Troubleshooting Vacuum Issues in Beckman Coulter Ultracentrifuges: A Comprehensive Guide

In an ultracentrifuge, it is crucial to remove air molecules from the 'leak-tight' chamber. To achieve this, Beckman uses a mechanical vacuum pump and diffusion pump in combination. However, in high-performance and high-speed model centrifuges, only a vacuum pump is necessary.

Mechanical vacuum pumps, also known as roughing pumps or forepumps, are the only types that can operate against atmospheric backpressure. The most commonly used mechanical pump is the vane type.

The actual removal of air molecules occurs during four stages of the pumping cycle: intake, transfer, compression, and exhaust.

Vacuum system in an ultracentrifuge

Beckman Coulter ultracentrifuges use vacuum pumps that are characterized by the following features:

 • Two-stage, oil-sealed, rotary vane type

• Maximum vacuum of 20 microns at the inlet

• Pump speed of around 7 cubic feet per minute (cfm)

• Direct drive design with motor in-line with the pump

• Anti-suckback system included

• Mechanical oil stirrer system

• Gas ballast to allow pumping of condensable vapors

• Inlet, outlet, and muffler connections

• Sight glass to indicate oil level

• Easy disassembly into major parts for cleaning and repair

• Motors that can be wired for different voltage requirements

Beckman Coulter ultracentrifuge systems utilize a combination of a diffusion pump and a vacuum pump in series to achieve high levels of vacuum. However, the diffusion pump alone is not capable of exhausting to the atmosphere. As a result, it is exclusively employed in the ultracentrifuge models.

As shown in the diagram below, the Diffusion Pump Assembly consists of the following parts:

• Pump body: a steel cylinder with an oil reservoir at the base of the pump

• External cooling jacket or fan assembly attached to the pump body

• Jet assembly: a hollow assembly with nozzle(s)

• Cold Cap assembly attached to the inlet

• Inlet and exhaust outlet

• Electrical heater assembly

• Low vapor pressure oil (Use only the Beckman Coulter recommended silicone diffusion pump oil.)

Schematic of a diffusion pump

During normal operation of a Beckman Coulter ultracentrifuge, the vacuum pump runs first. The diffusion pump fan assembly operates. The oil reservoir heater is activated depending on the vacuum level, heating the oil until it boils. The hot oil vapor is then released through the jet nozzles, expanding as it moves from high to low pressure. As gas molecules (air and water) enter the diffusion pump inlet, they collide with the heavy oil vapor stream and are directed towards the pump's exhaust outlet by the vacuum pump. The supersonic vapor jet of diffusion pump oil then strikes the cooled diffusion pump wall, causing the oil vapor to condense and flow back into the oil reservoir to begin the cycle anew.

To achieve the necessary vacuum conditions in ultracentrifuges, the diffusion pump must be used in series with a vacuum pump. The diffusion pump cannot be exposed to the atmosphere while the oil is hot due to potential oil degradation and vacuum system contamination.

The lowest pressure achievable in the ultracentrifuge vacuum systems is partly limited by the presence of oil vapor from the diffusion pump. This occurs due to "backstreaming" of oil vapor molecules from the diffusion pump nozzle towards the inlet, as well as "back migration" caused by re-evaporation of oil at the top of the pump body.

The amount of backstreaming can be reduced by optimizing the pump nozzle design and using cold caps, traps, or baffles above the pump body. Controlling the temperature of the pump housing and the baffle system can also reduce back migration.

While this backstreaming and back migration is not a significant issue for typical preparative ultracentrifuges, the oil vapor can be problematic for the optical systems of analytical ultracentrifuges.

The diffusion pump is a low-maintenance component, with no mechanical moving parts. However, it is important to perform regular maintenance to ensure optimal performance. Here are the recommended maintenance tasks:

Check the diffusion pump oil regularly and change it if it appears light to dark brown in color.

1. Remove the jet assembly once a year for inspection and cleaning.

2. Inspect the oil heater and check its resistance.

3. Inspect and clean the cooling fan and verify its operation.

Here are some troubleshooting tips for the diffusion pump: 

• Oil Heater Assembly - If the heater is burned out, the system will only achieve a normal mechanical pump vacuum level (less than 100 microns). The reason for heater failure may be due to loss of oil, hours of operation, or loss of cooling.

• Loss of Fluid - Normally, loss of fluid is due to a leak in the vacuum system.

• Cooling Fan Malfunction - This causes a loss of diffusion pump cylinder cooling.

