4.1 Design Unit Selection: The selection of a design unit for the liquefied petroleum gas storage tank system engineering shall be handled by the project organization department of the provincial (city, district) companies. The selection should be made from the shortlisted design institutes, and the supervisor's approval must be obtained after signing. The design unit should be qualified with petrochemical engineering design资质 and industrial pipeline (GC2) design资质. 4.2 Site Survey: 4.2.1 The site survey should be conducted by the project organization department of the provincial (city, district) companies, involving personnel from the construction, pipeline, quality safety departments of the branch company where the gas station is located, as well as the design institute. 4.2.2 The survey of the gas station should include understanding the layout and burial depth of the existing underground pipelines and cable laying. For stations that cannot provide site pipeline data, pipeline detection technology should be used to determine the existing process, electrical, and water supply and drainage pipelines. 4.2.3 The construction department of the branch company where the gas station is located shall propose suggestions for the scope and method of renovation (unloading vapor recovery system, refueling vapor recovery system [dispersed, centralized], oil and gas emission treatment unit], and related equipment facilities renovation, based on the principles of economy and practicality and relevant requirements of the local government. After approval from the supervisor and the project organization department of the provincial (city, district) company, the design unit shall carry out the design based on these proposals. 4.3 Design Proposal: 4.3.1 The design proposal submitted by the design institute should include general layout, oil vapor recovery process diagrams, and tables of main equipment and materials, among other technical documents. 4.3.2 The design proposal should be submitted to the project organization department of the provincial (city, district) company, which will then organize the pipeline, quality safety departments, and construction personnel of the branch company where the gas station is located, as well as the design institute, for proposal review, and the supervisor's approval shall be obtained. 4.4 Construction Drawing Design: 4.4.1 Equipment selection: The project organization department of the provincial (city, district) companies will provide a list of pre-qualified suppliers for vapor recovery equipment. The design institute will select the relevant equipment based on this list. Equipment selection should follow principles of safety, reliability, technical advancement, economic practicality, and compliance with emission standards, and should use products that are easy to install, convenient, and require minimal on-site modifications. Note the following: 4.4.1.2 It is preferable to choose equipment from the same manufacturer in the same area for ease of after-sales service. 4.4.1.2 Gas stations with an annual gasoline sales volume of over 3,000 tons and more than 10 gasoline guns should use centralized refueling vapor recovery systems; others should use dispersed systems. 4.4.1.3 Different types of vapor recovery technologies and equipment should be selected based on the internal space of the fuel dispenser. For example, a secondary recovery dispersed vacuum pump should use a lower power rating that can be driven by the existing power supply of the fuel dispenser, and it should not require additional power cable laying. 4.4.1.4 The oil and gas emission treatment unit should be selected based on the surrounding environment, site size, and business volume of the gas station. The maximum treatment capacity of the oil and gas emission treatment unit should be 10% to 20% of the maximum fuel volume. 4.4.2 Construction drawing design: 4.4.2.1 The design institute will carry out construction drawing design based on the approved design proposal. 4.4.2.2 The liquefied petroleum gas storage tank pipeline should use seamless steel pipes that comply with the current national standard GB/T8163 for fluid transmission. The design pressure of the oil pipeline should not be less than 0.6 MPa, and the design pressure of the oil vapor recovery pipeline should not be less than 0.13 MPa. It should not use thermoplastic plastic pipelines or other flexible material pipelines.

The diaphragm liquefied gas storage tank is mainly composed of an electric motor, base, crankcase, crank and connecting rod mechanism, cylinder components, oil and gas pipeline, electrical control system, and some accessories. It increases gas pressure through single or multi-stage compression to meet the customer's requirements for pressure, flow rate, temperature, and other process parameters. The electric motor drives the crank, connecting rod, and piston to propel hydraulic oil, which in turn drives the diaphragm. The vibration of the diaphragm compresses the medium. The diaphragm pressure machine is a special type of volumetric liquefied gas storage tank, with its working cylinder divided into two parts by a diaphragm. The upper part of the diaphragm is called the gas chamber, and the lower part is called the oil chamber. During operation, the piston moves upwards to drive the hydraulic oil, which then drives the diaphragm to expel the compressed medium outside the diaphragm cavity. The diaphragm liquefied gas storage tank compresses the gas by deforming the diaphragm. As the diaphragm moves, it must closely fit the cylinder head diaphragm cavity surface and have a small gap with the cylinder body diaphragm cavity surface. Through theoretical analysis and scientific selection of the diaphragm cavity curve radius, maximum deflection, and deflection index, a larger volume is ensured, allowing the diaphragm to work under approximately equal strength.

Liquefied gas storage tanks offer the following advantages and features:

1) The complete machine structure is reasonably designed, ensuring smooth and reliable operation with minimal vibration and noise, and ease of operation and maintenance. 2) The cylinder components feature a structure without an oiling disk, reducing assembly complexity; fewer sealing surfaces; and an alarm for compressed medium leakage, enhancing the overall reliability of the machine. 3) The new diaphragm cavity curve improves the volumetric efficiency of the liquefied gas storage tank, and extends the lifespan of vulnerable components like diaphragms and gas valves. 4) The built-in oil pump station provides a stable pressure, clean quality, and fully cooled lubricant for the liquefied gas storage tank and cylinder operation, also addressing the oil leakage issue of the original external storage tank. 5) A highly automated control system ensures the safe operation of the equipment. 6) The entire unit is mounted on a skid base for easy transportation, installation, and management.