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732 CHAPTER 11: Intermittent and Recirculating Packed-Bed Filters <br /> 1. System static head, hs <br /> 2. Minor headloss in the pump discharge assembly, hmd <br /> 3. Friction loss in the transport pipe from the septic tank filter vault (or external <br /> pump basin) to the filter, hftp <br /> 4. Headloss in the manifold pipe to which the transport pipe and filter pipe laterals <br /> are connected, hfn, <br /> 5. Headloss in the laterals, ht, <br /> 6. Residual head at furthermost orifice in lateral, ham, <br /> The total dynamic head(TDH) for the system is <br /> TDH = hs + hmd + hftp + hfm + ht, + h,,,, (11-5) <br /> The minor headlosses are computed as a function of the velocity head. The head- <br /> loss due to friction can be computed by the Darcy-Weisbach equation or the Hazen- <br /> Williams equation. The Hazen-Williams equation, commonly used for plastic pipe, <br /> as given previously in Chap. 6 is: <br /> ht = 10.5(L)(Q)1.85(D-4 g') (6-5) <br /> where hfP = headloss through pipe, ft <br /> L = length of pipe, ft <br /> Q = pipe discharge, gal/min <br /> C = Hazen-Williams discharge coefficient, 150 for plastic pipe <br /> D = inside diameter of pipe, in (see Table 6-4, Chap. 6) <br /> For a distribution lateral, it can be shown that the headloss between the first and <br /> last orifice in a series of evenly spaced orifices is approximately equal to one-third of <br /> the headloss that would occur if the total flow were to pass through the same length <br /> of distribution pipe without orifices (Fair and Geyer, 1954). Thus: <br /> hfdp = 1l3hfp (11-6) <br /> where hfdp = actual headloss through distribution lateral with orifices, ft. <br /> Variations in orifice discharge. The difference in discharge between orifices <br /> in a distribution manifold can be assessed as follows.Assume the discharge from any <br /> orifice is to be held to a value mql, where m is a decimal value less than 1 and ql <br /> is the discharge from the first orifice. The discharge from orifice n can be computed <br /> by the following equation. <br /> q,, = 2.45C(D2) 2gh„ (11-7) <br /> where q„ = discharge from orifice n, gal/min <br /> C = orifice discharge coefficient [usually = 0.63 for holes drilled in plastic <br /> pipe in the field; Ball (1996)] <br /> D diameter of orifice, in <br /> g = acceleration due to gravity, 32.2 ft/s2 <br /> hn = head on orifice n, ft <br />