Putting Together a Compact UHV (Ultra-high Vacuum) Chamber for Spectroscopy

Small, inexpensive UHV chambers have been the backbone of many commercial labs and universities for decades. The cost of larger, feature-rich systems has gone up dramatically in recent years, making compact, DIY chambers even more cost-effective for specialized applications and education.

RBD has a range of products available to add value to your compact chamber, and in fact built our own recently to develop and test our microCMA compact Auger analyzer.

RBD Kimball Chamber
Kimball Physics chamber with RBD miniZ, IG2, and microCMA compact Auger analyzer

The Chamber

We started with an 8 inch spherical octagon chamber from Kimball Physics. This chamber has two 8.00″ CF and eight 2.75″ CF mounts, with an internal volume of  106.6 cu. in. (1,747 cc):

Kimball Physics Chamber
Kimball Physics 8.0″ Spherical Octagon – Vacuum Chamber

The vacuum chamber was fitted with an ion pump from Gamma Vacuum, and valves and windows from MDC. Affordable turbo pumps can be sourced from Pfeiffer (HiCube 80 Eco) and Edwards (nEXT85).

Rough vacuum gauges are available from a number of companies including Digivac.

Rough Vacuum Gauge
Rough vacuum gauge

Ion gauges and ion gauge controllers are available from a number of companies including Stanford Research Systems

Ion Gauge Controller
Ion gauge controller


To assist with water vapor desorption, the chamber is fitted with RBD’s miniZ. The mini-Z uses UVC radiation to desorb water from the chamber walls, resulting in faster pump-down times and lower ultimate vacuum.

RBD miniZ
RBD miniZ water vapor desorption system

This chamber is also fitted with RBD’s IG2 2 kV low cost sputter ion gun for specimen cleaning:


The ultimate purpose of this system was to house RBD’s microCMA compact Auger analyzer (shown below with the Z translator attached):

RBD microCMA
RBD’s microCMA compact Auger Analyzer

For applications that require elemental analysis, this chamber, with the addition of a PC and CMapp AES acquisition and data massage software, is now a complete system providing quantitative, surface-sensitive Auger electron spectroscopy. At around $50,000 for all the components listed here, this is one example of a budget-sensitive spectroscopy system that can be assembled, repaired and upgraded without costly field service visits.

AVC Up to Air relay update

The Auto Valve Controller (AVC) is used to open and close valves on PHI surface analysis systems such as the 5000 series XPS and 660 scanning Auger systems.  The AVC has a small built in microprocessor and so it also has the ability to protect the user from inadvertently opening a valve out of sequence and dumping the system.

The AVC needs to know that the turbo pump is on before certain valve functions are available. For example the V4 ion gun differential pump valve will not open under any circumstance if the turbo pump is not on.

So, how does the AVC know that the turbo pump is on? The Up to Air relay in the AVC auto valve controller is energized by a voltage from the turbo pump controller.

Up to Air relay inside AVC

Up to Air relay inside AVC

When the AVC was designed PHI used Balzers (now Pfeifers) turbo pumps which had a 240 VAC output voltage when the turbo pump controller was ON.  So, the Up to Air relay in most AVCs has a 240VAC coil.

Fast forward to today and some of those original Balzers/Pfeifers turbo pumps and controllers are now obsolete.  So when one of those controllers fails, it needs to be replaced with a new state of the art turbo pump and controller.

These days most turbo pump controllers have a 24 V DC output voltage that can be used to control the AVC up to air relay.  Both Edwards and Pfeifers have low cost replacement packages that are 4.5” CF flange mounted and also dry pumped backed. See information on those pumps at the bottom of this post.

The direct replacement 24 V DC  Up to Air relay is Grainger part number 1YCZ6.  This relay is the same form factor as the original Up to Air relay only it has a 24V DC coil instead of a 240 VAC coil.

24V up to air relay

24V up to air relay

Updating an AVC to this relay is a simple two-step process;

  1. Replace the Up to Air relay in the AVC
  2. Connect the Up to Air cable to the new turbo pump controller.

To replace the Up to Air relay in the AVC first make sure that all valves are closed and that the turbo pump is OFF.

Turn OFF the AVC and also unplug the power from the back of the AVC control.  Depending on your system configuration the AVC is located in the front left hand side of the electronics console, or in the back of the vacuum console.

If the solenoid manifold is located on top of the AVC, remove the screws that hold the manifold to the cover and then remove the cover from the AVC.  You should be able to move the solenoid manifold towards the back of the AVC and not need to unplug the wire bulkhead connector. Just balance the manifold on the edge of the AVC chassis.

If your AVC has the solenoid manifold mounted on the back of the AVC, then just remove the AVC cover.

Slide the AVC out enough so that you can get at the screws which mount the Up to Air relay to the side of the AVC.  The Up to Air relay is located on the right hand side of the AVC chassis.

