Gate valves and taps. Ball valve or steel gate valve, a matter of choice
AT recent times It has become a practice in the pipe industry to use butterfly valves instead of ball valves and gate valves, whether they are wedge or parallel. Industrialists are actively introducing this pipeline fitting, as they consider it more practical for use, and valves and taps have been replaced by butterfly valves at almost all heat supply facilities. In this review, we will understand what they are guided by when choosing valves and why valves are chosen among valves, taps and gates.
The prefix "disk" speaks for itself about the design of the butterfly valve: it consists of a body, a valve in the form of a disk and a stem. The body is usually made from metals such as cast iron, aluminum and bronze; available in plastic and steel (stainless steel or carbon steel). Stainless steel closures are used, in particular, in Food Industry to regulate and block the flow of raw materials, finished products and cleaning solutions. The shutter disk is usually flat or complex in shape and is made of various metals. It can be malleable iron, stainless steel, teflon, bronze, brass, aluminum and so on. The axis of the valve stem may coincide with the axis of the disc, however, when the valve is made in a large diameter, the axes are spaced apart along the length of the valve in order to prevent leakage in the places where the stem fits into the body. The valve stem can be integral and separate. In conditions where greater tightness is required, a double seal is used in the stem. The valves can be operated both manually and by means of an electric, pneumatic, hydraulic and mechanical drive system. Valves can be mounted on pipelines in any position, however, for large diameters, a horizontal stem position is recommended, which minimizes the risk of jamming due to the ingress of any dense substances into the stem. With a flange connection, the diameter of the flanges on the valve is no larger than the diameter of the flanges on the pipeline, so installation is carried out without any special difficulties.
Advantages of Butterfly Valves over Gate Valves
In order to understand why butterfly valves are more cost-effective for various industries, it is necessary to understand the principle of operation of the wedge valve. A gate valve is a type of pipeline fittings, consisting of a body and a flange connection, in which the vertically translational movement of the locking element occurs perpendicular to the direction of the working medium. Typically, the valve is controlled manually, as well as using an electric or hydraulic drive. Very rarely, a pneumatic actuator is used to automate the operation of a valve. Thus, we see the first advantage of valves over valves: valves can be operated in any way, while actuator control options for valves are limited.
Secondly, the valves have a simpler design and, as a result, less expensive repairs and reduced dimensions. Thus, the weight of one valve is less than the weight of a valve of the same nominal bore (with DN more than 600) by about 8 times, which reduces the weight load on the pipeline and simplifies installation work, since powerful lifting equipment and special installation sites are not required.
Thirdly, less time resources are needed to open and close the shutter, since the design of the shutter provides for a change in position (rotation of the disk by 90 degrees) when the handle is turned. It is also possible to have several handle positions for smoother throttling of the working medium.
Fourth, butterfly valves have a more secure elastic seal that prevents leakage during valve operation. Gate valves have a metal-to-metal seal, so any ingress of solid particles will stop them from working. This implies the fifth drawback of valves: costly repairs and frequent due to the complexity and inconvenience of the design. Butterfly valves can last up to three times longer than gate valves.
Sixthly, butterfly valves do not have threaded working pairs "bushing - spindle". The presence of such pairs at valves increases the risk of corrosion, especially often this occurs on heating mains and open areas. Also, the gates do not have stagnant zones, in which various mechanical impurities of the working medium accumulate. The valve, unfortunately, has them, which often leads to jamming, after which the opening of this valve requires incredible effort.
The last thing to note is the cost of shutters. The price of gates is quite comparable to the price of a valve Russian production. In addition, if you take into account the repair of valves, it is likely that the valve will cost even less.
