To maximize your investment and produce repeatable high-quality process results, it is mandatory to institute a thorough pump preventative maintenance program. In a pump’s normal operating life, nearly all unexpected vacuum pump failures can be prevented, and when carefully maintained, a vacuum pump will provide years of reliable service.

Be Organized and Document Everything. Start by generating a checklist of routine maintenance activities. The pump manufacturer typically provides this as part of the operating manual. Second, incorporate a maintenance log documenting all routine maintenance, repairs and component replacement. The log will play a critical role in diagnosing future problems, scheduling various maintenance activities, and stocking spare parts. Install a running hour meter to document the number of operating hours on the pump between service activities and enter this into the log. If possible, measure and electronically record the vacuum before and after the pump during every operating cycle, as well as the pumpdown times and ultimate vacuum level achieved in the furnace. This information is often collected and stored as data points in the furnace’s data acquisition system for process reasons. It can also be useful for planning and scheduling maintenance. Changes in these variables can be programmed into the furnace control system to notify the operator when a maintenance inspection or a specific maintenance activity is necessary.

Booster pumps (aka Roots blowers or intermediate stage vacuum pumps) fall into the class of dry, gas transfer pumps. As a dry pump, they do not introduce oil or water into the pumped gas stream. Gas transfer is accomplished by mechanically means, that is the transfer of pumped gas molecules, rather than their collection, as with, for example, cryogenic or turbomolecular pumps. 

The words “Roots blower” are synonymous with these pumps and the reason they are also commonly referred to as booster pumps is that they are mounted at the inlet of a primary/backing pump (such as a rotary vane, claw pump, or screw pump). They “boost” the performance of the primary pump improving pumpdown speed (much as a relay race in which the baton is passed from one runner to the next). The combination of Root blower and primary pump provides roughly a seven-fold increase in pumping speed and a ten-fold increase in pressure, in comparison to a primary pump alone.

Just as vacuum pumps can be considered the heart of the vacuum furnace, so too can the oil be thought of as its circulatory system. The selection and properties of the oil are critical to proper furnace operation. Pump oil serves different purposes in different types of pumps, and even has different functions within the same pump. In addition to lubrication, it helps provide the seal on rotary vane and other wet pumps, and serves as the media to propel the pumped gas via kinetic action in diffusion pumps.

Oil Formulations – Different pump oil formulations are specifically designed for different pump applications and careful consideration must be given to the oil selection. Typical motor oil, for example, is not sufficiently refined for use in a vacuum pump, has insufficient resistance to chemical attack, and contains additives that may be detrimental to the process being performed in the vacuum furnace. In addition, the viscosity must be considered. Lower viscosity oils are used for lower operating temperatures, and for smaller pumps, and medium viscosity oils are used for medium to large pumps. Temperature resistance is also critical, as many pumps operate at high temperatures, and the oil must be rated for these temperatures. Many of the oils used in vacuum pumps are not traditional oils at all, but made of silicone or other non-hydrocarbon fluids.

Every industrial vacuum furnace system uses a primary (aka mechanical) pump, which is also commonly referred to as a “backing” pump when either used in series with a booster pump, or used with both a booster and secondary (“high vacuum”) pump combination, such as a diffusion pump. These primary pumps are further divided into “wet” pumps (e.g., oil sealed rotary vane style or liquid ring pumps) or “dry” pumps (e.g., claw, hook or screw). Of the dry primary pumps, the most common types are the claw pump and the screw pump. 

Dry pumps are being increasing popular as an alternative to oil sealed rotary vane pumps for many medium and high vacuum applications (e.g., in low-pressure vacuum carburizing where fine granular soot is carried from the process into the pump). Designers and users of vacuum furnaces must have a good understanding of how claw and screw pumps operate. This includes the principles of operation, pump design, sealing, operating characteristics, features, purging, and ancillary devices.

Well-designed piping of vacuum equipment, as well as proper component selection, increases production efficiency by minimizing the vacuum pumping time. It also minimizes energy use, making your equipment less expensive to operate. Ignoring the principle of conductance and designing the system with only physical configuration and flow rates in mind, can cause delayed equipment startup, plant downtime, and process inefficiency because if a problem is found after startup, it can take considerable time and money to correct.

To successfully process component parts in a vacuum furnace, we need to create and control the “atmosphere” surrounding the work. In general, applications run in vacuum furnaces can be broken down into five main (5) categories: 1) Processes that can be done in no other way than in vacuum; 2) processes that can be done better in vacuum from a metallurgical standpoint; 3) processes that can be done better in vacuum from an economic viewpoint; 4) processes that can be done better in vacuum from a surface finish perspective and, 5) process that can be done better in vacuum from an environmental perspective.

A principal difference between vacuum heat treatment and all other forms of thermal processing is the absence of, or perhaps better stated, the precise control of surface reactions. In addition, vacuum processing can remove contaminants, and under certain circumstances degas or convert oxides found on the surface of a material. Typical vacuum applications include industrial, food and packaging, coatings, analytical and medical technology, solar, semiconductor technology and research and development. In the heat-treating industry typical processes involve: Brazing, Hardening, Annealing, Case Hardening (e.g. carburizing, nitriding), Sintering, Tempering and Special Processes (e.g. degassing, diffusion bonding).