O-ring Seal Friction - Pressure equalized and Differential Pressure
O-ring Seal Friction - Pressure equalized and Differential Pressure
(OP)
My question is really regarding the difference between seal friction on a dynamic o-ring in several conditions. It is axial Piston seal on rod. The o-ring is 300 series HNBR because it is robust. It will only cycle 3 times then lock open and the seals will become static. The conditions are listed below. I believe I'll have over 300# friction on a single o-ring with pressure equalized downhole at 5,000 psi.
1)Used in downhole tool and friction will add to spring force. There will by hydrostatic pressure at the tool up to 5,000 psi.
2)Differential pressure is applied across a piston area created by o-ring seals.
3)I have a nomograph that gives me the approximate friction with differential pressure and it is magnitudes higher than static friction and is large enough it must be considered to determine the hydraulic force to move the part down with the spring.
4) The spring is a 90 Belleville stack with hysteresis that reduces the return force.
5. I have a concern when differential or surface pressure is bled to 0 psi that the pressure equalized seals with hydrostatic pressure will generate almost as much friction created by differential pressure at the O-rings. With pressure acting on both sides, it will create a high contact force with gland ID.
Is this hydrostatic friction a real concern? My colleague thinks it will force the o-ring into square shape as pressure is applied on both sides of the seal and the contact area with the seal surfaces will be large. The normal force would be slightly higher than the hydrostatic pressure created force because of initial squeeze.
I have never considered O-rings with no differential having such high breaking friction once surface pressure was bled off. We will test to see. However, I never recall having a problem due to this condition before.
Consider that a 348 HNBR Rod O-Ring would have over 300# friction at 5,000 psi. With another seal and static friction it could around 600#. Then you have the spring force...
Is this the proper method to calculate friction. Comments?
1)Used in downhole tool and friction will add to spring force. There will by hydrostatic pressure at the tool up to 5,000 psi.
2)Differential pressure is applied across a piston area created by o-ring seals.
3)I have a nomograph that gives me the approximate friction with differential pressure and it is magnitudes higher than static friction and is large enough it must be considered to determine the hydraulic force to move the part down with the spring.
4) The spring is a 90 Belleville stack with hysteresis that reduces the return force.
5. I have a concern when differential or surface pressure is bled to 0 psi that the pressure equalized seals with hydrostatic pressure will generate almost as much friction created by differential pressure at the O-rings. With pressure acting on both sides, it will create a high contact force with gland ID.
Is this hydrostatic friction a real concern? My colleague thinks it will force the o-ring into square shape as pressure is applied on both sides of the seal and the contact area with the seal surfaces will be large. The normal force would be slightly higher than the hydrostatic pressure created force because of initial squeeze.
I have never considered O-rings with no differential having such high breaking friction once surface pressure was bled off. We will test to see. However, I never recall having a problem due to this condition before.
Consider that a 348 HNBR Rod O-Ring would have over 300# friction at 5,000 psi. With another seal and static friction it could around 600#. Then you have the spring force...
Is this the proper method to calculate friction. Comments?
- CJ





RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
See attached and see if that explains why equalized hydrostatic pressure will create high friction just as differential pressure. I'm not claiming to be correct but I can't see how it wouldn't be almost as high as differential pressure friction.
- CJ
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
How can the contact pressure not increase? Just explain because I can't see how it does. Maybe you can draw what you are trying to explain to make it clear?
- CJ
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
- CJ
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
I have thought about it. I just haven't heard an explanation that explains why initial squeeze won't increase because of the way O-rings behave.
You are saying the initial squeeze remains the same as long as pressure is the same on each side of o-ring. The net forces are the same across the o-ring at 5,000 psi and at 0 psi. But the force at 5,000 psi would be much larger but equal in both directions compressing the "round" o-ring into a different or more rectangular shape with larger contact length and force at ID of seal and OD of gland. If the initial squeeze isn't lost, I don't see how it doesn't increase with pressure acting on the o-ring.
I have never experienced a problem with friction except with DP so I may be overthinking.
- CJ
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
Testing performed at the largest Oilfield Service company in the world proved my case. Differential pressure friction = Hydrostatic pressure friction.
- CJ
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
JOHN CHRane packing Co?
Rick Fischer
Principal Engineer
Argonne National Laboratory
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
Rick Fischer
Principal Engineer
Argonne National Laboratory
RE: O-ring Seal Friction - Pressure equalized and Differential Pressure
My colleagues have had had recent experience with this. Small hydraulic area, high pressure, large seal dia's. This resulted in much higher breaking friction than planned for. There were many variables but the friction from high static pressure made the load unmanageable (pressure would not move piston) until a PEEK debris barrier was removed in floating j-slot. It did not create a seal but put a bind that pressure could not overcome but hammering with a hammer and brass bar would.
The static friction was irrelevant from a functional sense. but with dynamic or hydrostatic pressure growing the peek ring maintained a load Ff > P x A(.785 sq. in)and up to 20,000 psi. I don't have the details. I do know Peek can behave erratically when it comes to moving force but this...
Maybe I can get a pic. It is a simple device but I'm too tired to sketch and scan.
Good evening...
CJ
- CJ