Detailed introduction of throttle valve and relief valve

A throttle valve is a valve that controls the flow of a fluid by changing a throttle section or a throttle length. The throttle valve and the check valve are connected in parallel to form a one-way throttle valve. The throttle valve and the one-way throttle valve are simple flow control valves. In the hydraulic system of the fixed pump, the throttle valve and the relief valve cooperate to form three throttling speed control systems, that is, the throttle throttle speed regulation System, return oil throttle control system and bypass throttle speed control system. The throttle valve has no negative flow feedback function and cannot compensate for the instability caused by the load change. It is generally only used in applications where the load does not change much or the speed stability is not high.
The performance requirements for the throttle are:
1. The flow adjustment range is large, and the flow-pressure difference changes smoothly;
2. The amount of internal leakage is small. If there is an external leakage port, the amount of external leakage should be small;
3, the adjustment torque is small, the action is sensitive.
The shape of the throttle valve is the same as that of the shut-off valve, except that the shape of the opening and closing members is different. The opening and closing members of the throttle valve are mostly conical streamline type, and the flow rate and pressure are adjusted by changing the cross-sectional area of ​​the passage. The throttle valve is used to reduce the pressure of the medium in the event of a large pressure drop.
The flow rate of the medium between the throttle flap and the valve seat is so great that the surface of these parts is quickly damaged - the so-called cavitation phenomenon. In order to minimize the influence of cavitation, the valve disc is made of cavitation resistant material (made of alloy steel) and is made into a streamlined cone with a tip angle of 140-180. This also enables the valve flap to have a large opening height, which is generally not recommended. Throttle under a small gap.
The throttle valve has the following features:
1. The structure is simple, easy to manufacture and maintain, and the cost is low.
2, the adjustment accuracy is not high, can not be used for adjustment.
3. The sealing surface is easy to be eroded and cannot be used for cutting media.
4, the sealing is good.
The throttle valve can be divided into straight-through type and angle type according to the channel mode; according to the shape of the opening and closing member, there are three types of needle shape, groove shape and window shape. The following items should be noted for the installation and maintenance of the throttle valve:
This valve often requires operation and should therefore be installed in an easy-to-operate position.
When installing, pay attention to the direction of the media and the direction of the arrow marked on the valve body.
Causes of throttle blockage:
1. The mechanical impurities in the oil or the colloid, asphalt, carbon residue and the like deposited by the oxidation are accumulated in the throttle gap.
2. Due to aging of the oil or the generation of charged polarized molecules after being squeezed, and there is a potential difference on the metal surface of the throttling gap, the polarized molecules are adsorbed to the surface of the gap to form a strong boundary adsorption layer, and the thickness of the adsorption layer It is generally 5 to 8 microns, thus affecting the size of the throttling gap. When the above deposits and adsorbates grow to a certain thickness, they are washed away by the liquid flow and then reattached to the valve port. This cycle, the flow of the flow is formed.
3. When the valve port pressure difference is large, the temperature of the valve port is high, the degree of liquid being squeezed is enhanced, and the metal surface is more susceptible to friction to form a potential difference, so that the pressure difference is likely to cause clogging.
Measures to reduce blockage at the throttle:
1. Select a thin blade orifice with a large hydraulic radius.
2. Precision filtration and regular oil change.
3. Appropriately reduce the pressure difference before and after the throttle.
4. Use metal materials with small potential difference, select oil with good oxidation stability, and reduce the surface roughness of the orifice.
The application of the throttle valve is due to the fact that the flow rate of the throttle valve depends not only on the area of ​​the orifice, but also on the pressure difference before and after the orifice. The rigidity of the valve is small, so it is only suitable for the load change of the actuator and the speed is stable. Where the sexual requirements are not high.

The relief valve is a hydraulic pressure control valve. In the hydraulic equipment, it mainly plays the role of pressure relief and safety protection.
Constant pressure overflow: In the metering pump throttle regulation system, the metering pump provides a constant flow. When the system pressure increases, the flow demand is reduced. At this point, the relief valve opens, allowing excess flow to overflow back to the tank, ensuring the inlet pressure of the relief valve, ie the pump outlet pressure is constant (the valve port often opens with pressure fluctuations).
Safety protection: When the system is working normally, the valve is closed. Only when the load exceeds the specified limit (system pressure exceeds the set pressure), the overflow is turned on, and the overload protection is performed, so that the system pressure is no longer increased (usually the set pressure of the relief valve is 10% to 20% higher than the maximum working pressure of the system). ).
In practical applications, it is generally used as an unloading valve, as a remote pressure regulating valve, as a high and low pressure multi-stage control valve, as a sequence valve for generating back pressure (string on the return road).
The relief valve generally has two structures: 1. A direct-acting relief valve. 2, pilot type relief valve