Air Receiver Fittings Guide: What You Need and Why
The fittings on your air receiver are as important as the vessel itself. Here is what each fitting does, which are mandatory under SANS 347, and how to specify your receiver correctly.
Speak to Our Technical TeamSafety / Pressure Relief Valve — Mandatory
The safety relief valve (SRV) is the most critical fitting on any pressure vessel. It is a spring-loaded valve set to open automatically if the vessel pressure exceeds the maximum allowable working pressure (MAWP), venting air to atmosphere to prevent over-pressurisation. Under SANS 347 and the Pressure Equipment Regulations, a correctly sized and calibrated SRV is a legal requirement on every air receiver. The SRV must be set at or below the vessel's design pressure, must be tested at each periodic inspection, and must be replaced if it fails to lift at the correct set pressure. Never block, bypass, or remove the safety valve under any circumstances.
Manual Drain Valve — Essential
Compressed air always contains moisture — even after passing through a dryer. This moisture condenses in the receiver and collects at the bottom of the vessel. The manual drain valve allows this condensate to be drained off regularly, preventing internal corrosion and moisture carry-over into the distribution network. A ball valve or needle valve at the lowest point of the receiver is standard. Manual drains should be opened at the end of each production shift, or more frequently in high-humidity environments.
Automatic Condensate Drain — Strongly Recommended
For compressors running continuously or in humid conditions, a manual drain depends on operator discipline to function effectively. An automatic electronic drain valve opens on a timed schedule or in response to a float sensor, removing condensate without operator intervention. Auto-drains significantly reduce the risk of condensate build-up and internal corrosion, and are particularly recommended for receivers in difficult-to-access locations, outdoor installations, and any application where the receiver is left unattended overnight.
Pressure Gauge — Mandatory
Every air receiver must have a pressure gauge displaying the current vessel pressure. The gauge must be readable from the operating position, rated above the vessel's working pressure, and in good working order. A glycerine-filled gauge is recommended for applications with vibration. Replace any gauge that reads inaccurately — operating blind to vessel pressure is a safety hazard and a compliance risk.
Inlet and Outlet Ports
Standard receivers are supplied with BSP-threaded inlet and outlet ports. The inlet receives air from the compressor (or aftercooler), and the outlet supplies air to the dryer, distribution network, or point of use. Port size is matched to the receiver capacity and the connected pipework. Specify your required port size when ordering — typically 1/2 inch to 2 inch BSP depending on receiver size and flow rate.
Isolation Valve — Recommended
Fitting an isolation ball valve on both the inlet and outlet allows the receiver to be isolated from the system for maintenance, inspection, or emergency shutdown without de-pressurising the entire system. This is particularly important in multi-compressor installations and large plant ring mains where shutting down a section should not affect the entire system.
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