Make a drawing or use your phone and take a picture of the connections to the Up to Air relay  to make sure that you put the connectors on the same way when you install the new relay. Remove the 240 VAC Up to Air relay bracket and install the new 24V DC relay.

Reattach the relay bracket to the side of the AVC.

Reattach the cover and solenoid manifold.

Reattach the power cord and slide the AVC back in.

Next, you need to attach the Up to Air cable to the new turbo pump controller.   Refer to the turbo pump manual for information on how to make that connection.   There will be a Setpoint output or some kind of external status connection that provides 24V DC when the turbo pump is ON.

Note the polarity of the wires on the Up to Air cable.  On the end that plugs into the back of the AVC, the larger connector is the negative (ground) wire and the smaller one is the positive (+24V) connector.   There are only two wires in the Up to Air cable.  Red is positive and Black is ground.

If your turbo pump controller has some other voltage for the status signal (such as 12V or 5 V DC) then you will need to find a version of the Up to Air relay with that same voltage.

Once the new Up to Air relay modification is complete then you should hear the V5 vent solenoid click when the turbo pump is turned ON.

The V5 vent valve is designed to vent the turbo pump in order to prevent back-streaming of oil vapors into the system in the event of a system dump.  When the AVC was first designed the backing pumps were all rotary vane mechanical pumps that used oil.

New state-of-the-art turbo pumps are typically backed with a dry pump and also have built in vent valves.   If your new turbo pump is also dry backed (both of the turbo pumps listed below are then you do not need the V5 vent function.

The V5 vent valve was mounted on the rough side of the old turbo pump. If your new turbo pump is dry backed all you need to do to disable the V5 vent valve is to close the little needle valve that is either on the V5 vent valve itself or on the solenoid manifold near the V5 vent solenoid.   (The largest solenoid is V1 and then you count out from there, V2, V3….)

If your new turbo pump is backed with a rotary vane oil pump then the V5 vent valve still needs to be connected to the rough line. The V5 needle valve is set to 1/4 turn CCW from the fully closed (full CW) position.

In addition, you want to make sure that the mechanical pump turns OFF when the turbo pump is turned OFF.  If you need help with that contact RBD Instruments.

The affordably priced turbo pumps below can replace the original Balzers TPU 040 thru TPU 062 turbo pumps on older PHI surface analysis systems.  If you order one, make sure that you order it with a 4.5” CF flange.  A 4.5” CF flange will make it easier to adapt the new turbo to the existing vacuum connections.

Pfeiffer Hi Cube 80 Eco

HiCube Eco 80

HiCube Eco 80


If you get one of the Pfeiffer  Cubes then this is the cable that you will need to connect to the Up to Air connector on the back of the AVC –  Digikey PN A120881-ND   made by TE and the TE PN is 22730001-1

Here is the Cable Data Sheet ENG_CD_2273000_A1

On the controller you will need to set option 36  Configure the Accessory B1 to 0.  Then the up to air relay will energize when the turbo pump control turns the turbo pump on.

Edwards T station nETX85H

T station

T station



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Removing oil from a turbo pump

This post will explain the procedure for removing oil from a turbo pump if the vent valve failed and oil was sucked up into the blades.

Under normal conditions, when an oil rotary vane mechanical backed turbo pump is turned off it should be vented (preferably with dry nitrogen) to prevent the back streaming of oil or oil vapors onto the turbo pump blades. Sometimes the vent valve will fail, or some other mishap can lead to oil being sucked up the roughing line from the mechanical pump into the turbo pump. When this happens, the symptoms are that the pump will not come up to full speed – usually only 50% to 75%. Or, sometimes the pump will come up to full speed (barely) but the pumping efficiency has been greatly reduced.

For Balzers turbo pumps, the procedure is to pull the turbo pump and place it in a beaker of isopropanol up to the bottom of the inlet as shown in the picture below. For other turbo pumps the procedure is probably similar, but you should check the turbo pump manual to be sure. NOTE: This procedure is only for turbo pumps that have a magnetic bearing on the front end.

turbo pump oil

Turbo pump shown upside down in container – motor is on top.










If you fill the container higher than the inlet shown in the picture above then you will get isopropanol into the motor (not good).  Let the turbo sit in the isopropanol for a few minutes and then move the turbo up and down a little bit to help remove more oil from the blades. Remove the turbo and if the isopropanol is yellow from the oil, discard the isopropanol (in the appropriate container so that it can be disposed of properly) and repeat.

Once the turbo is clean, remove it and place it on some Kim wipes or paper towels and let it dry thoroughly. Note that in the original Balzers procedure that Freon TF was used. Isopropanol has similar degreasing properties and is not nearly as bad for the environment.

As long as you have the turbo pump out, you should check the condition the bottom bearing. Remove the plug and inspect the felt washer or washer assembly. Clean or replace as needed.

Once the turbo pump is dry, it should be good to go.

You can also use isopropanol to clean the rough lines that go from the mechanical pump to the turbo pump.