![]() ![]() It relates the pressure drop between the valve and the allowable flow rates and varies with the size and type of valve. The flow coefficient (Cv) of a valve measures its efficiency to permit fluid flow. Selecting the right valve for viscous fluid service These systems require automated actuation systems such as hydraulic or pneumatic actuators, which supply sufficient actuation forces. Fluids with higher coefficients of viscosity need larger actuation forces to overcome frictional resistance. A considerable amount of force is required to overcome the static friction and the dynamic friction the fluid exerts on the valve. To actuate the valve, the stem of the valve must move from its static position. Valves have movable mechanical parts with allowable degrees of friction between them. The boiling fluid then moves past the plug and the seat, eroding the components over time. Choked flow conditions manifest when the pressure drop across the valve increases above the flashing point. Choking lowers the coefficients of flow at the valves. The boiling action results in a quick expansion of fluids, leading to a choked flow at the valves. Flashing is the boiling phenomenon of the viscous fluid at the constricted sections of the valve. In some situations, the pressure of the fluid drops below its vapor limit and causes flashing within the valve. Once the fluid reaches the wider portions of the valve, it restores the pressure. To maintain a steady fluid flow past the valve, the velocity at the vena contracta should be the greatest for the entire system. When viscous fluids move past the constricted portions of a valve (vena contracta), their kinetic energy/average velocities increase while the pressure drops. Subjecting valves to excessive and continuous throttling increases their susceptibility to cavitation. ![]() It induces additional frictional losses on the flow and increases the demand for actuation energy to overcome the resistance to fluid flow. They remain partially closed even when there is a requirement for maximum system flow rates. With this setup, the pumps operate with the valve opening, closing or throttling to permit fluid flow at the desired levels.įor viscous fluid flow service, the throttling valves are kept at a partially-closed position. The pumps work with the assistance of throttling valves which control flow rates. Piping systems utilize pumps to increase the pressure of viscous fluids and improve their flow rates. As the valves convey fluids, the solid particles erode valve components, which reduces the valve’s lifetime. Choke valves reduce the operating pressure and increase the velocities of fluids. These valves handle a mixture of solids, oil, gas and water. ![]() Oil and gas production facilities rely on choke valves to control flow and regulate downstream pressure. Corrosion leads to premature damage of seals, stem packings, valve seats and actuators. Moving viscous fluids past the valves at high process speeds accelerates the corrosive action of the particles. When clogging occurs around valves, more foreign material and debris accumulates within the valve body. Viscosity is responsible for erosion-corrosion of the valves used for viscous fluid service. The movement of fluids due to inertia between different layers drops, causing clogging around the valve body. When the magnitude of the pressure drop across the system is high, there is an increased restriction to fluid flow past the valve. It results in a significant pressure drop across the valve. Valve components do not add or boost the energy of the working media instead, they remove some potential and kinetic energy from the system. As viscous fluids flow past the valves, there is a sharp rise in the number of frictional shear forces. Internal valve components increase the roughness of the piping system by providing additional fluid contact surfaces. Valves on the path of the flowing fluid are obstacles that increase resistance to flow. Viscosity affects these performance parameters with direct and indirect implications on the integrity and safety of piping systems. When dealing with the performance of different valve types, engineers evaluate their sealing efficiencies, pressure drops, flow and loss coefficients. The fluid’s viscosity determines how fast it will move through a piping system. Effects of viscosity on valve performance Engineers need to ascertain the compatibility of the valve material with the fluid media, durability (valve’s lifecycle), response time and the valve’s maintainability. When designing or selecting valves, engineers pay attention to process variables, coefficients of viscosity of the working media and the desired type of flow. ![]()
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