Clean room light leakage detection and air leakage measurement method

A.1 clean room leakage detection

A.1.1 leak detection is A method to detect the tightness of the air duct of the system by using the strong penetration of light into the holes.

A.1.2 A safe light source with certain intensity shall be used for testing. Hand-held mobile light source can be used not less than 100W with a protective cover of low-voltage lights, or other low-voltage light source.

A.1.3 when detecting the light leakage in the air duct of the system, the light source can be placed on the inside or outside of the air duct, but the opposite side should be dark environment. The detection light source should be moved slowly along the interface and joints to be detected and observed on the other side. When light is detected, it indicates that the obvious air leakage has been detected and should be recorded.

A.1.4 the method of segmenting detection and summarizing analysis should be adopted for the detection of the air duct of the system. On the basis of strict installation quality management, the main duct and main duct are mainly tested. When light leakage method is adopted to detect the tightness of the system, the air ducts of the low-pressure system are qualified with no more than 2 light leakage points per 10m joints and no more than 16 100m joints on average. For every 10m joints of air duct of medium pressure system, the light leakage point is no more than 1, and the average of 100m joints is no more than 8, which is qualified.

A.1.5 the slit leakage found in the light leakage detection shall be sealed.

A.2 test equipment

A.2.1 the air leakage volume shall be tested with A special measuring instrument that has passed the inspection, or with A measuring device built with measuring elements in line with the current national standard "flow measurement throttling device".

A.2.2 the air leakage volume testing device can adopt the air duct type or the air chamber type. Air duct test device adopts orifice plate as measuring element; The air chamber type test device USES the nozzle as the measuring element.

A.2.3 the wind pressure and air volume of the air leakage testing device shall be selected to be 1.2 times greater than the specified test pressure and maximum allowable air leakage of the measured system or equipment respectively.

A.2.4 the adjustment of the test pressure of the air leakage measurement device can be made by adjusting the speed of the fan or by controlling the opening degree of the throttling device. The amount of air leakage must be measured under the condition that the system maintains steady pressure after adjustment.

A.2.5 the differential pressure of the air leakage measuring device shall be determined by A micromanometer with A minimum reading partition not greater than 2.0Pa.

A.2.6 duct type air leakage measurement device:

1. The duct type air leakage measurement device is composed of fan, connected duct, pressure measuring instrument, rectifier gate, throttle and standard orifice plate.

2. The device adopts the standard orifice plate with angular connection for taking pressure. The value range of orifice plate is 0.22~0.7(=d/ d); The distance between the orifice plate and the front and rear rectifying gate and the straight pipe section outside the rectifying gate shall be more than 10 times and 5 times of the circular pipe diameter D, respectively.

3. The connected air ducts of the device are smooth and round. The allowable deviation of roundness from orifice plate to upstream 2D is 0.3%. Downstream is 2%.

4. The orifice plate is connected with the air duct, and the allowable deviation of the perpendicularity between the front end and the pipe axis is 1°; The allowable deviation of concentricity between orifice plate and air duct is 0.015d.

5. After the first rectifier gate, all connection parts shall be tight and leakproof.

6. The relationship between the flow coefficient of the orifice plate and the flow coefficient of the orifice plate shall be determined. The applicable scope shall meet the following conditions.

105 < Re < 2.0 x 106

< 0.05 beta 0.49 or less

50 mm < D 1000 mm or less

When the Reynolds number is less than 105, the flow coefficient should be obtained according to the current national standard flow measurement throttling device.

8. The expansion coefficient of the air stream on the orifice plate is obtained.

9. When testing the amount of air leakage under the condition of negative pressure of the system or equipment, the device connection shall meet the requirements.

A.2.7 air chamber type air leakage measurement device:

1. The air chamber type air leakage volume testing device is composed of fan, connected air duct, pressure measuring instrument, flow balancing plate, throttle, air chamber, baffle and nozzle.

2. The test device adopts standard long-strength nozzle. Nozzles must be installed on the baffle as required, and the number may be one or more. The center distance between two nozzles shall not be less than 3 times the diameter of the throat of the larger nozzle. The distance from the center of any nozzle to the nearest side wall of the air chamber shall not be less than 1.5 times the diameter of the throat of the nozzle.

