Sample Pump is Key to Instrument Reliability

by Eric Pepe, KNF Neuberger, Inc.

High quality and long life required from medical equipment are pushing advances in compressor and vacuum pump technology.

While a pump often is the heart of pollution equipment and devices that use pumps, clear guidelines highlighting key criteria for selecting an appropriate pump have been seriously lacking. For pollution equipment designers and manufacturers, this situation can lead to disastrous product failures product failures: for end-users, it can be the difference between purchasing equipment that provides reliable data acquisition and durable performance, equipment that fails short of the mark.

The Wrong Pump

Imagine the case of a manufacturer that, after designing an air monitoring system and distributing test units, discover that virtually all of the monitors were failing. Countless hours of product development time and money were in danger of being compromised, not to mention the end-users that would have been compromised had the units marketed.

The problem was caused by a part of the system that designers tend to think of as commodity. It was a pump—the wrong pump!

Lack of Technical Information

This example is more common than it needs to be. While there have been major technical advances in the design of pumping systems during the past 10 years, many are not aware of the advances due to scant availability of reference material. Contributing to this problem is the manner in which many equipment designers and manufacturers purchase pumps. Late in the design process they try to select a standard product from a catalogue that will meet their system’s complex and interrelated needs.

In a sense, this approach entails trying to "retro-fit" the pump to a sophisticated pollution device, such as an air monitor, rather than trying to tailor the pump to the device early in the design proces.

Keys to Success

This can be a prescription for trouble, as the air monitor manufacturer discovered. However, there also are keys to success available.

Specifically, manufacturers can:

Understand that the pump is a sub-system—not commodity,
That it is a dynamic, interactive element of the equipment in which it functions,
communicate with suppliers early in the design process to clarify pumping needs and obtain information on the latest technology.

Critical Features

What are some of the most critical features that pollution equipment manufacturers need to consider and communicate to a supplier when selecting a pumping system? First, there are a number of general requirements including the pump’s application, as well as its size and structural materials; available power within the pollution device to drive the pump; and the appropriate price range for the pump.

Defining tolerances also is important specifying a pump’s power requirement at 115V is not enough: specifying 115 V, with a tolerance of plus or minus 10 V can be critical if the system that varies up to 10 V. The same principle applies to other system specifications such as vacuum and flow rate.

Corrosion was the Problem

A major problem might have been avoided had the air monitor manufacturer followed these guidelines. The company’s designer had selected a linear piston pump to perform an extractive sampling function in an ambient air monitor—an inappropriate application for this type of pump. The linear pumps were not producing the necessary vacuum because moisture was corroding the piston and cylinder, rendering the pumps—and ultimately the air monitors—inoperable.

The company approached a pump supplier to find a solution to the problem. The supplier eliminated the piston pump, substituting a diaphragm pump incorporating Teflon and stainless steel; and worked with the company’s design group to modify the architecture of the vacuum system to utilize the source of vacuum in the monitor.

This solution highlights the importance of communicating with pump suppliers, as well as the impact of a new advance in vacuum pump design.

Complex Factors

There are many factors that must be considered. One way to help insure reliability is to verify that the appropriate pump has been utilized for a specific application. Work closely with the pump manufacturer to assure proper product selection.