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Slurry pumps are sometimes subjected to severe shock loading and shaft whip as a result of presence of solids and system upsets. For these reasons soft compression packing is still favored as a means of sealing on the stuffing box.

The wantred methodology for packing a slurry pump is the “flush” seal shown in Figure thirteen-5a. Right here the lantern ring is positioned in entrance of the packing rings and a copious supply of clean liquid is injected at a pressure higher than the prevailing slurry pressure in the stuffing box. The clean liquid acts as a barrier and prevents the ingress of abrasive particles that cause packing and sleeve wear. The disadvantage of this system is that giant amounts of flushing water are required and the pumped product will be diluted. This system is really helpful for extreme abrasive services.

Another method for sealing is shown on Figure 13-5b. Here the lantern ring is positioned between packing rings. This configuration is called a “weep” seal. Once more, clean liquid must be injected at a pressure higher than the prevailing slurry pressure near the stuffing box. Product dilution is significantly reduced compared to the “flush” seal design. However, the barrier so created is not very efficient, inflicting abrasive particles to penetrate and cause wear. If the service is only mildly abrasive, then grease can be used in lieu of liquid.

An approximation of flushing necessities for a “flush” type packing arrangement for standard throat restriction devices the place no attempt has been made to curtail using flushing water and where the pressure differential is 15 psi is displayed in Figure 13-6. Such a restriction will have an annular radial clearance in the order of .007 times the sleeve diameter. The length of the throat bush will be about the identical as the width of one flip of packing.

It’s impossible to predict the precise quantity of flushing water required when the packing is “weep” type, since this relies on shaft deflection and gland maintenance. Nonetheless, under normal working conditions, weepage can be in the order of 5% of the values acknowledged in Figure thirteen-6 for “flush” packing arrangement.

In most cases, seals and flush necessities are provided in ignorance of the real pressure prevailing at the stuffing box, which ends in excessive use of gland water and increased maintenance.

Constructed into some slurry pump designs are strategies to reduce pumped pressure on the stuffing box by hydrodynamic means. (For instance, see Figures 13-7 and thirteen-eight for diagrams of pump out vanes on impellers and expellers.) The side-suction-pump configuration is subjected only to suction pressure and has an advantage over finish-suction pumps, one not totally acknowledged by users. By proper application of impeller pump out vanes and expellers, the pressure on the box could be reduced to virtually zero. This is called a dry box arrangement. In these cases, weep-type seal is satisfactory, with either water or grease being injected into the cavity formed by the lantern ring.

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