How does the flow direction through a globe valve affect its operation and efficiency?

The flow direction through a globe valve can significantly impact its operation and efficiency in several ways:

Pressure Drop: The direction of flow through a globe valve is a critical factor affecting the pressure drop experienced across the valve. Pressure drop, often measured in terms of head loss, refers to the decrease in pressure of the fluid as it passes through the valve. When fluid enters the valve from below the valve seat (under-seat flow), it encounters less obstruction, resulting in a lower pressure drop compared to when the fluid enters from above the seat (over-seat flow). This distinction is crucial because higher pressure drops require additional energy to overcome, impacting the overall efficiency of the system. 

Sealing Performance: The sealing performance of a globe valve is influenced by the direction of flow. In over-seat flow configurations, the fluid pressure assists in pressing the valve disk firmly against the seat, enhancing the seal integrity and preventing leakage. This configuration is particularly advantageous in high-pressure applications where maintaining a tight seal is crucial for operational safety and efficiency. However, in under-seat flow scenarios, the fluid tends to lift the disk away from the seat, potentially compromising sealing effectiveness, especially in low-pressure conditions. 

Cavitation and Erosion: Flow direction significantly impacts the likelihood of cavitation and erosion within the globe valve. Cavitation occurs when the pressure of the fluid drops below its vapor pressure, bring about the formation and collapse of vapor bubbles. In over-seat flow configurations, the pressure differentials across the valve are minimized, reducing the risk of cavitation and its detrimental effects on valve components. Conversely, under-seat flow conditions may increase the risk of cavitation and erosion due to higher pressure differentials and fluid velocities. Cavitation and erosion can cause significant damage to valve internals, bring about decreased performance, increased maintenance costs, and potential safety hazards.

Control and Stability: Flow direction plays a crucial role in determining the control and stability characteristics of the globe valve. In applications requiring precise flow regulation or modulation, such as in process industries, the flow direction can affect the valve's ability to accurately control the flow rate. Under-seat flow configurations may offer ascendant control capabilities due to enhanced fluid throttling properties, allowing for precise adjustment of flow rates to meet process requirements. However, over-seat flow configurations generally provide greater stability and resistance to pressure and flow rate fluctuations, ensuring consistent performance and operational reliability in dynamic operating conditions.

Noise and Vibration: The direction of flow through the globe valve has implications for noise and vibration levels during operation. Turbulent flow and fluid velocity fluctuations can generate noise and vibration, potentially bring about operational issues and discomfort for operators. In over-seat flow configurations, where fluid passage is smoother and more streamlined, turbulence and pressure fluctuations are minimized, resulting in reduced noise and vibration levels. Conversely, under-seat flow configurations may experience increased turbulence and fluctuations, bring about elevated noise levels and vibration. Excessive noise and vibration can impact system performance, reliability, and personnel safety.

UPVC Flange Type Globe Valve DN15-150