Fig. 97.—Cleaning Rod Joint.
If possible, both leaches and handler-pits should be provided with plugs and underground pipes, communicating with a liquor-well some feet below their levels. Glazed fire-clay is very suitable both for pipes and plug-holes, which should be in the pit corners. If fire-clay blocks for plug-holes cannot be obtained, they may be cast in good cement, the wooden mould being soaked with hot paraffin wax to prevent adhesion. Means must be provided for the ready clearing of the pipes when choked with tanning materials. A good plan is to let each line of pipes end in a liquor-well large enough for a man to go down. As it is almost impossible to make plugs fit without occasional leakage, it is not well to run pits with very different strengths of liquors to one well, but the layers, handlers, and different sets of leaches should each have their own, so as to avoid mixture. A good means of clearing pipes consists in a series of iron rods 3-4 feet long, connected by hooks fitting into double eyes, as shown in [Fig. 97]. It is obvious that in a narrow pipe or drain, these cannot become disconnected. Pipes may often be forced out by fitting a strong delivery-hose of a steam-pump into one of the plug-holes.
It is, as Schultz points out, of questionable advantage to lay wooden troughs under the alleys for supplying liquor to each pit, since it is almost impossible to preserve them from decay; but the same objection would not apply to glazed pipes, jointed with pitch or cemented. A good and cheap plan in practice, is to let the liquor-pump, or a raised liquor-cistern, discharge into a large and quite horizontal trough raised 6 or 7 feet above the level of the yard, and provided with plug-holes at intervals, from which the liquor can be run into the various pits by short spouts or sailcloth hose. In place of plugs in the raised trough, a simple and convenient valve devised by the writer may be advantageously employed. A lead weight is made by casting in a hemispherical tin basin of about 5 inches diameter and 2 inches deep in the centre, a loop of strong brass wire with turned up lower ends, being suspended in the middle, so as to become fixed in the lead. To prevent adhesion, the tin must be previously burned off, and the basin well blackleaded. This weight forms the valve, which rests in use on a 6-inch washer of good indiarubber with a 4-inch hole, which is held by a wood block against the bottom of the trough, through which a 5-inch hole is cut. The valve is raised by a lever or cord, and is absolutely water-tight in use. It is shown in section in [Fig. 79], [p. 333].
It is very advantageous in practice, instead of pumping direct into the pits, to have one or more tanks, into which liquor can be delivered by the pump, and which are sufficiently raised to allow it to be run from them into the horizontal distributing troughs which have been mentioned. This is specially important with regard to liquors for leaches and suspenders which are worked on a circulating system, since they do not run very quickly, and much time is lost in pumping out pits, if the speed of the pump has to be regulated by the rate at which the liquor will circulate. It also enables liquors to be run through suspender- and rocker-pits during the night or at meal-times while the machinery is standing; and it is often useful on beginning work in the morning, to have an empty tank into which the first liquor can be pumped.
Direct-acting steam-pumps without fly-wheels are very unsatisfactory for tan-yards, since they are usually uncertain in their action, difficult to run slowly, and apt to “hammer”; and they are also costly in steam, which cannot be used expansively. Steam-pumps with fly-wheels, operating the steam-valve by an eccentric, are free from these defects, and though more costly at the outset, soon save the difference in lessened repairs and consumption of steam. Pumps with a capacity of 8000 gallons per hour are very suitable, and can be used with a 3-inch hose pipe; smaller sizes are decidedly more liable to choke with tanning material. Rubber mitre-valves work satisfactorily, and do not choke frequently, but are costly, and easily damaged by hot liquors. On the whole brass clack-valves are the most satisfactory, but the hinge-pins, instead of fitting neatly in circular sockets, should be held in slots, allowing the back of the valve to rise half an inch, when it will clear itself of small hard myrobalan stones and suchlike things, which getting under a more tight-fitting hinge would prevent the valve closing, and so stop the pump. Whatever valves are employed, means should be provided for easy access without unscrewing too many bolts. If the several valve-chambers of the pump are closed by a single cover with an indiarubber washer, the spaces between them which make the joint should be faced with brass or gun-metal, as, if the least leakage takes place over an iron surface, the friction and solvent power of the liquors soon eat away the metal and render a good joint impossible. Where colour is of first importance, it is well to have the whole pump of gun-metal, but in any case the working cylinder should be brass-lined, and the piston and rod, and the valves and seatings should be of brass or gun-metal. Spring-rings are far better than pump-leather and are unaffected by hot liquors; chrome leather, however, will stand a good deal of heat. Double-acting force-pumps have practically superseded the older single-acting double or triple pumps. Instead of direct driving with a steam cylinder, it is sometimes advantageous to drive by belt, but at least one steam pump should be provided, so that pumping can be done when the main engine is not running, and the speed of the pump can be regulated to the work, which is impossible in a belt-driven pump. Steam pumps are sometimes very useful as fire engines.
Centrifugal pumps are very suitable for tannery work, where the liquor is drawn from a well, but are not well adapted for use with suction-pipes. If the form with vertical spindle is adopted, which is sunk below the liquor in the well, the pump fills itself, and needs no foot-valve, but unless the well is very large, or some convenient means is devised of withdrawing the pump, repair or cleaning is difficult. If the horizontal pattern is used, which is above the ground, repair, cleaning, and driving is much easier, but a foot-valve is necessary, which may itself give trouble, and some convenient means, such as a pipe from a raised tank, should be provided for filling the pump with liquor, as, unlike suction pumps, centrifugals will not start unless full, although they raise very large quantities when running, and from their steady flow, will deliver much more through a given pipe than an ordinary reciprocating pump with the same power. In selecting the pump, care should be taken that the pattern allows ready access, not only to the foot-valve, but to the body of the pump.
It is seldom satisfactory to use windbores or strainers to prevent tanning material getting into a pump, as they speedily become choked; and it will be found better, after taking such precautions as are possible, to have the pump and valve of ample size and suitable construction to pass what comes with the liquor. The writer has known a mop-head pumped and delivered through a 3-inch hose without stoppage, by a Tangye fly-wheel steam-pump with brass clack-valves such as have been alluded to.
Pulsometers have not, in the experience of the writer, proved satisfactory in tanneries, warming and diluting the liquor, consuming much more steam than a pump of the same power, and becoming easily choked. For the same reasons, steam-jet water-raisers are not to be recommended except where raising is to be combined with heating, as in some leaching devices ([p. 334]).