Reusable filter frame. Photo by E. Wilde, 2002 Feb 3.

As we noted, the typical, heavy, metal-frame filters, used in railway equipment, are difficult to find anywhere but even more so when you are on the road. Replacement, two-part, metal frames, that use readily available (e.g. from Grainger) 2" thick polyester filter material make it easier to change out the filter media, when necessary (a roll of it can be stashed under a bed and cut to size, when needed, or the material can even be washed, in a pinch). For those really odd, 4" thick filters, two layers can be used. Photo by E. Wilde, 2002 Feb 3.

Filter material holder. Photo by E. Wilde, 2002 Feb 3.

The heavy filter frame separates into two pieces. The side away from the air stream accepts the polyester filter material. It uses expanded metal to support and hold the filter firmly in the air stream. The frame is formed of #16 ga. m.s. sheet bent on a brake and welded on all corners. A coat of primer and a coat of two-part expoxy protect the frame from condensation, dust, etc. Photo by Eric Wilde, 2002 Feb 3.

Filter frame cover. Photo by E. Wilde, 2002 Feb 3.

The side of the filter frame that faces the air fits exactly over the other half of the frame. It has pads for the filter clamps and uses 1/2" hardware cloth to hold the filter material in place but keep the occluded area to an absolute minimum, thereby maximizing air flow. Photo by Eric Wilde, 2002 Feb 3.

Galvo filter frame. Photo by E. Wilde, 2003 Aug 1.

An alternative, less expensive filter frame can be fabricated from #18 ga. galvanized steel, employing spot welded construction and 1/2" hardware cloth on both faces. Check the parts department for filter frame prices and ordering information. Photo by Eric Wilde, 2003 Aug 1.

Galvo filter frame cover. Photo by E. Wilde, 2003 Aug 1.

The frames can be built to any size and shape. Thicknesses in multiples of the two inch filter media thickness are best (i.e. 2" or 4"). Here, a two inch frame has been provided with 1" clamp blocks so that it will fit into a location previously occupied by a 3" thick filter. The new, high-efficiency media will make up for any loss in filter performance due to reduced thickness. Photo by Eric Wilde, 2003 Aug 1.

Pleated filter and frame. Photo by Al Dykes.

Cardboard filters are readily available, including those that use pleated, high-efficiency filter material. The galvanized frames can be made to hold such cardboard filters and drop right in to the original filter location in the air duct. Photo by Al Dykes.

Pleated filter in frame. Photo by Al Dykes.

A pleated, cardboard filter is installed in the filter frame and is ready to go. Since these filters are commonly available, should one need to be replaced, on the road, there will be no problem finding them at the local supply depot. Photo by Al Dykes.

Frame, with pleated filter, installed. Photo by Al Dykes.

A 2" filter frame, with a pleated, cardboard filter, is installed in the air duct. Clamp blocks welded to the frame allow the existing 3" clamps to hold the filter. Photo by Al Dykes.

Frame, with bulk filter media, installed. Photo by Al Dykes.

Alternately, a frame with bulk, polyester filter material is installed in the air duct. Easily removed, the frame can be opened and the filter material removed for washing, should the filter become clogged on the road. Photo by Al Dykes.