# What is the leak rate of a UHV system at higher pressure?

• Dan Kennedy
In summary, the conversation discusses calculating leak rates in a UHV system. The system is constructed to adhere to strict standards and is evacuated to 10^-9 Torr, but backfilled with N2 and Xe to a higher pressure. The speaker is wondering how to calculate the leak rate at this higher pressure, and suggests using a residual gas analyzer to test for outgassing from the interior surfaces. They also mention that the loss of pressure in a good UHV system is typically due to outgassing rather than exterior leaks.
Dan Kennedy
I'm trying to figure out some things regarding leak rates. I have a system which is constructed to adhere to UHV standards (total leak rate < 10^-10 Torr*L/s), baked out and evacuated to 10^-9 Torr, and then backfilled to about 600 Torr with N2 and Xe. So, there's a leak of air from the outside world to the lower pressure. I'm wondering how to calculate this leak rate. If I were at 10^-9 Torr, I'd just use the stated leak rate. I'd also be able to use a pressure rise measurement. But what about at higher pressure? I'd imagine that the leak rate is now less than 10^-10 Torr*L/s since there's a smaller pressure differential. Any way to calculate the leak rate at this pressure given the leak rate at UHV? I can't do a pressure rise measurement here because the leak rate is many orders of magnitude smaller than my base pressure.

In my experience the loss of pressure in a good UHV system is due to outgassing from the interior surfaces, not exterior leaks. This is true even after you bake it for a few days.

Thus when I run at 10^-9 Torr I keep the ion pump running in order to maintain the pressure.

I'm not sure that this helps with your question, except that you probably don't have any actual leaks from outside; they are actually all inside.

In your case you can test the composition of your interior gas with a residual gas analyzer. Then for a well-baked UHV system the principle out gassing will be hydrogen. If you find oxygen then you may have a leak.

## What is UHV leak rate?

UHV leak rate is a measure of the amount of gas or fluid that escapes from a system under ultra-high vacuum conditions. It is typically expressed in units of pressure (such as Torr) per unit time (such as seconds).

## How is UHV leak rate measured?

UHV leak rate is typically measured using a leak detector, which is a specialized instrument that can detect small amounts of gas or fluid escaping from a system. The leak detector is connected to the system and measures the pressure change over a specific time period to calculate the leak rate.

## What factors affect UHV leak rate?

Several factors can affect UHV leak rate, including the type and quality of the vacuum seal, the design and construction of the system, and the type and amount of gas or fluid being used. Additionally, external factors such as temperature and vibration can also impact the leak rate.

## Why is UHV leak rate important?

UHV leak rate is important because it can affect the performance and efficiency of a system. A higher leak rate means that the system is not able to maintain a stable vacuum, which can lead to contamination, reduced accuracy, and decreased productivity. In some cases, a high leak rate can also be a safety hazard.

## What is an acceptable UHV leak rate?

The acceptable UHV leak rate can vary depending on the specific application and industry. In general, a leak rate of less than 1x10^-9 Torr·L/s is considered to be acceptable for most UHV systems. However, for more sensitive applications, a lower leak rate may be required.

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