Reciprocating Pump Dynamic Concepts For Improved Pump Operations
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In order to ensure safe, reliable, efficient and cost effective operation of reciprocating pumps, pump dynamics should not be ignored. Pump problems due to dynamics are often difficult to diagnose and solve. Dynamic problems usually lie in one or more of the following areas: *Pulsation control (piping acoustics) *Vibration control (piping mechanics) *Cavitation control (pulsation and pressure drop) *Pump valve dynamics (valve motion). All the areas can be interactive to such an extent that it is difficult to know where the most effective changes can be made. A clear summary of each area will be presented with a view towards understanding how these areas can interact. The topic will be approached from an engineering perception viewpoint (a spectral energy response overlay) with minimal emphasis on mathematical concepts. Following the energy as it transfers though the whole system reveals how inefficient energy transfer and local energy magnification (resonance) is key to understanding how to prevent or solve everyday problems. Problems such as vibration, bladder failure, valve failure, poor performance, fatigue failure, and safety concerns are usually linked to one or more dynamic areas. Along with a basic understanding of the physics involved in pump dynamic areas, it is also helpful to have a working knowledge of “rule of thumb” techniques that can be reliable and extremely cost effective. Pulsation control will be viewed using mechanical analogies with cause and effect scenarios. Vibration control will be focused on reducing the shaking force through reducing acoustic-to-mechanical coupling mechanisms, instead of brute force mechanical modifications. Cavitation and NPSHR (the inlet pressure required to prevent cavitation) problems will be viewed from a simple understanding of local instantaneous pressure compared to vapor pressure. Valve dynamics will be viewed in terms of simple fluid pressure forces, as they are exerted on a pressure controlled valve element. This engineering perception has a firm theoretical foundation but requires only fundamental mathematics to employ. Two short case histories will be presented illustrating pulsation/vibration control, cavitation control and pump valve problems. In almost all cases, piping vibration is the result of pulsation coupling into mechanical shaking forces yielding vibration with possible fatigue failures. Pump manifolds and external piping can be modified to ensure nonresonant acoustic systems that greatly reduce vibrational force. Once the shaking force is reduced, it remains to ensure that mechanical resonance is not present. Although cavitation is generally thought to be pressure drop related, in many cases it can be traced to acoustical resonances associated with the pump manifold and connected piping. Pump valve problems are generally solved through increasing spring stiffness, decreasing lift and employing more rugged materials. The use of newly developed materials has had the tendency of appearing as a universal fix where high pulsation levels can be tolerated. The best solution for many valve problems is reducing the pulsations that induce excessive impact forces. The use of a spectral energy response overlay or window is a concept that is in use by many who deal with dynamic problems. This type of approach is easily understood, but not as rigorous as the actual model approach. It should become apparent that most design quality can be determined by the overlay approach. It is not intended to replace the full model, but it will produce a good initial starting design and form the basis for analyzing existing field problems.
Blodgett, Larry E. (1998). Reciprocating Pump Dynamic Concepts For Improved Pump Operations. Texas A&M University. Turbomachinery Laboratories. Available electronically from