There are several important factors to note when designing a metal hose assembly: alloy, fittings, media, pressure, and so on. One of the most crucial factors that is often taken for granted in industrial applications is hose length. Utilizing the incorrect length in an assembly can be detrimental to its cycle life and potentially result in failure in an assembly. If an assembly is too short, there is potential for the corrugation geometry to be deformed as the assembly is stretched between the connecting points. Conversely, if an assembly is too long it risks being over-bent as the hose tries to move out of its own way.
When working with valves, flanges, and pumps, operators should never be complacent. The wrong gasket or packing in a deadly application could result in loss of life. Ensuring the correct materials are suitable for the application requires special attention because safety is critical. As Gordon DeLeys, compliance assistance specialist at the United States Occupational Safety and Health Administration (OSHA), said, “Safety should not be a company priority since priorities in an organization can and usually change. Safety and health need to be a core value of an organization. Safety is really a case of values versus priorities.”
In October 1990, the USS Iwo Jima was heading into port for routine maintenance in Manama, Bahrain. The ship was the first to be designed and built from the keel up as an amphibious assault ship in Puget Sound Naval Shipyard, Bremerton, Washington, on Sept. 17, 1960.
Valve 2MS-7 was a globe valve in the boiler room, and it needed to be repacked for a small packing leak and reconditioned while in port. The valve was worked on by an outside contractor who had limited understanding of military specifications and procedures.
The mechanic—who had 10 years of experience—decided to replace the fasteners on the bonnet because they were worn. Apparently, the mechanic asked one of the boiler room personnel for new nuts and bolts and was given permission to look through the boiler room’s spare parts bins. He selected four bolts, eight studs and 20 3/4-inch nuts. The mechanic had not noticed that some of the nuts were brass. Because those fasteners were covered with a manufacturer-applied black coating, they were mistaken for the correct grade 4 steel nuts. Closer examination and use of a scratch or magnetic test would have revealed their metal content, but instead the black brass nuts were installed.
The next day the valve was reinsulated with lagging. The foreman had not inspected the work done on 2MS-7.
The valve should have been reassembled using only B-16 steel studs—anything else was a violation of good engineering practice based on the service condition.
When the brass nuts were used on the studs holding down the bonnet of the valve, no one realized this was a critical mistake since the valve was going to be in service above 800 F and the temperature limit for brass is 400 F.
On Oct. 30, 1990, in preparation to get underway and proceed to her operating area, fires were lighted in the boilers of the vessel.
Shortly after, one side of 2MS-7 was initially pressurized with steam generated from Boiler No. 1. Three hours later, valve 2MS-7 was opened to supply steam to the generator that supplied electrical power to the vessel.
As steam at 600 pounds per square inch (psi) and 850 F began flowing through the valve, the brass nuts were expanding at a greater rate than the steel studs. The bolts started losing the strength to secure the bonnet to the valve body. After less than 30 minutes of operation, the valve failed catastrophically.
Through a new “scoop” feature, the enhanced Levitorq design is able to collect and push lubrication under the washer to enable higher critical speeds and enhanced performance. Levitorq is part of the company’s Low Emission Sealing Solutions (LESS) product portfolio.
The original Levitorq design was created to reduce weight, decrease friction, improve thickness/flatness control and often provide a cost benefit to the customer. It relies on the principles of hydrodynamic oil film technology and is designed to create a surface on which a bearing can roll, or a load can be applied. Traditionally, thrust washers are made from metals, but Freudenberg has used its material expertise and design knowledge, along with proprietary software and testing capabilities,
Gaskets are ubiquitous components in a processing plant. Every flange, equipment joint and connection point will have some form of gasket to prevent fluids from compromising (i.e., leaking from) a process system. However, effective sealing can pose challenges. A new form of polytetrafluoroethylene (PTFE) gasket, Gylon Epix, already has successfully addressed a number of persistent problems at plants.
The gasket, which is available in 3⁄32-in.-thick, 60-in. × 60-in. sheets, features a raised hexagonal pattern (Figure 1). It exhibits
Back in the mid 70’s, an engineer named Roy Edlund of Busak & Luyken designed a high-pressure seal that had an uncommon effect of rocking in the groove. This action occurred when pressure was created on the retract side of a cylinder as the rod was being retracted into the cylinder.
The material used for the seal was generally a bronze-filled Teflon, which could resist extrusion and have a long seal life. Because the seal ring was made from a grade of filled Teflon, a small amount of oil would leak under the lip as the cylinder was being extended.
One of the most unique features of this style seal was that as the rod was being retracted back into the cylinder, the buffer ring would rock or rotate slightly to the low pressure side thereby forcing leaked oil back into the retract side of the cylinder under the buffer ring.
This seal is commonly called a Buffer Ring (for reasons we’ll explore in this blog), but this seal helped usher Teflon into most high-pressure hydraulic systems today.
Manufactures of high-pressure hydraulic systems in equipment, such as back hoes or hydraulic cranes found that their products were having seal failures prior to reaching warranty. This resulted in downtime and large warranty expense to repair these cylinders in the field.
In normal operations, the standard U-Cup made from a variety of Urethanes did an excellent job of creating a “near” zero leak sealing system. The problems would occur as the “bulk” oil temperature rose due to usage, pressure spikes in the system would cause premature failure of the Urethane U-Cup.
It was the pressure spikes that usually wreaked havoc with the U-cup seal design, causing the urethane to break down and eventually crack, creating a leak, and resulting in equipment shut-downs.
The Buffer Ring turned out to be the answer. By adding another sealing element in front of the Urethane U-cup, the life of the U-cup was greatly extended, overall friction in the system was reduced, and the bulk temperature in the hydraulic system was lowered.
All these advantages came by adding a sealing element. The true savings showed up in dramatically improving equipment up time. This also reduced warranty costs of equipment to the OEM.
The answer to this question was initially difficult for many manufacturers to understand. Normally, putting one seal in front of another should cause a pressure trap, sending pressure loads much higher than relief valve settings, which locks up the cylinder.
The secret was in the way the Buffer Ring performed its job.
The seal leaking is very important to its design. If oil didn’t reach the U-Cup, the U-cup would generate heat and begin to wear out prematurely. So, since the Buffer Ring allowed a small amount of fluid to seep under the lip, this fluid lubricated the U-cup and kept its friction to a minimum.
Being elastomeric in nature, the U-cup did an excellent job of wiping the rod nearly completely dry.
But what about the pressure trap?
The Buffer Ring and its unique quality allowed fluid back into the system. Testing verified that this would happen anywhere from zero to about 100 PSI.
The U-cup spent most of its life in a well-lubricated, low-pressure / low-temperature environment compared to the original design.
The Buffer Ring also made suppliers of U-Cups extremely happy, as their failed seal had been given new life compared to the holes blown through the back of their urethane product.
Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.
Original content can be found on Parker’s Website and was written by Ben Nudelman, Market Development Engineer, Chomerics Division.
Form-in-place EMI gaskets, also known as FIP EMI gaskets, is a robotically dispensed electromagnetic interference (EMI) shielding solution that is ideal for modern densely populated electronics packaging.