VLI™ OPERATION & MAINTENANCE MANUAL
© 1998 - 2007 DH Instruments, a Fluke Company
Page 4
2.3
OPERATION
2.3.1
INTERFACING TWO LIQUIDS (OIL, WATER, ETC.)
Pressures can be generated from either side, or on both sides. The interface reference level
can then be changed by adjusting the volume on either side. When interfacing two liquids it
is preferable if they are easily identifiable. If both liquids are the same color, identification of
the interface level may be difficult.
2.3.2
INTERFACING A GAS WITH A LIQUID
It would not be possible to generate pressure by decreasing the volume in the hydraulic
pressure circuit. Pressure is increased through the gas pressure circuit. The hydraulic circuit
volume can be adjusted to fine tune the interface reference level. Again, unless the fluid
temperature or the volumes change, the level will stay the same.
Decreasing pressure is achieved by releasing gas pressure through the gas pressure circuit.
Never open a hydraulic exhaust to release pressure when using a VLI with gas. Equipment
failure and personal injury may occur.
An additional caution must be observed when interfacing a gas with a liquid in the VLI. This
is due to the fact that once a pressure is reached, there exists a possibility that some of the
gas will be dissolved into the liquid. This condition could lead to outgassing (rapid boiling)
when returning to zero.
To prevent boiling liquid into the gas or gas into the liquid, decrease pressures slowly to
approximately 200 psi (1.4 MPa). Hold that pressure until outgassing has apparently stopped
and then decrease to zero.
