80 



AGRICULTURE HANDBOOK 134, U.S. DEFT. OF AGRICULTURE 



SUGGESTED FILTER TRAYS 

 HEAVY GAGE METAL OR WOOD 



PN^791 



Figure 95. — A simple type of flat filter. A basket of 

 hardware cloth is supported above the two tanks for 

 holding the felt and above this is the support for the 

 prefilter. The prefilter is moved across the tray as new 

 filtering surface is needed. 



was first used in New York and is gaining in 

 popularity everywhere. The flat filter provides 

 a larger filtering area than does the cone- 

 shaped filter. Distribution of the filter cake over 

 this larger area results in a thiner layer, so the 

 filters can be used for longer periods before 

 cleaning is necessary. 



The felt sheet is supported in a shallow bas- 

 ket of hardware cloth with 2-inch walls {147). 

 The felt is cut at least 4 inches larger than the 

 bottom of the basket, and the edges are turned 

 up 2 inches to form a shallow tray (chart 18). 

 Usually the felt can be used two or three times 

 longer between cleanings if the sirup is first put 

 through a prefilter. However, because of the 

 physical form of the particles of sugar sand, 

 filtering may be more rapid if the prefilter is 

 not used. This can be determined only by exper- 

 iment. The prefilter is mounted above the felt 

 and is supported on a wire screen basket the 

 same size as that used for the felt (chart 18). 

 The prefilter is cut to fit across the basket, but 

 a length of filter paper is left hanging over the 

 edge of the basket. As the prefilter becomes 

 clogged, a new filtering surface is provided by 

 pulling the prefilter across the basket (fig. 95). 



The filters can be built in multiples over a 

 common tank (fig. 96). As one becomes clogged 

 with sugar sand, the assembly can be moved to 

 place a clean filter under the spigot. 



FELT FILTER 



Chart 18. — Sirup filter. A flat felt filter assembly, con- 

 structed on a milk-can washer that serves as a tempo- 

 rary storage tank from which the hot sirup can be 

 drawn for packaging. Shortening the legs and attach- 

 ing casters or wheels permits the assembly to be moved 

 easily into place under the sirup drawoff spigot. 



To maintain filtration at a rapid rate the flat 

 prefilters and felts must be cleaned often, espe- 

 cially if the sirup contains a large amount of 

 sugar sand. To clean the filters, the filter cake 

 is first scraped off with a wooden scraper to 

 prevent damage to the filtere. The entrapped 

 sirup is dissolved by dipping the filter into a 

 pan of hot water. The filters are folded with the 

 sugar sand on the inside so that it will not be 



PX-47y2 



Figure 96. — A more elaborate type of installation in 

 which three felt filter units are installed over a com- 

 mon tank. The units are mounted on rollers so that 

 they can be replaced by a fresh unit when necessan,-. 

 The tank is provided with a drawoff valve. 



