Figure 3-9. Vent valve.

ME 6120-250-12/3-9

Control knob

Valve body

Valve

Vent outlet

Figure 3-9. Vent valve.

(1 ) counterclockwise to open. Close the vent valve

h. Venting. The transformer should be vented to

when pressure gage shows no further drop, ap-

the atmosphere before placed in service if it has been

proximately zero. At higher altitudes, decreased air

pressurized for leak tests or storage, or if the unit has

density reduces transformer cooling efficiency and

been opened and resealed. Venting should take place

lowers bushing arc-over voltages. Lower atmospheric

with the liquid temperature at 25 . If it is necessary to

pressures may require venting of the transformer before

vent at other temperatures, re-vent as soon as the unit

putting transformer in service in order to equalize

returns to 25 . This operation is necessary to

internal and external pressures. If transformer is to be

prevent excessive operating pressures or vacuums.

used at elevations above 3300 ft. (para. 2-19).

To vent the transformer open vent valve (fig. 3-9) by

turning control knob

3-15