Running Friction

High running friction may cause difficulty by wearing soft metal parts. Metals such as copper, brass or aluminum can be rapidly worn away by a moving O-ring. This is especially true if high pressures are involved. If unexplained leakage occurs with these or other soft metals, it is good practice to check the metal dimensions for signs of wear.

The following formulas may be used for estimating the running friction of O-ring.

Piston Groove                            Rod Groove

  FC = f_c x L_p                                FC = f_c x L_r

  FH = f_h x A_p                               Fh = f_h x A_r

    F = F_C + F_H                              F = F_c + F_H

  A_p = Projected area of seal for piston groove

          applications.

  A_r = Projected area of seal for rod groove applications.

  F = Total seal friction in pounds.

  F_C  = Total friction due to seal compression.

  F_H = Total friction due to hydraulic pressure on the seal.

  f_c = Friction due to O-ring compression obtained from

        Figure 5-9.

 f_h = Friction due to fluid pressure obtained from Figure 5-10.

 L_p = Length of seal rubbing surface in inches for piston

         groove applications.

 L_r = Length of seal rubbing surface in inches for

       rod groove applications.

Example:

Parker 2-214 rubbing against OD of O-ring at 103.5 Bar (1500 psi), 10% compression, 70 durometer:

                F_C = 0.7 x 3.93 = 2.75

                F_H = 48 x 0.44 = 20.90

                F  = FC + F_H = 23.65 pounds

Data for the coefficients (fc and fh) are given in Figures 5-9 and 5-10. Projected areas and lengths of rubbing surface are given in Table 5-4.

Figure 5-9: Friction Due to O-ring Compression		Figure 5-10: Friction Due to Fluid Pressure

Table 5-4: Rubbing Surface for O-rings