Have you heard of rotary vane pumps, but are not sure what they are? Well, this is the place to be to find out.

On-premise, a rotary vane pump can be used as a vacuum pump but is most often used in low-viscosity gases and liquids. In this article, we will cover everything you need to know about it, as well as how it works so that you can use it.

Are you ready to become a technical wizard? Let’s jump in.

What Is the Rotary Vane Pump?

This device is a positive-displacement pump that makes use of several vanes that install in a rotating drum that pushes gases or liquids into smaller quantities. Thus, resulting in a pressure increase.

It’s considered positive-displacement because each of the vanes separates the concrete volume of the liquid or gas, and then pushes it into a smaller space. Thus, resulting in increased pressurization and in-flow.

As mentioned earlier, the pump is best suited for gases and liquids of low viscosity.

What Is It Used For?

The rotary vane pump can be used to evacuate gasses or air out of a vacuum system through the rough range of a vacuum.

Rough vacuum refers to the system, which accounts for air pressure between ambient 760 Torr and 1 Torr. There are many high-vacuum pumps available, which cannot operate in this range, such as the turbomolecular vacuum pump.

Thus, the rotary vane pump is often called the roughing pump. This pump can be used to take the absolute pressure of a vacuum system from ranges of 1 micron or 0.001 Torr in atmospheric pressure.

At that point, the other pump, such as the turbo one can switch on and take them over to help the vacuum system to reach higher states of vacuum. The pump can have many uses, given that you make sure to employ its use in limited constraints to allow its function.

Advantages Of the Pump

A rotary vane pump is versatile and practical because of its ability to bring absolute pressure down where other pumps can finally operate and be active.

Not to mention, a rotary vane pump can link with root exhausts, to exponentially increase the volumetric flow rate and pumping speed.

However, a root-linked vacuum pump will not be able to work on its own, so the rotary vane pump is necessary for exhaust relief.

The vacuum rating of this pump is 99.999%, which covers ranges that are not advisable to other types of pumps. This means it can be used in a variety of applications, except for the extremely high vacuum realms.

Rotary pumps are also great for smaller vacuum chambers because airflow on average is about 2-20 CFM or 4-35 cubic meters per hour.

However, some of these pumps do have a better airflow, sometimes up to 120 CFM. This makes them great for backing the service of diffusion and turbomolecular pumps.

Furthermore, a rotary vane pump is quite affordable. A high-quality heavy-duty pump can cost about $2000. However, you can go even cheaper and get a low-duty pump for as little as $100.

As such, you can see that you can save yourself a lot of trouble with the sheer variety that comes with rotary vane pumps.

With appropriate care, these pumps can last many years. Proper care refers to oil changes, corrosive or intense vacuum chambers without necessary protection, such as humidity traps.

How Does It Work?

The liquid or gas enters the chamber, and it is instantly compressed by rotor vane. As the rotor moves, it pushes the molecules around the chamber and in the direction of where the exhaust. That’s where it is expelled.

The vanes are usually spring-loaded, which is how an air-tight seal is made around the chamber and rotor housing. The rotor housing and vanes seal off by low vapor pressure oil, which acts as a lubricant, coolant, and sealant of the pump.

There are many types of drives that force the rotor to move. For instance, there is a direct drive, which links to the power source, usually an electric motor. This is done via a coupling and crankshaft.

Another type is of the belt-drive variety, which links to the source via a belt and pulley.

The first type operates at about 1750 RPM and 70 degrees Celsius of temperature. Pumps that make use of a speed-reduced operate at lower rates. The temperature of such pumps is about 20 degrees less than that of a direct drive system.

Nonetheless, these temperatures are heavily variable based on some factors. Such as viscosity of pump oil, quality of oil, rotating speed, age of pump, quality, and type of pump. As well as the quality of the liquid or gas being pumped out.

These pumps usually come in two forms, single or two-stage. The second stage has a connection between the second rotor intake and the first rotor exhaust. The advantage of this system is that a higher flow rate and lower vacuum is achiveable.

Additional Function

As with all other vacuum pumps, the volumetric flow rate decreases as the vacuum increases. This is because when less air is present, the harder it becomes to remove additional molecules out of the chamber.

However, the performance of the pump becomes even more significant as the pressure decreased. The pumping speed is practically the same in the rough range of vacuum, but as the pressure passes 1 Torr, the second-stage pump will continue to retain its pumping speed. Whereas, the single-stage pump will reduce the speed.

In rough vacuum circumstances, there is no difference between a two-stage or single-stage vacuum pump. Meaning that the single-stage pump will deliver the same performance at about half of the cost.

However, anything above 1 Torr automatically assumes the obvious overpowering and use of the second-stage pump.

Gas Ballast Valve

A gas ballast valve is necessary when operating a vane rotary system, so let us explain why. When the gas is being pumped out, the gas is not entirely clean and it will have traces of alcohols, acetone, water vapor, solvents, and other condensable.

These gases will cause condensation to happen inside of the housing of the chamber. This happens before the gas has been exhausted. Thus, resulting in the pump fluid contamination.

As the pump oil gets more and more contaminated, the pump will deteriorate significantly in performance. If the performance is down, the pump renders to be useless.

Not to mention, the ultimate pressure of the pump will decrease and deposits will start to build up in the pump housing. Continual deposit buildup will severely damage the components of the pump, resulting in an inoperable machine.

So this is where the ballast valve comes into play. It’s used to allow ambient air to enter the chamber of compression. This air ensures the exhaust valve to open, discharging any of the condensable gas before it condenses and deposits.

The contaminants are then exhausted out of the chamber before they had a chance to condense. Opening the ballast valve will protect the pump, but it will also decrease its performance. This means that the benefit does come with a trade-off.


Also, a gas ballast valve can help to diagnose the health of your pump by allowing insight into any contaminated fluid from leaks. When the ballast valve opens, the inlet of the pressure in the pump will drop.

You can close the valve and watch the inlet pressure. If it slowly rises have you closed the valve, your vacuum pump oil has contaminants. This is because the opened gas ballast valve helps to let out impurities.

So after you closed the valve, contaminants in the pump oil began to condensate. Thus, increasing the inlet pressure. At this point, you can investigate more or simply change the oil to protect the pump and eliminate unnecessary damage.

Pump Elaborated

Now that you know what a rotary vane pump, as well as how it works, you are well on your way to make use of it in your industrial applications. As long as you understand how it works and ensures proper maintenance, there is no reason that your pump will give out on you before its time.

These pumps have a purpose, and as long as the purpose is not outside of its limits, the pumps will perform to the best of their ability. In any case, if you’re interested in learning more about advanced machinery and technology, check out some of our other great articles on the sidebar.

Rich Seigel - Author

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