Whether a micro pump possesses good air tightness and one-way pressure retention capability is a key distinction between industrial-grade and consumer-grade micro pumps. In industrial applications, micro pumps are often used to transfer high-risk or high-value media. Therefore, having excellent air tightness to prevent media leakage is a typical characteristic of industrial-grade micro pumps. Customers frequently inquire about a pump’s air tightness or pressure retention. Many tend to conflate a pump’s one-way pressure retention with its inherent air tightness. While these two performance aspects are distinct, they also influence each other. This article primarily explains the differences between these two characteristics and introduces the air tightness testing methods for Hilin Technology’s micro pumps.
One-Way Pressure Retention of a Pump
One-way pressure retention in a pump refers to the ability where, after a micro vacuum pump evacuates a sealed container or a micro air pump pressurizes it, the vacuum or positive pressure inside the container can be maintained for an extended period even after the pump is powered off. This requires the pump to act as a check valve in this state, emphasizing the unidirectional nature of airflow, hence “one-way pressure retention.” This performance has been discussed in previous articles. A micro pump is a power element within a pneumatic system; its primary duty is to provide power to the system.
The function of a check valve cannot be entirely entrusted to the pump. While micro pumps do contain two internal check valves, they differ from standard one-way check valves available on the market. Their purpose is to reliably ensure unidirectional airflow during pump operation, focusing on dynamic performance, not on providing a tightly sealed closure under static conditions. If pressure needs to be maintained after the pump stops, a separate one-way check valve should be added to the pneumatic circuit, along with ensuring proper sealing of the tubing.
Inherent Air Tightness of a Pump
The inherent air tightness of a pump reflects the extent of leakage from the pump itself when used for gas transfer. A pump’s air tightness is influenced by factors such as mechanical structure and assembly precision. All Hilin micro pumps undergo air tightness testing before leaving the factory. Standard and Premium versions have strict testing standard requirements for air tightness, while the Simplified version has no such requirements. Below is an introduction to Hilin’s micro pump air tightness testing fixture and standards.
Introduction to Air Tightness Testing Fixture Principles and Standards
The air tightness testing fixture consists of two parts , connecting to the inlet and outlet of the pump under test. Before testing a pump with this fixture, the fixture itself must undergo an air tightness test. The testing principle involves connecting the two parts of the fixture together. The test is divided into positive pressure testing and negative pressure testing.
Gas is pushed in or drawn out by a source pump to reach the target test pressure (for positive pressure testing, the gauge pressure should exceed the maximum output pressure of the micro pump under test by 10 kPa; for negative pressure testing, the absolute value of the gauge pressure should exceed the absolute value of the maximum vacuum of the micro pump under test by 10 kPa, but not exceed -92 kPa). The ball valve is then closed. After stabilizing for 1 minute, the initial pressure is recorded. Pressure retention continues, and the sum of pressure changes on both gauges over 10 minutes must not exceed 1 kPa.
Introduction to Pump Air Tightness Testing Principles and Standards
Pump air tightness testing is also divided into positive pressure testing and negative pressure testing . The principle involves using a source pump to push gas in or draw it out to reach the target test pressure, closing the ball valve, stabilizing for 1 minute to record the initial pressure, continuing pressure retention, and recording the sum of pressure changes on both gauges over a specified period. The testing standards for some of Hilin Technology’s micro pump series are shown in Table 1.
Table 1: Micro Pump Test Pressure Values and Standards
| Micro Pump Series | Positive Pressure Test Value | Negative Pressure Test Value | Standard for Sum of Pressure Changes |
|---|---|---|---|
| C09 | Prohibited for positive pressure test | -45 kPa | Change ≤ 3 kPa over 2 min |
| C26 | 60 kPa | -45 kPa | Change ≤ 3 kPa over 2 min |
| C30 | 60 kPa | -65 kPa | Change ≤ 3 kPa over 2 min |
| C50 | 70 kPa | -70 kPa | Change ≤ 3 kPa over 2 min |
| C60 | 60 kPa | -93 kPa | Change ≤ 3 kPa over 2 min |
| D23 | 60 kPa | -30 kPa | Change ≤ 3 kPa over 2 min |
| D35 | 80 kPa | -45 kPa | Change ≤ 3 kPa over 2 min |
| D50 | 100 kPa | -70 kPa | Change ≤ 3 kPa over 2 min |
Furthermore, when testing a pump’s air tightness using the testing fixture, the sum of pressure changes includes the inherent air tightness condition of the fixture itself.
Summary
As a typical manufacturer of industrial-grade micro pumps, Hilin Technology has developed specialized testing equipment, methods, and standards for pump air tightness. We can provide strict factory inspection reports for product air tightness based on customer needs, thereby meeting the high standards required for industrial applications. We welcome all customers to consult our pre-sales engineers for further inquiries regarding air tightness, pressure retention, and related products.