throttle valve

A throttle valve is a valve that controls fluid flow by changing the throttle section or length. Parallel connection of throttle valve and one-way valve can be combined to form a one-way throttle valve. Throttle valve and one-way throttle valve are simple flow control valves. In a quantitative pump hydraulic system, the combination of throttle valve and relief valve can form three types of throttling speed control systems, namely inlet line throttling speed control system, return line throttling speed control system, and bypass throttling speed control system. Throttle valves do not have negative flow feedback function and cannot compensate for speed instability caused by load changes. They are generally only used in situations where load changes are not significant or where speed stability requirements are not high.

Performance Requirements

The performance requirements for throttle valves are:

·The flow regulation range is large, and the pressure difference between flow and pressure changes smoothly;

·The internal leakage is small, and if there is an external leakage port, the external leakage should also be small;

·The adjustment torque is small and the action is sensitive.

The external structure of a choke valve is no different from that of a globe valve, except for the shape of its opening and closing components. The opening and closing components of throttle valves are mostly conical streamlined, which can be used to adjust flow and pressure by changing the cross-sectional area of the channel. The throttle valve is used to reduce the pressure of the medium when the pressure drops greatly.

The medium has a high flow velocity between the throttle valve disc and the valve seat, causing rapid surface damage to these parts - known as cavitation phenomenon. In order to minimize the impact of cavitation, the valve disc is made of corrosion-resistant material (made of alloy steel) and made into a streamlined cone with an angle of 140-180 degrees. This also allows the valve disc to have a larger opening height, and it is generally not recommended to throttle in small gaps.

Characteristics of throttle valve

1. The structure is relatively simple, easy to manufacture and maintain, and the cost is low.

2. The adjustment accuracy is not high and cannot be used for adjustment.

3. The sealing surface is prone to erosion and cannot be used for cutting off media.

4. Poor sealing performance.

Main Categories

Throttle valves can be divided into two types based on channel mode: straight through and angle type; According to the shape of the opening and closing components, there are three types: needle shaped, groove shaped, and window shaped.

Adjustable throttle valve: The valve needle and valve core are made of hard alloy, and the product is designed according to API6A standards, with wear resistance and erosion resistance. Mainly used for wellhead oil (gas) tree equipment.

Sliding sleeve throttle valve: The valve core adopts a low-noise balanced structure, which is easy to open. The product is designed according to API6A standards, and the surface of the valve core is covered with tungsten carbide, suitable for harsh conditions such as flash evaporation, high pressure difference, high pressure, and cavitation. It has a long service life and improved flow regulation accuracy. Suitable for industries such as petroleum, natural gas, chemical, refining, hydropower, etc.

Installation and Maintenance

The installation and maintenance of throttle valves should pay attention to the following matters:

This valve often requires operation, so it should be installed in a location that is easy and convenient to operate.

When installing, pay attention to keeping the direction of the medium consistent with the arrow direction marked on the valve body.

Reason for throttle blockage:

1. Mechanical impurities in the oil or pollutants such as gum, asphalt, and carbon residue formed by oxidation accumulate at the throttling gap.

2. Due to the aging or compression of the oil, charged polarized molecules are generated, and there is a potential difference on the metal surface of the throttling gap. Therefore, polarized molecules are adsorbed onto the gap surface, forming a strong boundary adsorption layer with a thickness of generally 5-8 microns, which affects the size of the throttling gap. When the above accumulated and adsorbed substances grow to a certain thickness, they will be washed away by the liquid flow and then reattached to the valve port. This cycle repeats itself, creating a pulsation of traffic.

3. When the pressure difference at the valve port is large, due to the high temperature at the valve port, the degree of liquid compression increases, and the metal surface is more susceptible to friction, resulting in a potential difference. Therefore, when the pressure difference is large, it is easy to cause blockage.

preventive measures

1. Choose a thin blade throttling port with a large hydraulic radius.

2. Precision filtration and regular replacement of oil.

3. Reduce the pressure difference before and after the orifice appropriately.

4. Using metal materials with small potential differences, selecting oil with good antioxidant stability, and reducing the surface roughness of the throttling port.

Application field

Due to the fact that the flow rate of the throttle valve depends not only on the size of the throttle area, but also on the pressure difference before and after the throttle, the stiffness of the valve is small, so it is only suitable for situations where the load change of the actuator is small and the speed stability requirement is not high.

For throttle speed control systems with large load changes in the executing components and high requirements for speed stability, pressure compensation must be performed on the throttle valve to maintain the pressure difference before and after the throttle valve unchanged, thereby achieving flow stability.