A pressure vessel is the group of sealed pressure-rated components used to hold and regulate refrigerant in an industrial refrigeration system: the high-pressure receiver, the liquid separator, the oil separator and the intercooler. These components directly determine operating safety, compressor life and the energy efficiency of the whole refrigeration cycle.
Tan Long designs and manufactures pressure vessels to TCVN 8366:2010 and ASME, serving NH3, Freon and CO2 systems for seafood, food and beverage plants and large-scale cold stores. With more than 20 years of experience and full turnkey D&B capability, every unit comes with technical documentation, CO/CQ certification and support through safety inspection before it goes into service.
What is a pressure vessel? Operating principle and technical standards
In industrial refrigeration systems, a pressure vessel is a purpose-built sealed unit that holds refrigerant at above atmospheric pressure. It is not a single device but a group of key refrigerant storage and handling components that keep the whole operating cycle stable.
In principle, each type of pressure vessel sits at a defined point in the cycle to do one job: controlling flow, separating refrigerant phases and protecting the compressor pack from liquid slugging. That keeps suction pressure stable and minimises sudden shutdowns.
Under technical regulations such as TCVN 8366:2010 and QCVN 01:2008/BLĐTBXH, every pressure vessel used in cold storage installation must meet strict safety requirements from design through to manufacture. The critical factors are the use of high-pressure-rated steel, ultrasonically verified weld construction, and a matched set of protective fittings such as safety valves, accurate pressure gauges and a scheduled bottom drain line.
Which industries use pressure vessels?
Pressure vessels appear in almost every industrial refrigeration line with circulating refrigerant. These are the sectors Tan Long serves most often:
- Seafood processing: large two-stage NH3 systems, requiring a low-pressure receiver with an oil recovery sump and a float valve set to protect the liquid level.
- Food and agricultural processing: combining a high-pressure receiver with the compressor and condenser pack serving storage rooms and IQF freezer conveyor.
- Beverage and dairy: Freon or glycol systems, favouring a baffle-cone oil separator to protect the compressor in continuous duty.
- Commercial cold storage and logistics: standard liquid separators for R22 and R404A systems in distribution warehouses and cold chain hubs.
- Pharmaceutical and chemical plants: requiring complete inspection documentation and materials suited to corrosive environments.
Common types of industrial pressure vessel
The standard pressure vessel range at Tan Long comprises the high-pressure receiver, the low-pressure receiver (liquid separator), the oil separator and the intercooler. Each has a defined place in the refrigeration cycle. The table below summarises the suitable refrigerants and typical applications of each type:
| Pressure vessel type | Suitable refrigerants | Typical applications |
| Baffle-cone oil separator | NH₃, R22, R404A, R507 | Used in medium and large industrial refrigeration systems. |
| High pressure tank | NH₃, Freon | Applied to cold stores and high-capacity compressor and condenser packs. |
| Low-pressure receiver (liquid separator) | NH₃, CO₂ | Suited to two-stage systems or systems using pumped liquid circulation. |
| Intermediate tank | NH₃ | An essential component in large two-stage compression systems. |
| Standard O&F liquid separator | R22, R404A | A solution for commercial cold stores and HVAC systems at processing plants. |
Depending on the project, our engineering team will advise on the pressure vessel type, material and connection standard that best fits. You are welcome to contact Tan Long's engineering team for detailed specifications of each pressure vessel range.
The function of each pressure vessel type in the refrigeration cycle
In a complete refrigeration cycle, each pressure vessel is installed at a strategic point to keep the system stable and performing at its best. Understanding what each one does helps the investor and the technical team diagnose faults faster and more accurately, from compressor oil flooding to abnormal suction pressure.
| Pressure vessel type | Position in the cycle | Main functions |
| Oil separator | After the compressor, before the condenser | Separates lubricating oil carried in the discharge gas so that oil can be returned to the refrigeration compressor. |
| High pressure tank | After the condenser | Stores liquid refrigerant at high pressure and regulates a steady liquid feed to the whole system. |
| Liquid separator | Before the compressor, after the evaporator | Separates all liquid refrigerant from the suction vapour, protecting the compressor from dangerous liquid slugging. |
| Intermediate tank | Between the two compression stages (for two-stage systems) | Cools the refrigerant vapour at intermediate pressure and performs effective intermediate liquid separation. |
To guarantee safety, these units must be designed and built by a company with genuine specialist capability. You can also look through the projects Tan Long has delivered to get a clearer picture of the right solution for your plant.
Construction of a pressure vessel system to technical standard
For the system to reach peak efficiency, the operating engineering team must understand the construction and principle of each pressure vessel type.
