Why do some products have to measure the negative pressure after measuring the positive pressure? Precision Industrial Technology tells you the truth!

In today's world of increasingly demanding waterproof, dustproof and structurally sealed designs, theA single pressure model is no longer sufficient to fully reflect the actual sealing ability of the product under different operating conditions.The
This is why a number of businesses(especially consumer electronics, LED lighting, outdoor equipment, etc.)It will be adopted:

• First pass: Positive pressure test
• Second time: negative pressure test

Positive and negative pressure complementary combination testing.

Consumer electronics battery compartment video case usingPositive and negative pressure air tightness test equipment

This may seem like redundancy, but it's actually the savviest choice an engineer can make.

Ⅰ. Positive and negative pressures have different physical effects and can complement each other's blind spots

Positive pressure = inflate the product(internal pressure > external)
Detectable:

• assembly defect
• The rubber ring is not tight
• leakage from a small hole
• Air leakage due to flared seams

Negative pressure = pumping air from inside(internal pressure < external)
Detectable:

• Weak wall thickness leads to internal concavity
• Insufficient rebound of the rubber ring
• Microcracks open under negative pressure
• reverse leakage path

One sentence summary:These two forces act in completely opposite directions and they reveal very different types of defectsThe

Some leaks close under positive pressure but open up under negative pressure;
Some leaks are not noticeable under negative pressure, but leak faster under positive pressure.

Therefore, the two tests can complement each other to build a complete seal assessment system.

Ⅱ. Simulate the different stress conditions of the product in the real environment

The product will be experienced in real life use:

• Externally pressurized by water(similar to positive pressure)
• Internal gas expansion(similar to positive pressure)
• Internal pressure drop after high temperature cooling(similar to negative pressure)
• External pressure changes during transportation(similar to negative pressure)

If only one-way working conditions are tested, it is easy to cause:

• Mass production. - OK.
• Water/air leakage in actual use

Two-way testing ensures that:

The product is truly sealed under both "internal expansion" and "external suction" conditions.The

Ⅲ. Double pressure test can effectively improve the stability of waterproof grade

Using IP67 and IP68 as an example, the core requirements for these waterproof ratings areExternal pressure does not press water into the product. But engineers have discovered a more insidious threat:

The product's internal gas expands in a high-temperature environment and contracts quickly when the temperature is lowered, creating an internal vacuum. This vacuum creates a strong suction force that draws external water vapor, dust and even liquids into the interior.

So:

• positive pressure testSimulate the extrusion of water pressure from the outside to the inside to verify the sealing of the structure under pressure.
• Negative Pressure TestVacuum suction during internal shrinkage was simulated to verify the permeation resistance of the structure under negative pressure.

Only when both positive and negative pressure tests are passed, can we ensure that the product really meets the IP level of mass production standards.This is not a theoretical deduction. This is not a theoretical deduction, but an engineering consensus that has been pushed back by countless failure cases.

Ⅳ. Positive and negative pressure reveals defects in different structures

Precision Engineering's battery compartment case test data demonstrates an interesting phenomenon:

The positive pressure leakage of a good product is 4 Pa and the negative pressure leakage is 8 Pa, both within the 50 Pa limit. The defective product will directly display FAIL.

This difference in values reveals a key fact:Positive and negative pressures amplify different types of defect signals, respectivelyThe

Defect type	positive pressure sensitivity	Negative pressure sensitivity
Assembly clearance	your (honorific)	lower (one's head)
Poor rubber ring press fit	your (honorific)	your (honorific)
microcrack	lower (one's head)	your (honorific)
Shell deformation	lower (one's head)	your (honorific)
Deep cavity leakage point	your (honorific)	your (honorific)
one-way leakage path	your (honorific)	Very high (reverse)

A single pressure pattern may misclassify a true defect as a conforming item or determine an acceptable minor deviation as bad.Dual-voltage testing passes complementary validation, dramatically reducing false detection ratesThe

V. Some seal configurations have "one-way leakage" characteristics

Certain product mixes are naturally occurring.one-way leak" situation, for example:

• Membrane breathable structure
• Designed with exhaust valve and pressure relief hole
• Two-piece construction with stepped opening
• Injection molded parts with different clamping line directions
• The sealing tape is easier to open in a certain direction

Commonly found in battery compartments, charging ports, cameras, valve bodies, etc.

With this type of construction, either only positive or only negative pressure may be missed.

VI. Positive and negative pressure combinations contribute to process optimization and structural validation

During the product development phase, dual pressure testing can help engineers determine:

• Does the seal need to be thickened
• Whether the pressure plate force needs to be increased
• Does the structural clearance need to be tightened
• Stable assembly consistency
• Whether the sealing ring needs to be optimized for the material

This is an important source of data for R&D and process engineers.

VII. WhyPositive and Negative Pressure TesterCompetent for this kind of test?

● One unit with both positive and negative pressure capabilities

Precision EngineeringJC-HH100 Positive and Negative Pressure TesterBoth positive and negative pressure capabilities are available, covering a pressure range of -85 kPa to +800 kPa.

● Supports both pressure drop and leakage rate determination.

• Determination of pressure drop at Pa level
• ml/min Leakage rate determination can be automatically converted according to the volume of different products.

:: Real-life usage scenarios can be simulated

It can better reflect the sealing performance of the product under high temperature cycle, air pressure change and water pressure impact, and completely simulate the real working conditions of the product.

:: Can be used for R&D validation, mass production sampling or full inspection

Data is automatically recorded and analyzed, providing a quantitative basis for structural optimization. One machine is multi-purpose, lower enterprise cost.

Summarize

Positive and negative pressure represent two completely different states of stress, and only when both are passed is the sealing of the product truly reliable.

This is a fundamental shift in modern product design. Whereas we used to go for a simple Yes or No, now we need to know thatThe product remains sealed in all possible operating conditions.The

This is not over-testing, but a basic respect for quality. When your product is double-verified with positive and negative pressure, you are able to say with confidence:We tested every situation it could encounterThe

Free Technical Consultation: If you are looking for a reliable airtightness testing solution, Precision Engineering's professional team can provide customized testing solutions based on your product characteristics.

Original Statement:this paper was written byShenzhen Jingchenggongke Technology Co., Ltd.Written by the technical team, reproduced with attribution.Data sources:Precision Engineering internal test data and customer cases.