How to Select the Correct Seal Piping Plan for a Centrifugal Pump with a Single Mechanical Seal
Since 1986, Estabrook has served the Ohio, Erie, Pennsylvania, and Upstate New York regions with its distribution of industrial equipment. Originally founded with a focus on pump repair in 1965, Estabrook has developed its expertise around systems and applications with fluid movement, starting with the pump and evolving its acumen into technologies such as valves and seals. While Estabrook has been familiar with mechanical seals for over 55 years, we really started our journey of becoming a subject matter expert in sealing solutions in 2001, when we became a Chesterton distributor.
One of the critical elements of a pump is its ability to have a proper seal so that the fluid pumped does not leak. This blog will focus on mechanical seals and why selecting the correct seal piping plan is crucial. In fact, there are many ways in which you can seal a pump. These include packing, lip seals, cartridge seals, or even gas seals! For this blog, we will assume that a single cartridge mechanical seal is the sealing solution of choice and dive deeper into the aspects of the seal piping plan. So, let's get into this subject a bit more as we take an in-depth look into the basics of selecting the proper seal piping plan.
We all know that the first goal of a pump is to move a fluid from Point A to Point B. But, there are two correlated goals with this. A pump needs to a) move fluid from Point A to Point B as efficiently and long as possible. The mechanical seal and its piping plan relate to this third goal: longevity. Usually, increasing the equipment's mean time between failure (MTBF) relates to mechanical seal reliability.
So how can we increase the MTBF of a pump as it relates to a single mechanical seal? Improving the environment surrounding the seal can significantly reduce failures. These improvements decrease downtime due to seal leakage, which can cause bearing failure or other premature failures with the pump system.
Organizations can implement improvements for various seal piping plans. However, it's critical to select a seal piping plan carefully. First, you need to determine what needs controlling:
Temperature: decrease or increase the fluid temperature around the seal
Pressure: pressure can increase or decrease in the seal chamber
Circulation: increase circulation for solids and temperature control
In most cases, the goal is to improve the environment inside the seal chamber. However, there are times when a flush gets applied to the atmospheric side of the seal. Such an application is called a "quench." The flush media gets directed on the outside of the seal and must drain to a proper location.
Information Needed for Proper Selection
Estabrook likes to make sure we understand the application. Engineering constantly evolves, new technologies emerge, and systems change over time. What worked in the past is not necessarily what works today. As most continuous improvement processes suggest, it is best to look at the system and determine what may cause failures.
The market refers to this as "root cause analysis," which aims to correct, improve upon, or upgrade engineered products to increase the MTBF. The best way to understand the current application is to obtain the following basic information to validate the current selection or make a new & improved selection instead.
Cleanliness of fluid. Does fluid have any solids?
Speed of pump shaft
Do All Pump Applications Require a Piping Plan?
No. A flush plan may not be needed for most horizontally mounted pumps when using a clean fluid at a desirable temperature. Some units mounted vertically can benefit from using a piping plan to vent any air trapped in the seal chamber. Furthermore, newer technology in the design of seal chambers has helped eliminate the need for a piping plan. For example, the ITT Goulds patented TaperBore seal chamber is self-venting and directs solids away from the seal faces. This eliminates the need for a piping plan in a lot of applications.
See some examples of typical flush piping plans below:
Plan 01 or 11
Recirculation from discharge to seal the flush connection with or without flow control. For clean fluids only.
Increases circulation and seal chamber pressure creating a higher vapor pressure margin
Helps vent seal chamber
Recirculation from pump suction to seal the flush connection. Not for low vapor pressure fluids
Decreases seal chamber pressure
Helps to cool seal faces by reducing seal-generated heat
Helps vent seal chamber, especially vertical pumps
Recirculation of fluid through a cooler back to the seal. Seal with pumping ring and cooling water needed.
Cools seal while pumping hot and/or volatile fluids
Good for applications when increasing seal chamber pressure is not possible
Clean fluid flush from an external source to flush connection. Note: mixes with the transferred fluid.
Cleans seal faces when pumping fluids with suspended solids.
Helps lubricate seal faces
Helps reduce temperature
Can be used as a means of downstream additive
Steam, Nitrogen, or Water introduced to quench the connection
Helps clean seal faces when transferring fluids that crystalize or salt out
Can help avoid icing in cold/cryogenic services
Creates a barrier between the seal faces and the atmosphere
Selecting the proper seal plan, along with the proper mechanical seal, will allow for the proper selection to be made. At Estabrook, it has taken several decades to develop the expertise to quickly and reliably make the proper selection. It starts with understanding the customer, the customer's application, and the process information described in this blog.
When we think of understanding the customer, we refer to knowing the history of the service, what drives the customer's buying behavior of costs vs. benefits, and ultimately what they want to accomplish. As discussed, the typical objective is to increase the system's reliability. The pumping technologies are a primary factor with reliability, with one of the critical elements of keeping pumps running is to have properly designed seal plans!
We hope you found this blog helpful. If you would like to discuss a seal plan for your centrifugal pump, get in touch with our team today!