Gate valve is a kind of valve, whose movement direction is perpendicular to fluid direction. Gate valve can only be fully opened and closed, but can not be adjusted and throttled. The gate valve is sealed by the contact between the valve seat and the gate. Usually, the sealing surface is overlaid with metal materials to increase the wear resistance, such as 1Cr13, stl6, stainless steel, etc. There are rigid gate and elastic gate, according to the different stem, gate valve is divided into rising stem gate valve and non rising stem gate valve.
Table of Contents hide What is rising stem gate valve? Working principle of rising stem gate valve Installation and maintenance of gate valve with rising rod Characteristics of open stem gate valve: What is non rising stem gate valve? Rising stem gate valve VS non rising stem gate valve
What is rising stem gate valve?
The opening and closing part of the rising stem gate valve is the gate, and the movement direction of the gate is perpendicular to the fluid direction. The rising stem gate valve can only be fully opened and closed, and can not be adjusted and throttled.
The ram has two sealing surfaces. The two sealing surfaces of the most commonly used model gate valve form a wedge. The wedge angle varies with the valve parameters, usually 50. When the medium temperature is not high, it is 2 ° 52 ‘. The gate of wedge gate valve can be made into a whole, which is called rigid gate; it can also be made into a gate which can produce slight deformation, so as to improve its processability and make up for the deviation of sealing surface angle in the processing process. This kind of gate is called elastic gate.
The types of rising stem gate valve can be divided into wedge gate valve and parallel gate valve according to the sealing surface configuration. The wedge gate valve can be divided into single gate plate, double gate plate and elastic gate valve. The parallel gate valve can be divided into single gate plate and double gate plate. According to the thread position of the stem, it can be divided into two types: rising stem gate valve and Non rising stem gate valve.
When the rising stem gate valve is closed, the sealing surface can only rely on the medium pressure to seal, that is, only rely on the medium pressure to press the sealing surface of the gate to the valve seat on the other side to ensure the sealing surface, which is self sealing. Most gate valves are forced to seal, that is, when the valve is closed, the gate should be forced to the valve seat by external force, so as to ensure the tightness of the sealing surface.
Working principle of rising stem gate valve
Turn the handwheel to open and close the valve plate connected with the valve stem by the thread of the handwheel and the stem
The gate valve with rising rod has the following advantages:
The resistance of fluid is small, and the sealing surface is eroded and eroded by medium.
Opening and closing are more labor-saving.
The flow direction of medium is not limited, and it does not disturb the flow and reduce the pressure.
The structure is simple, the structure length is short, the manufacturing technology is good, and the application range is wide.
The disadvantages of the gate valve are as follows:
The sealing surfaces are easy to cause erosion and abrasion, and it is difficult to maintain.
The opening and closing time is long because of the large size of the opening.
The structure is complex.
The types of gate valves can be divided into wedge gate valve and parallel gate valve according to the sealing surface configuration. Wedge gate valve can be divided into single gate pole type, double gate plate type and elastic gate valve type; parallel gate valve can be divided into single gate plate and double gate plate type. According to the thread position of the stem, it can be divided into two types: rising stem gate valve and Non rising stem gate valve.
Installation and maintenance of gate valve with rising rod
Hand wheel, handle and transmission mechanism are not allowed to be used for lifting and collision is strictly prohibited.
Double gate valves shall be installed vertically (i.e. stem in vertical position and handwheel at top).
Gate valve with bypass valve shall open bypass valve before opening (to balance pressure difference of inlet and outlet and reduce opening force).
Gate valve with transmission mechanism shall be installed according to the product instruction.
If the valve is used frequently, lubricate at least once a month.
The structure characteristics of the gate valve with rising rod:
The common gate valve used in the market for a long time has been generally leaking or rusty. The company introduced the rubber and valve manufacturing technology of European high-tech to overcome the defects of sealing and rust. The elastic seat gate valve has achieved good sealing effect by using elastic gate valve to compensate for micro elastic deformation. The valve has the advantages of switch It has the advantages of light, reliable sealing, good elastic memory and service life. It can be widely used in the pipeline of tap water, sewage, construction, petroleum, chemical industry, food, medicine, light textile, power, ship, metallurgy, energy system and other body pipelines as regulating and intercepting devices.
