In the field of industrial vacuum applications, on off vacuum controllers have become a common choice for processes such as vacuum drying, impregnation, and defoaming due to their excellent cost-effectiveness and ease of operation. However, its inherent working mode also brings a classic technical challenge: the occurrence of pressure overshoot.

1、 The crux of the matter lies in

Why is it difficult to maintain stable on-off control?

The logic of on-off control is concise and clear, and its working principle is as follows:

1.Monitoring: The pressure sensor reads the vacuum degree of the chamber in real time.

2.Comparison: The controller compares the read value with the user set value.

3.Execution: When the pressure exceeds the set value, the controller connects the circuit and starts vacuuming. When the pressure is ≤ the set value, the controller disconnects the circuit and stops vacuuming.

The core contradiction of the problem lies in the lack of an adjustable "buffer" between the powerful "full speed pumping" capability of the vacuum pump and the small "inherent leakage/deflation" rate of the system.

Extraction stage: The pump operates at a high extraction speed of Z, and its extraction capacity far exceeds the slow leakage rate of the system, causing it to easily exceed the set point.

Stop phase: The vacuum extraction pipeline is cut off, but the gas source such as cavity material venting and minor leaks continues to introduce gas into the system, causing the pressure to slowly rise.

2、 The way to crack it

1Physical damping - installation of vacuum buffer tank

This is a targeted physical solution to address pressure overshoot.

Principle: Connect a vacuum tank (buffer tank) with a volume much larger than the chamber in series on the pipeline between the vacuum chamber and the pump.

Function: Significantly increase the total volume (air volume) of the system. According to the ideal gas law, the larger the volume, the slower the pressure change caused by the same gas load. This provides a longer response time for the on-off controller, greatly smoothing pressure fluctuations and effectively reducing overshoot.

Applicable scenarios: Especially suitable for working conditions with small chambers and large pumps, it is a practical solution for optimizing pressure stability.

2Mechanical flow restriction - installation of manual throttle valve

This is a low-cost and practical simple renovation plan.

Principle: Install a manual needle valve or precision ball valve at the front end of the pump inlet.

Function: By manually adjusting the valve opening, the flow conductivity of the pumping channel is mechanically restricted, thereby artificially reducing the effective pumping speed of the pump.

operation

1.When extracting air, first adjust the valve to the fully open position.

2.When the pressure approaches the target set value, slowly close the valve.

3.Observe pressure changes and stabilize them near the target value.

4.At this point, the on-off controller will perform small-scale start stop control on the restricted and smoother pressure curve, greatly improving the overshoot phenomenon.

Advantages: Simple, affordable, and effective immediately.

Disadvantage: It requires manual pre adjustment according to different target pressure points and cannot achieve fully automatic intelligent control.

Applicable scenarios: Applications that have strict requirements for vacuum stability, such as semiconductor processes, optical coatings, and high-level scientific research experiments.