Once a two-stage vacuum oil purifier has been installed, the first thing an operator is most likely to overlook is the order of the two pumps. The vacuum system consists of the X-100 vacuum pump on the front stage and the JRP-500 roots blower on the rear stage. They are not independent units; they sit on the same pumping path, and which of them runs first decides whether the machine can pull a vacuum at all.
Why the roots blower must not start first
A roots blower works differently from an ordinary mechanical pump. It does not remove gas itself; it compresses the gas entering the casing and pushes it towards the next stage, and the compression ratio is set by the pressure difference between inlet and outlet. With no negative pressure at the inlet and an outlet close to atmospheric pressure, air is simply moved back and forth inside the casing: nothing is extracted, and the rotors run in dry friction for longer than they should.
The front-stage X-100 vacuum pump therefore has to pull the path down to a negative pressure first, so that the roots blower has a gas source it can compress. Started at that point, it takes over and keeps drawing the gas out of the intermediate chamber, pushing the ultimate vacuum lower. The working vacuum of the ZYD-100 is -0.08 ~ -0.0999 MPa and the ultimate vacuum is ≤5 Pa. How far that second stage can be pushed depends on whether it is genuinely in operation.
The stop sequence is the other way round
Starting goes from the smaller stage to the larger one, and stopping goes from the larger back to the smaller. Stopping the X-100 while the roots blower is still turning creates the mirror image of the start-up problem: the rear stage is still compressing while the front stage has stopped extracting, the vacuum reading only rises, and the roots blower ends up running without gas flow. The correct stop order is to stop the JRP-500 first, let it clear the remaining gas out of the intermediate chamber, and only then stop the front-stage vacuum pump.
What a wrong order looks like on site
| What you see on site | The more likely cause | How to confirm it |
|---|---|---|
| A clear impact or metallic bang when the roots blower starts | The rear stage was started before the front stage had built a negative pressure | Stop the machine and start again with the X-100 first and the JRP-500 second |
| Vacuum builds up noticeably slowly and the gauge stays below the working range for a long time | The two stages are not in series, so only one stage is actually working | Run one start and stop sequence in the right order and watch how fast the reading enters -0.08 ~ -0.0999 MPa |
| After shutdown the vacuum reading rises instead of falling | The front-stage pump was stopped first while the roots blower was still turning | Stop the JRP-500 first and the X-100 second |
| The roots blower runs for a long time but the ultimate vacuum never reaches ≤5 Pa | The rear stage is not genuinely in operation, or the pump body and the pump oil are in poor condition | Check the start and stop order first, then look at the pump oil and the pipework |
Write the sequence into the operating procedure
Memory is not a reliable place to keep a sequence, especially on night shifts or wherever the machine is started and stopped repeatedly. The steadier approach is to put the start and stop order into the equipment documentation and the site operating procedure, down to the level of what to do first, what to do next and what should be seen before each step counts as finished. Models with PLC smart control and a touch screen can carry the sequence in the control logic and let it execute in order, which removes a human step from the chain.
Two things have to be kept apart: the sequence only decides whether a vacuum can be established, and once it is established the oil inlet and the atomisation still have to be right. The working vacuum reading of -0.08 ~ -0.0999 MPa only means something once the oil mist has actually entered the vacuum zone.
The start and stop order of a two-stage vacuum is set by the structure, not by habit: the front stage has to extract the gas before the rear stage has anything to compress.
