High pressure pumping systems - it`s all in the design

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Courtesy of Cat Pumps

High pressure pumping systems are used in a wide range of industrial processes. Careful selection of the components of the pumping system is essential for optimum safety and reliability. Failure to install a quality pump designed for the task could present a potential risk to human health or life or result in significant down-time and loss of production capacity with the associated costs to the user. At the heart of the process pumping system is the pump itself. There are a number of design criteria that are important to ensure that the pump is a quality fit for the application. Key parameters in pump design include seal integrity, materials of manufacture and accurate assessment of the stresses that the pump and associated equipment will experience in service. A prospective user would be well advised to work closely with a specialist high-pressure pump supplier familiar with all of these issues. CAT PUMPS triplex, positive displacement, reciprocating pumps are designed for heavy-duty industrial, process applications. Each pump has three synchronized plungers delivering a predictable, consistent flow, with single pump flows from 0.5 to 240 GPM [0.1 to 365 l/min] and pressures up to 7000 PSI [485 bar].

Materials of manufacture

A primary pump design component is the manifold. The choice of manifold materials depends very much on the liquids to be pumped and the required system pressure. In applications requiring a higher degree of corrosion resistance and strength, the block-style manifolds and internal parts such as valves and seats are machined from solid billets of material to minimize the possibility of porosity and inclusions and to provide superior surface metallurgy. CAT PUMPS are available with liquid-end components manufactured in stainless steels including 316SS, Duplex and Super Duplex grades as well as more exotic metals such as titanium or HastelloyT. Another important pump design component is the material and manufacturing process used for the plungers. Plungers should be extremely smooth and hard and accurately located for optimum sealing performance. CAT PUMPS uses a proprietary alumina ceramic material for our plungers and they are concentrically ground, hardened and polished for an extremely smooth and durable surface providing an excellent mating surface for our seals.

High integrity sealing

Another pump design component is the seal design. Sealing considerations for reciprocating pumps are similar to those in rotary pumps with seals performing between related moving components. It is important to realize that it is not possible to achieve a perfect surface to surface seal as there must always be a liquid film between the two moving components to provide cooling and lubrication. This means that a small amount of liquid will migrate from the high pressure chamber of the pump to the atmospheric area of the pump. In high pressure applications the use of a double-seal design deals with this problem, utilizing a second, low pressure seal behind the high pressure seal. This double seal arrangement provides containment of the small amount of liquid that migrates past the high pressure seal and is returned to the inlet port of the pump.

The high pressure seal has a high differential pressure across it, but the low pressure seal is only sealing the difference between the pump inlet pressure and the external (atmospheric) pressure. Because it is a moving part, all seals will wear with time, so design and material are important in optimizing seal life. By manufacturing the plungers with high concentricity and an extremely smooth surface finish, friction is reduced and the seal does not experience side loads from the plunger. Both our exclusive seal design and our concentric plungers contribute to long seal life of CAT PUMPS.

Flushed seals

CAT PUMPS offers optional pump designs for more difficult liquids. In the standard pump, the double seals are lubricated by the pumped liquid. However, for pumped liquids that have low inherent lubricity or are hazardous, hot or tend to change state (e.g. crystallize) on contact with air, a flushed double seal is preferred. CAT PUMPS flushed pumps have a special ported inlet manifold that permits a lubricating barrier liquid between the high and low pressure seals. This flushing liquid is not returned to the pump inlet port, but is recirculated to the external flushing supply creating a managed system. The flushing liquid is chosen to be compatible with the pumped liquid. This flushing liquid provides both lubrication and cooling to the seals. The flushing liquid dilutes and flushes away any seepage past the high pressure seal and prevents crystallization from fluids containing high concentrations of dissolved solids. The containment feature offered by this sealing system brings two additional key benefits:

  • For hazardous fluids, seepage can be disposed of safely
  • Monitoring the contained fluid provides early warning of wearing seals

Any sealing system will experience wear and the ability to monitor seal wearing allows timely replacement without the risk of catastrophic failure. A variety of monitoring parameters can be used to check changes in the flushed liquid. These range from increase in flushing liquid volume due to greater quantities of pumped liquid passing the high pressure seal to changes in temperature or pH, depending on the nature of the pumped liquid.

Stresses and strains

In addition to design of individual pump components, the overall pump design is also important. CAD and finite element analysis play a key role in the design of the pump itself. Finite element analysis allows designs to be analyzed, optimized, and revised quickly and accurately. Virtual testing and optimization is conducted early in the design cycle, thereby saving both time and money and assuring a consistent product each production run. It is essential to have a quality pump at the heart of your high pressure pumping system. for optimum safety and reliability.

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