3. The sectional area of the air chamber shall not be less than the fault area when the measured air volume is less than 0.75m/s according to the average sectional velocity. The installation position of the uniform flow plate (perforated plate) in the air chamber shall comply with the regulations.

4. The static pressure interface at both ends of the nozzle in the air chamber shall be multiple and distributed on the four walls. The distance between the static pressure outlet and the nozzle baffle shall not be greater than 1.5 times the diameter of the minimum nozzle throat. Then, and combined into a static pressure ring, and then connected with the pressure measuring instrument.

5.When measuring the amount of air leakage with this device, the flow velocity through the throat of the nozzle should be controlled within the range of 15~35m/s.

6. This device requires that all connections behind the nozzle baffle in the air chamber should be tight and leakproof.

7. When testing the air leakage under the condition of negative pressure of the system or equipment, the device connection shall comply with the requirements.

A.3. Air leakage measurement

A.3.1 there are two types of air leakage tests: positive pressure test and negative pressure test for the air duct and equipment of positive pressure or negative pressure system. Generally, it can be tested by the test under the condition of positive pressure.

A.3.2 the air leakage volume test of the system can be conducted as A whole or in sections. During the test, all openings of the system under test shall be closed without air leakage.

A.3.3 when the air leakage of the system under test exceeds the design and the provisions of this code, the air leakage location (can be heard, touched, observed, water or smoke leakage detection) shall be detected and marked; After the repair is completed, retest until qualified.

A.3.4 the measured value of air leakage shall generally be the measured value under the specified test pressure. Under special conditions, it can also be replaced by a test that is similar to or greater than the specified pressure, and the amount of air leakage can be converted according to the following formula:

0.65 Q0 = Q (P0 / P)

Where, P0 -- specified test pressure, 500Pa;

Q0 -- -- air leakage under specified test pressure {m3/(h·㎡)};

P -- air duct working pressure (Pa);

Q -- air leakage under working pressure {m3/(h·㎡)}.

B.1. Measurement of air volume or wind speed

B.1.1 for one-way flow clean rooms, the volume of air supply is determined by the product of the average velocity of the chamber section and the cross-sectional area. The section perpendicular to the airflow 0.3m from the hepa filter is used as the sampling test section. The distance between measuring points on the section should not be greater than 0.6m, and the number of measuring points should not be less than 5.

B.1.2. For the clean room with non-one-way flow, the tuyere method or air duct method is adopted to determine the air volume, as follows:

1. The tuyere method is to measure at the air inlet where the hepa filter is installed and connect the auxiliary air duct at the beginning of the tuyere. It is made of galvanized steel sheet or other non-dust producing material, which is the same as the beginning and the inner section of the tuyere, and the length is equal to 2 times the length of the tuyere. On the outlet plane of the auxiliary air duct, at least 6 measuring points are arranged evenly, and the wind speed of each measuring point is measured by hot-ball anemometer. Then, the measured air volume is obtained by multiplying the average wind speed of the tuyere section obtained by the net cross-sectional area of the tuyere.

2. When there is a long branch section on the windward side of the tuyere, and the air volume can be determined by the air duct method when the hole has been drilled or can be drilled. The measuring section shall be located at the position greater than or equal to 3 times the pipe diameter or the long side length in front of the local resistance component and 5 times the pipe diameter or the long side length in back of the local resistance component.

For rectangular duct, the measured section is divided into several equal sections. Each small section should be as close to the square as possible, the side length should not be greater than 200mm, the measuring point should be located in the center of the small section, but the number of measuring points on the whole section should not be less than 3.

For the circular wind pipe, the section should be divided into several concentric rings with the same area according to the diameter of the pipe, and each ring should measure 4 points. Determine the number of rings according to the pipe diameter, not less than 3.

B.2. Measurement of static pressure difference in clean room

B.2.1 the measurement of static pressure difference shall be made in the condition that all doors are closed, from high pressure to low pressure, starting from the inner room farthest from the outside on the plane layout, and then outward in turn.

B.2.2 the sensitivity of the differential pressure gauge shall not be lower than 2.0Pa.

B.2.3 there should be a reasonable flow of air at the entrance of the clean room of different grades with holes connected to each other. When the average wind speed at the mouth of the cave is greater than or equal to 0.2m/s, it can be detected by hot-ball anemometer.