GB/T 17926-2022Compressed natural gas cylinder valves for vehicles (English PDF)

3.1 Excess flow device

a device that can act and limit the gas flow when the gas flow or the pressure difference between the inlet and outlet exceeds the set value

4.4 Model indication method

The valve model shall consist of the following parts.

The code of the compressed natural gas cylinder valve for vehicles is represented by "CTF".

5.1 Design requirements

5.1.1 The connection thread specification of the air inlet of the valve shall be PZ27.8 taper thread or M25×2 ordinary thread.

5.1.5 The excess flow device shall be designed with a bypass channel.

5.1.6 The valve shall specify the design service life. Valves are designed for at least one cylinder inspection cycle.

5.2 Material requirements

5.2.1 Metal part material

5.2.2 Non-metallic seal material

5.2.2.1 Oxygen aging resistance

The non-metallic seals shall be kept for 96h continuously in oxygen with a temperature of 70°C±5°C, a test pressure of 2MPa and a purity of >=99.5%, and there shall be no visible cracks and damages.

5.3 Process requirements

5.3.1 The valve body shall be forged. There shall be no defects such as cracks, wrinkles, inclusions, porosity, shrinkage holes, and underfills on the surface that would impair valve performance. When the shot blasting process is used on the surface of the valve body, the size and depth of the pits on the surface shall be uniform.

5.4 Performance requirements

5.4.1 Valve performance

5.4.1.1 Open and close

At the nominal working pressure, the valve shall be able to fully open and close according to the temperature and test torque specified in Table 1.

5.4.1.2 Excess torque resistance

The threads connecting the inlet and outlet of the valve to external parts shall bear the following excess torque.

5.4.2 Safety pressure relief device performance

5.4.2.1 Extrusion resistance

After holding the pressure for 30 minutes at 1.2 times the nominal working pressure, increase the pressure to 2.25 times the nominal working pressure at a rate of 0.5MPa/s, and the fusible alloy of PRD shall not be extruded.

5.4.3.2 Pressure pulse

Apply the nominal working pressure to the air inlet and air outlet of the excess flow device respectively and perform 100 pulses each, which shall meet the requirements of 5.4.3.3.

5.4.3.3 Flow limiting

When the pressure difference between the two ends of the inlet and outlet of the excess flow device exceeds 0.65 MPa, the excess flow device shall be able to act and restrict the flow. When the pressure difference reaches 10MPa, the bypass flow of the excess flow device shall not be greater than 0.05m³/min (under the standard state).

6.1 Test conditions

6.1.1 Test environment

Unless otherwise specified, the tests specified in this document are carried out at an ambient temperature of 15°C~30°C.

6.1.4 Test flowmeters and pressure gauges

The accuracy of the test flowmeter is 0.5. The accuracy of the pressure gauge shall not be lower than level 1.6. The range of the pressure gauge shall be 1.5 to 2 times the test pressure.

6.2 Mechanical properties test and chemical composition analysis of metal parts materials

6.3 Material performance test of non-metallic seals

6.3.1 Oxygen aging resistance test

Place 3 non-metallic seal test pieces in the aging test device. Remove air from the device.

Fill with oxygen with a purity of >=99.5%. Make the pressure reach 2MPa. Warm up to 70°C±5°C. Keep 96h and take out. Visually inspect its changes, which shall meet the requirements of 5.2.2.1.

6.3.4 Medium compatibility test

6.4 Valve body appearance inspection

The appearance of the valve body shall be checked by visual inspection, which shall meet the requirements of 5.3.1 and 8.1.1.

6.5 Inlet and outlet thread inspection

The connection thread of the air inlet of the valve shall be checked with a gauge manufactured in accordance with GB/T 8336 or GB/T 3934. It shall comply with the provisions of 5.3.2.

6.6 Valve performance test

6.6.1 Opening-closing test

6.6.1.1 Opening-closing test at room temperature

Install the valve on the test special device. Keep the valve closed. Charge the air source from the valve air inlet to the nominal working pressure. Block the air outlet. Open the valve according to the torque specified in Table 1.

6.6.1.2 Opening-closing test at low temperature

Install the valve on the test special device. Place in a temperature-controlled box at -40°C. Keep the valve closed. Charge the air source from the valve air inlet to the nominal working pressure. Block the air outlet. Open the valve according to the torque specified in Table 1. The valve shall be able to open fully. Then close the valve according to the torque specified in Table 1. The valve shall be able to close and comply with the provisions of 5.4.1.1.

6.6.2 Excess torque resistance test

Use a nut or plug to screw the air outlet of the valve. Then tighten the nut or plug with 150% of the installation torque, respectively. The applied torque shall be maintained for more than 15min. Then remove the nut or plug.

6.6.4 Air tightness test

6.6.4.1 Type test air tightness

6.6.5 Vibration resistance test

Install the valve on the test special device. Block the air outlet. Open the valve. Fill the valve with air source to the nominal working pressure.

6.6.7 Stress corrosion resistance test

Pour ammonia water with a relative density of 0.94 (specific gravity) into a glass container with a lid. The ratio of the added ammonia water to the container volume is 21.2 ml/L (for example, 636mL of ammonia water is added to a 30L glass container).

6.8 Excess flow device performance test

6.8.3 Flow limiting test

Install the valve with the excess flow device on the test special device. Access with air source. When the pressure difference of the incoming gas exceeds 0.65 MPa, the excess flow device shall be able to act and restrict the flow.

7.1 Enter-factory inspection of materials and parts

7.1.1 There shall be a batch product quality certificate for the materials and parts when they enter the factory.

7.1.2 The mechanical properties and chemical composition of metal raw materials shall be re-examined according to the batch number of the factory entered, which shall comply with the provisions of 5.2.1.1.

7.2 Enter-factory inspection

7.2.1 Inspection one by one

Valves shall be inspected one by one before leaving the factory. The inspection items are specified in Table 4. During the inspection process, if one item fails, the valve shall be rejected.

7.2.2 Batch inspection

The batch inspection of valves shall be selected from the continuously produced products that have passed the inspection one by one in each batch (shall not exceed 5000 pieces).

7.3 Type test

7.3.1 Type test principles

7.3.1.1 The valve shall be type-tested by an inspection agency with type-test qualifications in accordance with the relevant regulations and technical specifications.

7.3.1.2 When the material and sealing structure of the valve are the same, the type test can be carried out according to the following principles.

7.3.1.3 Valves that have been type-tested in accordance with 7.3.1.2 may be type-tested according to the following principles when their local design conditions change.

7.3.2 Documents provided by type test

The manufacturer shall provide the following technical documents during the type test.

7.3.3 Type test items

The type test items of the valve are shown in Table 5.

7.3.4 Random inspection method and determination

Valves for type test shall be extracted from products that have passed the exit-factory inspection.

8.1 Marks

8.1.1 The valve shall have the following permanent marks.

8.1.2 The valve shall carry an electronic certificate in the form of a QR code and shall contain at least the following contents. […]

8.2 Packaging

8.2.1 Moisture remaining in the valve shall be removed before packaging. Keep the valve clean when packing. Inlet and outlet threads are not damaged. Packing list, user manual and batch product quality certificate shall be attached in the packing box.

8.2.2 There shall be the following signs on the packing box.

8.2.3 The packing list shall indicate the following.

8.2.4 User manual shall include the following.

8.2.5 The batch product quality certificate shall indicate the following contents. […]

8.3 Storage

The valve shall be placed in a ventilated, dry and clean room to prevent moisture and chemical erosion. When transporting, loading and unloading, it shall be handled lightly to prevent heavy pressure, drop and collision. […]