Document EdqagEm8R9JEMyo9aeMB3Vw8b

American Society of Heating and Ventilating Engineers Guide, 1936 VACUUM PUMPS A vacuum heating pump is employed to create a vacuum on the return side of a system to remove air and water from the return piping and to pump the condensate to the boiler or to a receiving tank. Pumps of this classification may be driven by steam or electricity; they may be continuous in operation, or automatic with float or vacuum control in one or more combinations. For rating purposes3, vacuum pumps are classified as low vacuum and high vacuum. Low vacuum pumps are those rated under operation at 5Hj-in. mercury vacuum, and high vacuum pumps are those rated at. vacuums above 53^ in. Fig. 19. Typical Installation Using 'Condensation Pump Return line vacuum, pumps are classified in the method of their per formance as follows: ' a. Those which perform the function of air separation under' atmospheric pressure. b. Those which perform the function of air separation under a partial vacuum. Pumps coming under the first classification will handle vacuum steam system condensation coming back by gravity at any temperature up to 205 F without either the sealing or the hurling water flashing into steam. These pumps, to operate under a combined water level and vacuum con trol; must be equipped with a float-control receiver between the vacuum pump and the system, but where they are intended for continuous opera tion, they do not require a receiver. Such pumps employ a single vacuum 3See A.S.H.V.E. Standard Code for Testing and Rating return line low vacuum heating pump. 550 Chapter 31--Steam Heating Systems producer which removes the condensate and air from the system and delivers it into a separating chamber under atmospheric pressure from which the condensate is delivered to the boiler or feed water heater. They are constructed on one of the following evacuating and discharge principles: 1. Hydraulic vacuum producer with one pump impeller. 2. Hydraulic vacuum producer with two pump impellers. 3. Water displacement vacuum producer with two pump impellers. 4. Piston displacement vacuum producer with one pump piston. The second classification of pumps will handle vacuum steam system condensation coming back by gravity at any temperature not exceeding 190 F without the flashing into steam of either the sealing or the hurling water. In order to operate under a combined water-level and vacuum control, these pumps must be equipped with a float-control receiver between the vacuum pump and the system; where intended for con, tinuous operation they do not require a receiver. Such pumps employ a vacuum producing impeller which removes air from the receiver or heating system under a partial vacuum and delivers it through an air separator against atmospheric pressure. The condensate is removed from the receiver under a partial vacuum by a separate impeller and is delivered to the boiler or feed water heater. For evacuating and dis charge, a water displacement vacuum producer with two pump impellers is used. Receiver Capacities for Vacuum Pumps Where receivers are used in connection with vacuum pumps there: is a definite relation between the capacity of. the receiver and the capacity of the pump. The receiver should have a capacity of not less .than V/z times the volumetric quantity of condensation per minute and should not have such a capacity that the pump will empty the receiver in less than half a minute. Receivers of larger capacities will'result in less frequent periods of operation. Piston pisplacement Vacuum Pumps , . Pistoii displacement return-line vacuum heatirig;pumps may be either power or steam driven. They should be provided with mechanical lubricators and. their piston speed in feet per minute should not exceed 20 times the square root of the number of inches in their stroke. While the volumetric displacement for such pumps was formerly figured at 8 to 10 times the volumetric flow of condensation to .be handled, the., more efficient..thermostatic.'traps used today-in connection with vacuum heating system's make it possible to change this proportion so that the. volumetric displacement of these pumps may not be less than 6 times the volume of condensation: . . ' i ;'' Vacuum Pump Controls In' the ordinary vacuum: system the vacuum-pump is-controlled by1 a vacuum regulator which cuts in when the vacuum drops to the iowest point desjrec}.and which cuts out when the Vacuum has been .inctea^e^ to the highest.point.'. , This is done largely to eliminate the constant' starting and stopping of the vacuum pump which would occur if the vacuum were 551