Page 355 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

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9.3 Theory of Backflow and Backsiphonage 315
the negative pressure or reversed force necessary to cause backsiphonage and backflow,
there must also be the cross-connection or connecting link between the potable water sup-
ply and the source of pollution. Two basic types of connections are used in piping systems:
1. The solid pipe with a valved connection
2. The submerged inlet.
Figures 9.17a and 9.17b illustrate solid connections. This type of connection is often
installed where it is necessary to1ay an auxiliary piping system from the potable source. It
is a direct connection of one pipe to another pipe or receptacle. Solid pipe connections are
often made to continuous or intermittent waste lines where it is assumed that the flow will
be in one direction only. An example of this would be used cooling water from a water
jacket or condenser as shown in Fig. 9.17b. This type of connection is usually detectable,
but creating a concern on the part of the installer about the possibility of reversed flow is
often more difficult.
Submerged inlets are found on many common plumbing fixtures and are sometimes
necessary features of the fixtures if they are to function properly. Examples of this type of
design are siphon-jet urinals or water closets, flushing rim slop sinks, and dental cuspidors.
Old-style bathtubs and lavatories had supply inlets below the flood-level rims, but modern
sanitary design has minimized or eliminated this hazard in new fixtures. Chemical and

Non potable Potable
(a)

City supply Condenser

Sanitary sewer
(b)

Figure 9.17 Valved Connections between Potable Water and
(a) Nonpotable Fluid; (b) Sanitary Sewer