Guardian Grease Filters
DPL provide three different types of grease filter, the most economical of which is the Guardian mesh type.
The filter relies on the grease-laden air depositing the particles onto the non-corrosive mesh, but is only suitable for use where low quantities of grease are produced, as Guardian filters only have a grease extraction efficiency of between 40 and 45%. Another factor to be taken into consideration is the spread of flame, as there is no barrier within the filter to stop any fire passing through the housing with the resulting risk of fire within the ductwork.
The Guardian filter is constructed using eight double layers of galvanised mesh within a 50mm wide casing. The media is contained within the housing by using front and rear diamond mesh aluminium fascia panels, and the completed filter is usually provided with handles to facilitate removal from the housing.
The performance of the filter varies a great deal with use, and has to be regularly maintained to avoid a build up of particles which increases the resistance to air flow. For applications that have a high temperature with little grease being produced, such as baking ovens or dishwashers, then Guardian filters can also be made entirely from stainless steel including the mesh, fascia and housing. The following data shows the results of testing carried out by a NAMAS approved company, of the pressure drops (in pascals) that occur for clean filters, at various air flows.
|
Air Flow m3/s |
Galvanised 500 x 250 |
Galvanised 500 x 400 |
Galvanised 500 x 500 |
Stainless 500 x 400 |
|
0.24 |
35 |
- |
- |
- |
|
0.27 |
40 |
- |
- |
- |
|
0.33 |
60 |
25 |
- |
31 |
|
0.35 |
65 |
28 |
- |
35 |
|
0.38 |
75 |
30 |
- |
39 |
|
0.40 |
80 |
35 |
- |
43 |
|
0.44 |
90 |
40 |
25 |
51 |
|
0.46 |
100 |
42 |
28 |
54 |
|
0.50 |
110 |
48 |
30 |
62 |
|
0.55 |
130 |
55 |
35 |
75 |
|
0.57 |
140 |
60 |
38 |
80 |
|
0.60 |
155 |
65 |
40 |
87 |
|
0.66 |
- |
75 |
45 |
- |
|
0.70 |
- |
85 |
50 |
- |
Guardian filters are normally 50mm wide and available in three standard sizes of 500 x 500, 500 x 400 and 500 x 250, and for design purposes, a pressure drop of around 40 pascals should be used to select the number and size of filters required.