Frequently Asked Questions
How can engineering and/or maintenance practices maximize seal life?
Maximum seal life can be achieved by the proper design of the seal cavity to allow adequate circulation of the fluid into and away from the seal area. All lubricating circuits should incorporate adequate filtration in order to provide clean fluid to the seal area. Incorporate sufficient lead chamfers for the o-rings to be assembled onto or into their interfacing surfaces. Adhere to the recommended axial shaft movement, shaft eccentricity, and surface finish requirements.
Use assembly tooling when necessary to ensure proper handing and installation of the seal. Care must be exercised when handling any seal so that the primary seal faces are not damaged or contaminated prior to installation. Seal faces must clean and free of any foreign material. The seal cavity must be free of any foreign debris or surface defects such as burrs that could damage the seal.
Magnetic Seal’s recommended installation procedures and handling and cleaning practices must be followed to ensure the proper operation of the seal.
What mediums can be sealed with magnetic and spring-loaded seal technology?
A MAGSEAL is limited to media that are compatible with its component materials. The Alnico V magnet is 50% iron; therefore, it cannot be used in any corrosive or caustic medium that is not compatible with the protective chrome plate surface coating.
MAGSEALS can operate in air, gases, water, steam, refrigerants, lubricants, fuels, and hydraulic fluids.
A MACHSEAL can operate in all of the same media as the MAGSEAL, but it can also seal corrosive and caustic fluids because of the large variation of materials that can be used in its components.
What are the temperature limitations of magnetic and spring-loaded seals?
The o-ring material dictates the temperature limits for both seal designs. Therefore, typical operating temperature limits are –65°F (-54°C) to 450°F (232°C) with fluorocarbon (FKM) o-rings. Perfluororelastomer (FFKM) o-rings can increase the operating temperature up to 572°F (300°C) with a substantial increase in cost.
The Alnico V magnet retains 95% of its magnetism at 500°F (260°C), and it has a maximum practical operating temperature of 1,000°F (538°C).
Can you expect attraction of ferrous material to the magnet?
Yes. The points of highest flux density of a MAGSEAL occur at the periphery of the magnet closest to the seal case. Any ferrous debris that comes near enough to this magnetic field will be retained at that periphery thus preventing it from contaminating the primary mating faces.
What are the effects of pressure reversal on magnetic seals?
The standard MAGSEAL designs are limited to maximum pressure reversal of 2 PSID because it is primarily designed to seal pressure in one direction. The MAGSEAL magnet and seal case have a clearance fit into the housing bore and onto the shaft diameter. They are secured to these surfaces by the secondary o-ring seal. When the external pressure is greater than the internal pressure, the magnet and seal case act as a piston and will move inboard. The seal faces will then separate when the internal pressure is greater than the external pressure because the resulting force acting on the magnet is greater than the force acting on the seal case.
The MAGSEAL design can be configured to operate with pressure reversals up to 30 PSID. This is accomplished by restraining the magnet with a non-magnetic retaining ring in the housing and by using a special seal case design that becomes positively loaded against the seal face when pressure is applied from either direction.
Are there any compatibility issues with the use of HTS oils?
O-rings that are compatible with HTS oils can be furnished in our seals.
Seal designs that were approved and qualified before the introduction of HTS oils must have their o-rings verified for compatibility. See our O-ring compatibility white paper, O-RING COMPATIBILITY ISSUES WITH HTS OILS, on this web site.
Do you have local representation in our area?
Yes, MAGSEAL has local factory trained representation in North America and Europe. Contact information can be found on our Sales page.
Is on-site factory commercial and technical support available?
Yes, upon request.
Electromagnetic Interference (EMI)?
The magnetic circuit is closed when the seal case is mated with the magnet thus eliminating any significant stray fields. The stray field strength is typically less than 3 gauss when measured at 0.5 in. [12.7 mm] from the magnet.
MAGSEALS are used in radars, wave guides, permanent magnet generators and alternators with no adverse affects.
What materials are used to produce magnetic seals?
The MAGSEAL comprises two main components, the seal case (rotor) and the magnet (stator).
The seal case is made from a ferromagnetic material, 416 or 410 stainless steel, 17-4PH for maximum corrosion protection, or 42 Alloy steel for low thermal expansion.
A seal ring is installed in the seal case with an interference fit. The seal ring is typically a carbon graphite material whose selection is based upon the application
The magnet is made from Cast Alnico V, a permanent magnet material that is composed mainly of aluminum, nickel, cobalt, and iron.
The secondary seals (o-rings) can be any one of the following elastomers: fluorocarbon (FKM-A or FKM-GLT), perfluorocarbon (FFKM), Nitrile or Buna-N (NBR), ethylene propylene (EDPM), Fluorosilicone (FVMQ), silicone (Q, tetrafluoroethylene/propylene (FEPM), or neoprene (CR).
Ancillary hardware that houses the magnet must be made from non-magnetic material such as 300 series austenitic stainless steel or aluminum. Sleeves and spacers that install onto the shaft or inside the seal case may be made from any magnetic or non-magnetic material.
What are the temperature limitations of the magnet?
An Alnico V magnet is stable with less than 5% reduction of magnetization at temperatures between –148°F (-100°C) to 598°F (300°C). The maximum practical operating temperature is 1,000°F (538°C).
What is the direction of the magnet flux lines?
The solid cast Alnico V magnet is limited to a maximum shaft diameter of 5 inches. This magnet is magnetized through the diameter so that the flux lines extend outward from the magnet’s outside diameter. The magnetic circuit is completed through the outside diameter of the seal case.
Seals for shaft diameters larger than 5 inches use a 440C stainless steel mating ring that has Alnico V bar magnets inserted into the face of the ring. These magnet inserts are magnetized through their length so that the flux extends axially. Again the magnetic circuit is completed through the seal case.
What is the shelf life of magnetic and spring-loaded seals?
The shelf life for either the MAGSEAL or the MACHSEAL is theoretically unlimited. However, we recommend that any MAGSEAL or MACHSEAL that is over five (5) years old should have the carbon seal ring surface flatness verified to be within our requirement of two (2) helium light bands, .0000232 in. [0.000589 mm] prior to use. If the surface flatness is beyond this specification, then the seal should be returned to Magnetic Seal Corp for relapping.
What are cure dates for O-rings?
The cure date identifies the quarter and year of manufacture of the o-ring (e.g., July to September of 2001 = 3Q01). The vast majority of the o-rings that are used in the MAGSEAL and MACHSEAL designs have an unlimited shelf life per ARP5316. Magnetic Seal Corp uses two o-ring elastomers that have a 15 year maximum shelf life. They are Nitrile or Buna-N (NBR) and Neoprene (CR).
Is loss of magnetism in the magnet possible?
The magnet is made from Cast Alnico V permanent magnetic material that is directionally oriented through the diameter for maximum magnetic energy and stability. The attraction force may undergo a maximum loss of 15% within ten (10) years.
Factors that affect attraction force:
- External magnetic fields that are applied to the MAGSEAL must be limited to 200 oersteds or less. A direct current magnetic field greater than 200 oersteds will partially demagnetize the magnet.
- The only significant cause of damage to the magnetic properties of MAGSEALS is mishandling.
- Contacting the magnet directly with ferromagnetic materials, such as pliers, screwdrivers, inspection equipment, or shelving is detrimental.
- The magnet is generally insensitive to shock, vibration, and impact. A mechanical stress large enough to significantly demagnetize the magnet would have to be so large that it would either fracture or physically damage the magnet.