Advantages of butterfly valves over ball valves
Following the same scheme, we will determine the principle of operation of ball valves and their design features. The crane was called "ball" is not accidental. Like any other water faucet, it consists of a body and a movable element. But in a ball valve, the movable element has a spherical shape and a hole for the flow of water (ball plug), which is very convenient, since the diameter of the ball is usually equal to the diameter of the pipe to which it is connected. To open the shutter, just turn the valve handle 90 degrees. Such taps are called full bore and are used not only in water and gas pipelines, but also in the heating system, as well as control valves. Besides, Ball Valves have a number of other advantages that you should pay attention to when choosing pipe fittings of such a plan. Among them, simplicity of design, small size, convenient operation and practicality in use. However, there is also a minus: cranes with a cantilever handle during a turn can get into the so-called "dead" zone. The crane is controlled both manually and with the help of a mechanized drive (for example, electric).
Actually, the main advantage of the butterfly valve follows from the lack of a ball valve. For users of ball valves, the problem of how to prevent jamming is the most pressing. The sealing area in ball valves is much larger than the sealing area in gate valves, which means that in ball valves there are gaps between the ball and the seal itself. Thus, during long periods of non-use, mechanical deposits accumulate between the seal and the ball. If the faucet is not used for some time, it stops turning. The gates do not stick and do not jam after long-term operation, since mechanical deposits can accumulate only at the junction of the disk to the seal.
Secondly, valves use less energy to actuate compared to ball valves. The reason is that the ball valve will operate with more torque (5 times less energy is needed to operate the valve). And again, it all comes down to design: the disc in the valve is only adjacent to the sealing surface, and the ball in the ball valve is between two O-rings, so there is a need for resistance.
Thirdly, ball valves are subject to water hammer when butterfly valves withstand them. The last one is the dimensions. The shutters have smaller dimensions and weight, and it is much easier to buy a shutter. The price of a gate is less than the price of a ball valve.
Disadvantages of Butterfly Valves
Speaking about the advantages of butterfly valves, one cannot but mention their disadvantages. In particular, ball valves have one significant advantage over gate valves: they can operate at a pressure at which butterfly valves cannot be operated. Thus, the operation of ball valves is possible at 20 MPa, and butterfly valves - only at 1.6 MPa.
Note that butterfly valves cannot be used in media with strongly crystallizing inclusions. It is possible to receive a hydraulic shock on the handle at the end of the stroke, which is due to the direct connection of the locking disc and the stem control handle. In this regard, experts recommend using a gearbox for butterfly valves, starting with a diameter of 150 mm. In addition, despite the high speed of position change, the adjustment accuracy of the shutter is not very high, and in order to avoid wear of the disk, it should be rotated in the range from 15 to 75 degrees.
It is important that for the smooth and efficient operation of the valve, it is necessary to carry out its qualified installation and install it in the right place on the pipeline. Otherwise, even the most expensive and high-quality shutter will be broken and will not provide a stable regulation of the working environment.
Internet review prepared by Daria Petshik,
journalist of the Media Center "Reinforcing Expert",
St. Petersburg, 2015
Despite the fairly obvious advantages that they have, individual enterprises still prefer wedge gate valves. According to some engineers at enterprises, a valve made of steel is allegedly more reliable than a ball valve. In addition, its use allows the regulation of the flow of the working material.
However, the engineers of the leading companies producing pipeline fittings are very categorical: unlike ball valves, they are in no way intended for LLP to regulate the flow of the working medium.
Features of gate valves
As practice shows, if valves are used as control valves, they fail after a fairly short period of time. And they cease to perform even their main function - they do not keep the flow of the working environment in a closed state. At the same time, it should be noted that we are talking specifically about valves made of steel, since in this context cast iron can not even be considered. This is due to the fact that cast iron is very demanding on operating conditions. So, for example, cast iron gate valves can be used in the temperature range from minus 20 to +350 degrees Celsius (these are devices made of best brands cast iron). There are also restrictions regarding the type of medium being pumped - in certain types of gas pipelines, cast-iron pipeline fittings are practically unrealistic to use safely. There are also restrictions on other parameters - the through hole, and so on.