• Loss of Vacuum - The system will initially achieve the correct vacuum. As the pump cylinder heats up, the vapor no longer condenses, and loss of vacuum occurs.

• Diffusion Pump Fluid Contamination - If the drive oil or liquid from the rotor spills into the diffusion pump, it may cause the pump to lose effectiveness.

• PMC Check - Check for the correct oil level, heater function, and air flow.

• Normal Loss of Vacuum - With a chamber vacuum of 150 microns or better, it is normal to see a slight loss of vacuum immediately after turning on the diffusion pump heater.

Vacuum System Troubleshooting: Finding and Fixing Leaks:

1. Check for obvious issues such as cracked hoses, tubing, and foreign material on "o" rings.

2. Confirm the mechanical pump is working properly by measuring the vacuum level at the pump inlet, which should be less than 20 microns. Replace vacuum pump oil on a regular basis.

3. Be aware that removing moisture from a vacuum system can take time, and during this period the vacuum level will remain at approximately 500 microns.

4. For larger leaks, turn off power and listen for a hissing sound to detect the source of the leak.

5. Try to isolate sections of the vacuum system to narrow down potential leak locations.

6. Use acetone to identify leaks: if you're able to obtain a vacuum of 300 microns or less, squirt acetone on possible leak areas. The vacuum indicator will exhibit a loss of vacuum at the area where the leak is present.

7. Ensure the diffusion pump is functional by following proper maintenance and troubleshooting procedures.

Procedure to change Vacuum Pump Oil used in Beckman Optima ultracentrifuges and Avanti J30I centrifuges

Prior to draining the oil, it is always best to operate the vacuum pump until it is at its normal operating temperature of approximately 65ºC.

•  Always take a test run in the ultracentrifuge with the vacuum pump running to warm up the existing oil. When the pump oil is warm it is less viscous and contaminants will mix with the oil.

•  Stop the test run. Release vacuum by depressing the "VACUUM" key on the ultracentrifuge keypad, which will stop the vacuum pump and release the vacuum. Turn off power to the instrument and unplug the instrument power cable from the AC Mains.

•  Disconnect the vacuum pump power cord. Disconnect the vacuum hose from the inlet port. Remove the vacuum pump from the centrifuge. Place the vacuum pump on the flat surface to perform the work.

• Remove the exhaust filter. Locate the vacuum pump drain plug. Place the waste oil container under the drain plug. Remove the drain plug. Drain the oil. Always consider and treat the waste oil as hazardous. Hand over the waste oil container to the laboratory safety official at the site for disposal.

•  Replace the drain plug.

•  Remove the oil fill plug (normally on top of the pump housing) Add Vacuum pump oil until the correct level is reached in the sight-glass. Replace the oil fill plug.

•  Replace the exhaust filter. It is good practice to always install a new exhaust filter after oil replacement as a part of the preventive maintenance procedure.

•  Replace the vacuum pump into the centrifuge. Inspect the vacuum pump hose carefully before reconnecting it to the vacuum pump. Replace hose if you observe faults or fine cracks in it.

•  Reconnect the power cord. Make a test run to verify proper operation of the vacuum pump and centrifuge.

 Important tips:

•  Do not mix hydrocarbon based oils with synthetic oil in vacuum pumps.

•  Use only “Beckman” Direct Drive Vacuum Pump Oil (Beckman PN. 341661 and Beckman PN. 392760) or oil that is recommended by vacuum pump manufacturer.

Optima ultracentrifuge flags persistent Diagnostic d63 Drive error

If your Beckman Coulter Optima ultracentrifuge flags d63; it is an indication that the drive thermostat mounted on the drive has overheated (causing an open circuit) during normal run, or that it did not cool down and get deactivated after a 5 minute waiting period on power up. When a power fail diagnostic occurs during a normal run, the ultracentrifuge will shut down with brake.

If this fault occurs, a Beckman trained and experienced expert will make it a point to check the drive, drive oil, drive fans,  and the drive control system of the ultracentrifuge.

website: www.serviceai.us ; email: support@serviceai.us; Technical Support: +1-510-899-1340

Steps required for physical installation of a Beckman Coulter Optima ultracentrifuge

Important Note: To ensure proper electrical installation and checkup as outlined below, it is imperative to engage a certified electrician for power requirements. Furthermore, we highly recommend that a qualified engineer handles the installation and thorough inspection of your Beckman Coulter Optima L ultracentrifuge, while also providing training to your staff on its correct usage and handling of the ultracentrifuge and rotors before operation.

