This blog explains how reciprocating pumps work and when to deploy them for maximum benefit.
Reciprocating pumps are not as well understood by many as centrifugal pumps and this can lead to mis-specification, resulting in operational inefficiencies, mechanical failure, and higher total cost of ownership. This blog explains how reciprocating pumps work and when to deploy them for maximum benefit.
Centrifugal v reciprocating
There are fundamental differences in the way centrifugal and reciprocating pumps operate. Centrifugal (kinetic) pumps work by converting rotational kinetic energy, typically from an electric motor or a turbine, to create a static fluid pressure. Flow velocity is increased in the impeller and this energy is subsequently converted to static pressure due to change in the flow area in the volute section.
Reciprocating pumps by contrast are positive displacement machines. Liquid is discharged at a fixed rate per revolution of the pump. The displacement rate is dependent upon the plunger diameters, the stroke length, and the number of plungers used. The reciprocating motion generated by use of the crank and the slider mechanism in the pump causes the liquid to be moved and energized from suction to discharge, with check valves ensuring the direction of flow is maintained.
Reciprocating pumps can therefore be used to achieve a precise capacity with a fixed volume of fluid because the flow rate is linearly proportional to the speed. Variable capacity is achieved by changing pump speed, while the pressure on the discharge side of the system is set by the system itself. This means we can generate near constant flow regardless of pressure to match process requirements.
Typical applications
Reciprocating pumps can deliver improved performance, efficiency, and energy consumption as compared to centrifugal pumps in certain installations. Recips are particularly suited to low flow, high pressure differential applications where centrifugal pump technology is uneconomic due to scale, or ineffective due to the process liquid viscosity.
Typical applications include systems for wash water, butane injection, glycol services, amine services, high pressure chemical injection, and hot oil catalyst transport. In these circumstances, reciprocating pump technology can provide a better and more efficient solution, with benefits including:
- lower erosion rates than centrifugal technology due to lower fluid velocities
- simplicity of deployment
- high efficiency (90% reciprocating v 50-70% centrifugal)
- near-zero emissions, when correctly applied and maintained
Optimizing the benefits
Always consider your reciprocating pump as part of the wider flow control system to achieve optimal results. Proper sizing of a reciprocating pump can greatly affect the operating parameters of the machine, while sealing arrangements can be configured based on process fluid, lubrication requirements, and environmental leakage concerns.
API 674 gives best practice guidelines for the correct specification of positive displacement pumps in a wide variety of services and conditions. There are speed limits imposed based on the stroke length of the machine to reduce the potential for piping vibration in the wider system, which left unchecked can produce water hammer, piping failures, etc. The pulsations produced by reciprocating pumps are typically also controlled by use of adequately specified pulsation equipment.
Expert advice about reciprocating pumps is readily available from the engineering team here at Celeros Flow Technology. Our reciprocating pumps portfolio is also designed to reduce design complexity and make it simpler to match the pump to the application.
For more information about reciprocating pumps, watch our free webinar.
