DESCRIPTION
The MKR-U profile is a rod seal that is preferably used in tandem sealing systems in conjunction with the PTFE version MKR seal. Redundant sealing systems are used where the application conditions no longer permit reliable sealing over the demanded service life with a single seal.
The property of the tandem sealing system is particularly important during cold starts when, due to the very high viscosity of the oil, the primary seal allows oil to pass as the piston rod is extended. In the tandem system the oil is
heated as a result of the friction at the primary seal and is then reliably wiped off - at a now lower viscosity - by the secondary seal, the MKR-U.
As the piston rod is retracted, the oil is stored in the reservoir between the seals, and is then pumped back against the system pressure by the hydrodynamics in the seal clearance of the primary PTFE MKR seal. The MKR-U is designed so that it also has the back pumping properties necessary when using a double-acting scraper in the rod sealing system.
When using the MKR series as the primary seal, a double-acting wiper must be used to contain fluid until rod retraction allows return of the fluid into the system. With strokes of more than 3 feet, the gland must be designed to provide an oil storage chamber between the seals. Please consult the H&D technical group for more information.
SEAL INFORMATION
Material Type (Primary Seal): POLYURETHANE
Material Type (Energizer): 70A NITRILE
Durometer (Shore D): 58
Temperature Range (F): -50 TO 230
Max Pressure (psi) - In Tandem System: 8700
Max Pressure (psi) - As an Individual Element: 3625
Extrusion Gap at Various Pressures (mm):
- 1,500 PSI: 0.50
- 2,900 PSI: 0.30
Max Speed (ft/sec): 16.0
Mating Surface Roughness - Ra (µm) - DYNAMIC: 0.1<>0.4
Mating Surface Roughness - Ra (µm) - STATIC: 1.6 MAX
Part Number Definition (Metric): MKR-(ROD DIAMETER)X(OD)X(SEAL HEIGHT)-U
Additional Part Number Definition (Metric): 70 X 85.5 X 5.9 = MKR-70X85.5X5.9U