguards water quality, prevents leaks, and ultimately extends the pipe's service life decades beyond unlined alternatives.