Is this a good place to talk about actual effect of having air in the system? I should preface all this will, if i was asked, I think I can definitely feel after doing a component change that the ride is harsher and eventually smooths out after bleeding/driving around. But in theory you should always be able to put numbers to what we are experiencing.
Let's start with some data:
No. 1 Gas Chamber | Front | Rear |
Sealed Gas | Nitrogen | Nitrogen |
Gas Chamber Volume | 24.4 In^3 (400cc) | 24.4 In^3 (400cc) |
Sealed Gas Pressure | 2.26 MPa | 1.90 MPa |
| | |
Relief Gas Chamber | | |
Sealed Gas | Nitrogen | Nitrogen |
Gas Chamber Volume | 7.3 In^3 (120cc) | 9.2 In^3 (150cc) |
Sealed Gas Pressure | 13.5 MPa | 10 MPa |
| | |
No. 2 Gas Chamber | | |
Sealed Gas | Nitrogen | |
Gas Chamber Volume | 7.3 In^3 (120cc) | |
Sealed Gas Pressure | 1.8 MPa | |
Brief background. The fronts have all 3 chambers acting at normal driving and shuts off the No. 1 chamber when in curves and during braking to stiffen up the front end. The rear always has both chambers acting on the actuator. The other piece to the puzzle is that all 4 corners can act on each other's individual system pressures.
Vehicle Condition Fluid Temperature | Fluid Temperature Condition | Reference Value |
When vehicle height changes from NORMAL to HI | 20°C (68°F) +/-10°C (50°F) | The oil pressure begins rising when control is started and reaches approximately 13 MPa (132.6 kfg/cm2, 1885 psi) when the vehicle height is almost finished changing to HI. |
When vehicle height changes from LO to NORMAL | 20°C (68°F) +/-10°C (50°F) | The oil pressure begins rising when control is started and reaches approximately 8 MPa (81.6 kfg/cm2, 1160 psi) when the vehicle height is almost finished changing to NORMAL. |
Situation A:
Let's say you let 200cc of air into the system at 1 bar (atmospheric pressure at sea level-ish). This could be your typical changing out a component, so the system has become completely decompressed, but you sealed it back up with air in it.
Now you start the truck up and push the vehicle up to 8 MPa (assuming functioning OEM system)
By Boyles law that 200cc of air is now 2.5 cc of air. The #1 gas chamber should now be at a volume of 95cc (at the rear, so i can avoid the math for gas chamber 2)
In affect you will have added a 2-3% (2.5cc/95cc) increase in volume of the No. 1 Gas chamber.
How much difference do we think that makes? Or am i missing something? I know that I'm essentially ignoring the force on the system from gravity (the ground pushing the actuator back into the system). But i'm having trouble wrapping my head around that.
Its easier to think of a system with only 1 force acting on it, but in reality, if you are looking at each corner of the trucks systems individually, there are inputs from:
A. The center control cylinder
B. Each of the Gas chambers (3 for front and 2 for rear)
C. Gravity acting on the shock actuator back into the system.
D. Any air that might be in the system.