Any engineering system must be equipped with a device that will stop its operation if necessary. So, the shut-off valves include cast-iron and steel valves for pipelines. They are installed in order to partially or completely block the path for the flow of liquid or gas. Metal products are characterized by ease of management and maintenance. The scope of such devices depends on the design, assembly, control methods and installation.
What are pipeline valves
A variety of valves is designed for installation on water supply networks and gas. They serve to completely or partially block the movement, distribute the contents through the nozzles, and adjust the pressure. Also, by means of valves, it is possible to control the flow of liquids and gases by changing the diameter of the path.
Valve markings include letters and numbers. They include the type of fittings and housing, the material of the seals and the method of control. For example, the decoding of some products is as follows:
- 30s41nzh — steel gate valve with a mechanical drive, cylindrical gear, stainless steel sealing rings.
- 30ch39r — cast iron gate valve with mechanical drive, electric transmission, brass rings.
- 30ch6br — cast iron gate valve with pneumatic actuator, bronze and brass seal.
The construction length of the valve must comply with GOST 3706–93. The only exceptions are devices for special purposes (isomorphic). In other cases, deviations from ±2 to ±14 mm are allowed.
The valve device is characterized by simplicity. Dependence lies in the location of the locking mechanism. It is built into a cylindrical metal body along its central axis. The equipment is mounted inside the caisson chamber or manhole.
Control can be manual or automatic. The second option allows you to adjust the position of the shutter remotely. To do this, the operator uses a push-button device.
The valve drawing is represented by a sealing ring and a metal valve. Its shape is convex, and on both sides. Locking mechanisms with mechanical control have a stem and a lever attached to it. Turning it (90॰) drives the valve.
Fixation of the device is carried out due to two conclusions on both sides of the disk. They can be represented by flanges, threaded elements or chamfers for connection to nozzles by means of a welding machine.
Principle of operation and technical characteristics
The principle of operation of the valve is based on changing the position of the valve perpendicular to the flow of liquid in the line (smoke in the chimney). Tightness is ensured by a tight fit of the valve to the seat of the device.
The classification of pipeline valves is carried out in accordance with the features of the structures, their assembly, installation, indicators of technical characteristics, control. They look like this:
- installation is carried out above or below ground, with and without wells, indoors or outdoors;
- resistance to seismic events, climatic features of a particular area;
- fixation flange, welded or combined;
- cast, sheet, cast-welded or stamp-welded assembly;
- manual and electric drive.
The release of valves corresponds to the permissible values of the diameter of the branch pipes. The indicators are from 5 cm to 2 m. The optimal pressure is considered to be 25 MPa, and the thermometer readings for the working environment are in the range of + 450- + 560 ℃.
Main types of pipe valves
Depending on the characteristics, design, drive and mounting methods, several types of gate valves can be distinguished. So, there are full bore valves, the seat of which corresponds to the diameter of the nozzle. And the narrowed ones have lower indicators of a similar saddle parameter.
According to the type of structure, products with a retractable and non-retractable spindle are distinguished. They are characterized respectively as follows:
- A part of the stem extends outward relative to the body during the rotation of the flywheel (leakage is prevented by the stuffing box located in the disk). At the same time, the durability of the running unit is ensured by the absence of direct contact of the mechanism with the contents of the line.
- Smaller dimensions, the mechanism is located inside the case. The stem does not change its position, only the spindle and the shutter move. This option is less resistant to aggressive environments, so there are installation restrictions.
According to the geometry of the saddle, there are 2 options:
- Wedge. The locking mechanism is represented by two discs. They are at an angle with respect to the horizontal axis. As the spindle rotates, the rings are lowered. Between them are spacer wedges, which in the process move towards the saddle.
- Parallel. In this device, the discs can have two positions. At the bottom, the flow is cut off, and at the top, the path for the contents of the pipeline is opened.
Wedges are available in three versions:
- Rigid strictly adjusted to the shape of the saddle. It is represented by a metal plate. Due to the weakness to changes in temperature, pressure, the field of application is characterized by relative constancy and low performance.
