“What is the best type of oil to use in my vacuum pump?” is a common question for sure, and one that may often yield confusing and conflicting answers. The rule of thumb is that it is always best to follow OEM recommendations, but why do they recommend the lubricants that they do? For the purpose of this article, we will focus on some of the general industrial vacuum pump applications and their lubricant choices.
Cooling, controlling contamination, reducing friction, and creating fluid seals are just a few of the many important responsibilities the lubricant serves. The chosen lubricant must fill all of these roles effectively and efficiently to promote healthy and long equipment life. Vacuum pump applications are somewhat unique due to the relationship between the oil’s volatility and vapor pressure. An oil that is more volatile is more likely to turn from a liquid to a vapor as temperatures increase. Because vacuum pumps operate with such tight tolerances in regard to pressure, any differentiating factor can be detrimental to the intended operation of the pump. Choosing a lubricant with a low vapor pressure will ensure the system operates efficiently.
How Does Viscosity Impact Pump Performance?
Often one of the first things that we look for will be the oil’s viscosity. Viscosity is the primary requirement to consider when choosing an oil. If the lubricant is not viscous enough (too thin), it will not create the proper lubrication seal the pump requires. This can lead to loss of efficiency due to leakage or flow reversal from stage to stage. Another thing to be mindful of is a lubricant’s function of preventing metal-to-metal contact causing excessive wear and premature equipment failure.
Conversely, choosing a lubricant that is too viscous (too thick) will restrict flow and cause lubricant starvation in essential machine areas. Different vacuum pump designs have different lubrication needs. Liquid ring vacuum pumps generally require an ISO 22 or ISO 32 viscosity. Rotary vane vacuum pumps normally utilize an ISO 68 (SAE 20) or ISO 100 (SAE 30) oil. Process pumps and other vacuum pumps driven by a gearbox will require a much more viscous oil, such as an ISO 220 (SAE 50).
Types of Oils for the Industrial Market
But what about all of the different oil types in the market? Terms such as hydro-treated or hydrocracked paraffinic oils, Polyalphaolefins (PAOs), diesters, Polyolesters (POEs), petroleum oils, mineral oils and even semi-synthetic oils may be a little intimidating. While there are other fluid types used in vacuum pump applications, let’s focus on just a few, beginning with some of these base oil types with which you may or may not be familiar. To simplify things, petroleum oils or mineral oils are one in the same. Hydro-treated, or hydrocracked oils, are simply a more refined, or further processed petroleum oil that will have some or most of the impurities removed.
PAO is short for polyalphaolefin and is a popular synthetic oil option. This is due to exhibiting excellent high and low temperature performance, good oxidative and thermal stability, and good compatibility with mineral oils and most synthetics. Esters, including both diesters and POEs, are forms of synthetic oils that are generally more thermally stable, and they are commonly used in applications where higher temperatures may be present. The high polarity of these esters helps to prevent varnish or sludge build-up. Another advantage is their cleaning ability, because they act as a natural detergent. Semi-synthetics are typically a combination of a synthetic base stock and a petroleum/mineral oil. In some cases, multiple synthetic oils may be used together to create unique blends that work best in some demanding applications.
The Importance of Additives
Now that we have covered some of the base oil types, what about some of the common additives used? This is where you may see a plethora of different options, all using the same base oils, and wonder why you would choose one or the other. Due to the wide range of applications, you will see different additive packages used. While some may require a greater amount of antioxidants, others may require additional anti-wear additives. You may see additives specifically used as a pour point depressant, corrosion inhibitor, or even an anti-foaming agent. Having the proper additive package in the proper concentrations (more is not necessarily better) is an essential focus to ensure that the finished lubricant will perform its duty satisfactorily. This is where years of experience in formulating these products, testing in the field, and investing in research and development will really set one manufacturer apart from another.
Other Variables to Consider When Choosing a Lubricant
While this article is designed to serve as an abbreviated summary of some of the different vacuum pump lubricants commonly used in industrial applications, it is also very important to note that there may be outside variables that may influence the lubricant choice. Severe or demanding conditions, unique applications, compatibility with different process materials, and harmful contaminants may need to be taken into consideration. Extreme temperatures can often put additional strain or stress on these oils. Many manufacturers may provide a guideline indicating how long an oil “should” last, assuming it is operating under normal or ideal conditions. A 20 to 30 degree temperature differential may cut the useful oil life in half. In other situations, a petroleum oil may varnish or develop harmful sludge if run too long at too high of a temperature. A successful oil analysis program is helpful when analyzing the condition of the oil and its expected life in different applications and environments.
For some applications it will be necessary to deviate from the OEM recommendation: this is where your trusted oil supplier, technician, or engineer will come into play. Original equipment manufacturers (OEMs) spend a great deal of time choosing a lubricant that will work best for its specific piece of equipment or intended application. The goal for any aftermarket oil manufacturer is to formulate a product that will meet and/or exceed the performance requirements of these OEM oils.
About Ultrachem, Inc.
Founded in 1965, Ultrachem Inc. is celebrating our 50th year as a specialty synthetic lubricants manufacturer. Over this period we have come to be recognized as a respected supplier to many OEM and industrial customers. We are a privately owned ISO 9001:2008 certified company with our corporate headquarters located in New Castle, Delaware. We strive to offer exceptional customer service, technical expertise, as well as manufacture our products with only the highest quality raw materials. Some of the products we manufacture include, but are not limited to: vacuum pump oils, compressor oils, gear and bearing oils, hydraulic oils, chain oils, food grade oils, greases, impregnating oils and gels, airline lubricants, refrigeration oils, and some other specialty chemicals and cleaners. We hope you have found this article informative, and we appreciate the opportunity to share this information with you.
To read more about Vacuum Generation, please visit www.blowervacuumbestpractices.com/system-assessments/vacuum-generation.