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3. Suction pressure is below 5 bar g.
4. Liquid has lubricating qualities.
5. Liquid is non-toxic and non-volatile.
When the liquid being pumped contains solids or is otherwise not compatible with packing materials, an
outside supply of seal liquid should be furnished. In general, external-injection liquid (from an outside
source) is required when the following conditions prevail:
1. Liquid being pumped contains dirt, grit, or other impurities.
2. Temperature of pumped liquid is below 0° C or above 70° C.
3. Liquid being pumped has non-lubrication properties.
4. Liquid is toxic or volatile.
5. Suction pressure is above 5 bar g, vacuum, or high lift.
The standard stuffing box consists of rings of packing (see assembly section for number of rings), a
lantern ring, and a gland. A shaft sleeve, which extends through the box and under the gland is normally
provided to protect the shaft.
A tapped hole is supplied in the stuffing box directly over the seal cage to introduce a clean, clear sealing
medium. The stuffing box must, at all times, be supplied with sealing liquid at a high enough pressure to
keep the box free from foreign matter, which would quickly destroy the packing and score the shaft
sleeve.
Only a sufficient volume of sealing liquid to create a definite direction of flow from the stuffing box
inward to the pump casing is required, but the pressure is important. Apply seal water at a rate of
approximately 1 l / min at the proper pressure.
One recommended method to minimize error in regulating flushing water is a "Controlled Pressure Sys-
tem" (Figure VI). Most important is the pressure-reducing valve adjusted to a value slightly exceeding the
maximum stuffing box operating pressure (assuming it's reasonably constant). A flow-indicating device
will serve to indicate a failing of the bottom packing rings allowing leakage into the pump.
External sealing liquid should be adjusted to the point where the packing runs only slightly warm, with a
very slow drip from the stuffing box (40-60 drops per minute). Excess pressure from an external source
can be very destructive to packing.
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