Oil separator
The oil separator is the pressure vessel installed immediately after the discharge of the refrigeration compressor unit. Refrigerant vapour leaving the compressor carries lubricating oil droplets at high velocity, between 18 and 25 m/s.
On entering the vessel the gas stream turns through 90 degrees, so its velocity drops abruptly to about 0.5 to 1.0 m/s. The oil, being heavier than the gas, loses momentum and falls to the bottom of the vessel, while clean gas continues on to the condenser. In large industrial systems using NH₃ or Freon, the baffle-cone type is the most common, thanks to its robust cylindrical shell and dedicated bottom oil drain valve.
High-pressure receiver
This unit receives liquid refrigerant from the condenser, stores it temporarily and supplies a steady liquid feed to the expansion valve. It is the pressure vessel that has to withstand the highest working pressure, usually above the compressor discharge pressure.
In construction, the liquid inlet sits on the upper part of the shell and the outlet at the bottom. A particular feature of Tan Long's design is that the liquid outlet always stands a set distance above the bottom, preventing sediment or metal particles being drawn into the refrigeration cycle. In single-stage systems, although the condenser can double as a liquid receiver, fitting a separate high-pressure receiver remains the better solution for keeping liquid refrigerant temperature stable.
Liquid separator, or low-pressure receiver
Installed on the suction line before the refrigerant reaches the compressor, the liquid separator is the pressure vessel that acts as the system's shield. Because a compressor can only compress vapour, any liquid refrigerant reaching the compression chamber causes liquid slugging and immediate damage.
Because it works at very low temperature, this type of pressure vessel needs dedicated polyurethane insulation 150 to 200 mm thick. On two-stage NH3 refrigerationprojects it also stores liquid refrigerant for the circulation pump. Its construction, with an oil recovery sump below and a three float valve set protecting the liquid level (maximum, medium, minimum), keeps the whole production line safely under control.
Refrigerants and pressure vessel materials: NH3, Freon, CO2
The refrigerant choice directly determines the material, the fittings and how design pressure is calculated. This has to be settled at the design stage; it cannot be changed once the vessel is built:
- NH₃ (R717): corrodes copper and copper alloys, so the shell, pipework, valves and fittings must all be in dedicated steel. This is the main refrigerant for large-capacity systems at seafood processing plants.
- Freon (R22, R404A, R507): has no material constraint of the kind NH₃ imposes, suiting commercial cold stores and HVAC systems at processing plants.
- CO₂ (R744): works at significantly higher pressure, which imposes stricter requirements on shell thickness and weld construction.
- Insulation: vessels working at sub-zero temperature need 150 to 200 mm of polyurethane to prevent heat loss and condensation, which would corrode the shell from the outside.
Design, manufacturing and inspection standards for pressure vessels
At Tan Long, safety comes first in every design and installation solution. Every pressure vessel we supply meets the applicable Vietnamese and international standards in full, giving the investor complete confidence throughout cold store operation.
Specifically, these units are manufactured and inspected against the following demanding standards:
- TCVN 8366:2010: The standard for pressure vessels setting out design and manufacturing requirements in detail. It covers material selection, calculation of shell thickness against internal and external pressure, and control of thermal stress and pipework loads.
- QCVN 01:2008/BLDTBXH: The national technical regulation on occupational safety for boilers and pressure vessels.
- TCVN 6155:1996 and TCVN 6156:1996: The standards setting out technical requirements for the installation, use and repair of pressure vessel.
- TCVN 6008:2010: Requirements and inspection methods for welds on pressure equipment.
Under Circular 36/2019/TT-BLĐTBXH, every pressure vessel operating in an industrial refrigeration system is subject to mandatory technical safety inspection before it is put into service. Keeping to the inspection cycle is not only a legal obligation; it protects both equipment and people:
- Normal cycle: Periodic inspection once every 3 years.
- Special cases: For the lines pressure vessel for vessels holding a corrosive refrigerant that have been in service more than 12 years, or equipment more than 24 years old, the inspection cycle shortens to once a year for maximum safety.
Key points in operating and maintaining pressure vessels
Operating a pressure vessel to the correct procedure extends the life of the whole industrial refrigeration system and is decisive in preventing occupational safety incidents. At Tan Long we recommend that technicians check the following critical items on a regular schedule:
- Bottom draining and scheduled cleaning: For the lines pressure vessel for vessels such as the oil separator and the high-pressure receiver, accumulated oil and sediment should be drained every 4 to 8 hours during operation. One important safety point: the technician should bring the vessel pressure down to atmospheric before draining oil, to avoid incidents caused by high pressure.
