Maintain consistent pressure to pumps regardless of upstream flow changes
PUMPS
When selecting fluid system valves, the type of hydraulic valve chosen can make a critical difference in the consistent operation and service life of that equipment. Changes in flow and pressure in one part of the system can have grave consequences for downstream equipment. Ongoing pressure fluctuation can increase component wear and drastically shorten pump life. Guided piston valves have unique flow and stability characteristics that provide reliable performance without chatter. Understanding the relative advantages of guided piston valves will ensure the long pump and system equipment life. Understanding Valve Types The terms pressure “safety” valve and pressure “relief” valve are often used interchangeably. On the face, they both perform the same function–let off pressure when a system becomes over-pressurized–but when and how they function is very different. A standard pressure safety valve is most often used on systems to meet ASME SEC VIII requirements for safety. It is actuated by inlet static pressure and characterized by rapid opening or popping action. A safety valve opens only in the event of a system failure. Pressure in the line is allowed to build until the valve reaches the set point. Then the valve opens fully to reduce
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Pipes, Pumps and Valves Africa - Jul/Aug 2021
the pressure as quickly as possible. This tight shut-off safety valve meets ASME’s basic requirements and protects people, equipment, and facilities from catastrophic overpressures but does little to protect downstream equipment from ongoing transient pressures. In contrast, a pressure relief valve is intended to control pressure in a system, ideally preventing systems from reaching the extreme pressures that would activate a pressure safety valve. While a pressure safety valve has two operating settings, totally closed or fully open, a pressure relief valve modulates, opening in proportion to the increase in system pressure. The relief valve doesn’t open fully in response to increased pressure; it opens gradually until the system returns to a preset pressure level. When the set pressure is reached without blowdown, the valve closes again. A pressure relief valve maintains consistent system pressure, reducing strain on downstream equipment. As pressure and friction build inside a pump, the temperature rises, creating vapour that can lead to cavitation which eats away at the impeller and casing.
