Hydrogen pumps are used to maintain an insulating vacuum in hydrogen pump storage and transfer tanks, piping and system components. They must be able to operate at high speeds and generate minimal heat.

Discover how these cryogenic pumps work to power the systems that transform methanol and water into clean, renewable hydrogen for fuel cell electric vehicles.

Vacuum Pumps

Vacuum pumps remove molecules from a space to create a full or partial vacuum. A typical industrial vacuum system needs to operate over an extraordinarily large pressure range (1.3 to 10-6 Torr / 1.3 to 13.3 mBar). In order to achieve this, different types of pump are used in a typical system, each covering a portion of the pressure range and operating in series at times.

Positive displacement pumps use mechanically trapped volumes that are repeatedly expanded and compressed by one-way valves to draw in the gas, compress it and expel it. Kinetic transfer pumps use high speed blades or introduced vapor to propel gas towards the pump outlet, providing increased likelihood that a molecule will move in that direction and can achieve high compression ratios at low pressures.

Liquid ring pumps use liquid, typically water, to spin the impeller and create vacuum by pushing gaseous molecules into motion. These types of pumps are extremely reliable, requiring minimal maintenance. It is important to follow the manuals for these pumps and to always change the oil as directed. Not changing the proper type of oil can lead to off-gassing, contamination and performance degradation or unit failure.

Rotary Mechanical Pumps

Rotary mechanical pumps use sliding vanes mounted in slots on a rotating rotor to capture and compress gas molecules into the pump chamber. They’re commonly used for lube oil service and transfer, tank stripping, and bilge pumping, but they can handle liquids over a wide range of viscosities.

Vane pumps operate on a positive displacement principle. Sliding vanes on an eccentrically-mounted rotor extend to trap liquid in crescent-shaped pump cavities that create liquid chambers. The rotor rotates to transport the liquid between each set of vanes until it’s forced out of the pump discharge port.

These pumps typically have very small clearances between rotating parts and stationary parts to prevent leakage and ensure accurate delivery of pressure. They’re also designed to operate at low speeds so that they don’t cause excessive wear and tear or erosion. This helps them achieve superior pump speed, ultimate vacuum performance, and a long lifespan. They typically require an appropriate chemical or mineral oil for lubrication and sealing.

Turbo-Molecular Pumps

Turbo molecular pumps (TMPs) are the workhorses of semiconductor fabs, helium leak detectors and scientific instruments. They are capable of producing the lowest pressures, typically down to 10-10 mbar nitrogen equivalent, in a few minutes from the start of pumping.

They work by sucking air molecules in from the surrounding chamber with spinning turbine-like rotors. The rotors are lined up in rings, some of which rotate around the rotor axis and are called rotors; others are held stationary and are known as stators. Each ring has many narrow, inclined blades.

The tip of each rotor blade moves at the mean thermal velocity of the gas being pumped, which differs between gases (heavier gases like helium have a higher thermal velocity than lighter gases such as air). This explains why TMPs offer lower compression ratios for heavier gases such as argon or nitrogen, and why they have significantly lower transmission probability than for hydrogen.

One disadvantage of TMPs is their high rotor speed, which requires that the system be vented. Agilent recommends a vent solenoid to intentionally slow the pump to a rate comparable to ramp-up time. This prevents the compressor from running at critical bearing frequencies and allows it to cool down before shutting down.

Cryogenic Pumps

Cryogenic pumps are a key component of cryogenic applications such as medical (MRI, tissue and organ preservation) and metallurgy (cooling of workpieces). They also play an important role in scientific research with particle accelerators, lasers and superconductivity and low temperature research itself.

Unlike vacuum pumps which use mechanical seals, cryogenic pumps are hermetically designed and do not have mechanical components leaking into the process fluid. This helps to minimize conductive and convective motor heat leaking into the cryogenic fluid.

Cryopumps are cooled by the two-stage cold head and cryopanels whose temperatures depend on their position within the pump. The cold surface of the second stage cryopanel is cooled to below 20K. Since light gases such as hydrogen, helium and neon cannot be condensed below 20K, they are adsorbed into the 15K cryopanel through the use of special porous materials. This allows the pump to achieve ultra-high vacuum without relying on condensation alone. The adsorption method is highly efficient and does not require any moving parts, thus increasing pump reliability and lifetime.