Grease for freeze dryers - neither too much nor too little

Every new user receives the high vacuum grease from us with AMARU Freeze Dryer. During training there are usually concerns about whether the 50g pack is sufficient and when it will be necessary to order more. We usually explain during the training that the whole pack should last at least one year on one AMARU, possibly two or more.

Why use High Vacuum Grease on vacuum systems anyway?

The deeper the vacuum we are trying to achieve, the more susceptible the system is to minor leaks where air can pass through. In the case of freeze dryers, we're talking about only 10 times the pressure on the surface of Mars. So every scratch or snapped human hair in the chamber door is a vacuum leak.

These leaks, usually invisible to the human eye, are difficult to find, and in practice it is almost impossible to manufacture parts to be perfectly smooth. That's where the carpet-bombing method of applying grease comes in. We don't need to know exactly where the unevenness is in the rubber seal, but simply grease it everywhere in the mating surfaces. The grease itself will then conform to both the gasket and the chamber door, sealing any possible vacuum leaks.

How to apply vacuum grease?

If we want to fill grooves in the gasket or unevenness in the stainless steel surface that are so small that they can hardly be seen, we don't need much Vaseline. A really thin layer is enough, but it should be spread evenly so that the carpet bombing actually occurs.

What exactly is a "thin layer" is subject to discussion with users during installation. It is best defined by a colleague who advises "Apply and spread as when applying sunscreen, where no clumps of white cream are visible but the surface of the skin is shiny".

What if there's too much grease?

We've seen that too. Too much high vacuum grease creates clumps that can turn out to be frustrating for the user. Vaseline itself is very good at trapping dust and dirt. The more of it there is, the more likely it is that some speck will get on the contact surface and simply create a path for air to flow into the chamber where we want to achieve a vacuum.

Too much of anything is bad for everything, and Vaseline is not meant to replace a freeze dryer door seal.

Similarly, a thin layer of old Vaseline that has not been cleaned for a long time can become an enemy of the deep vacuum.

When to reapply the grease and apply a new layer?

Here the answer is sometimes surprisingly simple - only when the lyophilizer has not reached the required vacuum. For companies that need to establish a consistent maintenance schedule, we recommend thoroughly cleaning the seals and applying a new coat of Vaseline once a month.

Does it have to be a grease designed for vacuum systems?

Yes. So far, none of our users have discovered a working alternative, although we have had a lyophilizer where the operator has tried using hand cream. At another customer, they used some sort of vaseline with a different intended use, which resulted in irreversible damage to the chamber seals, putting the lyophilizer out of service.