A valve is a pipeline valve with a translational movement of the closing element along the spindle to the seat. In technical catalogs, such a design is often called a shut-off valve, and in English-language documentation - a globe valve or stop valve.<\/p>\n\n\n\n
The main function of a valve is to shut off the flow of water, steam, coolant, or other compatible medium. Depending on the design, throttling is also allowed.<\/p>\n\n\n\n
The words "valve", "shut-off valve" and "isolation valve" in the market may refer to similar products, but suitability is determined by design, materials, tightness class, pressure and temperature. For a responsible area, the marking of a specific model is important, and not just the usual inscription on the price tag.<\/p>\n\n\n\n
The product works as follows - the rotation of the flywheel is transmitted to the threaded spindle and converted into linear motion, the spool or plate is lowered to the seat, compresses the sealing surfaces and blocks the passage. During opening, the element moves away from the seat, increasing the area of the passage. Thanks to such kinematics, the operator can change the opening gradually, and not with a single 90-degree turn.<\/p>\n\n\n\n
The flow inside the body changes direction, so even a fully open shut-off valve creates more noticeable hydraulic resistance than a full-port gate valve or ball valve. This is the price for more precise control and reliable pressing of the spool against the seat.<\/p>\n\n\n\n
In a gate valve, the wedge or parallel gate moves across the flow and in the open position almost leaves the passage section. Therefore, it is suitable for pipelines where low resistance is required and mainly two states: fully open or closed. A partially open gate valve is subject to vibration and erosion of the sealing surfaces, so it is a poor choice for regular adjustment.<\/p>\n\n\n\n
The valve has a shorter stroke of the closing element, reaches the working passage faster and seals better during frequent operations. On the other hand, its tortuous channel increases pressure losses, and the force on the spindle can increase with diameter and pressure drop. Therefore, on a large pipeline, hydraulics are first calculated, and only then it is decided whether this particular design is needed.<\/p>\n\n\n\n
A ball valve shuts off flow by turning a ball with a hole a quarter turn. It is compact, fast-acting and, in the full-bore version, has low resistance. This is a convenient solution for emergency or operational shut-off, but abrupt closure on a fast flow can contribute to a pressure surge. Standard soft seats also limit temperature and media compatibility.<\/p>\n\n\n\n
The valve closes more slowly, but gives the operator more control over the flow rate. A conventional ball valve should not be kept half-open for long: the local high-velocity jet will damage the ball and seal unless the product is specifically designed for throttling.<\/p>\n\n\n\n
\u00ab"Valve" is a broader concept. This group includes: <\/p>\n\n\n\n
In practical terms, a valve is a manual valve of a certain design, where the shutter moves translationally against a fixed seat. Therefore, a valve can be called a valve, but not every valve is a valve.<\/p>\n\n\n\n
It is equally important to distinguish between shut-off and control versions. If the passport allows only the "open\/closed" position, systematic throttling will accelerate wear of the seat and spool. To automatically maintain flow, pressure or temperature, a control valve with a calculated characteristic and actuator is required.<\/p>\n\n\n\n
From the outside, a valve seems to be a fairly simple device: a body, a handwheel, and pipes for connecting to the pipeline. However, behind the turn of the handwheel is the coordinated operation of several internal elements. The body directs the flow of the working medium, and the cover provides access to the parts during inspection, maintenance, or repair.<\/p>\n\n\n\n
When the operator turns the handwheel, the spindle transmits force to the spool. The spool gradually approaches the seat, reducing the passage cross-section and ultimately stopping the flow. It is the spool-seat pair that is responsible for the tightness of the valve: the accuracy of fit and the condition of these parts determine whether the valve will pass the medium in the closed position.<\/p>\n\n\n\n
At the same time, it is necessary to prevent leakage through the place where the spindle exits the body. For this, a stuffing box or bellows is used. Therefore, the tightness of the valve is ensured not by one part, but by the entire structure, in which each element performs its part of the work.<\/p>\n\n\n\n
The shape of the spool affects the flow pattern. A flat or conical surface can be optimized for tight shut-off, while a special profile is used in control versions. The bellows seal of the stem reduces the risk of leakage through the stuffing box, which is especially valuable in steam and hazardous environments, but does not eliminate the maintenance requirements and permissible cycles.<\/p>\n\n\n\n
Brass is common in water supply and small heating systems due to its corrosion resistance and convenient threaded connection. Cast iron is used in industrial networks within the permissible pressure and temperature limits, but it is more sensitive to shock loads. Carbon steel is suitable for higher parameters and welded systems, and stainless steel for corrosive, hygienic or clean processes.<\/p>\n\n\n\n
You also need to consider the seal, seat, spindle and gasket material. The word \u00abstainless steel\u00bb does not guarantee compatibility with any chemical, and a water shut-off valve does not automatically become suitable for steam of the same pressure rating.<\/p>\n\n\n\n
Such fittings are installed on water supply inlets and branches, in heating systems, on steam and condensate lines, in front of equipment and near control and measuring devices. The valve is appropriate where the flow needs to be shut off hermetically, operations are repeated, and increased resistance in the open state is permissible.<\/p>\n\n\n\n
In contaminated environments, the narrow seat and guide surfaces require protection from particles. For quick emergency shut-off, a quarter-turn valve is often chosen, and for large diameters with minimal losses, a gate valve or other design after calculation. <\/p>\n\n\n\n
The advantages include: <\/p>\n\n\n\n
The valve is convenient for frequent manual control and, if permitted by the passport, for moderate throttling.<\/p>\n\n\n\n
Disadvantages: <\/p>\n\n\n\n
Contamination can damage the sealing surfaces, and incorrect installation direction increases the force or disrupts operation. The arrow on the housing and the manufacturer's instructions should not be ignored.<\/p>\n\n\n\n
First, the medium, flow rate, operating and maximum pressures and temperatures are determined. Then, the DN, permissible drop, Kvs coefficient, materials of all wetted parts, tightness class and purpose (cut-off or also regulation) are checked. Threading is convenient for small diameters, a flange simplifies the dismantling of an industrial unit, a welded connection reduces the number of potential leakage points, but makes replacement more difficult.<\/p>\n\n\n\n
The location of the handwheel, access to the gland and cover, recommended spindle position and flow direction should be assessed. For steam, the temperature rating of the seals and the possibility of drainage should be checked separately. If remote shut-off is required, select a compatible electric, pneumatic or hydraulic actuator and verify the fail-safe position in the event of loss of power.<\/p>\n\n\n\n