THE EVAPORATION OF THE JUICE TO SYKUP. 



Wafe 



Steam 



Worthington type are often used ; a section through such a pump is shown 

 in Fig. 185. 



A wet vacuum pump that has heen extensively installed is the Edwards* 

 patent pump, which allows the air to pass naturally through the water, 

 instead of being churned up with it, as always happens to some extent in the 

 ordinary type. This pump is shown in vertical section in Fig. 186. Water 

 from the condenser flows by way of d to the reservoir c; the conical bucket I 

 on the down stroke forces the water into the barrel of the pump ; as soon 



as the bucket rises the entry of water by 

 way of d is closed until the bucket has 

 passed, and the water which has been 

 projected into the barrel is lifted and 

 discharged through the valves at a, passing 

 away at e ; at g is a relief valve. The 

 incondensible gases are free to escape to 

 the space above the water. These pumps 

 are made double or treble barrelled, so 

 that their action is practically continuous. 



Pumps used to remove the inconden- 

 sible gases in connection with the dry 

 vacuum are generally of the slide valve 

 pattern ; in the earlier pumps at each 

 stroke a certain amount of air was left in 

 the barrel of the pump, to the detriment 

 of the efficiency. To overcome this pumps 

 are fitted with an arrangement whereby 

 at the end of the stroke, communication is 

 made between the two faces of the piston, 

 and the compressed air in front of the 

 piston escapes into the exhausted space 

 behind. There are many excellent designs 

 obtaining this ' equalization of pressure,' 

 that due to the firm of Wegelin & Hiibner 

 being shown in Fig. 187. [There are three valves, a, b, and c, known 

 as the distributing, equalizing, and delivery valves ; the valve a is designed to 

 allow the air to enter or depart and to connect the suction or discharge to the 

 pan or atmosphere ; the delivery valve c on the valve a is for the escape of air 

 and to prevent air returning to the pump ; the equalizing valve b is for the 

 purpose of connecting the channels d when the piston is at the end of the 

 stroke When the piston is at the end of a stroke the valve a is nearly central 

 and the discharge and suction ports are closed ; at this moment the equalizing 

 valve b makes connection between the two faces of the piston by means of the 



FIG. 185. 



329 



