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Thread: question on dump valve on spread axle flat

  1. #1
    heavyhaulerss's Avatar
    heavyhaulerss is offline Senior Board Member
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    Default question on dump valve on spread axle flat

    i am trying to reduce the cracking that i am increasingly getting on trailer. i have a '94 transcraft 48 by 96 all steel. had for 9 years. so far it's held up pretty good considering. the cracks are just in front of the rear axle. ive had it welded more than once. (now the area in front of the front axle has never broke & never had to be welded.) my dump valve is hooked up that when i dump the air . it dumps the front axle. it was set up this way when i bought it. i haul only single coils. nothing else. sometimes i dump, sometimes i dont. i cant figure out if my dumping is helping or hurting my trailer. would it be any better if i moved dump valve to rear axle ? should i continue to dump ? i'm not too concerned about my tires wearing as i would rather replace tires more often than to keep cracking trailer. any suggestions appreciated.. thank you.


    my logic tells me that dumping my front axle is saving wear on my front axle tires but putting more stress on rear axle, so my thought is too not use dump valve ??? thanks, g-man for your advice as i know you will respond. :lol:

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  3. #2
    special k is offline Board Regular
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    I would make the dump valve work on the rear axle. Dump valves do stress the trailer more due to the fact that all the weight is on one axle. Older Transcraft are famous for cracking just where your's is. You'll see a lot of them with a plate welded on the web and a cross member going between the frame rails. I'm pretty sure the later ones came direct from the factory that way.

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    Doghouse is offline Senior Board Member
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    Heavy,
    It seem as though you are putting to much weight on the span (cracking a steel trailer) when your front axel is dumped. How heavy do you haul?
    It would seem to make more sense on a leverage issue,..if your dump valve were on the rear axle,...then your front could carry the weight while you do sharp turns and backing.
    Since most of your weight is already on the front axel anyway.
    I don't know,...just looking at it from a leverage point of view,..certainly not from actual expierience. I am thinking about putting a dump on my rear axle also.

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    rvrjr7 is offline Board Regular
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    on the trailers i pull the rear axle is the one that comes off the ground and I can pivot on 38 ft instead on 48 and dragging the axle

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    heavyhaulerss is offline Senior Board Member
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    i haul 45 to 48 thou lbs. almost always single coil. loaded 1 ft back from center of trailer.

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    heavyhaulerss's Avatar
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    i also have seen lately a lot of spreads with front axle lift. what is their purpose if not as the same as my front axle dump ?

  8. #7
    GMAN's Avatar
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    Heavyhaulerss, from a stress stand point I don't think it makes much difference which axle is dumped. The main advantage is the turning radius. When I installed the dump valve on my side kit, the dealer suggested that I dump the front axle. When you dump the front the trailer doesn't have as short a turning radius as if you dump the rear. Before I put a new dump valve on the trailer I broke two springs. If you have a dump valve, you save more than wear on the tires. It also saves stress on the suspension and frame. When you have a lot of weight on a trailer, especially a spread axle, you put a lot of stress on about everything. If properly used, a dump valve can help prolong the life of your trailer as well as the tires. The best way to use a dump valve is to dump it just prior to making a sharp turn. About half way into the turn re-inflate the air bags.

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    Default found interesting news on dump valve

    To alleviate the problems arising from spread axles, dump valves are being used for one of the two axles on the spread. By exhausting the air springs of one axle, the axle no longer is under load and can travel through a tight curve more easily. Most spread-tandem platforms dump the air from the rearmost axle. By doing so, the platform has the maneuverability of a trailer that is significantly shorter.

    Suspension manufacturers teach that the dump-valve system was intended for limited use, such as tight ninety-degree turns, backing into loading docks, maneuvering within a yard, and other "creep-speed" applications. But the improved maneuverability is leading some drivers to dump air when making moderate curves at speeds of about thirty miles per hour.

