1. Pressure loss.

Because liquids are viscous and have friction when flowing in pipelines, they must lose some energy in the process.
This part of energy loss is mainly manifest as pressure loss.
There are two kinds of pressure loss: the loss along the way and the loss in the place. Along loss is the pressure loss due to friction when the liquid flows through a distance in a straight pipe with constant diameter. Local loss is the pressure loss caused by sudden change of section shape. Change of flow direction or other forms of flow resistance.
The total pressure loss is equal to the sum of the loss along the way and the local loss.

2. Flow loss.

In the hydraulic system, each pressed element has a relatively moving surface, such as the inner surface of the hydraulic cylinder and the outer surface of the piston, because there is a relative movement, so there is a certain gap between them.
If one side of the gap is high pressure oil and the other side is low pressure oil, the high pressure oil will flow to the low pressure area through the gap and cause leakage. At the same time, because the hydraulic element seal is not perfect, part of the oil will leak to the outside. The actual flow loss due to this leakage is what we call a flow loss.
Flow loss affects motion speed, and leakage is difficult to absolutely avoid, so the rated flow of the pump in the hydraulic system is slightly greater than the maximum flow required when the system works.

3. Hydraulic impact.

Reason: the actuator element reversing and the valve close so that the flow of liquid due to inertia and some hydraulic components are not sensitive enough to respond to the action of the instantaneous pressure peak, said hydraulic impact. Its peak can exceed the working pressure several times.

Harm: cause vibration, produce noise; Make relay, sequence valve and other pressure components produce wrong action. And even cause some components, sealing device and pipeline damage.

Measures: find out the cause of the impact and avoid the sharp change of flow velocity. Delay the time of velocity change, estimate the pressure peak, and take corresponding measures. If the flow valve and solenoid valve used together, can effectively prevent hydraulic impact.