The core goal of installing a vacuum gauge is to ensure measurement accuracy and stabilityFlange interface matchingandPipeline layoutThese are the two key factors that affect this goal. If not handled properly, it can easily lead to leaks, reading deviations, delayed responses, and even equipment damage. This article will provide a detailed breakdown of relevant pit avoidance points and practical solutions.

1、 Flange interface matching avoidance: the core is “seal+compatible”

As the connection hub between the vacuum gauge and the system, the matching degree of the flange directly determines the sealing effect and measurement accuracy, which needs to be avoided in detail “Interface incompatibility”“seal failure”“Structural interference”Three major issues.

1. Strictly verify the flange standards and eliminate them“Non standard mixed use”

Common vacuum flange standards and characteristics

Key points for avoiding pitfalls

•Prohibition based solely on “Visual measurement of size”To determine compatibility, it is necessary to verifyNominal diameter (such asKF16TheCF35）Sealing groove type, bolt hole position and quantity；

•Ultra high vacuum system（10⁻⁵ PaThe following is strictly prohibited from useKFFlange direct connection, preferredCFFlange (metal oxygen free copper gasket sealing, leakage rate)≤10⁻ ¹¹ Pa・m³/s）；

•Non standard flanges require customizationSpecial transition jointIt is prohibited to polish or weld the flange sealing surface (which will damage the flatness and cause leakage).

2. Selection and installation of seals: details determine leakage rate

The material and installation method of the seal directly affect the sealing effect, and it needs to be accurately matched according to the vacuum degree and medium characteristics:

Installation operation specifications

•Used before installationAnhydrous ethanol or acetoneWipe the flange sealing surface to ensure that there is no dust, particles, or oil stains;

•Bolt fastening adopts “Tighten diagonally evenly”Law, division2~3Step by step tightening (to avoid flange deformation caused by unilateral force and uneven sealing surface adhesion);

•The size of the sealing element must match the sealing groove, and it is prohibited “Small pads with large slots”or“Large gasket hard plug small groove”.

3. avoid“Interface Steps”Measurement blind spots caused

If the diameter of the vacuum gauge flange is smaller than the diameter of the connecting pipeline, it will form “Stair like structure”Gas and condensate are prone to accumulate at the steps, resulting in measured values lower than the true vacuum level (especially during the low vacuum stage).

Evacuation plan

•Prioritize selection based on pipeline diameterSame or slightly largerThe vacuum gauge;

•When it is necessary to change the diameter, useGradient transition joint(Avoid right angle diameter change), transition length≤The diameter of the pipe2 Double (such as25mmTransition section length of pipe diameter≤50mm）.

2、 The impact of pipeline layout on measurement accuracy: the core is “shorten the path+reduce interference”

The connecting pipeline is for gas transmission “measurement channel”Its length, direction, diameter, and material will directly affect the measurement response speed and reading accuracy, and should be focused on“Reduce transmission resistance and avoid gas accumulation”Design.

1. Pipeline length and diameter: the shorter and thicker the better

principle

The transmission time of gas molecules in pipelines is proportional to the length of the pipeline and inversely proportional to the square of the pipe diameter ——Long and thin pipelines can lead to:

•Response lag: The system vacuum degree has reached the standard, but the vacuum gauge reading is not updated for a long time;

•False vacuum: Gas is adsorbed on the inner wall of the pipeline, which cannot be evacuated by the vacuum pump in a timely manner, resulting in high readings.

Key points for avoiding pitfalls

•pipeline lengthControl in30cmwithinThe maximum length shall not exceed50cm；

•Inner diameter of pipelineNot less than the inner diameter of the vacuum gauge interface(such asKF25Interface corresponds to the inner diameter of the pipeline≥25mm）；

•Suggestions for ultra-high vacuum systemDirect flange docking of vacuum gaugeCancel the independent connection pipeline (eliminate pipeline interference).

2. Pipeline Route: Avoid“Horizontal blind end”and“Liquid accumulation curve”

Common problems and hazards

•Horizontal blind end: The pipeline is arranged horizontally and the end is closed, making it difficult to extract gas from the blind end, resulting in “Additional gas source”, resulting in high measurement values;

•Liquid accumulation bend: When there is condensable vapor (such as water vapor or organic solvent vapor) in the system, the downward bending of the pipeline will form a liquid accumulation bend, and the accumulation of condensate will block the channel and corrode the sensor.

Evacuation plan

•pipelinePriority vertical arrangementInstallation position of vacuum gaugeAbove the system connection point, forming15°~30°Upward tilt angle (to facilitate the reflux of condensate to the system, rather than accumulating in the pipeline);

•When it is necessary to arrange horizontally, install it at the end close to the vacuum gaugebleed valveRegularly empty the blind end gas;

•The system containing condensed steam requires the installation of pipelinesheating tape(Temperature slightly above the condensation point of the medium) to prevent vapor liquefaction.

3. Reduce the number of pipelines“Impedance element”

Valves, filters, and elbows can increase gas transmission resistance, reduce pumping efficiency, and lead to measurement deviations. It is necessary to simplify the pipeline structure as much as possible:

Key points for avoiding pitfalls

•Between vacuum gauge and systemTry not to install valves as much as possibleIf installation is necessary, chooseLarge diameter ball valve(Resistance less than gate valves and needle valves), and the valve remains fully open throughout the entire process;

•Cancel unnecessary filters; If you need to filter particles, chooseLarge aperture（≥1mm）Metal filter screen, and regularly clean (to avoid blockages);

•Number of elbows≤2One, and the curvature radius of the elbow≥The diameter of the pipe3 Reduce the impact of turbulence on gas transport.

4. Pipeline material: Low gas release is key

Ordinary carbon steel and rubber pipes will adsorb a large amount of gas on the inner wall, which will be released in a vacuum environment and interfere with measurement accuracy.

Material selection suggestions

•priority choice304/316stainless steel pipe(The inner wall polishing treatment is better, and the amount of adsorbed gas is less);

•Ultra high vacuum system needs to be usedElectrolytic polished stainless steel tube(Lower inner wall roughness, air release rate)≤10⁻¹⁰ Pa・m³/(s・cm²)）；

•Do not use rubber hoses (unless temporarily connected by short distance rough vacuum) to avoid degassing or aging cracking of the inner wall of the hose.

3、 Extra Pit Avoidance: Installation Location and Environmental Requirements

1. The vacuum gauge sensor needs toFacing the direction of airflowAvoid facing away from the vacuum pump suction port (otherwise it may cause damage) “Airflow blind spot”Causing low readings);

2. Avoid installing the vacuum gauge onNear the heat source(such as ovens and motors), high temperatures can affect sensor accuracy (it is recommended to control the working environment temperature within0~40℃）If necessary, install a heat shield;

3. Stay away from vibration sources (such as vacuum pump bodies), as vibration can cause the sensor to loosen or be damaged. A shock absorber bracket can be installed.

4、 Installation acceptance self inspection checklist

Hangzhou Yushi Technology Co., LtdFocusing on providing technical services and solutions related to flow, pressure, vacuum detection and control for industrial and scientific research customers, the company acts as an agent and distributor in the United StatesALICAT、 Swiss Vogtlin, American MKS, Japanese EBARA and other brands, combined with their agent products, provide customers with high-quality flow and pressure monitoring solutions, aiming to improve customers' research and production efficiency, improve their manufacturing processes, and promote their scientific research and innovation progress.