OPERATING INSTRUCTIONS

For the

BALZERS CPD 030 CRITICAL POINT DRYER

•NOTE: All operations of the Balzers CPD 030 are displayed by LED's on the "Blind Schematic" diagram on the front console of the instrument surrounding the pressure gauge. Please refer to this diagram whenever opening or closing valves (e.g. MEDIUM IN. MEDIUM OUT, GAS OUT, etc.) to ensure the valves are in their proper position.

•TERMS:

Dehydration Fluid .........Absolute (100%)
Ethanol Transition Fluid............ Liquid Carbon Dioxide (CO₂)

1. CPD START-UP

a) Carefully close the specimen/pressure chamber with the screw-on cover prior to operation. Over-tightening can damage this cover. Screw the cover down until it is snug ...DO NOT crank down on the cover!!!

b) Switch on the CPD with the main switch (green switch on lower right side of panel).

2. COOLING THE SPECIMEN/PRESSURE CHAMBER

a) Depress the COOLING button: The cooling LED on the schematic lights up and the cooling unit comes on.

•Actual temperature of pressure chamber is shown on temperature display

•At room temperature (around 22∘C) the pressure chamber is cooled down to 8^∘-10^∘C in from 5-8 minutes and will subsequently fall below this temperature by 3^∘- 4^∘C.

•The cooling unit keeps the temperature of the specimen chamber at ≤ 10^∘C by switching on and off.

b) Once the specimen chamber is ≤ 10∘C, the CPD is ready to use.

3. INSERTION OF SPECIMEN INTO THE PRESSURE CHAMBER

a) Without letting the samples dry out, transfer the prepared specimen(s) into an appropriate specimen holder immersed in the dehydration medium (baskets, coverslip holders, etc.).

•NOTE: We ONLY use absolute (100%) ethanol as the dehydration medium in the CPD ...Do not use anything but!!!

b) Unscrew the cover from the pressure chamber and carefully set it aside.

c) Fill the specimen chamber with the dehydration fluid to a level which will completely cover the samples when they are placed in the CPD. ·

d) Quickly insert the specimen holder into the pressure chamber.

e) Make certain the O-ring is properly seated on the cover. Screw the cover onto the pressure Chamber and tighten.

•NOTE: The prepared sample must always remain covered by the dehydration fluid or the transition fluid until the critical point drying process is completed.

4. SUBSTITION INTO THE TRANSITION FLUID (ETHANOL TO CO₂)

a) Open the liquid CO₂ tank with the grey handle on top.

b) Press the button MEDIUM IN: the medium inlet valve opens allowing liquid CO₂ to enter the pressure chamber and the appropriate LED on the schematic comes on.

c) While watching through the front sight-glass, fill the pressure chamber to the upper edge of the sight-glass.

d) When the CO₂ is to the proper level, press the MEDIUM IN button again: the medium inlet valve shuts and the appropriate LED on the schematic shuts off.

e) Press the STIRRER button: the magnetic stirrer is switched on and the stirrer LED lights.

•NOTE: Stirring accelerates the dehydration-transition fluid substitution process. If your samples are extremely delicate, the stirrer should not be used

f) After about five minutes, press the MEDIUM OUT button: The medium outlet valve opens (The LED goes off) and a portion of the dehydration-transition fluid mix is ejected from the pressure chamber (through a hose in the back of the machine).

g) While observing the liquid height through the front window, allow the liquid level to drop to just above the top of the specimens. DO NOT allow the level to drop below the specimens.

h) Refill the chamber with CO₂ to the top of the sight glass using the MEDIUM IN button (LED comes on).

i) Let the transition fluid in and let the media mixture out as described in steps (d) - (h) several times (usually from 8-10 times) until the ethanol that was initially placed in the chamber with the specimen has been completely replaced with the CO₂ transition fluid.

