5th Wheel Pressure Gauge

Crappy gauges.

 

My scale gauge and Right Way both have to be calibrated. You can't move the leveling valve and if you do it has to be calibrated again.

When doing a proper weigh you have to dump the air bags and inflate to be close as possible to accurate. On level ground it's only accurate to within 200-400 pounds.

 

Why do they have to be calibrated if the air pressure "will be the same no matter what vehicle". I worked for a contruction company we had 10 T800 Kenworths, all identical, all built off the same spec sheets, everything was the same wheelbase, suspension, tires, everything. They all had suspension gauges in the dash and they were all a little different.

 

If you have a balloon with 10psi in it and put a 50 pound weight on it the psi will increase a lot. If you have a balloon with 100psi in it and put a 50 pound weight on it the psi will only increase a little.

All pressure gauges need to be calibrated at a known constant. That would be the ride height with regards to a truck. The truck will make the ride height proper no matter how much weight is on it thereby increasing or decreaseing the pressure. Once you have calibrated you can calculate off that known variable.

If your inclined to learn more you can start with Boyle's law.

 

On truck A, If pressure reading is 80 psi with 34,200 lbs on the group, and on truck B, a reading of 74 psi with 33,900 lbs ... how much is on the group with a reading of 76 psi on truck C?

Just sayin' you don't know until you can establish a reference or baseline for that particular setup.

 

Correct, you have to calibrate. Playing around with your ride height will throw your reference/baseline/calibration off.

 

Ok what if you change the size of the balloon? What if said balloon is supporting one end of a beam and the other end is supported by a fixed point (which is how most semi suspensions work) if you put that 50 pound weight on the beam you will have a specific psi. If you move the location of the balloon under the beam farther or closer to the fulcrum does the psi in the balloon not change to support the same 50 pounds?
Is this not the principle of leverage? My problem is your blanket statement "As far as air pressure, it will be the same no matter what vehicle" this is the experienced trucker advice forum, somebody will read this, get his new truck load it to 60 psi then get to the scales and find out the hard way that he's at 34,000 at 50 psi. There are WAY to many variables to make such a statement.

 

Here is an example. Get 2 bathroom scales. One foot on each one. Lean from side to side and the weight changes on the scale but they both add up to the same. If they were connected as are air bags they would read the same.

If you have a giant balloon connected by a straw to a tiny balloon the PSI is the same in both. Not a good example though. The tiny balloon would probably pop

 

What if you left foot is on the ground and you right foot is in the scale and you shift you weight? Does the scale reading not change? You ignored two things, my beam example and the fact that you used a blanket statement that can't possibly be true. Two ore more similar air bags supporting a given weight will have close to the same psi, but that doesn't apply to truck suspensions that have many variables.

 

What if it's snowing in Buffalo with a falling barometric pressure. Are my gauges in Phoenix going to be accurate?