[dsg-eic_dirc] [EXTERNAL] air pressure and trailer

[Shepherd, Matthew]

Hi Greg,

(I hope I have the right mailing list in the cc.  Please feel free to forward.)

First, there is a point that I forgot to stress:  when you discuss with the trucking company be sure you convey that you want a refrigerated trailer *and* an air ride suspension.  This combination is apparently difficult to get based on our experience.  You should put on your checklist to inspect the trailer suspension when it arrives.  (Despite our request on one trip we were delivered a trailer with leaf springs and we had to send it back.)

Regarding air pressure:   we used 19 psi for vertical support for most of the 2nd trip.  Our drawing says 25 psi.  From our development notes, we guessed that 25 psi was ideal.  John writes: "The spring and damper settings of 25-26 psi and 12 lb.-in./sec. respective, were finalized."

Here is the passage from my notes that discuss observation on the road.

"During the first day we also noticed that shocks on the bar box in the rear of the truck at the level of 1 g, or what we thought at the time (and now know to be underestimated) was our maximum shock for the first shipment, seemed to be typical for the rear box in this shipment (one every 10 - 20 minutes).  Nevertheless, these met our previously-agreed tolerance, and so we continued.  The 3 g shock did give us pause and resulted in very careful examination of the video.  After the first day we opted to reduce the air spring pressure in the vertical direction from about 23 psi to 19 psi.  Due to the check valves in the system, some time is required (perhaps a day) for the true pressure to reduce on all springs.  Due to systematically varying road conditions it is hard to compare quantitatively, but the frequency of >~ 1 g shocks on the back bar box seemed to decrease significantly after this air pressure adjustment.  This adjustability -- thanks John Frye -- is a huge argument in favor of an air spring system, rather than fixed mechanical springs."

I can't find the horizontal spring setting in my notes, but I think this should be about or less than the vertical.  There is much less load on the horizontal system.  It would be interesting to see where the regulators that you have sitting in that box are set.  I suspect you'll find one around 19 psi (that's the vertical), and the other is the horizontal.  I vaguely remember a problem calibrating the remote pressure sensors.

Also, attached again is the drawing, which is a little different from the crate drawing we were looking at.   Note that all crate springs in one direction are behind a single regulator.  You can also see the point of the extra check valve in our drawing that one of you were asking about.  That extra check valve upstream of the remote pressure sensor allows remote monitoring of the pressure when the bottles are disconnected.  This doesn't seem like a critical feature in your application.

If there are any other questions, I'm around tomorrow also.  I head back to Bloomington Wednesday morning.

Matt





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