Problems to be paid attention to in the design of vacuum system
(1) when vacuum components, such as valves, traps, dust remover and vacuum pump are connected with each other, they should try their best to make the suction pipe short, pipe flow guide large, the diameter of the pipe is generally not less than the diameter of the pump mouth, which is an important principle of system design. But at the same time to consider the installation and maintenance of convenience. In order to prevent vibration and reduce noise, mechanical pumps are sometimes allowed to be installed in the pump room near the vacuum chamber.
(2) mechanical pumps (including roots pumps) have vibration. To prevent vibration from spreading to the whole system, hose is usually used to reduce vibration. Hoses are available in both metallic and nonmetallic forms, regardless of which hose is used to ensure that it does not deflate under atmospheric pressure.
(3) after the completion of the vacuum system, it shall be convenient for measurement and leak detection. Production practice tells us that the vacuum system in the working process, often prone to leakage and affect production. In order to quickly find the leak hole, the leak detection should be carried out in sections, so that each section closed by valve should have at least one measuring point for measurement and leak detection.
(4) the valves and pipes configured in the vacuum system should make the system's pumping time short, convenient to use, safe and reliable. Generally there is a steam flow pump as the main pump (diffusion pump or oil booster pump); And a mechanical pump as the front pump system, in addition to the front pipe (steam flow pump series mechanical pump pipe), there should be a prevacuum pipe (vacuum chamber through the mechanical pump pipe). Secondly, there is a high vacuum valve (also known as the main valve) between the vacuum chamber and the main pump, and a front stage pipeline valve (also known as the low vacuum valve) on the front stage pipeline. Prevacuum pipeline valve (called low vacuum valve) is set in the prevacuum pipeline. High vacuum valve on the main pump, usually can not be in the vacuum state under the bonnet, and the valve on the bonnet under atmospheric pressure, this is to ensure safety through electrical interlocks. The front stage piping valve and the pre-vacuum piping valve should take into account that the valve itself can open at atmospheric pressure. In the vacuum system of the steam flow pump as the main pump, the main valve should be covered to the main pump, the front pipeline valve should also be covered to the main pump, and the pre-vacuum pipeline valve should be covered to the vacuum chamber. A vent valve shall be provided on the inlet pipe of the mechanical pump. When the mechanical pump stops working, the valve can be opened immediately, so that the mechanical pump inlet into the atmosphere, prevent the return flow of mechanical pump oil into the pipeline, so the valve and mechanical pump electrical interlock. The vacuum chamber should also be equipped with a vent valve for charging and taking materials. The setting position of the valve should take into account that the gas impulse force is large when the air is discharged, so as to prevent the weak components in the vacuum chamber from being damaged by the excessive impulse force. The size of the air release valve is related to the volume of the vacuum chamber, so the air release time should not be too long, affecting the work.
(5) the vacuum system shall be designed to ensure stable and reliable exhaust, easy installation, disassembly and maintenance, convenient operation, and interchangeability between components. In order to achieve stable exhaust in the work, the performance of the main pump is required to be stable, the valves operate flexibly, the seals are reliable, the joints of the components in the system are not leaky, the vacuum chamber has a good sealing performance, the vacuum components are connected in standard size to ensure interchangeability. In the design of vacuum system, in principle, there should be an adjustable size for each enclosed pipeline. This adjustable size in the past design, all use hose to solve, now design system, most do not use hose. By improving the dimensional accuracy of vacuum components and using the sealing rubber ring on the connecting flange to solve the installation error, the system strength and stiffness can be improved, the support used on the system can be reduced, and the appearance is more beautiful.
(6) new technology should be adopted in the design of vacuum system to achieve automatic control and interlock protection. With the development of vacuum technology, automatic operation is required in the whole pumping process. For example, vacuum relay is used to control roots pump to start work at 1333Pa pressure. Water pressure relay is used to control the pressure of the steam flow pump on a certain pressure, when the water pressure is insufficient or cut off, it can immediately power off and send an alarm. Prevent the pump from burning out. For complex vacuum system and equipment with strict requirements for process and parameters, microcomputer program control should be adopted, which is more safe and reliable.
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