- Liquid level control on the low-pressure receiver: The three float valve set protecting the liquid level in the pressure vessel low-pressure vessel must be watched closely. If the liquid level is too high there is a risk of liquid flooding, which directly damages the refrigeration compressor. If the level is too low the liquid feed pump runs unstably, affecting the cooling capacity of the cold storage.
- Checking pressure gauges and safety valves: The safety valve fitted on the pressure vessel must be able to relieve pressure automatically the moment internal pressure exceeds the design limit. Under TCVN 6153:1996, for systems fitted with a rupture disc the parameters must be calculated so that when the disc bursts, pressure in the vessel does not rise more than 25% above the rated working pressure.
- Maintaining the polyurethane insulation: Lines pressure vessel vessels working at sub-zero temperature (the low-pressure receiver) need standard-compliant polyurethane insulation and regular surface inspection. Damage to this protective layer not only causes serious heat loss but also allows condensation, leading to chemical corrosion of the shell from the outside and creating a hazard.
How Tan Long advises on and manufactures pressure vessels
Because it controls both the manufacturing technology and the D&B (design and build) process, Tan Long delivers everything from survey to handover, so the investor does not have to deal with several parties:
- Survey and requirement definition: engineers work directly at the plant to establish the refrigerant, system capacity, installation position and site constraints.
- Calculation and design: selecting materials, calculating shell thickness against internal and external pressure, and controlling thermal stress and pipework loads to TCVN 8366:2010.
- Manufacture at the factory: machining the shell, welding and inspecting the welds to TCVN 6008:2010.
- Fitting protective accessories: safety valves, pressure gauges, bottom drain line and, on low-pressure vessels, the float valve set protecting the liquid level.
- Support through safety inspection: preparing technical documentation and CO/CQ certificates and working with the inspection body before the equipment enters service.
- Handover and operational training: handing over the draining procedure, safety valve checks and insulation maintenance to the plant's technical team.
Latest pressure vessel manufacturing price guide
The unit price for manufacturing a pressure vessel depends on the type, the refrigerant, the design pressure, the volume and the insulation requirement. Because each unit is designed specifically for the system configuration, Tan Long quotes project by project:
| Pressure vessel range | Suitable refrigerants | Insulation requirement | Applicable standard | Reference price |
|---|---|---|---|---|
| Baffle-cone oil separator | NH₃, R22, R404A, R507 | Not required | TCVN 8366:2010 / ASME | Contact us for a quote. |
| High pressure tank | NH₃, Freon | Not required | TCVN 8366:2010 / ASME | Contact us for a quote. |
| Low-pressure receiver (liquid separator) | NH₃, CO₂ | Polyurethane 150–200 mm | TCVN 8366:2010 / ASME | Contact us for a quote. |
| Intermediate tank | NH₃ | To system design | TCVN 8366:2010 / ASME | Contact us for a quote. |
| Standard O&F liquid separator | R22, R404A | To system design | TCVN 8366:2010 / ASME | Contact us for a quote. |
Note: for the most accurate manufacturing quotation, please provide the system schematic, the refrigerant used, the cooling capacity and the expected working pressure. Tan Long's engineers will calculate and come back with a technical proposal and costs.
Specifications and scope of supply for Tan Long pressure vessels
Choosing Tan Long means being advised on equipment for your actual system configuration rather than picking from a catalogue. The table below summarises the current scope of supply:
| Parameter | Scope | Note |
|---|---|---|
| Volume and design pressure | Designed to the technical requirements of each project | Calculated from the heat load and the actual circulating refrigerant charge |
| Manufacturing standard | TCVN 8366:2010, ASME, ISO | Supplied with technical documentation and CO/CQ certification |
| Weld standard | TCVN 6008:2010 | Welds inspected by ultrasonic testing |
| Compatible refrigerants | NH₃ (R717), R22, R404A, R507, CO₂, Freon | Materials and fittings selected to suit the refrigerant |
| Insulation (low-pressure vessels) | Polyurethane 150–200 mm | Mandatory for equipment working at sub-zero temperature |
| Protective fittings | Safety valve, pressure gauge, bottom drain line, three-stage float valve | Float valves apply to low-pressure receivers |
| Safety inspection cycle | Every 3 years, shortened to every year for specific equipment | Under Circular 36/2019/TT-BLĐTBXH |
| Operating oil drain cycle | Every 4 to 8 hours | Applies to oil separators and high-pressure receivers |
Why choose Tan Long to design and build pressure vessels?
Tan Long is a refrigeration engineering joint stock company with more than 20 years in industrial refrigeration, with engineers and technicians who have worked on the ground at food and beverage processing plants and large-scale cold stores.
Tan Long pressure vessels are widely used to hold refrigerants such as ammonia (NH3), halocarbons and Freon. Every unit complies strictly with ISO or ASME standards, guaranteeing durability at extreme working pressure and temperature.