    Accordingly, some trailer and component manufacturers are starting to object to what they consider abuse of the dump valve. The Spicer Trailer Products Division of Dana Corporation issued an engineering update stating that the company would not warrant the axles used on spread-axle trailers equipped with dump valves. In pertinent part, the update reads as follows:

    "When a dump valve is actuated, the axle equipped with the dump system sees only its own weight and that of the attached suspension components, unless a regulator is used to maintain some air pressure in the air bag. The other axle sees the full load normally carried by both axles, causing severe overloading of that axle. Unless such dump valves can be provided to automatically apply air pressure above speeds of five mph, Spicer Trailer Products does not approve, and will not warrant axles used on spread axle trailers equipped with dump valves."

    Great Dane does not offer dump valves on spread-axle platforms for increasing maneuverability or reducing tire-scuffing. "We will put dump valves on both axles in order to control dock height, but we won't put them on just one axle," states Paul Crabtree, manager of engineering at Great Dane's platform plant in Memphis, Tenn. "We will put them on lift axles if a tandem is already in place, because we are assuming that the trailer will be operated with the axle lifted. The trailer will have to be built to handle that."

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    rank is offline Senior Board Member
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    Wilson won't do it either.

    Where are you located? I'll weld that SOB and it will never break again. Ever. If it does I fix it for free.


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    i live on the al/ tn line.. i just got it out of shop from decatur al wed. they do great work on welding. thats all they do. had 1 inch steel plate welded where the stress points are. i think it's almost impossible to prevent one from breaking ever. if both trailer tires could pivot & turn with the steer tires .. that invention may do the trick. i do think most of my breakage came from a while back when i daily had to jacknife trailer while backing into a dock while going down a steep hill. my trailer would twist every time & it looked like the tires wer going to come off the rims.

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    Quote Originally Posted by heavyhaulerss
    i live on the al/ tn line.. i just got it out of shop from decatur al wed. they do great work on welding. thats all they do. had 1 inch steel plate welded where the stress points are. i think it's almost impossible to prevent one from breaking ever. if both trailer tires could pivot & turn with the steer tires .. that invention may do the trick. i do think most of my breakage came from a while back when i daily had to jacknife trailer while backing into a dock while going down a steep hill. my trailer would twist every time & it looked like the tires wer going to come off the rims.
    Small world...I'm over in Florence.

    I work for PGT and we pull aluminum Reit's and MAC's with rear dump.

    I just hooked to a brand new Transcraft in Laredo Tuesday with front dump and as much as I like the trailer in general I'm missing that REAR dump already...

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    i see pgt a lot. in decatur.

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    9200IH is offline Member
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    Hi Heavyhauler I pull three different trailers, all spread axles. All of them have the dump valve on the rear axle.

    I think with you hauling a coil in the middle of the trailer and then dumping the bags on the front axle it is putting way to much stress on the trailer. The trailer is probably flexing enough that the front axle bags are bottomed out inside and still carring allot of weight. That might true with a flat bed because the bags are so tall, two of the trailers I pull are step decks an those bags are really short and they will bottom out.

    I put 48,000/50,000 on my aluminum flat, dump the rear bags as close to the turn as possible and fill them back up when I am 2/3's the way (takes a good 10 seconds for the bags to fill up) through the corner. Tires roll just a little.

    I think if you switch your dump to the rear you will be pleasantly surprised. Just corner slow an on and off as quick as possible with the switch.

    Thanks Mike

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    My reefer was a sliding spring ride tandem in its beginning. I have made an air ride spread axle out of it, with dumps on both axles, with individual switches. (I can dump either or both) I had to re-inforce the frame between the spread rather drastically but I've never had any cracking or breaking problems yet in 3 years. You would be amazed at the different turning radius when you dump the rear as opposed to the front.
    1999 FL Classic, N14+ 525 hp, RTLO16-9-13A
    1997 Van's Aircraft RV-6, IO-360

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