Rinsing – Options – Single Rinse Tank

Rinsing as it applies to aqueous parts cleaning is a final “cleaning” step which removes residues introduced by or resulting from the primary cleaning process.  There are several options to choose from when it comes to rinsing.  Making the proper selection is very important to the overall cleaning process as the final rinse inevitably defines overall cleanliness.  Despite the importance of good rinsing, “overkill” can be costly and, in some cases, even counter-productive.

The simplest rinse consists of a single tank with a water inlet and a water outlet.

Illustration of a Simple One Stage Rinse

Simple rinse tank with manual fill and manual drain.

The rinse is filled, used for a period of time, then drained and re-filled with fresh water.  This rinsing scheme, although simple, is wrought with problems and inefficiency.  First of all, as soon as parts are introduced into the rinse, contaminates start to build up and the quality of rinsing rapidly degrades.  The buildup continues until the rinse is drained and refilled.  Although a small amount of contaminant in the rinse may not be harmful (and may even be beneficial as we will see in a later blog), in this case the quality of rinsing varies drastically from the time the rinse is filled until it is drained and refilled.  The quality of rinse is totally dependant on the diligence of the operator in replenishing the rinse as needed.  Finally, changing the rinse water results in the rinse not being available for a period of time.  This is especially true if the rinse water must be heated or if the water source is not able to quickly supply the fresh water (a DI water source, for example) required to re-fill the tank.
A refinement to the single fill and drain rinse tank is a single tank with a continuous variable water supply and an overflow consisting either of a standpipe or side-mounted overflow fitting.

Illustration showing rinse with a standpipe and side-mounted overflow.

The immediate benefit of the overflow rinse using a standpipe or overflow fitting is that it offers the ability to flow water into and out of the rinse on a continuous basis.  Depending on the amount of carry-over coming into the tank, the rate of flow can be adjusted as necessary.  If the flow of work through the rinse is consistent, then rinsing will be consistent.  Another benefit of this type of rinse is that the water flow tends to be from the inlet to the overflow thereby distributing contaminants throughout the tank.  Although there is some skimming effect (removal of floating particles or oil), an overflow weir approach provides much more efficient skimming.

Illustration showing an overflow weir rinse.

An overflow weir in a rinse tank has the benefit that surface skimming to remove oil and floating particles is enhanced.

As the liquid overflows the weir, the surface tension of the water pulls floating contaminants across the tank and over the weir.  Overflow weirs are common in both industrial and precision cleaning applications.

Upcoming blogs will discuss other rinse tank features including the benefits of filtration, heat, multiple tank rinsing and spray rinsing both in air and above a cleaning or rinse tank.  Again, rinsing is as (if not more) important as rinsing in any cleaning process.  The steps preceding and following the rinse have a big impact on making the proper decisions for the rinse.

–  FJF  –