Application description: Hydraulic Pump

• Shaft diameter 0.750″ ±0.001
• Bore diameter OD 0.753″ ±0.001
• 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) – 0.004″
Groove Diameter = 0.749 + (2 x 0.100) – 0.004
Groove Diameter = 0.945 in ±0.001

2. Groove width = 0.110″ -0.000/+0.005

3. Calculate Minimum Groove Volume

Minimum Groove Volume = ((Min Groove Dia. – Max. Bore Dia.)/2) x Groove Width
Minimum Groove Volume = ((0.944 – 0.754)/2) x 0.115
Minimum Groove Volume = 0.0109 in2

4. Calculate Maximum Quad-Ring® Brand Seal Volume

Maximum Quad-Ring® Brand Volume = (Maximum Cross-Section)2 x 0.8215
Maximum Quad-Ring® Brand Volume = 0.1062 x 0.8215
Maximum Quad-Ring® Brand Volume = 0.0092 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 = (0.944 – 0.754)/2
• Minimum Groove Depth = 0.095
• Maximum Seal Squeeze = 1 – (0.095 / 0.106)
• 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 = ((0.946 – 0.754)/2) + (0.754 – 0.749)
• Maximum Groove Depth = 0.096 + 0.005
• Maximum Groove Depth = 0.101
• Minimum Seal Squeeze = 1 – (0.101 / 0.100)
• 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 = 0.754 – 0.749
• Maximum Clearance = 0.005″ (0.0025″ Radial)

This application has a max clearance of 0.0025″ 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 0.009, 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 >= 0.751″
Quad-Ring® Brand Seal Size = 4117