Function and working principle of check valve

Function and working principle of check valve:

Check valve, also known as one-way valve or reverse check valve, its role is to prevent the reverse flow of the medium in the pipeline. Water pump suction close the bottom valve also belongs to the check valve class.

The opening and closing parts depend on the media flow and force to open or close, in order to prevent the media reverse flow of the valve is called check valve. The check valve belongs to the automatic valve class, mainly used in the one-way flow of medium on the pipeline, only allow the medium to flow in one direction, in order to prevent accidents.

According to the structure, the check valve can be divided into three types: lifting high pressure check valve, swing check valve and welding lifting Angle check valve. Sandwich check valves can be divided into vertical and horizontal two. Swing check valves are divided into three types: single-valve, double-valve and multi-valve. Internal rib, socket welding vertical check valve for straight through, the above types of check valve in the form of connection can be divided into thread connection, flange connection and welding three.

The installation of check valves for socket welding and forging steel shall pay attention to the following matters: 1. Do not make the check valve bear the weight in the pipeline, and the large check valve shall be independently supported, so that it is not affected by the pressure generated by the pipe system. 2. When installing, pay attention to the direction of medium flow and the arrow direction of valve body. 3, lifting type vertical disc check valve should be installed in the vertical pipeline. 4, the vertical check valve should be installed in the horizontal pipeline.　

Check valve has been widely used in petroleum, chemical, liquefied gas, boiler steam system, minerals, water supply and drainage, food, pharmaceutical, power generation, urban construction, municipal engineering and other departments, as well as People's Daily life.

To clip lifting check valve should be installed in the horizontal direction of the pipeline, swing check valve can be installed in the horizontal pipeline, and can be installed in the vertical pipeline.

Install check valve so that the arrow marked on the valve body is in line with the direction of water flow, not upside down.

Multiple check valves or large caliber silent check valves should be used on large caliber water pipes to stagger or slow the closing time of each valve so as to reduce the damage effect of water hammer. When the pump works normally, the water pressure makes the tongue plate open automatically. When the pump stops suddenly, the tongue plate is closed under the action of self-weight and water backflow. However, since the piston is in the pushing position, it cannot be completely closed by pushing against the tongue plate, leaving about 20% of the open section to let the water flow back, thus reducing the pressure of the water hammer.　

Basic definition and reference standard conditions for check valves

Check valve is able to automatically stop the flow of the valve, check valve disc under the action of fluid pressure to open, the flow from the inlet side to the outlet side. When the inlet side pressure is lower than the outlet side, the disc will automatically close under the effect of the fluid pressure difference, gravity and other factors to prevent the fluid backflow. Check valves of this type are designed to allow flow in only one direction and to prevent flow in that direction. Normally the valve operates automatically and the disc opens under the pressure of the fluid flowing in one direction; When the fluid flows in the opposite direction, the pressure of the fluid and the disc self-coincidence disc act on the seat to cut off the flow. Among them the check valve belongs to this type of valve, it includes swing type check valve and lift type check valve. Swing check valves have a single hinged mechanism and a door - like disc that rests freely against the tilted seating surface. Basic principle of check valve

Check valve is to rely on the flow of the medium itself and automatically open, close the disc, to prevent the reverse flow of the medium valve. Check valve according to its structure can be divided into: 1, lifting type check valve: valve disc along the valve body vertical center line sliding check valve, lifting type check valve in the horizontal pipeline, in the high pressure small caliber check valve disc can be used round ball. The lift check valve is the same as the valve (can be used with the globe valve), so its fluid resistance coefficient is larger. Two, swing check valve: disc around the seat of the pin outside the rotation of the check valve, swing check times. Disc check valve: a check valve in which the disc rotates around the pin in the seat. Disc check valve knot is installed in horizontal pipe, poor seal. Pipe check valve: valve with disc sliding along center line of valve body. Pipeline type check valve, its volume is small, the weight is lighter, the processing technology is good, is one of the development directions of check valve. Slightly larger than swing check valves.

Working principle of silent check valve

This silent check valve is mainly composed of valve body, disc, flow guide, spring, etc. The valve body is made of gray cast iron (HT250), and the disc and flow guide are made of copper alloy (H62). It works as follows:

When no medium flows through the valve body, the disc is always closed under the action of the spring force. The opening and closing of the disc and the degree of opening are mainly determined by the pressure difference between the inlet end and the outlet end of the valve. If the pressure at the inlet is greater than the sum of the pressure at the outlet and the spring force, the disc opens. As long as there is a pressure difference, the disc is always in the open state, with the size of the pressure difference also determines the size of the disc opening. If the sum of the outlet pressure and spring force is greater than the inlet pressure, the disc is closed and remains closed.

Since the disc is opened and closed in a dynamic force balance system, no matter how the media pressure changes at the inlet end, the valve is stable, noiseless and with few safety failures.

Silent check valve use and performance characteristics

The mute check valve is mainly used in water supply, drainage system, fire fighting piping system, agricultural irrigation system, etc. This valve is installed at the outlet of the pump to protect the pump and other piping equipment from damaging water energy due to backflow of media. The main performance characteristics of the valve are as follows:

The flow path inside the valve body adopts streamlined design with less loss of head;

The disc close travel is short, can realize the valve close quickly, and the operation balance, no vibration, no noise, safety, very few faults;

Reasonable structure, good sealing performance;

Wear resistance, long service life.

Stop check valve

I. purpose:

Stop-check valves are installed in the main steam line of the combined cycle waste heat furnace to prevent backflow of media. When the boiler is out of order, the valve will be closed quickly by the pressure of the medium to protect the boiler.

Two, structure brief

1. Pressure self-tightening sealing structure is adopted. The higher the medium pressure is, the better the sealing performance is.

2. The disc moves up and down in the valve body, lift the stem before running, and open the valve automatically by the medium pressure. When the boiler failure, the valve inlet pressure is reduced, the medium reverse flow, the valve will be closed quickly.

3. The valve bracket is connected with the electric device to achieve a better sealing of the valve.

4. The sealing surface of disc and seat is made of cobalt-base hard alloy by plasma spray welding, with high hardness, erosion resistance, abrasion resistance and durability.

5. The surface of valve stem is treated with corrosion nitriding, which has good corrosion resistance and abrasion resistance.

6. Valve can be manually operated. When manual, the power is automatically cut off and the handwheel rotates clockwise to close the valve.

Iii. Installation instructions:

1. Valve must be installed vertically in line with stem up. The medium is flowing under the seat.

2. The working environment of the electric device is -20~40℃, the relative humidity is 80%, and there is no corrosive and explosive gas in the environment.

3. When the temperature of the electric device is lower than 350℃, the semi-fluid lithium lubricating oil (qsy1002-65) is used; when the temperature of the pipeline is higher than 35℃, the sodium grease gb492-2n-4 is used for lubrication