is illustrated in Fig. 239. The Titan
battery uses a somewhat similar seal, as shown in Fig. 293.

Some of the older Willard batteries have a chamfer or groove in the
under, side of the cover. The posts have a ring of lead in the base
which fits up into the groove in the cover to make a tight joint.
This is illustrated in Fig. 13. The later Willard constructions, using
a rubber gasket seal and a lead cover insert, are illustrated in Figs.
278 and 287.

Filling Tube or Vent Tube Construction. Quite a number of designs have
been developed in the construction of the filling or vent tube. In
double covers, the tube is sometimes a separate part which is screwed
into the lower cover. In other batteries using double covers, the tube
is an integral part of the cover, as shown in Fig. 10. In all single
covers, the tube is moulded integral with the cover.

[Fig. 14a Vent hold in U.S.L. battery]

Several devices have been developed to make it impossible to overfill
batteries. This has been done by the U. S. L. and Exide companies on
older types of batteries, their constructions being described as
follows:

In old U. S. L. batteries, a small auxiliary vent tube is drilled, as
shown in Fig. 14. When filling to replace evaporation, this vent tube
prevents overfilling.

[Fig. 14b Filling U.S.L. battery]

A finger is placed over the auxiliary vent tube shown in Fig. 14. The
water is then poured in through the filling or vent tube. When the
water reaches the bottom of the tube, the air imprisoned in the
expansion chamber can no longer escape. Consequently the water can
rise no higher in this chamber, but simply fills up the tube. Water is
added till it reaches the top of the tube. The finger is then removed
from the vent tube. This allows the air to escape from the expansion
chamber. The water will therefore fall in the filling or vent tube,
and rise slightly in the expansion chamber. The construction makes it
impossible to overfill the battery, provided that the finger is held
on the vent hole as directed.

[Fig. 14c Filling U.S.L. battery (old types)]

Figure 15 shows the Non-Flooding Vent and Filling Plug used in the
older type Exide battery, and in the present type LXRV. The new Exide
cover, which does not use the non-flooding feature, is also shown. The
old construction is described as follows:

[Fig. 15a Sectional view of cover in older type Exide battery.
Top view of cover and filling plug, plug removed]