Performing Glove Box Leak Tests
If you suspect a leak, you should perform a leak test. This can be achieved by raising the glove box to an extreme positive or negative pressure, then measure the rate of change of pressure over a period of time. The resulting change, known as the leak rate, indicates how well your glove box is sealed.
The most common test uses positive pressure. However, in some glove box systems, a negative pressure leak test can be performed. It is unusual for leaks to be revealed only under negative pressures. Both tests can identify if there a significant leak within the system. Yet, they are not thorough enough to provide exact leak rate or demonstrate where the leak is coming from.
Positive Pressure Leak Tests
Our glove box has an automated leak test programme to simplify the process. This calculates the leak rate of the system by:
- Pressurizing the system to a set overpressure value between 5 mbar and 10 mbar
- Stabilizing the internal temperature
- Monitoring the system pressure
- Measuring the internal and external pressure every 5 minutes to update the current leak rate
The test can run for up to an hour before allowing the overpressure to return to its normal value.
Importantly, the leak rate calculated may not match the leak rates listed in your glove box specifications. Finding an exact leak rate requires specific conditions to prevent variations in external pressure, and internal and external temperature. It is difficult to prevent these variations in laboratory conditions. Additionally, glove box classification values are usually taken with the gloves removed and the ports blanked.
How to Perform a Leak Test
The video below shows how to perform an automated leak test in our glove box.
To begin, select ‘leakage test’ in the menu page. Here, you can define the pressure and test duration. We recommend holding the glove box at 5 mBar overpressure for at least 5 minutes. Once you have started the purge, the system will initially prepare for the test before a countdown begins.
During the test, the glove box will reach the desired overpressure, then measure pressure of the system over the defined period of time. When the test is finished, a leak rate will be displayed. Pressure values under 0.05 are acceptable to maintain an inert environment.
A successful leak test indicates that there are no significant leaks in your glove box. If a leak is detected, the next step is to find the source so that it can be fixed.
Finding and Fixing Leaks
The easiest way to find where a glove box leak is coming from uses leak detecting fluid. Cover suspected leaky point with soapy water while the glove box is trying to achieve an overpressure. If the soap begins to create large bubbles, that is where gas is escaping from the glove box.
There are a number of places where leaks can occur in a glove box, including:
- Holes or tears in the gloves
- Seals on internal or external doors
- Gas lines, inlets, or exhaust connectors
- Glove seals
- Power feedthroughs
- Window or wall seals
Leaks in the Gloves
Holes in the glove box gloves are the most common source of leaks in a glove box. The gloves are the thinnest, most delicate element of glove boxes, making them vulnerable to punctures. They are also heavily used and often undergo significant stress during use.
Small holes can be fixed with electrical tape, but spare gloves should always be available in case a complete replacement is needed. With care, you can replace the gloves without compromising the internal atmosphere.
Leaks in Seals and Joins
Doors seals are also heavily used and may be exposed to solvents, so are likely to deteriorate quickly. Compromised door seals can affect the pressure within the glove box when the antechamber is used, or prevent the antechamber from cycling correctly.
To avoid this, check the door seals for signs of damage or dirt. Clean them and coat with vacuum grease if necessary. Every seal will begin to degrade over time, so it is important that seals are regularly checked and replaced when needed.
If the seals and the gloves are not the cause of the leak, check every join in the glove box. Ensure the sealant material is not damaged. Clean the seals and tighten all bolts (the vibration of the vacuum pump may cause them to come loose over time). Additionally, check the window is securely fixed to the glove box front, and a tight seal is formed around it.
Glove Box
