4.1 Design Unit Selection: The selection of a design unit for the liquefied petroleum gas storage tank system engineering shall be responsible by the project organization department of the provincial (city, district) companies. It should be chosen from the list of design institutes shortlisted in the sector, and the supervisor's signature of approval is required. 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, organizing the construction, pipeline, quality safety departments, and design institute personnel from the branch office located at the gas station site. 4.2.2 For the research and survey of the gas station, it should be understood the existing internal underground pipeline routes, cable laying directions, and burial depths. 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 office at the gas station site, in accordance with the principles of economy and practicality and relevant local government requirements, should propose suggestions for the scope and methods of renovation (unloading oil vapor recovery system, refueling oil vapor recovery system [dispersed, centralized], and oil and gas emission treatment facilities), and related equipment and facility renovations. After approval by the supervisor and the project organization department of the provincial (city, district) company, the design unit shall base the design on these proposals. 4.3 Design Proposal: 4.3.1 The design proposal submitted by the design institute should include technical documents such as general layout, oil vapor recovery process diagrams, and lists of main equipment and materials. 4.3.2 The design proposal should be submitted to the project organization department of the provincial (city, district) company, which will organize the pipeline, quality safety departments, construction personnel from the branch office at the gas station site, and the design institute for proposal review, and then report for the supervisor's approval. 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 oil vapor recovery equipment. The design institute will select the relevant equipment based on this list. Equipment selection should follow the principles of safety, reliability, technical advancement, economic practicality, and compliance with emission standards, and use products that are easy to install, convenient, and have minimal on-site modification. 4.4.1.2 It is advisable to select equipment from the same manufacturer in the same region 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 oil vapor recovery systems; others should use dispersed systems. 4.4.1.3 Different types of oil vapor recovery technology 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 smaller power, 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 facilities should be selected based on the surrounding environment, site size, and business volume of the gas station. The maximum oil and gas treatment capacity of the emission treatment facilities 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 pipelines should be made of seamless steel pipes that comply with the current national standard GB/T8163 for fluid conveyance. The design pressure for oil pipelines should not be less than 0.6 MPa, and the design pressure for oil vapor recovery pipelines should not be less than 0.13 MPa. Flexible materials such as thermoplastic plastic pipelines should not be used.

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 pipelines, electrical control system, and some accessories. It increases gas pressure through single or multi-stage compression to meet customers' 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 whole machine has a rational structure design, operates smoothly and reliably with minimal vibration and low noise, and is easy to operate and maintain. 2) The cylinder components use a structure without an oil distribution plate, reducing assembly difficulty and the number of sealing surfaces; alarms are triggered when the compressed medium leaks, enhancing the machine's reliability. 3) The new diaphragm cavity curve improves the volumetric efficiency of the liquefied gas storage tank and extends the lifespan of the vulnerable diaphragm and gas valve. 4) The built-in oil pump station provides a stable pressure, clean quality, and well-cooled lubricant for the liquefied gas storage tank and cylinder operation, and also addresses the oil leakage issue of the original external liquefied gas 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, facilitating transportation, installation, and management of the equipment.