Taylor-Wharton Liquid Withdrawal Device - Manual (Page 3)

Operation
Installation
(cont.)
11. To remove the LWD, first open the VENT valve to
release all pressure in the Dewar. Then loosen the band
clamp enough to allow it to pass over the Dewar flange,
disengage the cable snap from the ring on the LWD and
lift the withdrawal unit out of the Dewar.
Filling – It is not necessary to remove the LWD unit from
the Dewar for filling. You may fill the Dewar by pressure-
transfer of liquid nitrogen through the LIQUID valve of the
LWD.
WARNING: Over pressurization of the Dewar could
result in serious bodily injury or property damage.
Never exceed the 10 psig (0.7 bar/69kPa) relief valve
pressure setting of the LWD.
To fill, remove the spout assembly and connect a 22 psig
(1.52 bar/152kPa) or lower pressure liquid supply cylinder
to the withdrawal device using a liquid nitrogen transfer
hose and the fill adapter with the LWD.
WARNING: The transfer hose must be used with a
pressure relief valve to prevent excessive pressure
buildup in the hose when the valves are closed at both
ends of the hose. If liquid nitrogen is trapped between
the valves of the liquid cylinder and the LWD, it has no
escape path as it warms and expands. The resulting
pressure can cause the hose to rupture and may cause
personal injury. The current model LWD is equipped
with a pressure relief valve. Previous versions of the
LWD must be used with a transfer hose equipped with
a pressure relief valve.
Once the transfer hose is connected, open the LWD VENT
valve first and then open the LWD LIQUID valve. Then
slowly open the liquid valve on the supply cylinder until
liquid flow is established. Adjust the VENT valve to maintain
a back pressure of 8 to 10 psig (0.6 bar/55 kPa to 0.7 bar/
69 kPa) in the Dewar. When liquid sputters from the VENT
valve, quickly close the liquid vavle on the supply cylinder,
next the LWD LIQUID valve and then the LWD VENT valve.
WARNING: Closely monitor Dewar pressure
througout the fill process. Never let the pressure
exceed 10 psig (0.7 bar/69 kPa). If the pressure ap-
proaches 10 psig, immediately fully open the LWD
VENT valve and/or close the LWD LIQUID valve as
necessary to control the pressure in the Dewar.
Loosen the hose connection slowly and allow all pressure
and any remaining liquid to be verified before completely
disconnecting the hose.
The primary relief valve, set at 10 psig (0.7 bar/69 kPa),
maintains the normal operating pressure of the LWD. A
secondary relief valve, set at 15 psig (1.0 bar/103 kPa),
prevents hazardous pressure rise in the event of primary
relief valve malfunction or if its capacity is exceeded. Never
replace either of these parts with higher value relief valves;
increasing the pressure in the Dewar beyond 15 psig (1.0
bar/103 kPa) may burst the Dewar and cause personal
injury/property damage.
To fill the Dewar by pouring liquid from another container,
(This is not the recommended filling method) first open
the VENT valve to release pressure. Then, loosen the band
clamp, unsnap the safety cable, and remove the LWD unit.
When replacing the LWD on the filled Dewar, leave the
VENT valve open until the flanges are securely clamped. To
pressurize the Dewar for liquid withdrawal, refer to “Pres-
sure Building” below.
Note: Be sure flanges surfaces are warm, clean and dry.
The o-ring must be cleaned and lightly lubricated before
replacing the LWD.
Liquid Withdrawal – When the liquid valve is opened,
pressure in the Dewar forces liquid to go up through the
withdrawal tube and out through the valve. The liquid
nitrogen can be dispensed through the spot or through
plumbing connected to the liquid outlet.
Pressure Building – If the Dewar is filled properly, liquid
nitrogen evaporation will normally maintain a pressure
sufficient to sustain liquid withdrawal. However, if pressure is
lost, bubbling dry nitrogen gas through the liquid may restore
proper operating pressure. This adds heat to the liquid,
causes evaporation, and increases pressure. Connect a
pressure-regulated – 8 to 10 psig (0.6 bar/55 kPa to 0.7 bar/
69 kPa) – source of dry nitrogen gas to the LIQUID connec-
tion. Open the LIQUID valve and adjust the VENT valve to
maintain a back pressure of 8 to 10 psig (0.6 bar/55 kPa to
0.7 bar/69 kPa) while the gas bubbles up through the liquid.
After several minutes, close the valves and read the pres-
sure gauge. If the pressure does not remain above the 5
psig (0.3 bar/34 kPa), resume the gas flow until the liquid
has warmed enough to provide normal operating pressure.
External pressurization can be applied while withdrawing
liquid from the Dewar by connecting a supply of nitrogen
gas, regulated to a pressure of 8 to 10 psig (0.6 ba/55 kPa
to 0.7 bar/69 kPa), to the vent valve connection.