1, open the stem gate valve. The handwheel (or other driving device) is fixed on the stem nut. When the handwheel (or other driving device) rotates to drive the stem nut to rotate, the stem moves up and down, thus driving the gate valve to move up and down to realize the opening and closing of the pipeline.
2. When the open-stem gate valve is opened, the valve stem extends from above the handwheel, which can directly display the opening degree of the gate valve. The trapezoidal thread of the valve stem is in the upper half of the valve stem, which is not in direct contact with the medium and is not corroded by the medium, and plays a lubricating role. Therefore, it is suitable for gate valves with corrosive medium, dirty medium and high temperature steam medium. The opening and closing degree of the valve can be directly seen from the thread, and the convenience of operation is also one of its advantages. The disadvantage is that because the thread leaks, it is easy to stick to the dust in the air and accelerate the wear of the thread, so try to install it indoors. Nevertheless, it is widely used.
3. Blind stem gate valve. The handwheel (or other driving device) is fixed on the valve stem, and the valve stem thread is fixed on the top of the gate. When the handwheel (or other driving device) rotates, the valve stem thread drives the ram to move up and down. The valve stem can only do rotary motion. The advantages are that the valve stem does not rise when opening, and the required installation space is small. Therefore, it is often used as a large channel gate valve, or where the installation space is limited. Because the valve stem doesn't move up and down, the opening can't be displayed by the length of the valve stem like the open-stem gate valve, so an opening indicator should be installed.
Because the stem thread and stem nut are in contact with the medium in the valve cavity, the hidden stem gate valve is easy to be corroded by the medium, and the stem thread is difficult to lubricate. Valve body and bonnet are mostly used for flange connection. Most of the medium channels in the valve body are cylindrical with equal cross section. For gate valves with larger diameter, the valve seat is also contracted, that is, the passage gradually shrinks and then gradually expands after passing through the valve seat. Its advantages are as follows:
1, the valve parts are reduced in size, weight and materials. The sealing surface is reduced, and the finishing quantity is reduced.
2. With the decrease of the gate size, the force acting on the gate decreases, and the opening and closing force of the gate valve also decreases accordingly.
Because the channel contraction will increase the resistance of water. Therefore, in order to reduce the resistance of high-pressure steam pipeline, a conduit is often connected below the closing piece to reduce the resistance and prevent particles in the medium from falling into the valve body. According to the gate form, it can be divided into wedge parallel type.
1, wedge gate. The sealing surface of wedge-shaped gate forms a certain inclination angle with the vertical center line of the gate, and the inclination angle depends on the temperature of the medium and the size of the channel. Generally, the higher the temperature of the medium, the larger the channel and the greater the inclination angle, so as to prevent the gate from being stuck and unable to open when the temperature changes. Wedge gate has better sealing performance than parallel gate. Can be used for high-pressure gate valves.
Wedge gate is divided into elastic gate, wedge gate and double wedge gate.
First, the elastic impact hammer. The vertical bisection plane of the gate is machined with an annular groove, which makes the gate have certain elasticity. It is this elastic deformation that compensates the deviation of wedge angle between the sealing surface of the gate and the sealing surface of the valve seat when the gate is closed, so as to achieve good coincidence and ensure sealing.
The sealing surface of elastic gate valve is reliable. It is suitable for small and medium-sized gate valves with various pressures and temperatures. It requires less solid particles in the medium to prevent it from being blocked in the annular groove of the gate and affecting the elastic seal.
B. Wedge-shaped single gate is an integral wedge gate. In the process of opening and closing, the sealing surface is easy to be scratched, and the temperature change is easy to wedge the gate. It is a kind of ram at normal temperature, moderate temperature and various pressures.
C, a wedge-shaped double gate, which consists of two gates and is hinged with the spherical center to form a wedge-shaped gate. Its advantages are low requirement of sealing surface angle accuracy; After the sealing surface of the ram is worn, a gasket can be added in the center to compensate; Temperature change is not easy to cause jamming and should not be scratched. Because the gate is movably connected, there are many parts, which are easy to get stuck in viscous medium and affect the sealing. Especially the upper and lower baffles, after years of corrosion, fall off at will. It is usually used in water, steam and gas pipelines.
2. Parallel doors. Parallel gate means that the two sealing surfaces of the gate are parallel to each other and perpendicular to the center line of the channel. Parallel gates can be divided into parallel gates and parallel double gates.
A. The structure and processing of parallel single gate are simple, but the sealing performance is poor. Suitable for medium and low pressure; Large and medium caliber, often used for oil or natural gas and natural gas pipelines.
B. Parallel double brake, as opposed to parallel single brake. According to its structure, it can be divided into automatic sealing type and opening type.