•NOTE: The number of times this process must be carried out depends on how much ethanol was initially placed in the chamber and how bulky the specimen is. The larger the specimen, the more runs it will take to exchange all of the ethanol in the sample with CO₂. Any ethanol left in the sample prior to achieving the critical point will result in damage to the specimen.

•NOTE: Do the initial 3-4 exchanges- 5-10 minute intervals to remove the majority of ethanol from the chamber. For the last 4-5 exchanges, lengthen these times to 30-60 minutes to remove ethanol from the sample itself.

•NOTE: see if all of the ethanol has been removed, hold a paper towel against the outlet hose (the Tygon tube in the sink behind the machine), press the MEDIUM OUT button (LED goes off) and let it drain onto the paper towel. If any residual ethanol remains in the chamber, you will be able to smell and/or see a wet spot on the paper. Continue exchanges until all trace of ethanol is removed.

5. DRYING THE SAMPLES

a) When you are certain all of the dehydration fluid has been replaced with the transition fluid, critical point drying can be carried out.

b) Switch off the magnetic stirrer by pushing the STIRRER button (LED goes off).

c) Fill the pressure chamber with CO₂to a level approximately 2-3mm below the upper edge of the sight glass by pushing the MEDIUM IN button (LED goes on). Push the MEDIUM IN button again to stop the filling (LED goes off).

d) Make certain all of the valves are closed by checking the schematic diagram. The LED's for MEDIUM IN, MEDIUM OUT, and GAS OUT must be off.

e) Switch off the cooling for the pressure chamber by pressing the COOLING button. The cooling LED on the schematic will shut off.

•WARNING:DO NOT LEAVE THE CPD UNATTENDED WHILE THE HEATER IS ON.
Over-pressurization will result in an explosive decompression of the chamber when the safety blow-out valve ruptures. These blow-outs will then need to be replaced and they are expensive.

•NOTE: Critical point is achieved at about 74 bar. The blow-out valve is set to rupture at 150 bar.   You should NEVER, NEVER, NEVER allow the pressure to go above 100 bar.

f) Press the HEATING button to turn the pressure chamber heater on. The heating LED will light on the schematic. NOTE: The maximum heating temperature is pre-set by the technician at 40°C. This should never be changed. If you have any questions, see the technician.

•NOTE: Temperature and pressure in the pressure chamber will both rise (note the pressure gauge in the center of the console and the LED temperature readout to it's left).

•NOTE: When the temperature reaches approximately 20^∘C, the level of the CO₂ will slowly drop until the critical point has been reached due to the transition of the liquid into the gaseous state.

•The critical point of CO₂ is:
Critical temperature of CO₂.....31.1^∘C 
Critical pressure of CO₂........73.8 bar (1073 psi)

g) Once the critical point of CO₂is reached, the sample begins to dry. Raise the temperature and pressure slightly above the critical values prior to releasing the gas from the pressure chamber.

•IMPORTANT NOTE: There is no reason to heat the chamber all of the way to 40^∘C if thecritical pressure has been reached at a lower temperature. Depending onthe initial level of CO2 in the pressure chamber prior to heating, thecritical pressure of 74 bar can be achieved at temperatures ranging from32-38^∘C.

6. RELEASING THE GASEOUS TRANSITION MEDIUM

a) Once the critical values have been achieved, the gaseous CO₂ can be released.

b) Make certain the manually operated gas dosing METERING VALVE is closed (all the way clockwise). This is a needle valve so it does not have to force-tightened when it reaches its clockwise stop. DO NOT FORCE-TIGHTEN THIS VALVE!!!

c) Press the button for GAS OUT: the gas outlet valve will open and the appropriate light on the schematic will light

d) Carefully turn the METERING VALVE counter-clockwise. Read the next step before proceeding.

e) Watch the flow meter on top of the CPD: Open the METERING VALVE until the indicator ballfloats in the upper half of the flow meter measuring tube.

f) You will continually need to readjust the METERING VALVE as pressure in the chamber decreases to keep the ball in the upper half of the tube.

g) Pressure decrease to atmosphere should take from 15-20 minute