Hydraulic oil cooling requirement

What is this calculation used for?

In a hydraulic machine, part of the pump power turns into heat instead of work and heats the oil. If the oil gets too hot, motion and pressure become inconsistent, cycle time drifts, and part dimensions shift. This calculator finds how much capacity the oil cooler needs and how much cooling water must flow to it. Used when sizing a chiller, tower and piping for a new machine or line, or to check whether cooling is sufficient on a machine that raises an oil-temperature alarm in summer.

How do I choose temperatures for a new line?

• On a line that is not yet installed, you cannot measure inlet and outlet temperature; these are design values, not measurements, and you choose them.
• The inlet temperature is set by your cooling source: a cooling tower delivers roughly 28–32 °C in summer, a chiller roughly 12–20 °C depending on its setting. Design for the worst-case summer day.
• Hydraulic oil is usually kept between 40–50 °C. The cooling water must be sufficiently lower: 40 °C water will not cool 45 °C oil. If tower water stays too hot in summer, a chiller may be needed.
• The inlet–outlet difference (ΔT) is a design choice, usually set at 3–8 °C. A smaller difference needs more water and larger piping; a larger difference reduces flow but the outlet water is hotter and cooling becomes weaker. 5 °C is a good starting point.
• The outlet temperature follows automatically: inlet temperature + difference. This difference is how much the water heats up; it does not show how many degrees the oil will cool. Oil temperature is a separate target (40–50 °C); the water simply carries heat away from the oil.
• The most reliable approach is to check the machine manufacturer’s catalog: it usually states the required water temperature and flow rate for the oil cooler. Before ordering, ask: “will 30 °C tower water keep this machine’s oil at the target temperature, and what flow rate and pressure are required?”

How is it calculated?

• Heat load = motor power × fraction converted to heat
• Water flow rate = heat load ÷ (4.186 × temperature difference)

Results are general engineering estimates; the machine catalog, material data sheet and trial run take precedence.