GB/T 20735-2025Pressure regulators of CNG vehicles (English PDF)

3.1 Nominal working pressure; P1

The maximum allowable pressure at the inlet when the pressure regulator is working normally.

3.2 Lock-up pressure; PL

The maximum stable outlet pressure of the pressure regulator when the flow rate is zero within the allowable inlet pressure range.

3.3 Maximum flow rate; Q

The ambient temperature is 20°C±5°C, the input pressure of the pressure regulator is P1, and the upper limit of the flow rate that can be achieved when the deviation is within the specified range under a given outlet pressure.

3.4 Safety valve open pressure; P2

The pressure when the pressure relief valve is initially opened.

3.5 Safety valve emission pressure; PRV

The lower limit of pressure at which the pressure relief valve is fully open.

3.6 Safety valve emission flow; QRV

The emission flow rate at which the pressure relief valve is fully open.

4.1 General

4.1.1 The materials of the pressure regulator in contact with natural gas shall be compatible with natural gas.

4.1.2 The pressure regulator should be heated by circulating engine coolant. The material of the heating pipes of the pressure regulator shall be compatible with the engine coolant.

4.1.3 The surface of the pressure regulator, connecting threads, and inlet and outlet sealing surfaces shall be free from dents, scratches, rust, cracks, burrs, and dirt.

4.1.4 The markings on the valve body surface of the pressure regulator shall be clearly visible.

4.2 Performance requirements

4.2.1 Hydrostatic strength

After undergoing the hydrostatic strength test according to the test method specified in 5.2, the pressure regulator shall not exhibit cracking, permanent deformation, or other similar phenomena.

4.2.2 Pressure relief valve performance

The pressure regulator shall be equipped with the pressure relief valve, which shall continue to function normally after pressure is released. After the pressure relief valve is tested according to the test method specified in 5.3, its performance shall meet the following requirements:

a) No leakage occurs when the inlet pressure is 95% of P2;

b) It can release air when the inlet pressure is 105% of P2;

c) After 600 pressure relief tests, it still meets the requirements of a) and b);

d) The safety valve emission flow QRV is no less than the measured value of the maximum flow rate Q of the pressure regulator.

4.2.3 Leakage

4.2.3.1 When the pressure regulator is tested for leakage according to the test method specified in 5.4.1, if no bubbles appear within the specified time, the sample shall pass the test. If bubbles are detected, its leakage rate shall be <=15 x 10^-6 m³/h (standard conditions).

4.2.3.2 When the pressure regulator is tested for lock-up pressure according to the test method in 5.4.5, the final value of PL within the specified time shall not exceed 20% of the initial value.

4.2.4 Maximum flow rate

The flow rate Q of the pressure regulator, measured according to the test method specified in 5.5, shall be no less than the manufacturer's specified value.

4.2.5 Cycle life

After undergoing a cycle life test according to the test method specified in 5.6, the pressure regulator shall meet the requirements of 4.2.1, 4.2.3, and 4.2.4.

4.2.6 Corrosion resistance

After the pressure regulator undergoes a salt spray test according to the test method specified in 5.7.1, the metal plating shall not be damaged or peeled off and shall comply with the provisions of 4.2.3.

For brass pressure-bearing components with a zinc content higher than 15%, after testing according to the test method specified in 5.7.2, inspection with a 25× magnifying glass shall show no cracks.

4.2.7 Ozone resistance

After the non-metallic components of the pressure regulator in contact with natural gas undergo an ozone resistance test according to the test method specified in 5.8, no cracks shall appear.

4.2.8 Compatibility

After the non-metallic components of the pressure regulator undergo a compatibility test according to the test method specified in 5.9, the volume change rate shall not exceed 20%, and the mass change rate shall not exceed 5%.

4.2.9 Vibration resistance

After testing according to the test method specified in 5.10, the pressure regulator shall meet the requirements of 4.2.3.

4.2.10 Dry heat resistance

After the non-metallic components of the pressure regulator in contact with natural gas are tested for dry heat resistance according to the test method specified in 5.11, the change in tensile strength shall not exceed 25%, and the elongation shall be -30% to 10%.

4.2.11 Electrical performance

4.2.11.1 Insulation resistance

The insulation resistance of the pressure reducing regulator is tested according to the test method specified in 5.12.1, and the resistance value shall be >=240 kohm.

4.2.11.2 Minimum opening voltage

When the minimum opening voltage of the pressure regulator solenoid valve is tested according to the test method specified in 5.12.2, the solenoid valve shall be able to open normally. For a 12 V system, the minimum opening voltage of the pressure regulator solenoid valve shall be <=8 V; for a 24 V system, it shall be <=16 V.

4.2.11.3 Overvoltage

After the pressure regulator undergoes an overvoltage test according to the test method specified in 5.12.3, all electrical components, or components containing electrical sub-components, shall function normally.

4.2.12 Water jacket

After the pressure regulator undergoes a water jacket test according to the test method specified in 5.13, it shall meet the requirements of 4.2.3.

4.2.13 Bending moment

After the pressure regulator is tested according to the test method specified in 5.14, the components shall function normally without cracking or leaking.

4.2.14 Torque

After the pressure regulator is tested according to the test method specified in 5.15, the threaded connections shall withstand at least 1.5 times the manufacturer-specified installation torque value without deformation, breakage, or leakage.

5.1 General

5.1.1 Test conditions

Unless otherwise specified, the test shall be conducted under the following conditions:

a) Ambient temperature of the test. 20 °C ± 5 °C;

b) Test gas. clean, dry air, nitrogen, or a nitrogen-helium mixture. Natural gas may also be used if appropriate safety measures are taken;

c) Test liquid. clean water or a non-corrosive liquid;

d) Maximum deviation range for all pressures. ±5%; maximum deviation range for all dimensions. ±5%.

5.1.2 Test instruments

The test instruments shall meet the following requirements:

a) Pressure gauges. Accuracy no lower than Class 1.5, measuring range 1.5 to 3 times the measured value;

b) Flow meters. Accuracy no lower than Class 1.5, measuring range 1.5 to 3 times the measured value;

c) Temperature instruments. Accuracy is ±0.5 °C, minimum resolution no greater than twice the accuracy (i.e., 1°C).

5.2 Hydrostatic strength test

Remove the pressure relief valve of the pressure regulator and seal it. Block the outlet of the pressure regulator. Apply a hydrostatic pressure of 2.5 times P2 to the inlet and maintain it for at least 3 min. Then check the pressure regulator.

NOTE: Components that have undergone this test will no longer be used.

5.3 Pressure relief valve performance test

The test of pressure relief valve of the pressure regulator can be performed on the pressure regulator or separately. The inlet diameter of the air source shall be no less than the inlet […]