Positive pressure sampling system is a safety protection device that maintains a positive pressure environment inside the equipment to prevent the intrusion of flammable, explosive or toxic gases from the outside. It is widely used in high-risk industries such as chemical, petroleum, natural gas, and medicine. The core principle is to continuously input inert gas or clean air, so that the internal pressure of the equipment is always higher than the external environmental pressure, thereby forming an "airtight barrier" to ensure the safety and reliability of the sampling process. The following are the usage details and key precautions of the positive pressure sampling system.

1、 System composition and functions

1. Positive pressure generating device

It is usually composed of a compressed air source, inert gas (such as nitrogen) cylinders, or fans to provide a continuous and stable positive pressure airflow for the system.

-Gas source requirements: The pressure should meet the system design value (usually 0.1~0.5MPa), and be equipped with a stabilizing valve and filter.

-Inert gas priority: For flammable and explosive environments, it is recommended to use inert gases such as nitrogen to avoid oxygen from participating in the reaction.

2. Pressure regulation and monitoring module

-Pressure regulating valve: precisely controls the input air pressure to maintain stable positive pressure within the system.

-Pressure sensor and alarm device: Real time monitoring of pressure values, triggering sound and light alarms when the pressure is below the set threshold, indicating the risk of pressure relief.

3. Sampling pipeline and interface

-Material selection: The pipeline should be made of corrosion-resistant and anti-static materials (such as stainless steel, PTFE) to avoid reaction with the sampling medium.

-Sealing design: The interface adopts metal sealing or fluororubber gasket to ensure airtightness.

4. Pressure relief and emergency exhaust device

-Pressure relief valve: It automatically opens when the internal pressure of the system exceeds the safe value, releasing excess gas.

-Emergency exhaust port: manually opened, used for rapid pressure relief or emergency shutdown.

5. Sampling containers and collection units

-The container needs to have pressure resistance (such as stainless steel sampling bottles) and sealing to prevent sample leakage.

-Two stage condensing devices (such as heat tracing sampling tubes) can be configured to avoid pipeline blockage caused by high temperature or high humidity sample condensation.

2、 Preparation before use

1. System inspection

-Confirm that the air source pressure is sufficient, the filter is not clogged, and there are no signs of damage or aging in the pipeline.

-Check if the pressure sensor and alarm are working properly, and set the alarm threshold (usually 10%~20% below the positive pressure value).

-Test the opening and closing function of the pressure relief valve to ensure there is no blockage.

2. Environmental assessment

-Confirm that there are no ignition sources such as open flames or static sparks in the sampling area, and detect the concentration of flammable gases in the environment (which should be below 10% of the lower explosive limit).

-Clean up the debris around the sampling point and reserve sufficient operating space.

3. Equipment preheating and blowing

-Activate the positive pressure device and introduce gas into the system for at least 5 minutes to replace residual air or impurity gases.

-Check the temperature of the pipeline (the heat tracing pipeline should reach the set value) to avoid sample condensation.

3、 Operation process

1. Activate the positive pressure system

-Slowly open the gas source valve and adjust the pressure to 0.02~0.05MPa (adjusted according to the characteristics of the sample).

-After observing the stable value of the pressure gauge, confirm that there is no leakage (which can be detected by soap water or electronic leak detector).

2. Connect the sampling container

-Connect the sampling bottle or collection bag to the system through a dedicated interface, paying attention to emptying the air at the interface.

-For liquid sampling, it is necessary to first eliminate the gas inside the pipeline; For gas sampling, it is necessary to control the flow rate to prevent turbulence.

3. Sampling process control

-Flow rate adjustment: Adjust the sampling flow rate (usually 0.5-5L/min) according to the properties of the sample to avoid pressure fluctuations caused by excessive speed.

-Continuous monitoring: Real time observation of pressure gauge and alarm status. If the pressure drops, sampling should be stopped immediately and leakage points should be checked.

-Multi level sampling: If multi-point sampling is required, the pipeline should be purged for at least 3 minutes before switching sampling points to prevent cross contamination.

4. End and shutdown

-Close the sampling container valve, stop the gas supply, and open the pressure relief valve to release the residual pressure in the system.

-Disassemble the sampling container, seal and store it, and label the sample information.

-Clean up residual samples in the pipeline, close all valves, and disconnect the power supply.

4、 Key precautions

1. Negative pressure operation is strictly prohibited

The core of a positive pressure system is to maintain an internal pressure higher than the external pressure. Any operation that causes negative pressure (such as rapid exhaust) may lead to the backflow of combustible gases from the external environment, posing a risk of explosion.

2. Regular calibration and maintenance

-Verify pressure sensors and alarms monthly to ensure accuracy error<± 5%.

-Replace the air source filter and sealing gasket every quarter, and check the corrosion of the pipeline.

-Conduct annual system airtightness testing (using helium mass spectrometer leak detector).

3. Handling of special working conditions

-High humidity environment: Add desiccants (such as silica gel) or heat tracing devices in the pipeline to prevent water vapor condensation.

-Corrosive medium: Use polytetrafluoroethylene (PTFE) coated pipelines or Hastelloy materials.

-High temperature sampling: equipped with cooling jacket or secondary cooling device to avoid pressure loss caused by gas volume expansion.

4. Personnel safety protection

-Operators are required to wear anti-static clothing, gas masks, and explosion-proof tools. It is prohibited to bring electronic devices such as mobile phones into the site.

-During the sampling process, two people need to work together and be equipped with a portable combustible gas detector to monitor the environment in real time.

5、 Common faults and emergency response

1. Sudden drop in pressure

-Reason: Pipeline rupture, seal failure, or pressure relief valve malfunction.

-Solution: Immediately stop sampling, turn off the gas source, evacuate personnel, and ventilate and replace the gas in the system.

2. Excessive pressure

-Reason: Blockage of pressure relief valve or malfunction of pressure regulating valve.

-Solution: Manually open the emergency exhaust port, check and clean the pressure relief valve.

3. Sample contamination

-Reason: Incomplete pipeline blowing or poor sealing.

-Disposal: Discard contaminated samples, re blow the pipeline and replace the seals.