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bigredhdt

Rear Leveling Valve

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I'm thinking my rear leveling valve is not working correctly.  My truck is not singled.  When I take the trailer off the truck it takes about 60-90 seconds for the bags to release to the required level.  How quickly do ur tractors adjust?

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Many leveling valves have a built in delay, but I am not aware of any that are as long as 90 seconds (I did some research on valves & delay when I selected one for my hitch).  If at all possible, get the manufacturer and model number of your valve then look up the specs.  If that is not feasible ask Scrap - the man is a living legend for knowing about such things.

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I know my hitch goes way up when unhitching. Wonder if I have a problem with it's leveling valve.It's an ET

Edited by GlennWest
spelling

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12 hours ago, GlennWest said:

I know my hitch goes way up when unhitching. Wonder if I have a problem with it's leveling valve.It's an ET

Bigredhdt,

When I left the ECR in 2018 I stopped at the first rest stop on I40 and noticed the rear of the Volvo was hyper extended from the tires.  When we got to the CG in Oliver Springs I crawled under the truck and released the leveling rod - nada, nothing.  So I called NAPA and gave them the part number of my valve.  They had the valve the next day.  Once installed (easy job) ride was normal again.  BTW - previously I learned that the rubber pieces on the end of a leveling rod can deteriorate over time to a point where the rod does not actuate the valve properly.  If the rubber rod ends move sideways on the rod you need new ones - that can make  the valve appear bad.

The thing is when the height extends or lowers the leveling rod moves a lever attached to a valve that either expels or adds air.  Through the use of fairy dust and magic oil some valves have a delay on movement so you do not go down the road like a basketball.

................................................................................................................................................

Glen,

When I put a valve on my TSLB I also included a cut-off and evacuation in-line valve as part of the plumbing.  What I had noticed was that when I unhooked the fiver the hitch would go up as you described.  But, even with the valve lever up in the exhaust position the hitch tended to stay up (it would eventually come down, but it took several hours).  I could lower the hitch by opening my added evacuation valve.  What I determined from hooking up and unhooking was that the valve didn't do much without the added weight of the trailer pin.  Apparently it needs x amount of weight to work the way we want.  I have found for me that hook-up and unhook is easier when I close my supply valve and then open my exhaust valve so the air bags are completely empty.  So, my armchair guess is nothing is actually wrong with your ET and valve.  That's just the way it is.

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Glenn, remember, your bags are under a certain pressure to hold your trailer weight at a certain height.  Remove that weight and the pressure will push the hitch up.

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Glen Our ET seems like it takes a minute or too for the hitch head to start lowering after I have raised the trailer up to unhook. I will be hooking up tomorrow and then unhooking on Saturday once we get to our campground. I will see if I can time it. 

On 6/25/2019 at 8:01 PM, GlennWest said:

I just wondering why the leveling valve don't bleed off as hitch going up. The truck will. 

Dave

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Let's assume the hitch is operating in it's sweet spot of about 50 psi.  When you unhitch, the head rises, and we would expect to hear a rush of air escaping, at 50 psi.  But in reality, your pressure is near zero, because you've removed the load.  Thus, the air escapes very slowly.  It's likely that the leveling valve is fine.

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2 hours ago, rickeieio said:

Let's assume the hitch is operating in it's sweet spot of about 50 psi.  When you unhitch, the head rises, and we would expect to hear a rush of air escaping, at 50 psi.  But in reality, your pressure is near zero, because you've removed the load.  Thus, the air escapes very slowly.  It's likely that the leveling valve is fine.

Better said by a farmer!  Or would that be former farmer?

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I raised my camper up but didn't get clearance under it. Have in past and it wouldn't come out. When it came out, hitch slamped upward and even cause springs to come out. That don't sound right.

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Glenn, that is kind of a confusing statement.  If you didn't get clearance under it, it wasn't raised up enough.  If you slammed it up, you still didn't have it raised up enough.

For anyone reading this still, slow down the unhitch procedure and let your leveling valves do what they do.  Watch for the gap between the pin plate and the hitch.

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Gauge on the air line after a $4.95 reducing valve from Horrible,  cut off valve & dump valve.  Simple, no self leveling valve

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Glenn the valve on your hitch might be haywire...