Continuing to talk about valves, it is worth noting the following. Despite the fact that valves are still the most popular type of pipeline fittings in pipeline systems various kinds, however, recently it has been observed that in many systems they are beginning to replace gate valves with ball valves. This is not difficult to explain: in addition to the fact that the use of gate valves provides for constant monitoring of their technical condition (for example, cleaning of stuffing box seals), such gate valves do not perform well in cases where emergency situations arise, during which the flow of the working medium must be blocked as much as possible. fast. In addition, the valve design is not able to provide good tightness, and this statement applies to almost all elements of the device - both the body and the shutter. Further, it would be useful to note that wedge gate valves have not only solid dimensions, but also an appropriate weight, and besides, they are often prone to breakdowns, as a result of which various emergency situations regularly occur.
Features of ball valves
Compared to wedge valves, ball valves are a newer type of shut-off valve, despite the fact that the design of a ball valve is already a century old. Already from the name itself, it can be understood that in this type of taps, the locking element has the shape of a ball. In practice, ball valves have shown themselves to be more advantageous than gate valves.
Firstly, depending on the design, ball valves can be successfully operated with almost any media: steam, water, oil products, gas, and much more. Ball valves are more durable than gate valves, due to which the range of their operation is much wider. Secondly, unlike gate valves, ball valves without harm to equipment can be successfully used not only as shut-off valves, but also as control valves.
It is also worth noting that modern ball valves have a much greater tightness than wedge valves. This is because manufacturers have been able to solve the problem that was the real scourge of ball valves of the past, namely low tightness, by using modern materials. In modern ball valves, the seat is not made of metal, as it used to be, but of polymer compositions. In addition, this solution made it possible to significantly facilitate the control of the crane along the way, so that now in order to change the position of the locking element, it is not necessary to make significant efforts.
Another feature inherent in ball valves is that they have a compact design, which is similarly different from wedge gate valves. This is especially true for housing and communal services, however, even in pipelines large size in terms of their dimensions, ball valves outperform wedge gate valves.
Regarding the control of this type of pipeline fittings, it can be carried out using,. Of particular note is how ball valves are controlled in gas pipelines, where the control of the valve pneumatic drive is carried out by the medium itself.
It remains to add that today manufacturers produce ball valves made of brass, cast iron, steels and other materials. However, brass ball valves cannot be used in systems in which the temperature of the working medium is more than 100 degrees Celsius. They also don't perform well in sub-zero temperatures. In addition, brass ball valves are usually made with a not very large diameter, no more than 80 millimeters. But a steel ball valve can cope with temperatures even at +200 degrees. He will also feel great at minus 50 degrees Celsius, thanks to which this shut-off valves is simply indispensable in systems for pumping media located in the North. Another plus of steel reinforcement is that the diameter of the through hole is also significantly increased - up to 300 millimeters in standard versions, and up to 500 for special orders.
Summary: advantages of ball valves over wedge valves
Summarizing all the above, we can distinguish 10 main advantages that ball valves have over wedge valves:
- Wedge gate valves are mainly manufactured with a maximum diameter of 80 millimeters, while ball valves can be made for almost any diameter;
- Ball valves are able to withstand a significantly higher level of pressure;
- Ball valves have a significantly larger operating temperature range than wedge gate valves;
- Ball valves practically do not have such an unpleasant feature as jamming, and besides, they are much easier to manage. Gate valves jam quite often, especially after being in the open or closed position for a long time;
- Ball valves differ in that they have a higher tightness;
- Ball valves are universal, as they can be operated with almost any working medium, while wedge valves in most cases are used only for water;
- Ball valves in comparison with wedge gate valves are more compact in size and lighter in weight;
- Ball valves serve much longer, fail much less often and are more reliable than wedge gate valves;
- Wedge gate valves need regular inspection and maintenance, while ball valves do not need constant monitoring of their condition and performance, and also require minimal maintenance;
Wedge gate valves can only be used as shut-off pipeline valves, while ball valves can be used both as shut-off and shut-off and control pipeline valves.
