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RequirementsForPositivePressureExplosion-ProofStructures|TechnicalSpecifications

Technical Specifications

Requirements For Positive Pressure Explosion-Proof Structures

1. Structural Materials

The enclosure of positive-pressure explosion-proof electrical equipment, known as a “positive-pressure enclosure,” typically uses steel or stainless steel. If plastic is used, its anti-static properties must also be considered.

explosion proof positive pressure cabinet

2. Structural Strength

The positive-pressure enclosure and its connected conduits must possess sufficient mechanical strength to withstand up to 1.5 times the maximum positive pressure without deforming or damaging. They must also withstand a minimum pressure of 200Pa.

3. Doors and Covers

Doors and covers of positive-pressure electrical equipment should be interlocked with the electrical circuit. Non-explosion-proof electrical components automatically cut off power when doors or covers are opened. Power cannot be restored until doors or covers are securely closed. For static positive-pressure equipment, opening doors and covers requires special tools, and the electrical enclosure must prominently display a warning sign: “Warning! Do not open in hazardous areas!”

4. Air Intake and Exhaust Port Location

The position depends on the relative density of the protective gas. When the relative density of the protective gas is >1, the air intake is located at the top of the enclosure, and the exhaust port at the bottom; when the relative density of the protective gas is

5. Enclosure Protection Level

Typically, the protection level of a positive-pressure enclosure is not less than IP5X, and in damp and dusty environments, not less than IP54.

6. Baffles

To ensure that the enclosure of positive-pressure explosion-proof electrical equipment is thoroughly purged, baffles are installed inside the positive-pressure enclosure.

7. Spark and Hot Particle Baffles

When the exhaust port of positive-pressure electrical equipment is in an explosive gas environment, spark and hot particle baffles are used to prevent hot particles and potential discharge sparks from escaping the enclosure and creating ignition sources. These baffles should cause the exhaust airflow to change direction by at least 8 times at 90° in its flow direction.

8. Electrical Clearance and Creepage Distances

Since the electrical insulation materials used in positive-pressure electrical equipment are the same as those in other types of explosion-proof electrical equipment, the electrical clearance and creepage distances are also the same.

9. Temperature Limitation

For px and py types: the combination of the highest surface temperature of the exterior of the enclosure and the highest surface temperature of the internal components is used for the equipment temperature classification. For pz type: the highest surface temperature of the exterior of the enclosure is used for the temperature classification.

10. Explosion Protection Type for Pressure Monitoring Automatic Safety Devices

Px type: “i,” “d,” “e,” “m,” “o,” “q” types.
Py and pa types: “i,” “d,” “e,” “m,” “o,” “q,” “nA,” “nC” types.

Moreover, before, during, and after the operation of the positive pressure protection system, various types of pressure monitoring automatic safety devices should provide reliable safety protection. Therefore, the power supply for the pressure monitoring automatic safety device should not share a power source with the main circuit and should be before the main circuit breaker.

11. Protective Gas

Clean air, nitrogen, and other inert gases are typically used as protective gases.

12. Temperature of the Protective Gas

The temperature of the protective gas at the air intake of the positive-pressure enclosure is around 40°C. The highest or lowest temperature should be marked on the positive-pressure electrical enclosure. Sometimes, condensation or freezing due to high or low temperatures, and the “breathing” effect caused by alternating temperature changes, need to be considered.

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