Drywell or Not? Is It a Fit For My Application?
April 9, 2021
Chester W. Chen, PMP • Sumitomo Drive Technologies
Drywell – a term that many of us in the power transmission business often encounter whenever a conversation would come up about the features and benefits of a particular gearbox or drive to be used in the industrial mixing or agitating equipment. Intuitively, we know that a drywell must be an essential feature in the gearbox, but do we know how the drywell works, when to use it, or if it is ideal for the application? After all, a mixer/agitator can be found in hundreds of applications across two dozen industries, such as wastewater treatment plants.
Here, we will explore the basic but crucial aspects of the drywell that will provide us with an insight to answer these typical questions.
PURPOSE
As the name suggests, "dry"-"well" is a well-like structure that shapes and functions like a dam, intending to keep the exterior and output area of the gearbox dry by preventing its gear lubricant (typically oil) from contacting or leaking through its outboard seal. In other words, the drywell averts a possible contamination scenario by reducing the likelihood of the gearbox oil coming into contact with the medium being mixed by the gearbox. Undoubtedly, the gear oil mixing with the processing medium is an undesirable event for most applications and could be even more detrimental in applications that include mixing ingredients for food, beverage, chemical, or pharmaceutical goods.
This cutaway image shown here is a Hansen® P4 right-angled mixer drive with the drywell integrated into its housing. This drywell is a stationary structure, which extends from the bottom of the housing up to the gear separating the oil from the outboard shaft, bearing, and seal, thereby eliminating the potential of oil leak down the shaft during its regular operation.
DESIGN
Since the drywell resides inside the gearbox as an internal object, the user would not see or access it to troubleshoot if leakage occurred. The gearbox designer bears the burden to ensure that the drywell is oil-tight and maintenance-free. At Sumitomo, this is our top performance objective of a proper drywell. To further expand on the associated design criteria, based on Sumitomo-Hansen's decades of experience serving the mixer/agitator OEMs and end-users worldwide, the optimal drywell design would be...
- ...made from a one-piece solid metal or iron
- ...stationary or fixed and does not move during the gearbox operation
- ...modular--instead of permanently cast or welded in--without changing the gearbox's footprint
- ...completely sealed or closed-off from the top rotating gear or shaft.
FLEXIBILITY
As previously mentioned, a drywell can be wholly integrated into the housing. This type of design is solid since the drywell is a structural member of the housing and eliminates a potential oil leakage path at the bottom of the oil sump. However, such an integrated design generally comes at a higher manufacturing cost because the gearbox's housing would require a particular casting pattern and special machining and/or welding operation (if the casing is made by steel). In short, the integrated drywell is extremely strong, but the gearbox becomes unique and costs more than its standard counterparts. Though it is suitable for a dedicated group of customers, it might not be an optimal solution for every customer across the industry.
To be flexible and reduce the gearbox's overall cost yet still able to provide customers with a robust drywell option, we looked deep into a modular design approach. This approach means the customer can use the gearbox without the drywell if their mixing/agitating application does not require it or opt to have it added into the gearbox specifications if the drywell is deemed necessary, thus changing the dimensional envelope.
With the modern world of manufacturing advances so quickly in the machining accuracy, quality and process control, and the superior sealing methodology available, approximately 60% of OEMs and end-users with aerating, mixing, or agitating applications have been operating satisfactorily and do not require the presence of the drywell in their gearboxes. On the other hand, for the remaining 40% of customers whose mixing mediums are to be consumed or otherwise impact public health, the drywell is required and mandated in their machinery specifications. It is an additional line of defense against a potential disaster of gear oil contamination. Therefore, the new mixer/agitator drive solution should consider the needs of both types of these customers.
An example of a flexible drive with a modular drywell design is our Sumitomo Cyclo® BEVEL BUDDYBOX (BBB.) The BBB drywell is made from precision machined cast iron and can be added to the gearbox without affecting its mechanical or thermal performances. The drywell is bolted, torqued, and sealed against the bottom housing cover, converting the interior into a leak-free oil sump.
To close the drywell to prevent any chance of oil splash getting through from above, we employed a heavy-duty V-ring seal that rotates with the shaft and rides against the smoothed machined surface on the drywell. In addition to being a cap, the V-ring also acts as an oil slinger. As the shaft rotates, the V-ring redirects the oil that comes into contact. The higher the rotational speed, the stronger the redirection effect.
In summary, we recommend choosing a gearbox with the drywell if the end-user or OEM requires it. It's also highly recommended if there is a safety and health concern should the gear oil leak out of the gearbox and contacts the medium being processed or the processing plant's surrounding environment.
The ideal drywell should be an option of a standard gearbox to be flexible to all users. Needless to say, it should be priced reasonably, prevents or eliminates potential oil leakage, and does not require any maintenance throughout the life cycle of the mixer/agitator drive gearbox. Sumitomo mixer/agitator drives are all equipped with proven drywell designs that are field-tested and preferred worldwide. Contact us today to place your order.
