1. Fluid Viscous Resistance
Hydraulic oil has a certain viscosity. When hydraulic oil flows in the channel inside the valve body, friction will be generated between the oil molecules and between the oil and the channel wall. Just like a viscous liquid flowing in a narrow pipe, the viscosity of the liquid will hinder its smooth flow. This friction will consume the energy of the hydraulic oil, resulting in pressure loss. For example, in the slender oil channel of the valve body, when the flow rate of the hydraulic oil is high, the pressure loss caused by the viscous resistance will be more obvious. Moreover, as the oil temperature changes, the viscosity of the hydraulic oil will also change, which will affect the size of the pressure loss.
2. Changes in channel shape and size
The internal channel of the hydraulic valve body is usually not a simple straight pipe with equal cross-section. When the hydraulic oil flows through the sudden contraction, expansion or bending part of the channel, the flow state of the oil will change. For example, where the channel suddenly contracts, the flow rate of the hydraulic oil will suddenly increase. According to Bernoulli's principle, the increase in flow rate will cause a decrease in pressure. When the oil passes through the bend, centrifugal force will be generated, causing the pressure on the outside to increase and the pressure on the inside to decrease, resulting in pressure loss. In addition, the roughness of the channel surface will also affect the pressure loss. If the inner wall of the channel is not smooth enough, more vortices and turbulence will be generated when the oil flows through, increasing energy loss and leading to pressure loss.
3. Resistance of internal components
The valve body may contain various components such as valve cores and valve seats. When the hydraulic oil pushes the valve core to move or flows through the gap between the valve core and the valve seat, it will encounter resistance. For example, in a sliding valve type hydraulic valve body, the valve core slides in the valve body. Although the matching gap between it and the valve body is very small, the hydraulic oil will produce a throttling effect when passing through this gap, resulting in a pressure drop. Moreover, the movement of the valve core also needs to overcome a certain amount of friction and hydraulic force, which will consume the energy of the hydraulic oil and produce pressure loss.
4. Local resistance
Inside the valve body, there may be some local factors that hinder the flow of hydraulic oil, such as filters, throttling holes, etc. The filter is used to filter impurities in the hydraulic oil, but it also creates resistance to the flow of the oil. The throttle hole is set to control the flow rate, but when the hydraulic oil passes through the throttle hole, a significant pressure drop will occur, which is also an important source of pressure loss.
