How can a higher vacuum level be achieved? Should I use a fan or a pump?
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This post was last edited by jmdc on 2018-1-16 at 16:53. How can a higher vacuum level be achieved? Should I use a fan or a pump to extract it? If all the equipment and pipelines in front of the fan or pump are perfectly sealed, will the system ahead of it necessarily reach a ultimate vacuum after the fan or pump has been operating for a certain period of time? (In that case, the performance of the vacuum pumping equipment doesn’t matter; as long as it can pump air out, that’s enough. The level of vacuum that can be achieved depends entirely on the sealing quality of the system before the pumping equipment.) What happens once extreme vacuum is reached, and pumping continues? I often hear that fans cause pipelines to collapse – is the strength of these pipes not sufficient to withstand an external pressure of one atmosphere? No matter how hard the fan pumps, it can’t possibly make the external pressure acting on the pipeline exceed one atmosphere, right? I remember that two years ago, on a spray drying tower project, someone said that the induced draft fan should be turned on first and the blower later; otherwise, dust would fly everywhere ； Some people say that the blower should be turned on first and the exhaust fan second; otherwise, the spray tower may collapse. Which approach is correct?
If all the equipment and pipelines in front of the fan or pump are perfectly sealed, then after the fan or pump has been operating for a certain period of time, an extreme vacuum can be achieved in the system ahead of it; this extreme vacuum level depends on the equipment. The limit values vary among different devices, and even for the same device, these limits change before and after wear.
Fans (generally referring to centrifugal fans) have a relatively low rated air pressure; high-pressure fans only reach around 10 KPa (a little over 1 meter of water column), which means they are not capable of achieving high levels of vacuum. The spray tower won’t get collapsed, unless it’s made of 1mm thick iron sheet or has an extremely large diameter. Pumps are different; here we are talking about air pumps and vacuum pumps, which have a strong vacuum-pumping capacity. If the walls of the spray tower are thin, it can easily be collapsed under the effect of this vacuum. If the wall thickness of the spray tower is thick, no vacuum level can collapse it.
Water ring vacuum pumps, Roots pumps, and jet pumps can all create a vacuum, with a vacuum level that is much higher than that of fans
No vacuum pump, no matter how powerful, can possibly collapse a spray tower. If the wall thickness of such a tower is only 1 mm, then think about how it is secured and how insulation is provided for it
Fans for positive pressure or slight negative pressure； A vacuum pump is required for high vacuum levels. Different pumps have different maximum pressure limits.
If the vacuum extraction is carried out in a timely manner, the pressure level can reach a certain value; vertical vacuum pumps and water-jet vacuum pumps can achieve pressures of over -0.09, and by connecting a Roots pump or similar device to them, pressures of over -0.1 can be attained.