The working principle of the section of the pressure reducing valve
The pressure is stabilized to a constant value so that the regulating valve can obtain a stable air source power for regulating the control. According to the structure, it can be divided into film type, spring film type, piston type, lever type and bellows type; the number of seat seats can be artificial single seat type and double seat type; according to the position of the valve flap, it can be divided into positive action type and Reactionary.
Type of pressure reducing valve
(1) Acting pressure reducing valve
The simplest pressure reducing valve, direct acting pressure reducing valve with flat diaphragm or bellows. Because it is a stand-alone structure, there is no need to install an external sense line downstream. It is the smallest and most economical of the three pressure reducing valves and is designed for medium to low flow. The accuracy of the direct acting pressure reducing valve is typically +/- 10% of the downstream set point.
(2) Piston pressure reducing valve
This type of pressure reducing valve integrates two types of valves - pilot valve and main valve - in one. The design of the pilot valve is similar to that of a direct acting pressure reducing valve. Exhaust pressure from the pilot valve acts on the piston causing the piston to open the main valve. This design uses the inlet pressure to open the main valve if the main valve is large and cannot be opened directly. Therefore, this type of pressure reducing valve has a higher capacity and accuracy (+/- 5%) at the same pipe size compared to a direct acting pressure reducing valve. The same as the direct-acting pressure reducing valve, the pressure inside the pressure reducing valve senses that there is no need to externally install the sensing wire.
(3) Membrane pressure reducing valve
In this type of pressure reducing valve, the double diaphragm replaces the piston in the internal pressure reducing valve. This increased diaphragm area enables the opening of a larger main valve and, at the same pipe size, has a larger capacity than the internal pilot piston relief valve. In addition, the diaphragm is more sensitive to pressure changes with an accuracy of +/-1%. The higher accuracy is due to the positioning of the downstream sensing line (the outside of the valve), where the gas or liquid is less turbulent. The pressure relief valve is very flexible and can be used with different types of pilot valves (eg pressure valves, temperature valves, air load valves, solenoid valves or several valves)
Basic performance of the pressure reducing valve
(1) Pressure regulation range
It refers to the adjustable range of the pressure reducing valve output pressure P2, within which the specified accuracy is required. The pressure regulation range is mainly related to the stiffness of the pressure regulating spring.
(2) Pressure characteristics
It refers to the characteristic that the output pressure fluctuates due to input pressure fluctuation when the flow rate g is constant. The smaller the output pressure fluctuation, the better the characteristics of the pressure reducing valve. The output pressure must be lower than the input pressure—the set value does not substantially change with the input pressure.
(3) Flow characteristics
It refers to the input pressure-timing, the output pressure changes with the change of the output flow g. When the flow rate g changes, the smaller the change in the output pressure, the better. Generally, the lower the output pressure, the smaller the fluctuation with the output flow.
The role of the pressure reducing valve
The working principle of the pressure reducing valve is to reduce the water pressure by the local resistance of the flow passage in the valve to the water flow. The range of the water pressure drop is automatically adjusted by the pressure difference between the inlet and outlet of the membrane or the piston connected to the valve flap. In recent years, some new types of pressure reducing valves have emerged, such as fixed ratio pressure reducing valves. The principle of constant pressure reduction is to use the water pressure ratio control of the floating piston in the valve body, and the pressure reduction ratio at the inlet and outlet ends is inversely proportional to the ratio of the piston area on the inlet and outlet sides. The pressure reducing valve works smoothly without vibration; there is no spring in the valve body, so there is no spring corrosion and metal fatigue failure; the sealing performance is good and does not leak, so the pressure is reduced (when the water flows) and the static pressure is reduced (the flow rate is 0 o'clock); especially during decompression without affecting water flow.
Although the water flow through the pressure reducing valve has a large head loss, it is still energy-saving in general due to the reduction of water waste and reasonable distribution of system flow and improvement of system layout and working conditions. Each spring of the pressure reducing valve is only applicable within a certain range of outlet pressure, and the spring should be replaced beyond the range. In the case of high working temperature of the medium, a pilot piston type pressure reducing valve or a pilot bellows type pressure reducing valve is generally used. When the medium is air or water (liquid), it is generally preferred to use a direct acting membrane pressure reducing valve or a pilot diaphragm type pressure reducing valve. When the medium is steam, a pilot piston type pressure reducing valve or a pilot bellows type pressure reducing valve should be used. For ease of operation, adjustment and maintenance, the pressure relief valve should normally be installed on a horizontal pipe.
