RS AND RD SERIES PUMPS
OM-03989
PAGE C - 2
OPERATION
the spring located on top of the rotor forces the
group grind into its maximum eccentric position to
automatically evacuate the air vapor through the
priming tube and into the pump discharge.
When the pump is installed under unusual
conditions, the priming tube(s) may vi
brate abnormally. If this occurs after the
pump and piping are properly secured,
contact the factory to obtain optional
springs for the priming pump group grind.
If vibration is not corrected, the tubing
could fatigue and spill the liquid being
pumped, resulting in a fire hazard.
As air and vapor is evacuated and the main cen
trifugal pump begins to deliver liquid, the resulting
priming pump discharge pressure builds up
against the underside of the slide and moves it to
ward the neutral (centered) position. After all the air
and vapor is removed and the centrifugal pump
reaches full capacity, the priming pump discharge
pressure overcomes the spring pressure on the
slide and moves it towards the neutral position
where it remains until air or vapor enters the sys
tem. While in the neutral position, the priming
pump operates at minimum capacity and circu
lates only a small amount of liquid. See Figure 2 for
the theory of priming pump operation.
FULL PRIMING
(SPRING FULLY EXTENDED,
SLIDE AT BOTTOM, MAXI
MUM VAPOR EVACUATION)
PARTIAL PRIMING
(SPRING SLIGHTLY COMPRESSED,
SLIDE MOVING TOWARD CENTER,
VAPOR MOSTLY EVACUATED)
NEUTRAL
(SPRING FULLY COM
PRESSED, SLIDE CENTERED,
VAPOR FULLY EVACUATED)
Figure 2. Automatic Priming Sequence
Priming is rapid, but not instantaneous. The prim
ing pump will prime an absolutely dry line of four
inch diameter in approximately two seconds per
foot of suction pipe. Thus, if the suction line is 10
feet long, the pump will prime in approximately 20
seconds. If the pump continually handles dry liq
uids, such as gasoline or solvents, priming pump
vane wear may result, causing a loss of priming
vacuum. If priming time increases significantly
over a period of time, check the priming pump
vanes for excessive wear.
NOTE
A special seal is available for pumps which are to
handle solvents. When ordering a pump or replace
ment parts, specify what solvent the pump is to han
dle.
Priming Pump Group Grind Check
With the pump inoperative, remove the group
grind drain plug and drain any liquid from the
group grind. Remove the spring cap and pressure
regulating spring. Insert a screwdriver or other suit
able tool into the drain plug hole, and move the
slide up and down. The slide should travel 1/8 inch
(3,2 mm) from the full priming position to the neu
