Pump displacement describes how much fluid a pump moves per revolution. A fixed-displacement pump has essentially fixed geometric displacement; a variable-displacement pump can change it within its design range. The machine cycle determines whether that flexibility creates enough value to justify the added controls and complexity.
Compare supply with demand over time
Plot pressure and flow for movement, holding, idle and peak-load phases. Parker’s pump training notes describe fixed pumps as useful for relatively constant demand and variable pumps for changing flow or pressure. Speed-controlled fixed pumps can also vary output by changing motor speed. Therefore “fixed” does not imply constant flow in every system. Compare complete motor, drive, pump and valve arrangements rather than pump purchase price alone.
Comprobaciones técnicas
- Identify simultaneous actuator flows and the longest high-pressure dwell.
- Estimate losses and heat in low-demand phases.
- Check pump control response and minimum stable speed or displacement.
- Compare noise, maintenance skills and spare-parts availability.
- Review cold-start viscosity and inlet-pressure requirements.
Un error habitual que hay que evitar
Sizing the electric motor from peak hydraulic power alone may miss acceleration and transient duty. Conversely, multiplying unrelated peak pressure and peak flow can greatly overstate the continuous demand.
Datos que hay que enviar junto con la solicitud
- Phase-by-phase pressure-flow-time table.
- Required response and position-control accuracy.
- Electrical supply, noise and installation constraints.
- Fluid, temperature and service requirements.
Ask suppliers to show predicted energy use and heat rejection for the same duty cycle so proposals can be compared fairly. For related selection guidance, see our Guía para el dimensionamiento del ciclo de trabajo de las HPU.
Referencias técnicas: Parker Hydraulic Pump Basics; Parker drive-controlled pump solutions. Portada: esquema conceptual original, no es una fotografía del producto.