J SERIES M ICROV A CJ SERIES M ICROV A C VA CUUM PUM P V A CUUM PUM P
PAGE 1 -1
1.01.0 DESCRIPTIONDESCRIPTION
1.11.1 General (Principle of Operat ion)General (Principle of Operation)
The Stokes J Series M icrovac Pumps are self-contained, rotary, oil sealed piston type units. An eccentric mounted on
the drive shaft drives the piston. Two floating hinge bars that are free to oscillate in the pump housing guide the piston
slide. The piston assembly rotates clockw ise w hen facing the drive end. Air enters the pump through the intake and
passes through the piston slide as the piston performs its intake stroke. As the piston nears the top center position the
intake port is closed, separating the system from the pump (See Figure 1). At this point the air is entrapped in front of
the piston as it begins the next stroke. As the piston continues to rotate the entrapped air is compressed and
discharged through the exhaust valves and out the reservoir exhaust outlet. The exhaust valves are of a corrosion-
resistant, heavy duty, poppet type.
When the pump is in operation, lubrication of the internal parts is completely automatic. Oil is forced by atmospheric
pressure from the reservoir through internal oil passages to the shaft bearings. The oil is then fed into the pump to
provide the necessary piston-to-cylinder oil seal. The oil in the pumping chamber is forced out through the exhaust
valves with the compressed air and returns to the reservoir. A solenoid valve automatically prevents oil from flooding
the pump in the event of a power failure, or w hen the pump is shutdown w ithout vacuum being broken.
M ODEL 2 12M ODEL 2 12 --J M ODEL 412J M ODEL 41 2 --JJ
FIGURE 1 PUM P CROSS SECTION VIEWFIGURE 1 PUM P CROSS SECTION VIEW
LIGHT ECCENTRIC (FAR SIDE)
HEA V Y ECCENTRIC (NEAR SID E)
PISTON
OIL M A N IFOLD
ASSEM BLY
OIL RESERV OIR
COVER
EX HAU ST
VALV E DECK GASKET
HINGE BA R
IN TAKE
SLIDE
LIGHT ECCENTRIC (FAR SIDE)
HEA VY ECCEN TRIC (NEAR SID E)
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