Leak finder for vacuum systems is explained and demonstrated in this short video. All you need is a spectrometer tuned for helium and a tank of helium. In order to find the leak, you need to expose the vacuum system locally to helium. If a leak is present then the gas is sucked inside and pumped out into the mass spectrometer. The beeping noise immediately alerts the user if helium has reached the spectrometer and the leak is found. The most common places for leaks are usually at the connections of the vacuum systems parts.
The quadrupole mass spectrometer (QMS) is used to detect and measure the abundance of gas phase ions. These ions have to pass between electrically connected rods in order to reach the detector. By combining alternating and direct voltage on these rods, it is possible to ensure that only ions with specific mass-to-charge ratio are capable of reaching the detector.
The hot-filament ionization gauge is widely used for measuring the level of vacuum. The electrons are emitted from a hot cathode and accelerated towards the anode. In that process the electron may ionize a gas molecule. That gas molecule is pulled towards the collector and ion current is measured with an ammeter.
The Penning Ionization Gauge, also known as cold cathode gauge is used to measure the level of vacuum. High voltage between the anode and the cathode causes gas discharge and the resulting ionic current is measured with an ammeter. The measured amperes are then converted into pressure units such as Pascals or Torrs.
The thermocouple gauge is a device used to measure low vacuum. A filament is heated up by passing a current through it. When gas molecules interact with the filament, heat is carried away. Therefore higher pressure in the chamber means that more heat is taken away. The temperature of the filament can be measured with a thermocouple where the generated voltage depends on the temperature. Therefore in this system the voltage of the thermocouple is measured and converted into pressure units like millibars or pascals.
Diaphragm pump (membrane pump) is an oil-free vacuum pump that is used for obtaining #prevacuum of about 0.5 mbar. The pumping in this device is based on the movement of the membrane. As the membrane is pulled down, the volume of the chamber increases, causing a drop of pressure and gas enters the chamber through the inlet. Next, the inlet is closed, outlet opened and the membrane pushed up. This causes the volume of the chamber to decrease and pressure to increase. So the gas is forced to leave the system through the outlet.
The sorption pump is an oil-free #prevacuum pump that is based on the adsorption of gases on cold surfaces. The colder the surface, the more efficient the pumping is! Therefore liquid nitrogen with a temperature less than 77 degrees Kelvin is used for cooling the adsorber. The adsorber is a porous zeolite with a very large surface area as the pores have a diameter in the range of a few nanometers (or less). If the pump is full, then it needs to be renewed by degassing, which is basically heating the adsorber so that the gas can remove the pump through the outlet.
Rotary Vane Pump is an oil-based vacuum pump, that can be used to obtain #prevacuum or even medium vacuum (depending on the system). In this device the rotor and vane(s) are in the housing, that is filled with oil. When the gas enters the chamber through the inlet, it gets trapped in the oil and is transported through the working chamber with the help of the rotor and vane(s) to the outlet, where the gas exits the system. The oil acts as a lubricant and also allows the pumping of some corrosive gases, as it protects the metal to some degree. Although this pump is quite fast and efficient for obtaining pre vacuum, it also may contaminate the vacuum system with oil. Therefore the use of oil traps is highly recommended.
Scroll pump (scroll compressor) is an oil-free vacuum pump used for obtaining #prevacuum with a level of 0.1 mbar. The #scrollpump is based on two scrolls, that are placed insede the working chamber. One of these scrolls is fixed and the other one mobile. Once the gas enters the system through the inlet, it gets carried to the outlet in the middle by the mobile orbiting scroll. This is possible due to the fact that during the mobile scrolls movement a wide gap is locally kept between the two scrolls and the gap moves to the middle, carrying the gas in it. As the volume of the gap decreases at the outlet, the gas is pushed out of the system. Due to wear the orbiting scroll needs to be replaced about twice a year.
The #cryopump is a high vacuum pump that is based on the adsorption of gas on cold surfaces. The cooler the surface – the better the pumping! For that purpose liquid helium is often used for cooling the system parts as it is extremely cold, having a temperature only four degrees above absolute zero. The pumping is done in multiple stages, where each stage has a different temperature. The „warmest“ part is the first stage, that has a temperature of 100 degrees Kelvin (or lower) and that causes water to condensate on it. During the #condensation of water also some other gases may also be trapped under the water and that process is called #cryotrapping. However, in order to effectively pump gases such as nitrogen, even colder surfaces (less than 17 degrees Kelvin) are required. In this stage the metal may also be coated with porous activated charcoal and that allows to adsorb even smaller gas molecules such as helium and even hydrogen (this is called #cryosorption ). So basically the pumping of gases with this #vacuumpump is based on three processes: condensation, cryotrapping and cryosorption.