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the systems. For the machine that its system has already been opened, the pipe welding
shall be finished at once.
As the machines have strict requirement for system moisture content, so, when a
machines pipe is opened, the opening of pipe shall be sealed with tape at once to prevent
air from entering in system, and pipe welding of opening shall be finished within 20
minutes.
As the system of DW‐86L386 series of ultra‐low temperature cabinet products has very
strict requirement for vacuum degree, the system will occur bad refrigeration or non‐
refrigeration due to insufficient vacuum. Therefore, it is required that maintenance shop
shall spend more time in vacuumizing this series of products than normal refrigerators;
vacuum pump above two liters needs more than 6 hours, vacuum pump below two liters
needs more than 8 hours. To ensure vacuum degree, when one system is being repaired, it
is required that two vacuum pumps (high and low pressure) shall vacuumize separately at
the same time, pressure gage and gage valve shall be installed on high and low pressure
infusion tubes.
When evacuation time has been reached, firstly, stop high pressure evacuation, and the
opening of high temperature infusion tube shall be sealed and welded immediately(as the
pressure of freezing medium is too high, when a machine is refrigerating, high pressure
can not seal the opening), low pressure evacuation shall continue for an hour. During this
period, prepare freezing medium needed for infusion and relevant equipment. After one
hour low pressure evacuation, turn off pressure gage valve; now, it is required that the
machine shall keep the state of negative pressure for more than one hour to check if
machine system is in vacuum state or not. During this period, check if pressure gage
appears the condition of rising, otherwise, re‐vacuumize for more than one hour, then
keep the state of negative pressure for more than one hour, carry out such evacuation
operation until pressure doesn't rise, then infusion can be carried out.
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