- Double-disk provides maximum tightness and is allowed for use in pipelines with maximum sensor values (up to 25 MPa, +560 ℃).
- Elastic is represented by disks connected by a dynamic element. Compared with previous versions, such a device is easier to manufacture. It is suitable for medium operating conditions.
Most often, cast iron is used for the manufacture of the body and valves, and less often alloyed or stainless steel. Other materials are practically not used. They cope less with pressure, temperature and water hammer in the pipeline.
The weight of the cast-iron valve is noticeably greater than that of the first. They are installed in pipelines with pressure up to 1 atm., where only 2 valve positions are needed: open and closed. Devices are controlled manually. Steel pipes are allowed for installation on a pipeline with high temperatures and pressures, as well as with aggressive media.
Installation of gate valves for pipelines
The connection of branch pipes, valves using welding equipment is considered the most durable and tight. Therefore, this option is used for highways in which high pressure is supplied. In other cases, other methods are also relevant: a flange or a combination of methods.
The procedure for installing a valve for a pipeline consists of four steps:
- Rise, installation of the device in the set place.
- Alignment of the central axes of the nozzles and the body of the device.
- Installation of a sealant, fasteners.
Finally, the bolts are tightened with a wrench or adjustable wrench. Welding work takes place almost according to the same algorithm. Only the device must first be fixed in the desired position with tacks and check the alignment of the axes. And after that, weld the elements.
In the case of plastic pipes, the process looks a little different. The process looks like this:
- the flange is put on the sleeve;
- the sleeve is welded to the pipe;
- a rubber seal is laid;
- using a key (open-end), the flange and the valve are connected;
- bolts are tightened crosswise.
The design with a clamping flange and a rubber cuff is installed as follows:
- the pipe is cut at an angle of 90॰;
- the cast-iron flange is put on the branch pipe and shifted towards the main line;
- clamping ring is strung;
- structural elements are centered;
- the flange is pushed onto the cuff until it stops;
- preliminary fixation and alignment check;
- fasteners are tightened with a wrench.
Chimney valves are installed in accordance with the instructions, which may vary. Installation takes place during the laying of the hood.
Important! If constant ventilation of the firebox is necessary, then additional perforation is organized in the valve. The diameter of the holes in this case can be from 10 to 15 mm.
Recommendations and typical mistakes
Experts advise before installing devices to check them for leaks. To do this, the valve is doused with hot water, and after drying, an audit is carried out. A faulty condition will be detected immediately.
Before installing a cast-iron valve, the work surface must first be prepared. Horizontal or vertical pipelines must be cleaned of scale, impurities, scale and dried. The valve flywheel must be directed upwards, and fasteners must be tightened evenly, without distortion. In the passport, the manufacturer always indicates the procedure for installing the device. It is unacceptable to deviate from it.
There is also a set of rules that applies to the installation of any type of shutter:
- steel reinforcement during welding must remain open;
- closing the flow path is accompanied by a small force so as not to lead to twisting and subsequent breakage;
- heavy devices for installation are provided with props;
- before choosing, it is important to consider the allowable pressure limits;
- installation is possible only on a straight section of the pipeline, where there is no risk of overpressure, which leads to fatal water hammer.
When choosing a shutter instead of a valve, it is worth considering some of the weaknesses of the devices:
- cannot be used if the contents of the pipes have solid and large components;
- there are restrictions on the permissible pressure in the line;
- there is a risk of water hammer valves due to the relatively low rate of blocking the flow path.
In addition, the valves are noticeably more difficult to repair, replace worn seals. And the installation is accompanied by a greater height than is required for the shut-off valve.
Important! Electric devices do not have strict regulations regarding the position. It is important that the drive itself is not at the bottom. And if the spindle is located horizontally, then an additional support must be provided under the mechanism.
Butterfly valves, despite the relatively low pressure limits, can be installed in almost any pipeline with liquids or gases. You can do the installation yourself, but it is important to follow strict rules in order to avoid alterations or complete replacement of the device. The damper position can be controlled manually or remotely using the remote control. And as a material for manufacturing, cast iron, alloyed or stainless steel are used, which are responsible for the strength and durability of the shutter.