59 BULLETIN 1370, U. S. DEPARTMENT OF AGRICULTURE 
in this tank, after which it is ready to be pumped to the filter presses. 
If filter presses are not available, the mud is simply washed by 
decantation. 
FILTER PRESS PUMP 
The centrifugal pump, giving a uniform pressure, is ideal for filter  — 
press work when the installations are large enough to warrant the use 
of a pump of such size that the mud passes readily through the 
impeller. For 50, 100, 200, and 300 ton plants, however, a direct- 
acting or power-driven piston pump, such as one of the triplex, 
single-acting, plunger type, is better. Pumps which are capable of 
working against a 60-pound gauge pressure should be selected. An 
overflow with relief valve should be so connected that it will discharge 
back into the mud-mixing tank. With this arrangement the valve 
may be set for any desired pressure; if the pump handles more mud 
than will pass through the filter press at the given pressure, the 
excess ae will discharge through the relief valve and be returned 
to the mud-mixing tank. 
FILTER PRESSES 
There is some question as to whether or not it is a good plan to 
use filters for the muds. In other words, dees it pay to install a 
filtering station? 
Assuming that the mill in a 50-ton plant extracts 70 per cent of 
juice on weight of cane and that without filtering or resedimenting 
the mud the loss of juice in the mud at the bottoms of the defecators 
will be 15 per cent (approximately what occurs in actual practice), 
the quantity of sirup obtained from 1 ton of Louisiana cane will 
average 20.5 gallons. If the mud remaining at the bottom of the 
defecators is diluted and again allowed to sediment (p. 30), the loss 
of juice will be 10 per cent instead of 15 per cent of the original weight 
of juice. This saving, which increases the yield of sirup from 20.5 to 
21.7 gallons per ton of cane, represents a gain in yield of sirup of 5.8 
per cent. The value of this increased yield, when extended over a 
grinding season of 60 days, with sirup selling at $0.50 per gallon, will 
amount to $1,800. When filter presses are used, the quantity of 
mud remaining from defecation is not much more than 30 pounds per 
ton of cane. Under these conditions the increase in yield of sirup 
over the resedimenting process is 8.7 per cent, which, with sirup at 
$0.50 per gallon, amounts to a saving over the resedimenting 
method of $2,850. The saving from the use of filter presses over 
the method of discarding the mud at the bottoms of the defecators 
without any resedimentation whatever will be the sum of $1,800 and 
$2,850, or $4,650. 
The extra cost during a 60-day season of a filter press installation 
in a 50-ton plant is $275, itemized as follows: Man on night watch, 
at $1.50 per day, $90; man on day watch, at $1.50 per day, $90; 
fixed charges on press, $70; increased cost due to space occupied, 
$10; cost of filter cloth per season, $15. The fixed charges consist of 
depreciation (8 per cent), upkeep (2 per cent), interest on the original 
investment over entire period (3 per cent), and taxes and insurance 
(3 per cent). The cost of the press is shown in Table 11. These 
figures prove the economy effected by the use of filters. 
