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Appendix A: Compressed air systems – milk and milk product contact surfaces

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Introduction

The following are recommended sanitary design aspects for compressed air systems used to supply air under pressure for contact with food or food contact surfaces.

Material

Filter media

Use air intake and pipeline filters that consist of fibreglass, cotton flannel, wool flannel, spun metal, electrostatic material or other equally acceptable filtering media, that are non-shedding and do not release to the air toxic volatiles, or volatiles which may impart any flavour or odour to the product.

Use disposable media filters that consist of cotton flannel, wool flannel, spun metal, non-woven fabric, absorbent cotton fibre or suitable inorganic materials which, under conditions of use, are non-toxic and non-shedding. Ensure chemical bonding material, contained in the media, is non-toxic, non-volatile and insoluble under all conditions of use. Do not clean and reuse disposable media.

Filter performance

Ensure the efficiency of intake filters is at least 50 percent as measured by the National Bureau of Standards "dust spot method" using atmospheric dust as the test aerosol.

Ensure the efficiency of either air pipeline filters or disposable filters is at least 50 percent as measured by the DOP (dioctyl phthalate) fog test.

Piping

Use sanitary milk piping for air distribution piping, fittings and gaskets between the terminal filter and any product contact surface, except where compressing equipment is of the fan or blower type. When the air is used for operations such as removing containers from mandrels, other non-toxic materials may be used.

Fabrication and installation

Air supply equipment

Design the compressing equipment to preclude contamination of the air with lubricant vapours and fumes. Produce oil-free air by one of the following methods or their equivalent:

Take the air supply from a clean air space or from relatively clean outer air and pass through a filter upstream from the compressing equipment. Locate and construct this filter so that it is easily accessible for examination, and the filter media is easily removable for cleaning or replacing. Ensure the filter is protected from weather, drainage, water, product spillage and physical damage.

Moisture removal equipment

If it is necessary to cool the compressed air, install an aftercooler between the compressor and the air storage tank for the purpose removing moisture from compressed air.

Filters and moisture traps

Construct filters to assure effective passage of air through the filter media only.

Have the air under pressure pass through an oil-free filter and moisture trap for removal of solids and liquids. Locate the filter and trap in the air pipeline, downstream from the compressing equipment and from the air tank if one is used. Air pipeline filters and moisture traps, downstream from the compressing equipment, are not necessary where the compressing equipment is of the fan or blower type.

Locate a disposable media filter in the sanitary air pipelines upstream from, and as close as possible to, each point of application for ultimate use of the air.

Air piping

Ensure the air piping from the compressing equipment to the filter and the moisture trap is readily drainable.

Install the product check valve of sanitary design in the air piping downstream from the disposable media filter to prevent backflow of product into the air pipeline. A check valve is not needed if the air piping enters the product zone from a point higher than the product overflow level which is open to atmosphere.

The recommendations of this section do not apply when the compressing equipment is of the fan or blower type. See illustrations depicting various air supply systems.

Note: For additional details, see 3-A Accepted Practices for Supplying Air Under Pressure in Contact with Product or Product Contact Surfaces, Number 604-05.

Compressed air systems

Figure 1: Individual blower type air supply

Figure 1: Individual blower type air supply. Description follows.
Description of image – Individual blower type air supply

This image shows an individual blower type air supply, which consists of:

  1. Blower or fan, 34.5-103.5 kPa (5-15 psi)
  2. Air line or duct
  3. Pressure gauge (when used)
  4. To point of application
  5. Final filter (when used)
  6. Intake air filter

Figure 2: Individual fan type air supply

Figure 2: Individual fan type air supply. Description follows.
Description of image – Individual fan type air supply

This image shows an individual fan type air supply, which consists of:

  1. Blower or fan, below 34.5 kPa (5 psi)
  2. Intake air filter
  3. To point of application

Figure 3: Central compression-type air supplies

Figure 3: Central compression-type air supplies. Description follows.
Description of image – Central compression-type air supply

This image shows a central compression-type air supply, which consists of:

  1. Compressing equipment
  2. Intake air filter
  3. After-cooler
  4. Safety relief valve
  5. Air pipe line coalescing filter and moisture trap
  6. Pressure gauge (optional)
  7. Dryer (when used)
  8. Sanitary piping downstream from this point
  9. Product check-valve (where required)
  10. Final filter
  11. To point of application
  12. Drain valve
  13. Moisture leg or trap
  14. Air storage tank
  15. Air gap
  16. Trap and drain valve
  17. Condensate pipe

Figure 4: Individual compression-type air supply

Figure 4: Individual compression-type air supply. Description follows.
Description of image – Individual compression-type air supply

This image shows an Individual compression-type air supply, which consists of:

  1. Compressing equipment
  2. Drain valve
  3. After-cooler (when used)
  4. Pressure gauge (optional)
  5. Dryer (when used)
  6. Air pipe line coalescing filter and moisture trap
  7. Final filter
  8. Product contact valve (where required)
  9. Sanitary piping downstream from this point
  10. To point of application
  11. Intake air filter

Figure 5: Rotating mandrel assembly

Figure 5: Rotating mandrel assembly. Description follows.
Description of image – Rotating mandrel assembly

This image shows a rotating mandrel assembly, which consists of:

  1. Compressing equipment
  2. After-cooler (when used)
  3. Pressure gauge (when used)
  4. Air pipeline coalescing filter and moisture trap
  5. Drain valve
  6. Dryer (when used)
  7. Final filter
  8. Intake air filter
  9. Fixed air passage
  10. Rotating mandrel assembly

Reference

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