Selecting Lab Glassware Washers For Special Applications

In many research projects, locating a fast, effective laboratory glassware washer is key for ensuring accurate experimental results. Significant challenges arise when selecting a washer for special applications like cleaning narrow-necked glassware or glassware soiled with petroleum compounds. Although it seems counterintuitive, systems with high water circulation rates are more effective than systems that use high water pressure. When selecting a washer, consider five main variables.

Washing Challenges

1. Mechanical Action
2. Direct-Injection Baskets
3. Temperature
4. Time
5. Detergent

Washing Challenges (Back to Top)

During the course of their research, many laboratory professionals must clean thousands of narrow-necked laboratory glassware vessels such as Erlenmeyer and volumetric flasks, BOD bottles, pipettes, autosampler vials, and test tubes. Although hand washing is an option, it does not guarantee adequate cleaning, is labor intensive, and more costly than an automated system in the long run. For this reason, an effective laboratory glassware washer is often required.

Some experimental materials are particularly hard to remove from laboratory glassware, and require a multi-step wash process to clean. Petroleum compounds such as refined hydrocarbon distillates are an excellent example of these, as they usually leave oily, molasses-like residues on laboratory vessels that they contact. Traditionally, these compounds have been cleaned using hydrocarbon solvents such as diesel fuel; however, this process can be hazardous to personnel and can create environmental disposal problems. In addition, some solvents are now illegal because they have been found to deplete the ozone layer. Flammable solvents are also difficult to use because they can only be employed in a class I, division II explosion-proof area. Converting to an aqueous-based method for cleaning petroleum residue can eliminate these concerns and reduce the cost of the washing process.

Although these two application challenges raise different problems, automatic glassware washers can be selected to thoroughly clean both of these vessel types. When selecting a system, consider these five variables:

1) Mechanical Action (Back to Top)

Although many assume that high-pressure washing systems create the best cleaning environments, this is not true in practice. With high-pressure systems, it is more likely that delicate glassware will be broken. To clean glassware and minimize breakage, look for a system that provides a high circulation (turnover rate) of water at a low discharge pressure.

The number of times that the water and detergent contact the surface to be cleaned is more important than how hard it hits the surface. Glassware washers from Miele (Somerset, NJ), circulate 106 or 156 gal/min of water, compared with 25 gal/min for typical household dishwashers and 60 gal/min for typical lab washers. High circulation rates ensure analytically clean results, reduce the required wash time, aid in energy efficiency, and decrease the amount of detergent that is required.

Miele's washers also feature spray arms equipped with nozzles that angle and feather the jet spray for maximum coverage and impingement. Some of the other washer models that are available simply provide drill holes in the spray arm which do not direct the water in this way. Directed nozzles are particularly important for cleaning persistent petroleum compounds.

2) Direct-Injection Baskets (Back to Top)

When cleaning narrow-necked items such as volumetric or Erlenmeyer flasks, look for direct-injection baskets that expel water from each injector with equal pressure, regardless of the injector's distance from the source. Some washers utilize a grid-type injector design, in which water pressure may be inadequate in injectors that are farthest from the water-feed tube—this is not the best option for cleaning narrow-necked vessels.

Injector-tube sizes are another variable to consider when purchasing a washer. Look for injector tubes that come in a variety of diameters and lengths as these will accommodate various glassware sizes. If they are removable, the tubes can be arranged easily into custom configurations.

When evaluating injector baskets, also consider the following features:

• Clips for holding glassware firmly at optimal height should be available
• Injector baskets should be interchangeable with other baskets
• Injection capability should be possible on either one or two levels of the washer
• A large number of injectors should be provided on each basket
• If the washer includes a forced-air drying cycle, it should blow air through the injectors to dry the interior of the vessels

3) Temperature (Back to Top)

In laboratory washers, a deionized water rinse (DI) is necessary to ensure the best cleaning results for laboratory glassware. The washer's ability to perform a DI rinse is one of the most basic characteristics distinguishing lab washers from home dishwashers. In general, hotter water provides a better environment for both cleaning and DI rinsing.

Because hotter water is better, most Miele devices can heat wash and DI water up to 93°C. Some brands will only heat wash water to 55 or 65°C, or only provide ambient temperature DI rinsing capability, which is not as effective as heated DI rinsing. On well-designed devices, wash and DI water temperatures are independently adjustable for maximum flexibility to fit each cleaning application.

For cleaning petroleum-based compounds, a wash temperature of 95°C is normally recommended, followed by a DI rinse with acid neutralizer, then one or two DI rinses heated to 95°C.

4) Time (Back to Top)

Increasing the time of a wash cycle will improve the cleaning results. Despite this, most labs cannot afford to spend time waiting for a washer to complete long cycles. To minimize cycle times, look for washers that use small amounts of water per cycle, as less time is wasted waiting for the water to be heated to the appropriate temperature. Washers from Miele heat 2.5 gal/cycle of water with 6000 W at 220 V.

For petroleum residues, it is even more important to increase the time of the wash cycle than with residues from other materials. Instruments featuring programmable wash times are best for customizing wash cycles to project needs.

5) Detergent (Back to Top)

In addition to selecting the best glassware washer, it is also important to purchase the best type of detergent. When specifying a detergent, consider powder and liquid detergents, as well as acid neutralizers. Ask the vendor of your laboratory washer to suggest the best detergents and neutralizers for your project. This guidance can be particularly helpful when cleaning petroleum compounds from vessels.

Special Petroleum Considerations (Back to Top)

The door and sump-pump seals in laboratory glassware washers are likely to deteriorate quickly and cause leaks when the washers are used to clean petroleum compounds. When specifying a washer for cleaning petroleum residue, make sure that all gaskets are chemically resistant to hydrocarbons. Miele utilizes grease-resistant NBR polymer gaskets for this purpose.

Because petroleum compounds are very thick, they can clog the sump-pump filters. Plan for this problem when purchasing a lab washer by finding a unit that features a filter system that can be easily removed for cleaning. Remember to clean this on a regular basis so that the washer does not have to be serviced before its regularly scheduled time. Occasionally, run an extra wash cycle without any dirty glassware to clean the washer filter.

To effectively migrate from a solvent-based system to an aqueous laboratory glassware washer when cleaning petroleum products, choose a system that is fully programmable, so that the proper balance of time, temperature, and detergent can be achieved.

For more information: Ken Austin, marketing manager for Professional Products, Miele, 22D Worlds Fair Drive, Somerset, NJ 08873. Tel: 732-560-0899. Fax: 732-560-7469.