Pressure reducing valve operation
1. Avoid storing dirt and debris into the pressure reducing valve decompression guarantee system. The decompression system pipe network of the newly built or renovated project is likely to leave sand, hemp and debris. Before being put into operation, water rinsing should generally be carried out. After meeting the cleaning requirements, the pressure reducing valve and the filter element should be installed at the end to avoid the flow of impurities into the pressure reducing valve and prevent the core of the pressure reducing valve. After the system enters the work, ensuring the smooth flow of the water in the decompression system is closely related to the filter capacity of the filter installed on the system. If the filter element is heavily adsorbed by debris, it will affect the work of the pressure reducing valve. The filter is regularly inspected to remove contamination in a timely manner. Practice has shown that this work must be carried out once every two to three months. Some adjustable (spring type, membrane type) pressure reducing valves, the main valve or the pilot valve itself set the filter, also need to periodically remove the filter element.
2.1 The pressure reducing valve group with 1 should be rotated regularly. Most of the high-rise building life water supply pressure reducing valve decompression guarantee system is set up in the vertical division of the water supply, generally located in each water supply zone main pipe. Considering the reliable safety of water for many users (there are dozens to hundreds of houses in each sub-district, public buildings such as hotels and restaurants, dozens of rooms in each sub-district...), the design of the pressure reducing valve should be juxtaposed Installation (1 with 1). Both sides of the decompression passage are supplemented with gate valves or butterfly valves, which can open and close any decompression passages. In order to make the two sets of decompression valve passages in parallel work normally, the conventional one-month exchange is performed once, and the idle time is too long. Fouling, the decompression element spool will become stuck.
3. The gas in the pipeline should be removed in time. When the air enters the decompression pipe network or the pipe network, the gas is separated from the water when the pressure changes. At this time, the water pressure of the user in the area is extremely unstable; at the most unfavorable point of the water supply, the water pressure is a sudden change of pressure, sometimes showing a false Peak pressure, sometimes pumping water, and the pipe network will accompany the impact. This phenomenon will affect the stable operation of gas water heaters, electric water heaters, etc., and will be destroyed in severe cases; the influential connection pipe of various washing appliances is also very destructive, especially some composite type connecting hoses that are commonly used at present. The strength is poor, so the occurrence of squibs occurs frequently; some water meters cannot be metered correctly, and the user will not use water, and the water meter will continue to rotate. In order to prevent such accidents, it is necessary to check whether the water storage elevation of the roof water tank living water main pipe is satisfied. If the water tank outlet is not satisfied, water swirl will be generated and air will be taken in. Excluding this fault can adjust the minimum water level elevation of the liquid level controller in the water tank. Experience has shown that the general minimum water level should be no less than 0.3m from the water outlet. It is also possible to repeatedly open the pressure gauge venting cocks disposed on both sides of the partition and the pressure reducing system, and the air that has entered the pipe network is slowly discharged. If the above measures are taken, the above phenomenon may occur in some water heaters below the end of the section main pipe, and an automatic exhaust device may be added to these parts.
4. Pay attention to the pressure relief system of the pressure reducing valve. Regardless of whether a proportional or adjustable pressure reducing valve is used, the decompression ratio P1:P2 should not be too large, and should generally be controlled within 5:1. Exceeding this range is prone to cavitation, damage to the valve and whistling noise. Some piston type pressure reducing valves, the manufacturer processes a small hole with a diameter of about 1.5mm on its valve body. Its function is to make the valve core move through the suction function. Please pay attention to the small hole when maintenance and management. Plugged, otherwise it will affect the normal operation of the pressure reducing valve.
5. Strengthen the management inspection of the pressure reducing valve support system, pay attention to observe the working dynamics of the pressure reducing valve itself. The pressure values ​​before and after the valve are close, indicating that the pressure reducing valve itself has a fault. That is, the flat seal rubber member between the valve core and the valve body of the piston type pressure reducing valve is damaged; the diaphragm of the main valve of the diaphragm type adjustable pressure reducing valve is cracked and the O-ring is damaged, and the connecting pipe of the pilot valve is blocked, resulting in decompression The valve decompression is weakened or disabled. This is extremely harmful to the zoning pipe network. In particular, many water equipment may explode due to overpressure and must be repaired in time. If there is a leak in the small suction hole on the valve body of the proportional (piston type) pressure reducing valve, it indicates that several O-ring seals on the valve core have worn out, and the seals have to be replaced. However, when repairing the disassembled and decompressed components, be careful and change the inner seals; when cleaning debris, you should use the advantages of metal bars and hard stem valves, and use wooden hoes and wooden handles to strike the vibrations. Slowly remove the valve components. When reinstalling after repair is complete, be sure to match the flow direction indication on the valve.
