MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

74Several names which are also appliedto the Persian wheel are:chain-bucket pump chain-of -potsbucket wheel paternoster wheelEgyptian sakia rahat (Pakistan)Egyptian noriascoop wheelOther names which refer to specific variations of this device are taboot,when bags are used instead of buckets, and potgarland, when a wheel withhorizontal “carrier-pegs ” drives the bucket loop (as in Figure 3.20). Untilabout 70 years ago, the name sakia was also used for the Persian wheelbut is now applied to the tympanum (see Section 3.3.1.6).By lengthening the chain of buckets, this device can lift water fromgreat depths. Two Persian wheels in series (i.e., one below the other)were the lifting mechanism for Joseph’s Well (see Section 1.2) which wasapproximately 300 ft deep. They are usually constructed entirely of wood,except for the containers, however modern versions have begun to use moremetal parts. Roberts and Singh (1951) report that Persian wheels withmetal gears, bearings, etc. are about 28 percent more efficient thanwith wooden components, Ball bearings in axles can also improve efficiencyand are almost mandatory when engines or electricmotors are supplyingthe power. Schioler (1973) reports the efficiency of a wooden Persian wheelwith metal bearing surfaces to be about 60 percent. Table 3.4 lists avail-able performance data on some typicalwooden Persian wheels.The cost of constructing a Persian wheel comprised primarily of wood,with some metal fasteners and wearing surfaces, could be expected to beabout $60. (This cost estimate reflects the use of inexpensive laborand materials in developing countries.) Thorkild Schioler’s Roman and