As far as I know, a dump valve for a spread axle trailer is legal. A dump valve for a tag axle is not. This may have changed.

Lots of good info here, appreciate it

I have been but i have also been busted and paid my share of fines.

This is how it works in MI every axle that is a spread is good for 18k lbs, and every axle that is a closed quad or tandem or tridem is 13k lbs for each axle. Drives are good for 32,500, and if you have the balloon tires up on the steer they are good for 14,600. I didnt so all i could do was 12k lbs. Ofcourse this is for trains only, normal tandem axle OTR trucks fall under the normal 12/34/34 or 12/28/40 for spread axle.

I have manual lifts AKA cheaters, on mine and yes they are illegal but thats how these trailers were built in 94 so they cant make me change it. A electric dump valve operated by a switch, or lift axle, is NOT illegal. This is called "air over electric". Now a manual lift which is operated by an air valve from the cab is illegal and is called "air over air". The 8 axle train is the biggest in MI, you have your single axle trailer with 8 axles but you dont have enough of a spread on them to legally gross 161 or 164,500 like on the B train. A 6 axle with 2 of them being a spread is good for 136k in MI and 134,500 in IN...... Yeah it gets a lil consufing lol.

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LOAD EM LIKE RAIL CARS, DRIVE EM LIKE RACE CARS!!!!

Stop dumping that axle and start making wider turns.

I know a trailer maker who will void a warranty on their trailers if a dump valve is hooked up on it. From what I was told (how true it is I don't know but it does make sense) they did a study on their trailers. Using a dump valve causes more harm on the suspension and the trailer than going without. They said by dumping the back axle with a gross of 40,000lbs on the spread puts alot of that weight on the front axle and on the frame of the trailer and when turning it puts more of a bind on it.

Think of it this way....You have a 20,000lbs coil on the front and a 30,000lbs over the spread. You dump the back axle to make a turn, you go from only having 20,000 on the front to say 25 or 30,000lbs. You still have 10,000lbs on the back axle which is causing drag. So your either dragging 30,000lbs around the corner on the front axle or your dragging 10,000lbs on the back which ever way you want to look at it your still tearing something up! I would much rather have it 20,000 on each axle that way the weight is carried evenly.

Nope, it's the best thing for the unit, tractor & trailer. Large swing areas to turn are pretty uncommon on jobsites.
Never heard of this but that doesn't mean it's not true. Most dealers sell valves & will install a dump valve for you.
I've read & reread this & just can't grasp what you're saying.

I've got a #20,000 coil on the front of the trailer & a #30,000 pound on the rear over the spread axles?

Anytime you can reduce the drag on one axle over the other axle by reducing the weight on one, it's easier on the trailer.
I've turned corners where it would bog down my tractor without dumping the air on the rear axle. If the tractor bogs, it has to be a super amount of drag on the axles.

When you turn a spread axle with a 10'-1" spread without a dump valve the axles are working against each other. You're creating massive amounts of torque to each axle in opposite directions. Dump valves allow the trailer to pivot mostly on the front axle & stops the axles from trying to work against each other. A valve also helps considerably on tire wear & the edges of the tire.

I'd much rather back a spread up then a 53' trailer. I'd dump the dump valve allowing me to pivot the trailer into a parking space & when I was close to straight I'd stop & air up the back axle.

You can't get over weight on the trailer tandems if you gross 80000 and have a 10 ft spread. I owned one.

kaiwren986: In theory, there is no difference between theory and practice, in practice there is.

BTW/ It is legal to have an electrically operated dump on a tandem spread. I ran all 48 and before that pulled dump trailers that had them. You have to dump the air out of the front tandem before rainsing it.

I've read & reread this & just can't grasp what you're saying.

I've got a #20,000 coil on the front of the trailer & a #30,000 pound on the rear over the spread axles?

I take it you've never hauled coils?

Anytime you can reduce the drag on one axle over the other axle by reducing the weight on one, it's easier on the trailer.

I don't know about you but it only takes me a cpl of seconds to get around a corner and unless you have one hell of a fast air system and i mean FAST, your putting alot of pressure on the front axle while dragging the back one around with weight on it also. Your making it sound like when you dump your axle there is no weight on it...your wrong! The best way to explain this is for you to see for yourself. Take and go to the back of a truckstop and dump your valve and make your turn, in mid turn stop get out and walk back. You'll see how much stress your putting on your trailer and you'll also see how much weight is still on the back axle. So, the axles are still fighting eachother but you have more weight on the front one than the back. I don't see how that will be esier on the trailer.

To each their own....

Yes, there will still be weight on the rear axle, but the amount of weight decreases exponentially, thereby reducing the effect of the axles working against one another. No one said the rear axle would be off the ground completely, but reducing the pressure on that axle causes the front axle to become the pivot point reducing the impact on the suspension components.

Oh, and I've hauled many coils.

Do you dump your axle long before your gonna makea turn?

What kind of suspension did you have under your trailer?

Did you put the dump valve on and run the airlines or was it done from the factory.