Basic knowledge of valve

I. regulating valve
In the automatic control of modern chemical plants, the control valve plays a very important role in the production of these plants depends on the correct allocation and control of the floating medium. These controls, whether energy exchange, pressure reduction, or simple vessel feeding, require certain final control elements to be completed. The common control loop consists of three main parts, the first being the sensitive element, which is usually a transmitter. It is a device that can be used to measure process parameters such as pressure, level of liquid, or temperature. The output of the transmitter is sent to adjust the instrument - regulator, it identified and measured the given value or expected value deviation between the actual and the parameter values, one by one, the correction signals are sent to the final control element - regulating valve. The valve changes the flow of the fluid and the process parameter reaches the desired value.

Performance characteristics:
The regulating valve has simple flow path and small resistance, and is suitable for direct use (installation) under normal conditions. However, in high pressure drop occasions, the control valve reverse use, in order to improve the imbalance force and reduce the damage to the spool, but also conducive to the flow of medium, to avoid the valve coking and clogging. In general, the valve is not recommended for reverse use, only in high pressure, high viscosity, easy to coke and suspended particles of media, it is recommended reverse use. Reverse use, should avoid prolonged case of small opening run, especially when the test should pay attention.

Two, throttle valve
Throttle valve (Chokevalve) configuration and cut-off valve is no difference, but they open and close parts of the shape is different. Throttle valve headstock parts are mostly conic streamlined, through which change the cross-sectional area of the channel to achieve regulation of flow and pressure. The throttle valve for the pressure drop under conditions of great pressure to reduce media use.

Performance characteristics:
1, the structure is simple, easy to manufacture and maintenance, low cost.
2, the adjustment accuracy is not high, can not be adjusted to use.
3, the sealing surface is easy to erosion, can not be used as cutting medium.
4, poor sealing.

Three, reducing valve
The relief valve has a piston or diaphragm structure that acts on the piston or diaphragm by means of an output pressure to overcome an adjustable spring force to balance. Adjust the two pressure with the adjusting screw, set the spring, load the main valve, and let the air flow from the initial pressure P1 inlet to the two pressure P2 outlet. When the loop connection output reaches the set pressure, the air in the air acts on the diaphragm to produce a lifting force relative to the spring force. If the flow rate decreased, P2 increased slightly, also increased the effect on the diaphragm relative to the spring force, the diaphragm and the valve immediately until ascension, and spring force to re balance the air flow through the valve will be reduced, its consumption and output pressure balance until now. If the flow rate increases, the P2 decreases slightly. This decrease forces the force acting on the diaphragm relative to the spring force, and the diaphragm and valve fall until they are again in line with the spring force. This increases the air flow through the valve until its consumption and output pressure remain balanced. The valve is closed without air consumption.

Performance characteristics:
The difference between relief valve and relief valve
(1) static state, the pressure relief valve often open, overflow valve port closed;
(2) the pressure reducing valve controls the outlet pressure to be stable, and the overflow valve controls the inlet pressure to be stable;
(3) the outlet of the pressure reducing valve is closed with the increase of the outlet pressure, and the opening of the overflow valve is opened with the increase of the inlet pressure;
(4) the inlet and outlet of the pressure reducing valve are all pressure oil circuits, and the return oil of the pilot valve must be taken back to the oil tank independently, while the overflow valve is combined with the outlet to flow back into the tank.

Four. Check valve
Check valve refers to rely on the flow of the media itself and automatically open and close the valve flap, used to prevent media backflow valve, also known as check valve, one-way valve, counter flow valve, and back pressure valve. The check valve belongs to an automatic valve, whose main function is to prevent the backflow of medium, prevent the reverse of pump and drive motor, and release the container medium.

Performance characteristics:
The check valve is used to prevent the backflow of the medium in the pipe. It opens when the medium is running upstream and closes automatically when the medium is flowing upstream. Normally used in pipes that do not allow the medium to flow in the opposite direction to prevent backflow of the medium, damage to equipment and machinery. When the pump stops running, the rotary pump is not reversed. In the pipeline, the check valve and the closed circuit valve are often used together. This is due to the poor sealing of the check valve, when the media pressure is small, there will be a small part of the media leakage, the need to close the valve to ensure that the pipe closed. At the end of the valve is a check valve, it must dive into the water, water can not be installed in special self suction or no vacuum pumping water pump at the front end of the pipe.

