Sizing determines whether a high-pressure pump runs reliably for years or wears out early. Two figures drive everything else: the required operating pressure and the required flow rate. From them follow motor power, speed and the drive concept.
If you already know your duty point, the pump finder lists every suitable model – the smallest sufficient pump first. For final sizing including fluid and drive, reach our technical sales team via the contact page.
How do I calculate the required motor power?
As a rule of thumb: power [kW] = pressure [bar] × flow rate [l/min] / 480. Example: 320 bar × 20 l/min / 480 gives approximately 13.3 kW. The next standard motor size above that figure is then selected.
How can I reduce the flow rate of a pump?
Through speed. Example: a pump delivers 15 l/min at 1450 min⁻¹ and 10 l/min is required – 1450 / 15 × 10 gives 967 min⁻¹. Speed is set using pulleys, or continuously via a variable-frequency drive. The choice of motor also plays a part: its number of poles determines the speed, and 4-, 6- or 8-pole designs are common. Important: a plunger pump is never run faster than its rated speed. Flow rate is always adjusted downwards, never increased by overspeeding.
What should I consider with a belt drive?
Two rules. First, the maximum reduction ratio is 3:2 – larger reductions require a gearbox. Second, never gear up: the pump always turns slower than the motor, never faster.
Why should a pump run slower in continuous duty (S1)?
In continuous 24/7 operation, the typical rated speed of four-pole drives of around 1450 min⁻¹ is too high and promotes wear. We deliberately size continuous-duty pumps larger and run them at reduced speed – preferably with a 6-pole motor at around 960 min⁻¹, or via belt reduction or a variable-frequency drive. The pump then reaches the required flow rate at low speed, runs more quietly, and the service life of seals and valves increases markedly.
What should I consider when using a variable-frequency drive?
The usual control range is 20 to 50 Hz. Below 20 Hz the motor fan no longer provides sufficient self-cooling, so a separately powered fan is required on the motor. 50 Hz is the upper limit: the pump is never operated above its rated speed.
How do I select the right nozzle?
Nozzle size follows from operating pressure and flow rate: only when the two match will the system build the intended pressure. An oversized or worn nozzle is the most common cause of pressure loss. We calculate the correct nozzle size for your combination of pressure and flow – just ask us.
What information does CAT PUMPS need for a quotation?
For accurate sizing we need: operating pressure in bar, flow rate in l/min, the fluid (water, demineralised water, chemical and so on), fluid temperature, duty type (intermittent or continuous), inlet conditions (tank or line pressure) and, where relevant, details of installation, controls and power supply.