6. Pay attention to check the installation position of the proportional pressure reducing valve. The design and installation of the high-pressure internal pressure reducing valve is not proper. The pressure will be high and low after the pressure reducing valve will occur. The pressure of the pipe network will seriously deviate from the allowable range, accompanied by accidents such as damage to the shower, water pipe bursting and damage to the user's water meter; sometimes The water flow is not smooth, and there is an irregular water cut in the partition, which affects the user's water. Similar accidents occurred, check the entire pressure reducing valve decompression zone water supply system, no doubt can be found; disassemble the pressure reducing valve filter and other components are not abnormal; some property management units even suspect the technical performance of the pressure reducing valve, repeatedly exchanged new The pressure relief valve does not solve the problem. At this time, it is possible to check whether the design and installation position of the proportional pressure reducing valve is reasonable, and carefully check whether there is an equipotential inverted rainbow phenomenon in the pipe network system, that is, the output pipe of the partition is high. Such a situation is likely to occur in the same roof tank in the main and auxiliary buildings, and in the lower feedwater supply system. If you find these problems, you can consider raising the installation position of the proportional pressure reducing valve to one level (cannot be raised too high, you must consider the pressure requirements of the water equipment in the district); you can also set up two separate groups in the main and auxiliary buildings. Proportional pressure reducing valve feedwater system.
Pressure reducing valve installation
Installation requirements
1. The installation of the pressure reducing valve should be carried out after the water supply pipe network is tested and flushed.
2. The pressure reducing valve should be inspected before installation: its specifications and models should be consistent with the design; the connecting parts of the external control line and the pilot valve should not be loose; the appearance should be free of mechanical damage, and the foreign objects in the valve should be removed.
3. The flow direction of the pressure reducing valve should be consistent with the water flow in the water supply pipe network.
4. The filter should be installed on the inlet side and the control valve should be installed before and after it.
5. The adjustable pressure reducing valve should be installed horizontally and the valve cover should be upward.
6. Proportional pressure reducing valve should be installed vertically; when horizontally installed, the single breathing port pressure reducing valve should have its orifice downward, and the double breathing hole pressure reducing valve should have a horizontal position.
7. When installing a pressure reducing valve without a pressure gauge, install a pressure gauge on the front and rear adjacent parts.
Precautions
1. For ease of operation and maintenance, the valve is generally mounted upright on a horizontal pipe.
2. The installation of the pressure reducing valve must be consistent with the direction of fluid flow in strict accordance with the direction of the arrow on the valve body. If the water is not clean and contains some impurities, the filter must be installed at the upstream inlet of the pressure relief valve.
3. In order to prevent post-valve pressure overpressure, a pressure reducing valve should be installed at not less than 4M from the valve outlet.
4. The pressure reducing valve plays a certain role in the pipeline. In order to prevent the damage of the water hammer, a small expansion tank can also be installed to prevent damage to the pipeline and the valve. The filter must be installed in front of the inlet pipe of the pressure reducing valve. The expansion tank must be installed after the pressure relief valve outlet!
5. If the pressure relief valve needs to be installed in a hot water system, you must install a check valve between the pressure relief valve and the expansion tank. In this way, the expansion tank can absorb the volume of water increased due to thermal expansion, and can prevent the influence of hot water return or pressure fluctuation on the pressure reducing valve, and ensure the long-term normal operation of the pressure reducing valve.
skills
5公斤/厘米之间。 The setting of the driving pressure is higher than the back pressure of 1-1. 5kg / cm2 (15-20psig). This is true in most cases. But sometimes to achieve the pump's required displacement, the drive pressure needs to be set slightly higher. When the driving pressure is high, the unfavorable side is that it is easy to cause wear on the intake valve. If the driving pressure is higher than the required value, the intake valve will be severely worn and the intake valve must be replaced in advance.
In this case, it is recommended to use a pressure reducing valve or a pressure reducing valve station. The pressure relief valve allows the drive pressure to be maintained at a set pressure that satisfies the pump displacement while also protecting the intake valve from wear. In addition, when the application space is narrow, it is recommended to use a pressure reducing valve station with a collector pipe. During the pumping process, the collector pipe supplies steam to the pump to provide a buffer for the pump. This buffer softens the movement of the entire unit and reduces wear on the pressure reducing valve.
The pressure reducing valve mainly controls the fixed outlet pressure of the main valve, and the main valve outlet pressure is not changed by the inlet pressure change, and the outlet pressure is not changed due to the change of the main valve outlet flow rate. Applicable to industrial water supply, fire water supply and domestic water pipe network system.
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