In a refrigeration system a pressure vessel consumes no electricity directly, yet it is a key factor in the energy efficiency (COP) and the safety of the whole cycle. Because it controls both the manufacturing technology and the D&B design process, Tan Long commits to an optimised pressure vessel solution that saves the customer both operating and maintenance cost.
The system of pressure vessel catalogs at Tan Long includes:
- High pressure tank
- Low-pressure receiver
- Thermosyphon bottle (Fluid level monitoring bottle)
- Pressure vessels and intermediate storage tanks
- Surge drum protecting the refrigeration compressor
Every unit we supply comes with complete technical documentation and CO/CQ certificates of origin, and is supported through a rigorous safety inspection process before entering service. For in-depth technical advice and a pressure vessel quotation for your project, please call the hotline on (+84) 933357058.
- Tan Long Refrigeration and Electrical Engineering Joint Stock Company
- Headquarters: 86 Dong Den, Ward 14, Tan Binh District, Ho Chi Minh City
- Website: tanlongvn.com
- E-mail: info@tanlongvn.com
For items not available off the shelf — receivers of unusual volume, liquid separators to a system-specific configuration — Tan Long manufactures pressure equipment to order at its factory, complete with inspection documentation.
Equipment that works alongside pressure vessels in the system
The pressure vessel is the pressure-bearing item, tied directly to the rest of the cycle:
- Refrigeration compressor — the refrigerant charge and working pressure of the compressor determine the volume and pressure rating of the vessel.
- Evaporative condenser — the high-pressure receiver takes liquid immediately after condensing.
- Industrial refrigeration system — the liquid separator protects the compressor from liquid returning from the air coolers.
See the full range of industrial refrigeration equipment built by Tan Long.
Frequently asked questions about pressure vessels
How does a refrigeration pressure vessel differ from a water pump pressure tank?
They are completely different devices. A water pump pressure tank has a rubber bladder and an expansion diaphragm and works with water at low pressure. A pressure vessel in an industrial refrigeration system is a sealed welded steel vessel holding NH3 or Freon refrigerant, built to TCVN 8366:2010 and ASME, and subject to mandatory safety inspection. Tan Long manufactures the second kind.
Is safety inspection mandatory, and how often?
Yes. Under Circular 36/2019/TT-BLĐTBXH, every pressure vessel in an industrial refrigeration system must pass technical safety inspection before entering service. The normal cycle is once every 3 years. For vessels holding a corrosive refrigerant that have been in service more than 12 years, or equipment more than 24 years old, the cycle shortens to once a year.
Are a liquid separator and a low-pressure receiver the same thing?
In practice in Vietnam the two names are used interchangeably for the same unit installed on the suction line before the compressor. Its main role is to separate all liquid refrigerant from the suction vapour, protecting the compressor from liquid slugging.
Why must a low-pressure receiver have 150 to 200 mm of insulation?
Because the unit works at sub-zero temperature. Thin or damaged polyurethane causes heat loss and condensation on the shell, leading to chemical corrosion from the outside. This failure mode is dangerous precisely because it is hard to spot by eye.
How often should the vessel be drained of oil?
On oil separators and high-pressure receivers, oil and sediment should be drained every 4 to 8 hours during operation. Before draining, the technician should bring the vessel pressure down to atmospheric to avoid incidents caused by high pressure.
How do pressure vessels for NH3 and for Freon differ?
They differ in materials and fittings. NH3 corrodes copper and copper alloys, so all pipework, valves and fittings must be in dedicated steel, whereas Freon systems have no such constraint. Design pressure and weld construction are also calculated separately for each refrigerant.
What volume of high-pressure receiver is appropriate?
The volume is calculated from the system's actual circulating liquid refrigerant charge, not chosen from a catalogue. Engineers need data on heat load, compressor pack capacity and pipework length to make the calculation. Send us the system schematic and Tan Long will calculate and propose a solution.
Does Tan Long build pressure vessels to a customer's drawings?
Yes. Tan Long undertakes new designs or manufacture to drawings and specifications supplied by the customer, complete with technical documentation, CO/CQ certification and support through the safety inspection process before the equipment enters service.
Related technical reading
- auxiliary equipment in refrigeration system
- expansion valves in the refrigeration cycle
- how to adjust an expansion valve
Related pages
- Industrial refrigeration compressors – the equipment pressure vessels protect directly
- Evaporative condensers – the unit preceding the high-pressure receiver in the cycle
- NH3 refrigeration systems – turnkey design, manufacture and installation
- Industrial cold storage – turnkey design and installation
- PLC and SCADA control panels for refrigeration systems
- Selected projects delivered by Tan Long
