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5.9 Appurtenances 189
valves are commonly found in areas where a water district has contracted with another dis-
trict or a private developer to limit the maximum demand to a value that will not adversely
affect the provider’s system.
5.9.9 Throttle Control Valves

Throttle control valves simulate minor loss elements whose head loss characteristics
change over time. With a throttle control valve, the minor loss K is adjusted based on some
other system flow or head.
5.9.10 Manholes

Access manholes are spaced 1,000 to 2,000 ft (300 to 600 m) apart on large conduits. They
are helpful during construction and serve later for inspection and repairs. They are less
common on cast-iron lines than on steel and concrete lines.
5.9.11 Insulation Joints

Insulation joints control electrolysis by introducing resistance to the flow of stray electric
currents along pipelines. Modern insulation joints make use of rubber gaskets or rings and
of rubber-covered sections of pipe sufficiently long to introduce appreciable resistance.

5.9.12 Expansion Joints
The effect of temperature changes is small if pipe joints permit adequate movement. Steel
pipe laid with rigid transverse joints must either be allowed to expand at definite points or
be rigidly restrained by anchoring the line.

5.9.13 Anchorages
Anchorages are employed (a) to resist the tendency of pipes to pull apart at bends and other
points of unbalanced pressure when the resistance of their joints to longitudinal stresses is
exceeded, (b) to resist the tendency of pipes laid on steep gradients to pull apart when the
resistance of their joints to longitudinal stresses is inadequate, and (c) to restrain or direct the
expansion and contraction of rigidly joined pipes under the influence of temperature changes.
Anchorages take many forms as follows:
1. For bends—both horizontal and vertical—concrete buttresses or kick blocks resist-
ing the unbalanced pressure by their weight, much as a gravity dam resists the
pressure of the water behind it, taking into consideration the resistance offered by
the pipe joints themselves, by the friction of the pipe exterior, and by the bearing
value of the soil in which the block is buried
2. Steel straps attached to heavy boulders or to bedrock
3. Lugs cast on pipes and fittings to hold tie rods that prevent movement of the pipeline
4. Anchorages of mass concrete on steel pipe to keep it from moving, or to force mo-
tion to take place at expansion joints inserted for that purpose—the pipe being well
bonded to the anchors, for example, by angle irons welded onto the pipe
5. Gate chambers so designed of steel and concrete that they hold the two ends of
steel lines rigidly in place.
In the absence of expansion joints, steel pipe must be anchored at each side of gates and
meters in order to prevent their destruction by pipe movement. In the absence of anchors,
flanged gates are sometimes bolted on one side to the pipe—usually the upstream side—and on
the other side to a cast-iron nipple connected to the pipe by means of a sleeve or expansion joint.