Application Example: Quad-Ring® Brand Rotary Seal

Application description: Hydraulic Pump

• Shaft diameter .750" ±.001
  
• Bore diameter OD .753" ±.001
  
• 150 psi Hydraulic oil
  
• .103" cross-section Quad-Ring® Brand seal

1. Calculate groove dimensions
   Groove Diameter = Minimum Shaft Diameter + (2 x Min Cross-Section) - .004"
   Groove Diameter = .749 + (2 x .100) - .004
   Groove Diameter = .945 in ± .001
   
2. Groove width = .110" -.000/+.005
   
3. Calculate Minimum Groove Volume
   Minimum Groove Volume = ((Min Groove Dia. - Max. Bore Dia.)/2) x Groove Width
   Minimum Groove Volume = ((.944 - .754)/2) x .115
   Minimum Groove Volume = .0109 in2
   
4. Calculate Maximum Quad-Ring® Brand Seal Volume
   Maximum Quad-Ring® Brand Volume = (Maximum Cross-Section)2 x .8215
   Maximum Quad-Ring® Brand Volume = .1062 x .8215
   Maximum Quad-Ring® Brand Volume = .0092 in2
   
5. Compare Minimum Groove Volume to Maximum Ring Volume
   In this application the Maximum Ring Volume is less than the Minimum Groove Volume; everything appears to be OK.
   
6. Calculate Minimum and Maximum seal squeeze
   These calculations look at both ends of the worst case stack up
   tolerance, including rod shift, to determine the maximum and
   minimum ring squeeze.
   Maximum Seal Squeeze =
   1 - (Minimum Groove Depth / Maximum Ring Cross-Section)
   Minimum Groove Depth = (Minimum Groove diameter – Maximum Bore)/2
   Minimum Groove Depth = (.944 - .754)/2
   Minimum Groove Depth = .095
   Maximum Seal Squeeze = 1 - (.095 / .106)
   Maximum Seal Squeeze = 10.3%
   Minimum Seal Squeeze = 1 - (Maximum Groove Depth / Minimum Ring Cross-Section)
   Maximum Groove Depth = ((Max. Groove Diameter. –
   Max Bore)/2) + (Max Bore – Min. Rod)
   Maximum Groove Depth = ((.946 - .754)/2) + (.754 - .749)
   Maximum Groove Depth = .096 + .005
   Maximum Groove Depth = .101
   Minimum Seal Squeeze = 1 – (.101 / .100)
   Minimum Seal Squeeze = -1.0%
   In this application, if every dimension went to the worst side of
   the tolerance and the piston was side loaded, the seal would leak. To avoid these problems:
   1. Reduce the clearance between the bore and piston.
   2. Reduce the tolerances of the bore and piston.
   3. Use a larger cross section Quad-Ring® Brand seal to absorb the extra tolerance.
   4. Support the piston so that it can not move off center.
   
7. Calculate Maximum Clearance and Evaluate Possible Extrusion Issues
   Maximum Clearance = Maximum Bore – Minimum Rod
   Maximum Clearance = .754 – .749
   Maximum Clearance = .005" (.0025" Radial)
   This application has a max clearance of .0025" and must withstand 150 PSI without extruding the Quad-Ring® Brand seal. Refer to the clearance chart. A 70 Shore A material at 150 PSI can withstand a maximum clearance of .009, so a 70 Shore A material will work. Making improvements to the Minimum Seal Squeeze issues in Step 6 will also reduce any possible issues with seal extrusion.
   
8. Select seal size
   For all rotary rod seal applications select a Quad-Ring® Brand seal that has an ID larger than the maximum shaft diameter.
   Part ID >= .751"
   Quad-Ring® Brand Seal Size = 4117