What Causes Hydraulics to Run Slow?

When it comes to a hydraulic system, a common complaint can be that it is operating slowly or less effectively than before. There are many reasons why this can occur, but this is mainly down to an issue with fluid flow and faulty or failing parts. Here we discuss the critical role that individual components play in hydraulics and why it may be that these components are causing the system to slow down.

Hydraulic Tank/Reservoir – to avoid any issues a good tank or reservoir should always come fitted with a filler breather, suction strainer, site glass, removeable inspection/service plate and drain plug.

Suction Strainer – this is designed to remove any foreign bodies that may have contaminated the tank. Filters must be checked and cleaned on a regular basis. If they become blocked, they will restrict the flow of the hydraulic fluid entering the inlet side of the pump, causing the system to slow down and ultimately causing damage to the pump.

Filler Breather – this should also be checked regularly, to make sure that the cage is intact and free from foreign bodies. Check the breather cap and if required, clean using an appropriate solvent, to avoid the breather element from becoming clogged. If blocked, this can cause the tank to vacuum, which will lead to a restricted flow of oil to the pump.

Suction Hose – a short piece of hose is fitted between the outlet of the tank and the inlet of the pump. Over time, the rubber hose can degrade, becoming porous, and even delaminate internally, causing a restriction of fluid flow into the pump.

Hydraulic Pump – modern day pumps are extremely complex pieces of engineering and usually will not tolerate any form of contamination. Any foreign bodies in a pump can cause severe damage to its integral moving parts, resulting in low pressure and restricted flow. Any problems can be identified with a good quality flow meter.

Power Unit – one component that definitely needs to be checked for any problems is the power unit that is driving the hydraulic pump. This can be an electric motor or either a combustion engine. These can be checked by loading the pump with a flow meter. The tone of the power source should alter slightly under load but not die. If the flow drops and the power source stays the same, it may be worth checking the drive coupling between the output shaft and the input shaft of the unit.

System Relief Valves – these are prone to overheating and will change colour when the incorrect pressure rating is too high. This can cause damage to the seating face in the cartridge, causing oil flow to pass over the seat of the relief valve and return back to the tank via the tank line. A faulty or dirty relief valve can also have the same effect if set to low, the valve will run continuously open, losing flow and causing heat.

Directional/Proportional Control Valves – these can be fitted with additional or external valves that can be easily altered or damaged causing them to pass oil across and dumping it back to the tank. Always remember, any fluid will always take the easiest route away from the tank. The smallest imperfection on a seat, that cannot be felt but can be seen, will allow oil to pass.

Hydraulic Cylinder – just because there are no external signs of leakage does not mean to say that the internal piston seals of the cylinder are not worn or damaged. Although, usually there are identifying signs that the piston seals are worn. For instance, the cylinder may be dropping or have no lifting force.

In general, if your hydraulic system is running slowly when the fluid warms up, then this is due to the oil thinning and therefore able to pass easily across worn or damaged surfaces. Carrying out a simple flow test with a flow meter will help eliminate any of the key factors mentioned above.



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