I add weight to the landing gear until I see them taking a bit of weight. Then I hop into my Big KW release the brakes and dump the suspension as I skillfully pull forward gently , intending to show the audience that invariably gathers what a Sooper Trucker I am. This is the part where:

a. I find out I forgot to release the 5th wheel jaws

b. I forgot to put the truck in gear and am trying to hang the tractor on the king pin

c. All of the above.

Edited by noteven

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1 hour ago, noteven said:

Then I hop into my Big Volvo release the brakes and dump the suspension as I skillfully pull forward gently , intending to show the audience that invariably gathers what a Sooper Trucker I am. This is the part where:

a. I find out I forgot to release the 5th wheel jaws

b. I forgot to put the truck in gear and am trying to hang the tractor on the king pin

c. All of the above.

d. Forget to release the air in the Trailer Saver hitch glowing to rise forcefully and quite loudly as I pull away from the king pin.

 

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Glen, the suspension valve and the ET valve should dump air at about the same rate as you raise the fifth. The "technique" is, you raise the fifth in small increments and every time you crank it up the truck air valve and the ET air valve should hiss releasing pressure since you are taking weight off from both. The last "increment" should produce no hissing and the king pin plate on the fifth should separate slightly from the top of the hitch head showing a gap, 1/8 inch or so. That indicates that all the pin weight of the trailer has been removed from the truck suspension (truck airbags) and ET suspension (ET airbags). If the ET slams up when you pulled away. It could be a number of things.  First and foremost you didn't raise the fifth to the point where there is no more weight on the truck and the ET. Second the ET valve might be slow dumping or perceived slow (some folks are "impatient"). Third, ET valve might be defective, rare but possible. One way to tell if the valve is working, is to place a finger on the back side of the ET valve after you raised the fifth another increment, there is a rubber membrane there with cross-cut in that membrane, if the valve is working you will feel on your fingertip the air escaping from the airbags through the valve. When it stops the hitch is ready for another increment of raising the fifth and the valve is working. If you pulled away and the hitch slammed up, watch for two conditions. If the hitch stays up against the stops, the valve is bad. If the hitch settles down after few moments to its operating height (2 inches down from the stop plates), the valve is fine and you pulled away too soon, you didn't raise the fifth high enough to take all the pin weight off the hitch and the truck..

Dump valves are not needed if the valve is OK and this technique is used. If you want to dump the ET for "whatever reasons" (need clearance over the hitch, etc.) you need two valves. One to shut off the supply air to the valve (top airline on the valve) and the dump valve on the airbags (bottom airline on the valve).

Edited by phoenix2013

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On 6/27/2019 at 3:59 AM, rickeieio said:

Let's assume the hitch is operating in it's sweet spot of about 50 psi.  When you unhitch, the head rises, and we would expect to hear a rush of air escaping, at 50 psi.  But in reality, your pressure is near zero, because you've removed the load.  Thus, the air escapes very slowly.  It's likely that the leveling valve is fine.

The bags were at 50psig, which is about 4.5x atmospheric pressure, and therefore they had about 4.5x the (normal) volume of air in them. If you remove the load, that air will expand the bag to the limit, probably doubling the volume and thereby lowering the pressure to 2.25x atmospheric, or about 20psig. At that point or perhaps after a short delay, the valve should begin releasing pressure to bring the height to where it belongs (a point of equilibrium of pressure/volume/weight of the suspended part of the hitch).

If you crank down the landing gear and release the load gradually, it should equalize steadily either as fast as you release the load or at least by the time you climb back in the cab and separate the rig.

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All airbags are rated at 100 psi for their maximum load. Typical air hitch bag are 2,500 lbs at 100 psi. They are linear meaning that each psi the they develop a force of 25 pounds at, 10 psi they are pushing with a force of 250 pounds, at 50 psi they are pushing with a force of 1,250 pounds. 50 psi is a very common pressure at load in air hitches. So if you "decide" to pull away with 50 psi in the hitch, it will slam up into the stops with a force of 2.500 pounds in a two bag hitch and 5,000 pounds of force in a 4 bag hitch. That's why air bag manufacturers are very insistent that you have an adequate stop at  "Not to exceed" height. Unloaded hitch will sit with about 3-4 psi, just enough to keep the head and other components of the hitch level.

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