84 SWEETENED CONDENSED M11,K—CONDENSING 
necessary to briefly consider it at this point. ‘The suction end 
of the vacuum pump is connected with the condenser. The 
vacuum pump exhausts the pan, forming a partial vacuum. 
There are principally two types of vacuum pumps used in 
the milk condensery, the dry-vacuum pump and the wet- 
vacuum pump. ‘The dry-vacuum pump is used in the factories 
with the dry-vacuum system, i. e., where the cooling water 
and the condensation water escape to the sewer direct 
and without passing through the vacuum pump, as is the case 
with the surface condenser and the barometric condenser. The 
wet-vacuum pumps are used with the wet-vacuum system, where 
the cooling water and the condensation water pass through the 
cylinder of the pump. The dry-vacuum pumps have the advan- 
tage of permitting the operation of the machine at a higher 
piston speed than the wet-vacuum pumps in which the water 
must be displaced at the end of each stroke. The cylinders of 
the dry-vacuum pump are cooled by water jackets. The initial 
cost of the dry-vacuunm pumps, however, is greater than that 
of the wet-vacuum pumps. 
The efficiency of the vacuum apparatus depends very largely 
on the vacuum pump. Rapid evaporation at a relatively low 
temperature necessitates the maintenance of a high vacuum, The 
type, material, construction, workmanship, installation and oper- 
ation of the vacuum pump should be such as to insure the maxi- 
mum efficiency. 
The pump should be placed on a good foundation and as 
near the vacuum pan as practicable in order that the full benefit 
of the vacuum may be realized. ‘The suction pipe and all con- 
nections must be tight. The suction pipe must be of the size 
directed by the manufacturer, as short as possible and with few 
and easy bends. The grade of the suction pipe should be uni- 
form in order to avoid air pockets. 
The water should be turned into the condenser before the 
vacuum pump. is started. The pump should not run at a higher 
speed than is necessary to secure the required vacuum. Exces- 
sive speed means high steam consumption and heavy wear and 
tear on the pump. The amount of water supplied to the con- 
denser should be regulated to suit the requirements. Ordinarily, 
and with a vacuum of twenty-five to twenty-six inches, the 