Characteristics of open stem gate valve:
Light weight: the body is made of advanced nodular iron, which is about 20% – 30% lighter than the traditional gate valve, and is easy to install and maintain.
Flat bottom gate seat: traditional gate valve usually deposits in the groove of valve bottom due to external objects such as stone, wood block, cement, iron chips and sundries after water washing, which is easy to cause the leakage phenomenon which cannot be closed tightly. The bottom of the valve sealed by elastic seat adopts the flat bottom design with the same water pipe machine, which is not easy to cause debris deposition and make the fluid flow unobstructed.
Overall rubber: the ram adopts high-quality rubber for the whole internal and external rubber. The first-class rubber vulcanization technology in Europe enables the vulcanized ram to ensure the exact geometric dimension, and the rubber and the ductile cast RAM are then reliable, and it is not easy to fall off and has good elastic memory. water
Precision casting valve body: the valve body is precision cast, and the precise geometric dimension makes the valve body internal without any finishing to ensure the sealing of the valve.
What is non rising stem gate valve?
The opening and closing part of the Non rising stem gate valve is the gate. The movement direction of the gate is perpendicular to the fluid direction, which can be adjusted and throttled. The ram has two sealing surfaces. The two sealing surfaces of the most commonly used model gate valve form a wedge. The wedge angle varies with the valve parameters, usually 50. When the medium temperature is not high, it is 2 ° 52 ”. The gate of wedge gate valve can be made into a whole, which is called rigid gate; it can also be made into a gate which can produce slight deformation, so as to improve its processability and make up for the deviation of sealing surface angle in the processing process. This kind of gate is called elastic gate.
Non rising stem gate valve is also called rotary stem gate valve (also called non rising stem wedge gate valve). The valve stem nut is set on the gate, and the handwheel rotation drives the valve stem to rotate, so as to lift the gate. Generally, there are trapezoidal threads at the bottom end of the valve stem. Through the thread at the bottom end of the valve and the guide groove on the valve disc, the rotary motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. When the valve is opened, when the lifting height of the ram is equal to 1:1 of the valve diameter, the fluid channel is completely unblocked, but in operation, this position cannot be monitored. In actual use, the apex of the valve stem is used as the mark, that is, the position that can not be opened is used as its full open position. In order to consider the lock phenomenon of temperature change, usually in the open to the top position, and then back 1 / 2 ~ 1 turn, as the full open valve position. Therefore, the full open position of the valve is determined by the position of the RAM (i.e. stroke).
The advantages of this structure are: the height of the gate valve always remains unchanged, so the installation space is small. It is suitable for gate valves with large diameter or limited installation space. This kind of structure should be equipped with opening and closing indicator to indicate the opening and closing degree.
The disadvantage of this structure is: the stem thread is not only unable to be lubricated, but also directly subject to medium erosion, easy to damage.
Rising stem gate valve VS non rising stem gate valve
1. The stem of the rising stem gate valve is exposed and can be seen, while the stem of the Non rising stem gate valve is not seen in the valve body;
2. The rising stem gate valve drives the gate up and down through the thread transmission between the stem and the steering wheel; the Non rising stem gate valve drives the gate up and down through the rotation of the stem at a fixed point. When switching, the steering wheel and the stem are connected and relatively fixed.
3. The transmission thread of the Non rising stem gate valve is located inside the valve body. During the opening and closing process of the valve, the valve stem only rotates in place, so the opening and closing state of the valve can not be judged by naked eyes. However, the transmission thread on the rising stem gate valve stem is exposed outside the valve body, which can directly judge the opening and closing position of the gate;
4. The height of Non rising stem gate valve is small, and the installation space is relatively small; the height of rising stem gate valve is large when it is fully opened, which requires large installation space;
5. The stem of the rising stem gate valve is outside the valve body, which is conducive to maintenance and lubrication; the stem thread of the Non rising stem gate valve is inside the valve body, which is difficult to maintain and lubricate, and the stem is easy to be directly eroded by the medium, so the valve is easy to be damaged. In the scope of use, rising stem gate valve is more widely used.
Source: China Gate Valves Manufacturer – Yaang Pipe Industry (www.steeljrv.com)