Power:

a. Check for correct wall receptacle and voltage at the outlet. Power required is 180 to 264 Volts AC measured as shown. It is advisable to test the line voltage at the plug while the instrument is accelerating and cooling; therefore, we would strictly recommend that the ultracentrifuge always be installed by a Beckman trained engineer. Service AI has Beckman Coulter trained service experts. You can email us at support@serviceai.us, or call us at our technical support line at +1-510-899-1340 for more information.

b. Remove console cover, front panel and top cover.

c. Make sure jumper connector on the power supply boards plugged into the correct voltage range socket J52 A, B, or C. (Select the jumper for the lowest voltage reading during maximum power consumption.)

J52 VOLTAGE RANGE

A 180 - 206

B 207 - 233

C 234- 264

---

Physical installation procedure:

a. Position ultracentrifuge in desired location. Maintain 6" minimum clearance at rear and 3" minimum clearance at each side.

b. Position the four pads provided under the leveling legs. Mark the position of each pad on the floor.

c. Roll out instrument away from pads.

d. Glue (epoxy) pads to floor.

e. Roll instrument back into position and screw the four leveling legs down into the pads until they have bottomed out.

f. Now screw each leveling leg down five additional turns. Make sure all four casters are off the floor.

NOTE: A solenoid inter-lock prevents the chamber door from being opened during operation and/or with the power off. The chamber door can be opened with the door handle only when the power to the ultracentrifuge is on and the vacuum is off.

g. Open the chamber door (see note above). Level the ultracentrifuge as if it had only three legs. Adjust level by placing the spirit level on the drive shaft (crown) and adjust the leveling legs so the air bubble is centered. First level it front- to- rear by adjusting the left front and left rear legs. Then level it left to right by adjusting the right front leg only. (Make sure you do not tilt the instrument). Screw in the right rear leg until it just touches the pad. Now screw it down 1/4 turn more. This does not affect the level of the instrument.

h. After instrument is leveled, make sure all four casters are off the floor and all four leveling legs are still bottomed out.

---

website: www.serviceai.us; email: support@serviceai.us; technical support: +1-510-899-1340

Why do centrifuge tubes leak?

Most leaks are due to improper handling or sealing. Always refer to the Rotors and Tubes manuals before attempting to use the rotor.

 1.     OptiSeal™ : Make sure the neck area is dry and tubes are correctly filled.

 2.     Quick-Seal™ : Fill to the base of the neck leaving a small (approx. ¼" diameter) air bubble and seal with the proper Beckman Coulter heat sealer and seal former. For best results, follow the Quick-Seal™ user's booklet directions.

 3.     Open top tubes: Thinwall tubes must be capped and filled for use in fixed angled rotors (torque the cap to 120 inch-pounds). In swinging bucket rotors the fill level is 2 - 3mm from the top. Thickwall tubes (without caps) in fixed angled rotors need to be filled between half to three-quarters full. In swinging bucket rotors fill to within 2 - 3mm from top.

4.     Bottles: Always ensure all sealing surfaces and O-rings are dry. Wet O-rings can act as a pathway for fluids, causing a leak. Be sure all O-rings are present, in good condition, and are dry.

website: www.serviceai.us ; email: support@serviceai.us

What RPM can one use with a Beckman Coulter rotor to obtain the desired "g" force ?

The RPM/RCF information is included in each rotor operator's manual. You can also use the G-Calculations program found at this Beckman Coulter website link to obtain this information. Also, many Beckman Coulter centrifuge models can be programmed using RCF ("g") or RPM so that this calculation is not necessary when using these models.

website: www.serviceai.us ; email: support@serviceai.us

What is the minimum/maximum fill volume for my tubes?

Fixed angle rotors: all open-top, thinwall tubes, requiring multi-piece metallic caps, are to be filled as far as possible and sealed. For thickwall tubes and bottle assemblies, the minimum fill volume is half of its maximum fill volume.

Swinging bucket rotors: all thinwall tubes should be filled to 2 - 3mm from the top. 

All OptiSeal TM and Quick-Seal TM tubes are to be filled per instructions in the Rotors and Tubes manuals (LR-IM-, TLR-IM-, and JR-IM-). 

It will be important to note that there are exceptions to these guidelines. More detailed information and fill volumes for each tube and bottle type used in a given rotor is found in each rotor operator's manual and in the Beckman Coulter Rotors and Tubes manuals , which are available from Beckman Coulter.

website: www.serviceai.us ; email: support@serviceai.us

---