Everybody knows that a rotating part or pump is going to produce vibration. Service personnel in the pump repair business, the air compressor industry, and electrical power generator providers all install products that helps eliminate those vibrations. Nobody wants to see a long run of pipe vibrate and pull the pipe hangers out of the ceiling. Falling pipe produces frowns from building owners.
The simple answer is to simply throw a braided pump connector between the pump housing and piping, and do whatever is needed to make this part fit. Stretch the connector, compress it, twist and rotate it, weld brackets to it, or just break open the farmer's grease and bolt it in. Why all the fuss? It is a flexible connector, right?
You really need to review your application and determine whether you have a vibration issue, or more of a compression/extension/axial movement that requires a true expansion joint. Then you can install the right product for the job, and leave the grease and crowbar at home.
Stainless steel or bronze flex connectors are designed to eliminate vibration and a small amount of offset. They are not expansion joints and will fail early if they are stretched, compressed, or torqued in any way. As long as the braid is tight upon the inner hose and not stretched and ripping the braid out from under the collars, you have installed this connector properly and should be high-fiving your coworkers.
The great advantage of stainless steel or bronze flexible connectors is that any type assembly can be manufactured and custom made by most fabricators. Need a reducer? Need a 300# flange on one end only? Need ports for gauges or meters? Do you need a longer length to cover the ¾-in offset that the HVAC engineer has specified? Just make that call to your flex connector salesperson and get the right product.
An expansion joint is a connector that is designed to compress, extend, allow lateral offset or even axial rotation, or a combination of everything. The most common is the single or double sphere rubber expansion joint. They are usually used in water/glycol applications and are seen everywhere in the industry. They compress and extend and are usually installed with limit rods (control rods/tie rods) to stop the overall growth under full pressure.
Many times a failure is due to installing the rubber joint without limit rods, not restraining the piping properly, or allowing the pressure to increase exceedingly. Most pump reps sell these rods as a set with every rubber expansion joint that goes out the door. They see it as cheap insurance!
These rubber expansion joints are limited by temperature, ozone, age, and chemical applications. Many options are available which allow Teflon lining, concentric reducers, eccentric reducers, higher pressures, different flanges, and other chemical applications.
You really need to know the media involved, the working pressure and working temperature, and the overall outside atmosphere of the application before you can just throw a rubber joint into the system. Another option is that you can get them built to the exact requirements for your system, so a custom rubber joint is available quickly.
Rubber expansion joints are used in quite a few other industries. Sanitation design engineers will ask for a filled arch joint that does not allow waste product to settle in the arch. Chemical engineers will ask for Teflon or hypalon and usually want a full-faced flange so the product conveyed never touches the rubber joint. Sometimes a product shield is used to protect against a spill or blowout.
The rubber joints are also seen as an insulator, and they are able to help reduce noise in a system. In a high-rise apartment, condominium, or office building, rubber joints are used to quiet the system and not transmit the sound waves that occur naturally. Rubber spacers are also requested so that the tie rods also don't transmit these sound waves. In an industrial building or remote pump station, noise is not always a factor.
Readers are encouraged to consult FSA's Technical Handbook on Non-Metallic Expansion Joints and Flexible Pipe Connectors (especially page five) for different types of rubber pump connectors. This Handbook is available at www.fluidsealing.com.
Teflon expansion joints were originally used for chemical pump applications, but some markets in the U.S. use them for water applications. This is acceptable except for the fact that Teflon costs much more than the rubber or metal joints. These joints are available in narrow widths, in comparison to rubber expansion joints, and already have the limit rods installed.
Stainless steel bellows-type expansion joints are also available, but are usually in the piping runs rather than used as a pump connector. They involve a little more information to specify, as thermal growth is a concern along with the pipe guides and anchors involved - a subject that is beyond the scope of this review of pump connectors.
Another connector that has been on the market for many years is the stainless steel bellows pump connector. This is a multi-ply stainless steel bellows with carbon steel 150# flanges on the ends. These already have the control rods (limit rods) attached and do what the rubber joints can do, except that they can withstand higher temperature limits of almost 700-deg F, be installed outside without any issues, and serve as insulation, something a rubber joint cannot take. One version of these has the exact face-to-face dimensions of the single sphere rubber joint, so a changeover is simple and easy.
In order for these connectors to work properly, all manufacturers' installation instructions must be followed. You would be shocked to know how many of the failures we see are due to somebody trying to make a connector work. Hey, they are flexible connectors, right? Can't we just stretch them to make it work?
A pump connector is a valuable part of a properly operating system. The last thing you need is the failure of a simple part and that disturbing call back late in the night. So contact your flex connector manufacturer and get their recommendation.
The most flexible part of the system is your flex connector salesperson!
Pumps & Systems, May 2007