Five. Relief valve
The safety valve is opening and closing parts under the action of external force in a normally closed state, when the medium pressure equipment or pipeline increase exceeds the set value, the medium outside the system to prevent discharge within the medium pressure piping or equipment exceeds the special valve value. Safety valve is an automatic valve, mainly used in boilers, pressure vessels and pipes, control pressure is not more than the required value, and plays an important role in the protection of personal safety and equipment operation. The relief valve must be subjected to pressure test before use.

Performance characteristics:
1 、 heavy hammer lever type safety valve
Hammer lever safety valve has the advantages of simple structure, easy adjustment and accurate, the increase of load will not increase while the valve of the larger increase, suitable for high temperature applications, the past used more widely, especially in high temperature boiler and pressure vessel. But the weight lever type safety valve structure is relatively heavy, the loading mechanism is easy to vibration, and often due to vibration and leakage, its back seat pressure is low, it is not easy to shut and remain tight after opening.

2 、 spring type safety valve
The spring type safety valve has the advantages of light weight, compact structure, high sensitivity, unlimited installation position, and low sensitivity to vibration, so it can be used on a moving pressure vessel. The disadvantage of this safety valve is that the load will change with the opening of the valve, that is, with the increase of the valve, the compression of the spring increases, and the force acting on the valve increases as well. This is detrimental to the rapid opening of the safety valve. In addition, the spring on the valve will be reduced by a long time due to the impact of high temperature. When used on a high temperature container, the problem of heat insulation or heat dissipation of the spring is often considered, which complicates the structure.

3 、 pulse type safety valve consists of main valve and auxiliary valve, through the auxiliary valve pulse action to drive the main valve action, and its complex structure, usually only applicable to the safety of a large volume of boilers and pressure vessels.

Six, reversing valve (switching valve, diverter valve)
Reversing valve is a combination of several types of DC valve type, which is used to change the flow direction of the process medium, and to control the confluence or diversion of multiple media. For example, gear pump and polymer filter system flow direction control, as well as polymerization system process medium multi-channel distribution. Reversing valves are widely used in the chemical industry, petroleum industry, metallurgy, power sector, pharmaceutical industry, beer, food, dairy, beverages, cosmetics and various types of piping systems.

Performance characteristics:
1, stainless steel material;
2, polishing accuracy, reaching food grade, drug level requirements;
3, according to the actual user configuration of the control system, to achieve fully automated operation, improve work efficiency;
4, shell and main parts are casting casting, solid structure, high strength, not easy to deformation, beautiful appearance;
5, the conveying channel is smooth and smooth, and the material circulation is smooth without clogging;
6, in the pressure sealing requirements, can be configured with a special sealing structure, fully meet the use requirements.

Seven, drain valve
The valve according to the temperature change in the hair cavity to create a sense of temperature, so that the bimetallic sheet meets the corresponding temperature will automatically change, drive the valve to do the reset movement, close the valve seat hole, to shut down steam excluded. On the contrary, if the valve chamber condensate, the cavity temperature caused by deformation of the bimetal will not, so the spool and the valve seat to remain open, so will always put the condensation water, condensed water discharged after the valve chamber temperature will immediately change, double sheet metal deformation will immediately close the valve seat hole so repeatedly open.

Performance characteristics:
1, control fluid speed about 30m/S, to prevent cavitation damage, fluid channel labyrinth, and constantly change the direction of the fluid, allowing pressure difference 25MPa.
2, separate, cutting surface and the sealing surface according to the drainage flow with different throttle components, valve components of surface hardening, the hardness can reach HRC70, closed tight, long life.
3, body components from the internal pressure sealing structure, the greater the pressure difference, the better the tightness.
4, The valve body and the actuating mechanism adopt the floating type connection, which can eliminate the sticking phenomenon caused by the misalignment between the valve core and the push rod.