Over the past ten years, according to the modern approach to valves in utility networks, cast iron and steel valves are increasingly being replaced with ball valves. This moment pleased both Russian manufacturers of modern fittings and consumers.
Undoubtedly, a ball valve has advantages over valves:
- ball valve has higher performance characteristics, reliability and quality;
- the ball valve has an absolute tightness of the shutter, hence the absence of leaks and, consequently, water savings;
- due to low quality water, the valves fail very quickly, which leads to the need to replace the valve with a new one;
- ball valve is more durable.
Any ball valve?
Despite all the advantages of modern fittings, the factor is very important - how outdated cast-iron gate valves and a ball valve are interchangeable in the field. In order not to create a difficulty in the further operation of the pipeline, how quickly and efficiently is it possible to replace the fittings? Therefore, it is important to understand which ball valves are better than valves, that is, what properties should fittings have in order to replace old valves in existing pipelines? Consider these properties: 1. Size (building length of the ball valve)When a pipeline is being repaired, where steel or cast iron gate valves are installed, the construction length of the ball valve plays an important role. If you choose the right ball valve, you can get rid of additional installation work, which is not always convenient or not feasible due to the technology and safety conditions. Here you can expect a few surprises. The construction length standards used in Russia for gate valves and ball valves are different, and the construction lengths of ball valves of various domestic and foreign manufacturers also differ. But the optimal choice still exists - some Russian manufacturers take into account " national characteristics» utility piping and manufacture ball valves to gate valve face-to-face standards. Such valves are fully consistent with the valve being replaced. In the event that you are installing a new pipeline, the choice of the valve face-to-face length can be more independent. But you can be sure that the face-to-face length of used fittings is not exclusive and if you need to replace it after a few years, you will not have to look for one single ball valve manufacturer with a unique face-to-face length. When using a ball valve, very often, due to the design features, the construction length turns out to be closely dependent on another important parameter of the reinforcement - the nominal bore.
2. Full and partial passageThe choice of a full or partial passage of a ball valve depends on the operating conditions of the structure in the pipeline system and its allowable hydraulic resistance.
Two most characteristic cases can be distinguished: when the structure is installed on the main line with big expense medium, it is necessary to have fittings with low hydraulic resistance in order to avoid high energy costs for transporting the medium, especially liquid, but in dead-end positions it is quite acceptable to use fittings with an increased coefficient of hydraulic resistance.
Energy costs for compensating the pressure drop created by hydraulic resistance are proportional to the cube of speed, the square of the passage diameter, the coefficient of hydraulic resistance and the density of the medium. It follows that the greatest energy losses will be created in pipelines in which liquids move at high speed. Under these conditions, it is necessary to use valves with small values of the coefficient of hydraulic resistance. Approximate values of the coefficient for various types of cranes: full bore - 0.1-0.4; incomplete bore - 0.4-1.6.
Which manufacturer to choose?
The vast majority of ball valves of well-known foreign brands are produced according to standards that are somewhat different from the valve standards previously used in Russia and the CIS countries. And it is the face-to-face length of the valve that is the first and most obvious difference - foreign-made ball valves with a face-to-face length “to fit the valve” can be manufactured by the manufacturer only on order. Of course, the cost and term of such an order inevitably increases.
The next significantly different characteristic of imported fittings is the effective passage of the crane. Most foreign-made ball valves have a reduced (standard) diameter of the effective passage in relation to the connecting diameter.
Under such conditions, only a small number of ball valves of foreign manufacturers can be recognized as analogues of the most popular gate valves in public utilities. One of these foreign manufacturers is Temper, a Danish company that has its own production in Russia in the city of Kurgan. Temper ball valves are fully adapted to Russian standards for pipeline fittings, and due to local production, the price for these valves is significantly lower than for imported valves.
You can pick up ball valves, place an order in our online store or contact the TSK company manager by calling or leaving a request on the website.