Basics of valves

Basics of valves

The function of the hydraulic control valve

The function of hydraulic control valve hydraulic control valve is a control and regulation element in the hydraulic transmission system, used to control the flow direction, pressure or flow of fluid to meet the direction of movement of the executive components (hydraulic cylinder and hydraulic motor), the size of the force (or torque) and the speed of movement requirements to ensure that the executive components and the entire hydraulic system to work in accordance with the required requirements.

Classification of hydraulic valves

(1) according to the structure form classification

(See Figure 1-1) [Illustration] Figure 1-1 Classification of hydraulic valves

① slide valve: slide valve for the gap seal, the spool and the valve mouth there is a certain seal length L, so the slide valve movement there is a dead zone, there is leakage between the movement gap.

② Cone valve: cone valve spool half cone angle φ is generally 12 ° ~ 20 °, the valve mouth closed for line sealing, good sealing performance and sensitive action. ③ ball valve: the same performance as the cone valve.

(2) According to the different control mode classification

Hydraulic valves can be divided into switching control valves, proportional control valves, servo control valves, digital control valves.

(3) According to the classification of use

Hydraulic valves can be divided into pressure control valves, flow control valves, directional control valves.

(4) According to the installation connection form classification

Hydraulic valves can be divided into pipe connection valve, plate connection valve, stacked connection valve, cartridge connection valve.

The diameter of the hydraulic valve

Nominal diameter (diameter of the main valve port) is used to indicate the size of the hydraulic valve specifications, commonly used legal unit of measurement using mm. In general, the small diameter of the valve allows the flow through less, the large diameter of the valve allows the flow through the large. Many of the operating conditions or performance indicators of hydraulic valves depend on the flow rate through them.

However, the same diameter of the same form of valve, the actual valve port diameter size slightly different (such as the actual valve port diameter of the solenoid directional valve for 10 diameter from φ9.8 to 11.6 are called 10 diameter), obviously allow the flow through the difference; nominal diameter of the same and different models of hydraulic valves, at different pressures, the nominal flow may not be the same; and, even if the nominal diameter of the same and Even if the hydraulic valves with the same nominal diameter and different models, the nominal flow rate may not be the same under the same pressure due to the structural performance limitations. For these reasons, in recent years, many hydraulic manufacturers (companies) of its hydraulic valve products flow indicators, in the normal operating conditions of the maximum flow allowed through the value of the same time, but also to give the following maximum flow, through the different flow of the relevant performance parameters change in the characteristics of the curve, in order to reflect the working characteristics of the hydraulic valve and for different types of users to use the selection.

Commonly used hydraulic valve components with clearance

The working principle of hydraulic valves is to use the spool in the valve body to do relative movement to control the control valve opening and valve opening size, to achieve the control of pressure, flow and direction. The degree of fit of the spool and the valve hole has a great impact on the performance of the valve, so it is necessary to ensure that the spool and the valve hole have a suitable fit clearance.

Through the valve’s rated flow rate of the provisions

① Different diameter valves, at the same pressure, the maximum flow rate allowed to pass is different. Liquid flow through the valve of different diameters, at the same pressure (such as the highest use pressure 31.5MPa), the maximum flow rate allowed to pass is different.

The maximum allowable flow rate through a valve with different diameters at the same pressure (e.g., maximum operating pressure of 31.5 MPa) is different.

Internal leakage (leakage loss)

As the valve spool and the valve body (sleeve) hole need to have relative movement, and thus a certain clearance between them is required, so that internal leakage is inevitable. And the spool outer diameter and the valve body (sleeve) hole concentric and not concentric (eccentric gap), the amount of internal leakage between the two is different.

Dirt clamping and hydraulic clamping

The meaning of two kinds of clamping phenomenon

Dirt clamping means that when the spool moves in the valve hole, the dirt enters the gap between the two to produce dirt clamping phenomenon, affecting the reliability of the spool action.

Hydraulic clamping is another phenomenon of clamping the spool, even if there is no dirt in the gap between the spool and the valve hole, it will also produce the phenomenon of clamping the spool due to the radial force of the liquid flow on the spool, called “hydraulic clamping”. It affects the spool action reliability and commutation performance, but often not understood by people.

If the spool and the valve body hole for the ideal cylindrical, and the two assembly concentric, radial clearance everywhere equal, the gap and not stuck in the dirt, the spool on the role of the radial force on the entire circumference, will cancel each other and there is no hydraulic clamping force. However, due to the processing quality, the spool and the valve body may exist taper, the assembly can not be 100% concentric and absolutely no dirt, so there will inevitably be radial hydraulic clamping force.

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