184 NEW DEVELOPMENTS IN HIGH VACUUM APPARATUS. 



sometimes three or even four air ejectors working in parallel are being used with 

 two condensate pumps. 



This subdivision also gives an absolute assurance against a total shut-down, 

 which may easily occur when using a single reciprocating type air pump. 



As the condensate pump forms an essential part of an air-ejector installation a 

 short description of several types of condensate pumps will be given. 



A centrifugal type of condensate pump, driven directly by a steam turbine, 

 which has been extensively used, is shown in Plate 78. It has a single-inlet impeller 

 mounted on the overhung end of the turbine shaft. The pum.p casing is bolted di- 

 rectly to the turbine casing, thus forming a rugged unit with only two bearings. 

 This construction makes it impossible to throw the shaft out of alignment when 

 bolting the pump down to the foundation or when connecting the piping. A vent is 

 provided ahead of the inlet of the impeller and connected to the condenser to per- 

 mit any air which may have been drawn into the pump through whirling of the con- 

 densate as it enters the suction pipe to return to the condenser and prevent the 

 pump from becoming air-bound. The turbine is running at a constant speed which 

 is regulated by a speed governor ; it also has an emergency trip. Carbon packings 

 are generally used on the turbine glands. The pump has to remove the condensate 

 under a high vacuum, and therefore has to overcome a suction head of 30 feet or 

 more. This makes it necessary for the condensate to flow by gravity to the pump 

 impeller, and it is advisable that the pump be submerged not less than 2 feet below 

 the lowest water level of the condenser. 



Direct-acting reciprocating piston pumps, either vertical or horizontal, are also 

 used for the removal of the condensate. Their 'design is adapted to the features 

 peculiar to condensate pump service. Their submergency is more than that for the 

 centrifugal type and is never less than 4 feet from the top of the discharge valves 

 to the water level of the hot well. The stuffing boxes are water-sealed, and the 

 piston speed does not exceed 25 to 30 feet per minute when handling the normal 

 capacity. The speed of the pump is controlled by a float arranged in the hot well 

 of the condenser so as to prevent racing of the pump at light loads. 



The arrangement of an air-ejector installation with turbine-driven condensate 

 pump is illustrated in Plate 79. Live steam at boiler pressure is delivered through 

 the steam strainer to the pressure regulator ; passing through the pressure regula- 

 tor the steam is delivered to the main steam valve of the air ejectors at practically a 

 constant pressure for which these have been designed to operate, the pressure regu- 

 lator taking care of variation in the boiler pressure. The suction of the condenser 

 is connected to the air suction of the ejectors by a tee, a gate valve being arranged 

 so to permit the shut-oft' of each eiector. The discharge of the ejectors leads into 

 the feed and filter tank. 



A swing check valve is arranged close to the tank to prevent any water from 

 rushing back into the air ejector if shut down before breaking the vacuum in the 

 condenser. 



