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To ensure representative sampling of the transformer oil, it is important that the oil inlet and outlet
valves on the transformer be distant as stated in the following section, to prevent oil re-circulation.
The valves should have a minimum diameter of 1.3 cm (½ in.), and be located near the
monitor.
Optional shutoff valves (preferably ball valves) are recommended below the monitor on the
oil RETURN and SUPPLY lines to isolate the monitor if unmounting is required.
Female, ball or gate type valves with a minimum diameter of ½ NPT are recommended for
the transformer valves.
The inlet and outlet valves must not be close to a pump.
The oil RETURN line must not exceed 11 m (35 ft).
The oil SUPPLY line must be longer than 1 m (3 ft) to reduce mechanical stress.
The distance between the two transformer valves should be a minimum of 1 m (3 ft).
The inlet valve should be at least 0.45 m (18 in.) above the main tank bottom.
Do not make straight lines between the transformer tank and the monitor. Include one loop
or bend in the oil line.
In very hot conditions, it is strongly recommended not to insulate the oil lines.
In very cold conditions, it is strongly recommended to permanently insulate the oil lines.
Most transformer manufacturers will install two 1.3 cm (½ in.) oil valves directly on the main tank
close to the location where the monitor will be installed. Both of these valves will generally be
accessible from the ground level.
When installing a Calisto/Calisto 2 monitor with a Precision Oil Temperature Probe, a
special probe fitting must be attached to the transformer valve before installing the oil
SUPPLY line. Refer to the Precision Oil Temperature Probe Manual.
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