Several valves commonly used in chemical production and their use

The four kinds of valves introduced here are the most commonly used shut-off valves in chemical industry. Their main function is to connect and cut off the medium circulation in the pipeline. Although some of them can play a role in adjusting the flow rate, they cannot be completely used as control valves.

 

1. ball valve

 

This is a very comprehensive valve, improved in the plug valve and valve center ball rotation control opening and closing, flexible action, small size, light weight, medium flow resistance is small, good sealing effect.

 

Ball valve is divided into floating type and fixed type. The difference is mainly in the support method of the middle sphere. Floating ball valve has no support shaft on the lower side of the sphere and is supported by the force of the valve seats at both ends of the sphere. The sphere will slightly deviate from the outlet after being compressed. If the pressure is too high, the wear of the sealing layer will be aggravated. The ball of the fixed ball valve is fixed up and down with the valve stem. The other end of the valve stem is connected with the bearing. After the work is compressed, the ball will not deviate. It is supported by the bearing seat. The pressure of the sealing surface of the valve seat is not high. The fixed internal structure is more complicated and the price is relatively high.

 

Floating ball valves are generally used for medium and low pressure pipelines below DN200, while fixed ball valves will be selected for high pressure and large pipe diameters. Although ball valves can play a partial adjustment role in use, it is generally not recommended to use ordinary ball valves to adjust flow. Ball valves are partially opened for a long time, which will greatly reduce the service life of ball valves. The impact of medium will damage the edge of ball inner hole and valve seat sealing layer, causing internal leakage.

 

2. gate valve

 

As one of the most commonly used valves in chemical industry, it is also the valve with the longest history and has a wide range of uses. The closing key of the gate valve is the gate plate. The gate plate moves in the vertical direction of the medium flow in the pipeline and is closed with the valve seat to realize the interruption of the medium in the pipeline. The gate valve has a simple structure. When the medium flows through the gate valve, it does not change its flow direction. The fluid resistance is small, the seal is stable, reliable and durable.

 

However, its stroke is large, the opening and closing time is long, the opening and closing must be fully open or fully closed, the external dimension is high, and a certain space is required. The gate valve is divided into wedge gate valve and flat gate valve. The difference between them is mainly in the gate and the valve body. The two sealing surfaces are in a parallel state, or a wedge state with a certain angle.

 

The pressing force of the flat gate valve gate plate to the valve seat is provided by the medium pressure and the opening mechanism between the double gate plates. The sealing surface is always in a fit state during the opening and closing process, which can avoid the influence of particles and suspended substances in the medium on the sealing surface and achieve self-cleaning. The medium pressure will affect the force degree of the downstream sealing surface, and the high pressure and high flow rate can also be well sealed.

 

The sealing principle of wedge gate valve is to achieve sealing by combining the wedge gate with the sealing surface on the valve body. The sealing surface pressure comes from the downward pressure of the medium and the gate, because the gate of the wedge gate valve has a slope, the sealing surface can be separated faster in the opening process, with less wear and tear, but it is easier to attach deposits. Impurities of hard particles will damage the sealing surface, and the cleanliness of the medium directly affects the valve life.

 

The gate valve has almost no adjustment effect. Like the ball valve, it can only be used as fully open or fully closed. The gate is partially opened, which will produce obvious vibration and impact, destroy the valve seat seal and reduce the service life.

 

3. stop valve

 

The shut-off valve opening and closing key is a plug-shaped valve. The sealing surface is flat or conical, the valve flap up and down the movement to change the distance between the valve flap and the valve seat, just like our open water bottle stopper, closed medium flow path, the valve flap stroke is short, the switch quickly wear-resistant, long life, single sealing surface, easy maintenance. Medium in the valve will cause changes in flow rate and flow direction, fluid resistance, opening and closing process and medium pressure confrontation, for large diameter, high pressure opening and closing more difficult.

 

The cut-off valve is directional, and the medium flows from bottom to top to facilitate opening and reduce leakage at the packing. It is generally used in medium and low pressure pipelines. Medium flow from top to bottom will facilitate the closure, improve the disc sealing, suitable for high pressure pipeline.

 

Valve commonly used straight-through and DC, their main difference is the flow of the medium in the valve. Direct flow will make the pressure loss of the medium a little smaller.

 

Straight-through is the most common type, the internal structure is similar to the Z-shaped, they can play a part in the use of the role of regulating the flow, relative to the ball valve and gate valve, the adjustment of the sealing surface wear is small, suitable for small diameter.

 

Direct flow has little effect on the flow direction of the medium, and is generally used when the pressure of the medium is required.

 

4. butterfly valve

 

Butterfly valve through the center of the circular butterfly plate, with the rotation of the valve stem to achieve the role of opening and closing the fluid channel, butterfly valve structure is simple, small size, light weight, large diameter, flexible and rapid operation, ordinary butterfly valve in the low pressure situation can achieve a good seal, relative to the other three valves, sealing stability and durability is slightly worse, but better regulation.

 

Butterfly valve classification a lot, but I generally only divided into the center of the butterfly valve and eccentric butterfly valve, one is based on the sealing surface material elastic adaptive seal, one is can assist the application of external force, strengthen the seal, somewhat similar to the relationship between parallel gate valve and wedge gate valve.

 

Eccentric butterfly valve and there are single eccentric, double eccentric, three eccentric, respectively, the center of the sealing surface and the valve disc rotation center of the axial eccentricity, valve flow to the center and the valve disc rotation center of the radial eccentricity and sealing surface angle eccentricity, these are the design improvements, to enhance the sealing, reduce wear purposes.

 

Summary:

 

1. ball valve wide applicability, low pressure with floating type, high pressure with fixed type, try not to be used to adjust the flow, unless it is a special adjustment type and v-type ball valve.

 

2. The gate valve is durable and has wide applicability, but the operation time is relatively long. Do not use the booster lever at will during operation. Damage to the sealing surface is irreversible. Like the ball valve, it is not used to adjust the flow.

 

3. cut-off valve on the fluid resistance, only recommended for the medium pressure loss is not required, small diameter use.

 

Butterfly valve, in fact, is also a more comprehensive valve, with the development of technology, butterfly valve sealing, durability, applicability has been greatly improved, flexible operation can be adjusted, commonly used in low-pressure large-diameter pipeline.