The pump is howling, the machine is starting to feel sluggish, and touching the oil tank could result in burns? Heating (or even "boiling") hydraulic oil is one of the most dangerous warning signs in the system.
When oil temperature exceeds a safe 60-70°C, its viscosity drops dramatically. The oil becomes as thin as water, no longer lubricating the pump, and the seals in the cylinders harden and begin to crack. This phenomenon never occurs without a cause – excess heat is always the result of energy that has been converted into friction instead of machine operation .
BRhydraulic experts have prepared a list of the 5 most common reasons why your hydraulic system turns into a furnace.
1. "Bottleneck", i.e. too small distributor (Choking)
This is the number one mistake when modernizing machinery and building DIY units. If you use a powerful pump (e.g., 100 l/min), but you route this oil through a small distributor with a flow rate of 40 l/min (e.g., a standard CETOP 03 or a small monoblock), you create a massive bottleneck. Oil squeezing through undersized channels under enormous pressure generates drastic hydrodynamic friction. This results in a rapid increase in temperature.
👉 Solution: Always choose a distributor that matches the pump's maximum capacity. Switch to a larger one. CETOP 05 distributors (80-120 l/min) or larger monoblocks.
2. Hydraulic hoses cross-section too small
The principle is similar to that of a distributor. Hydraulic hoses that are too thin force the oil to flow at extremely high speeds. Flow that is too fast (turbulent) causes oil molecules to rub against the hose walls, which immediately increases its temperature.
👉 Solution: Check the recommended diameters. The suction line (from the tank to the pump) needs to have the thickest hose possible to prevent the pump from cavitating (sucking in air bubbles). Don't skimp on the cross-section on the return line either.
3. Oil tank too small (No cooling)
The hydraulic reservoir isn't just a container for fluid—it's your system's main heat sink . Oil returning from the cylinders must have time to slow down in the reservoir, release heat through the steel walls, and expel air bubbles. If the reservoir is too small, the oil circulates continuously through the system, accumulating temperature with each cycle.
👉 Golden rule: In mobile systems (agriculture, construction), the tank capacity should be at least 1-1.5 times the pump capacity (l/min). In stationary industrial power supplies, it should be as much as 2 to 3 times that. If you can't enlarge the tank, you'll need to install an oil cooler with a fan.
4. Overflow valve (safety) open all the time
The relief valve protects the system from bursting by dumping excess oil into the reservoir when the actuator encounters resistance. However, if the valve is damaged, jammed with dirt, or improperly adjusted (e.g., set to a lower pressure than the machine requires), it will continuously allow high-pressure oil to flow back into the reservoir. Releasing pressure (e.g., 160 bar) directly to the drain is the fastest way to bring the system to a boil in minutes!
5. Worn hydraulic pump (internal leaks)
When a gear or piston pump is severely worn, it develops gaps. Instead of pumping all the oil into the working system, some of the oil, under enormous pressure, "returns" through the gaps back to the suction side of the pump itself. This constant grinding and forcing of the same oil through the gaps generates enormous amounts of heat, and the pump itself becomes as hot as an iron.
👉 Solution: If the pump does not hold pressure and burns your hands, it is only suitable for replacement.
Summary
Hot hydraulic oil is the silent killer of your machine. Ignoring this problem will lead to the destruction of seals and distributors, and the seizure of the new pump. Analyze your system step by step: check hose diameters, distributor flow capacity, and relief valve settings.
All the necessary components for modernizing the system, including appropriately sized distributors and valves , can be found in the BRhydraulic offer.