Self-sealing parallel double gate valve. The gate valve consists of two disks, both of which are sleeved in the lifting ring of the valve stem. According to the pressure of the medium, both discs are pressed on the sealing surface of the door seat at one end of the medium outlet to achieve the purpose of single-sided sealing. If it is low pressure, the sealing performance will be poor. Therefore, a spring is placed between the two discs, and the disc is pressed to the valve seat by the spring force to achieve sealing. The valve is easy to scratch and wear when opening and closing. So it is used less.
Open the parallel double gate valve. There are also two kinds: top wedge and bottom wedge. Rabbit 2-5 is a double ram with parallel top wedge. When closing the ram, after the ram descends to the bottom, the valve stem continues to move forward, forcing the top wedge downward. Under the action of the top wedge, the two rams move backward in the horizontal direction, generating sealing force and realizing sealing.
When the valve is closed, the gate is pushed by the valve stem, and then pushed upward by the top wedge, so that the gate is separated to both sides and contacted with the valve seat to achieve the purpose of closing.
The main parts of electric gate valve are ZG1Cr18ni9tizg00cr18ni18ni12mo2tizg00cr17ni14mo2wcb. Ni9TizG00Cr18Ni10ZG18Ni12MO2TizG00Cr17Ni14Mo2WCB door ZG18Ni9TizG00. 438+00zg18ni12mo2tizg00cr14mo21Cr13 valve stem18ni9tioocr 65438+Cr18438.
Graphite +304 gland ZG 1 81Ni10zg00cr18ni18ni12mo2tizg00cr/kloc-. Cr654+08Ni9Ti00Cr18Ni654838+071Ni2171Ni21Ni21Ni1Ni. 5438+08Ni9Ti18Ni9Ti18Ni9Ti18Ni9Ti45 Main dimensions GB 1.6MPa(BTL). Dn 50 65 80100150 200 250 300 350 400 450 500 600 700 800 l 250 265 280 300 350 400 450 500 550 600 650 700 800 9001000h 2700 2850 H 1 (with dzw) 620715 765 840 8751513513751485/. 990 2040 2285 2345 2345 345 h1(with dzw) 620715765840151351375/kloc-. 9902040280d02400d02402803204005005064075080900 weight/radio frequency (kg) 2835476815023537450680905gb 6.4mpa dn50 6580/kloc-0. 00 200 250 300 350 400 45017301980 2130 2500 2660d0 280 320 400 450 55 550 640 750 800 900 9001000 weight. 44 64 84119 266 388 500 550-GB 64 weight/(kg) 48 65 85 120 268 446 535 670
Precautions for use and installation
Gate valves can be installed on horizontal or vertical pipelines, single and double gate valves should be installed on horizontal pipelines, and the handwheel should be above the valve, and downward installation is not allowed. The flow direction of gate valve medium is not limited.
Gate valves are usually connected by flange, and welding connection is also very useful in special occasions.
For gate valves with large diameter and high pressure, the opening and closing torque is large. To reduce the opening and closing torque, a bypass valve can be installed. The bypass valve is installed outside the main gate valve, and its inlet and outlet are connected in parallel with both sides of the main gate valve. Before opening the main gate valve, the bypass valve should be opened. After entering the valve, the pressure difference before and after the main gate valve decreases, thus reducing the opening torque of the main gate valve. The selection of bypass valve diameter should be considered according to the main valve diameter and application requirements.
Gate valve is a block valve, and its sealing performance is not as good as that of globe valve. The main "duty" of gate valve is to "stop flow" and "continue flow" with minimum resistance. Not suitable for adjusting the flow and pressure of medium. If it is used for a long time, the sealing surface will be easily washed and worn by the medium, which will affect the sealing performance.
Attention should be paid to the reliability of the temperature and pressure of the medium used for gate valves. Under high temperature and high pressure, the gate may be locked due to temperature change, and it is also easy to unseal due to uneven medium temperature everywhere. Wedge valves are particularly obvious. See Chapter 1 for the common faults of various valves, and see Table for the analysis of common special faults of gate valves:
Causes of manufacturing quality problems, user-related reasons and corresponding user explanations.
Can't open 1, T-shaped groove is broken (unqualified casting or processing) 1, T-shaped groove is broken (it has exceeded the top dead center, and it is still twisted vigorously).
2. The hammer is stuck
3. The inner nut was corroded and failed.
4. After closing, the valve stem is heated to the top of 1, and opening is not allowed to exceed the top dead center.
2. The closing force should be appropriate, and the lever should not be too long.
3. Choose correctly according to the media.
4. The corresponding unloading regulations shall be applied during operation to prevent hot jacking.
The valve does not close tightly 1, and the valve stem center is suspended.
2. The sealing surface is disconnected
3. Incline and bend the guide rail
4. The ram reverses to 1, and the wedge-shaped double ram falls off.
2. The valve stem and ram fall off.
3. There are scratches on the sealing surface. 1. Correct selection of wedge double gate valve.
2, the correct choice of gate valve
The operation intensity should be appropriate.
3 Correct selection (gate valve is not suitable for hard media), and repeatedly leave a thin seam when closing to wash away foreign objects.