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PRINCIPLE OF DESIGN
The Duravac RP-50B is a cam (eccentric) and piston (Slide) design. Within the pump, the piston is driven by the cam. The open head
which the shaft extends, has a shaft seal set-up to prevent air leakage into the pump and an outboard bearing to handle the belt pull
force.
The piston has an integral hollow extension (called a slide) which extends through the slide pin (hinge bar). One side of the slide con-
tains diagonal slots; as the slide passes back and forth through the slide pin, these slots are covered and uncovered to form an inlet
valve. Outlet valves are over the discharge port on top of the cylinder. All working parts are precisely machined to suitable
clearances for high vacuum requirements.
The covering and uncovering of the slots in the piston slide by the slide pin constitutes a mechanical inlet valve. Air of gas is admitted
Through these slots from the high vacuum side of the slide pin into the space between the piston and cylinder at certain parts of the
cycle. As there is no spring loading, no pressure difference is required to operate this valve. The outlet (discharge) valve is opened
automatically by the compression of the air or gas in the pump against atmospheric pressure, plus a slight spring pressure.
Since the success of the pump depends on its being sealed and lubricated, an oil reservoir is mounted above the pump. The sealing
oil needs to be free from gases or moisture. Otherwise, the vapors will be pulled out of the oil (outgassing) and will prevent obtaining
low absolute pressures.
In view A from the figures below, the piston is moving in the direction of the arrow and is rapidly creating more space into which some
of the gas is admitted through the inlet port; at the same time, view B is compressing the gas previously trapped and is taking place on
the opposite side of the piston. As the piston reaches the end of it’s compression cycle in view B, it expels all the air or gas and sur-
plus sealing oil through the outlet valve and into the oil reservoir tank. The reservoir tank is where the oil is retained for recirculation
and the air or gas being pumped is expelled out the discharge port of the reservoir.
Fig-1
OIL
OIL SEPARATOR
EXHAUST
INLET
SLIDE PIN
DISCHARGE
VALVE
CAM
PISTON
