Design and selection of pipe fittings and valves in clean workshops of pharmaceutical factories
Design and selection of pipe fittings and valves in clean workshops of pharmaceutical factories
The main reason why air can flow in a clean air conditioning system is that there is a pressure difference in the pipe section, not the pressure. To make the entire purification air-conditioning system operate correctly as expected, it requires us to reasonably arrange the pipelines, especially the reasonable design of each pipe fittings, just...
Text label: clean workshop of pharmaceutical factory, selection of pipe fittings and valves, design of clean workshop
Design and selection of pipe fittings and valves in clean workshop of pharmaceutical factory
The main reason why air can flow in a clean air conditioning system is that there is a pressure difference in the pipe section, not the pressure. In order to make the entire purification air-conditioning system operate correctly as expected, it requires us to reasonably arrange the pipelines, especially the rational design of each pipe fitting, the correct selection of the air valve, and to maintain a suitable pressure difference between each section of the air duct. Ensure that a certain amount of clean air is sent to each clean clean room modular as required, and ensure that each clean clean room modular maintains the required positive pressure.
As mentioned above, the local resistance caused by the pipe fittings and the air valve is much higher than the resistance along the air duct. Therefore, when designing the pipeline, special attention should be paid to the design of the pipe fittings and the selection of the air valve. Pipe fittings mainly include elbows, gradually expanding pipes, reducing pipes, three-way pipes and four-way pipes. When ducting, try to minimize the local resistance of these fittings. If the radius of curvature of the center of the elbow should not be smaller than the diameter of the duct (or the side length of the rectangular duct), generally a large-section duct with a diameter of 1.25 times the diameter (or the side length of the rectangular duct) is used. resistance. Right angle elbows have much lower resistance than general elbows. The pipe fittings used for reducing the diameter of air ducts should not be suddenly enlarged or reduced, but should be gradually expanded and reduced. The expansion angle of each side of the gradually expanding pipe should not be greater than 15°, and the shrinking angle of each side of the gradually reducing pipe should not be greater than 30°.
The tee of the rectangular air duct should be bent and branched along the airflow elbow, and the branch pipe should also consider a certain curvature radius. Many pipe fittings have become standardized and can be found in the relevant national standard diagrams.
The valve in the purification air conditioning system is indispensable, such as the fresh air closed valve or the exhaust closed valve mentioned above, this is an on-off valve, it only acts as a switch, so it is required to have low resistance when fully open and fully closed Good sealing performance. As mentioned above, in order to prevent the system from fluctuating too much air volume due to dust accumulation or renewal of the tertiary filter, valves are often installed on the supply and return air pipes. This kind of valve belongs to the regular regulating valve, because it needs to be adjusted frequently during operation. If automatic adjustment is used, the stroke of the valve actuator is required to have a linear or close to linear relationship with the change in air volume. Split multi-leaf valves are often used. When the air valve is opened at any angle, the overall direction of the air flow is always parallel to It is located in the center of the pipeline and has better adjustment performance, but its resistance is larger than that of the parallel multi-leaf valve. In order to balance the resistance of the pipeline and not cause imbalance, in addition to careful design, it is essential to adjust the balance by the valve; because the designed system is always different from the actual system after construction, before the system is used, always After debugging; this kind of valve will not be adjusted after only one adjustment during debugging. It is a regulating valve specially designed for the system and each air pipe section to achieve the designed air volume, which is called a primary regulating valve; in fact, this valve only serves as a To increase the resistance effect, only the position of the valve is required to remain unchanged after adjustment. Commonly used are butterfly valve, three-way regulating valve, multi-leaf valve (parallel type and split type) and flapper valve. Butterfly valve is suitable for supply and return air branch pipes with small air duct section. When the side length of the rectangular air duct or the diameter of the circular air duct is greater than 600mm, a multi-leaf control valve should be used, and the three-way control valve is used to adjust the air volume ratio of the two branch pipes.
Using the above ordinary valve to adjust the air volume, one is inaccurate, the other is the change of the lag working condition, the third is related to the pressure in the pipe, and the fourth is troublesome.
The variable air volume valve and constant air volume valve, which are valued and commonly used now, can make the air volume independent of the pressure in the pipe. As long as the pressure difference between the front and rear of the valve changes, the blade angle of the air valve can be adjusted, and the passing area can be appropriately reduced or increased, so that the air volume can be kept constant within a certain accuracy range.
When the pressure difference between the front and the back of the valve changes, the air bag is automatically inflated, and the elastic action of the spring sheet wrapped around the cam adjusts the angle of the blade. As long as the starting pressure of the valve is greater than 20
Pa or 50Pa, it can work. The valve can be used for both constant air volume control (CAV) and variable air volume control (VAV). There is a cone assembly in the valve body, which has a built-in stainless steel spring. As the system resistance rises, the static pressure on the cone decreases, the spring expands and the cone moves away from the valve body, and the opening area increases. The combination of lower pressure and larger opening area keeps the air volume constant within a certain accuracy range. At the same time, the variable air volume is achieved through closed-loop feedback (pneumatic or electric). Zhongjing Global Purification can provide supporting services such as consultation, planning, design, construction, installation and transformation of purification workshops and sterile rooms.
Currently, electric dampers are often installed in the system. It should be noted here that the running time of the electric dampers from opening to closing should be 100s or even longer. Fan and electric valve, delay 10s and then turn off the blower; since the exhaust electric valve is still in the process of opening to closing, the indoor positive pressure has disappeared, so that the outdoor air may enter the clean room modular along the exhaust pipe, so in addition to the like As mentioned above, a check valve should be installed on the pipeline, and the blower should be delayed until the electric valve is fully closed before shutting down, which takes about 120-150s.
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