VacuumChambers VC0918SS, User Manual, Page: 6 / 9

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E. Vacuum cold trap.
A vacuum cold trap is a type of vacuum chamber. It is used to protect vacuum pump against harmful compounds that may
evaporate in the vacuum chamber. Such compounds can be, for example, water or ethanol. Due to the low pressure inside the
vacuum chamber, water and ethanol can evaporate at room temperature. Vapours can cause oil turbidity, deterioration of
pump performance, corrosion and damage to individual elements of the vacuum pump. The vacuum cold trap is used as an air
purifier for the air passing from the vacuum chamber to the pump. In the vacuum cold trap the vapours undergo a process of
deposition (a direct change from a gaseous state of matter to a solid state of matter). The cold trap is not a filter and does not
protect the pump against all harmful factors, e.g. dust. It is used only to ensure appropriate conditions for the deposition
process.
Photo 16: Vacuum cold trap.
The vacuum cold trap (Photo 16) consists of two tanks - the outer tank (5), where the deposition process takes place, and
the inner tank, in which the cooling agent (e.g. dry ice) is placed. The outer tank is equipped with the vacuum pump connecting
valve (1) and the vacuum chamber connecting valve (6). The vacuum pump connecting valve is equipped with an unsealing valve
(2) with an air filter. The inner tank has a polycarbonate lid with a gasket. The wide flange of the inner tank (4) functions also as
a cover for the outer tank. The tightness of the vacuum cold trap is ensured by a blue silicone gasket put on the outer tank.
Photo 17 shows inner tank, outer tank, blue silicone gasket and ice formed as a result of deposition.
Photo 17: Inner tank, outer tank, silicone gasket and ice formed on the internal tank.
The inner tank lid with the gasket is designed to limit the contact of the cooling agent with the environment. This slows
down cooling agent heating-up speed, and thus prolong its useful life. However it is not possible to completely prevent heating
of the cooling agent during its use. Gases are released from the cooling agent as a result of heating. Allow these gases to escape
inner tank
ice formed as a
result of deposition
outer tank
silicone gasket
1
2
1. Vacuum pump connecting valve.
2. Unsealing valve.
3. Inner tank lid with a gasket.
4. Inner tank flange.
5. Outer tank.
6. Vacuum chamber connecting valve.
3
4
5
6
outer tank
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from the inner tank, as their accumulation may result in dangerous pressure build-up in the inner tank. Therefore, the inner tank
lid must not be loaded with other objects, nor have limited free lift. The inner tank should not be tightly closed. After placing the
cooling agent inside the cold trap, it is recommended to gently lay the lid on the inner tank (flat side up), without pressing it
down. When the pressure inside the inner tank increase, the accumulated gas can push the lid up. If the lid can move upwards
freely, the pushing out should not be sudden. If the ability to move the lid up is limited by the user, ejection can be sudden and
dangerous.
The cooling agent should be placed only in the cold trap internal tank (Photo 18).
Photo 18: Vacuum cold trap filled with dry ice.
The deposition takes place inside the outer tank. The outer tank receives air sucked from the vacuum chamber. Air rapidly
cools down as a result of contact with a very cold inner tank wall. This causes vapour deposition on the inner tank walls. Photo
17 shows the ice formed as a result of a deposition. The purified air from the cold trap goes then to the vacuum pump.
Photo 19 shows the result of the cold trap work. Vacuum pumps visible in this photo were used to degassing water in the
vacuum chamber. Pump on the left were used in vacuum set with vacuum cold trap between the chamber and the pump. This
allowed the air to be purified of water vapour and prevented the vacuum pump from contaminating with water. The oil
remained clear. In the pump, shown on the right side of the photo, no cold trap was used. The vacuum pump was contaminated
with water and the oil became damp and turbid.
Photo 19: The result of the cold trap work - oil in vacuum pumps clarity (left: clear oil when using a cold trap, right: turbid oil
when no cold trap is used).
To use the vacuum cold trap:
1) Connect the cold trap to the vacuum chamber (connect one end of the pneumatic hose to the vacuum chamber connecting
valve and the other end to the vacuum chamber exhaust air valve).
2) Connect the cold trap to the vacuum pump (connect one end of the pneumatic hose to the vacuum pump connecting valve,
and the other end to the vacuum pump).
3) Place the inner tank centrally in the outer tank. The outer tank blue gasket should not protrude beyond the inner tank
flange.
clear oil visible in
the sight glass
turbid oil visible in
the sight glass