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Author Topic: Spring brakes....should I have a relay?  (Read 2684 times)

Offline zubzub

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Spring brakes....should I have a relay?
« on: August 27, 2009, 05:40:54 AM »
It's time to install my spring brakes.  I have the cans ready to go so now it's time for plumbing.  I have read that some use a relay, my question are.... 
1>Is the added  complexity of a relay valve neccessary/desirable?
2. Will the p brake still set fairly quickly without one?
3. Will having a relay save wear and tear on the dash button/valve?
4. How much noisier is the dash unit without a relay, ie, I guess I'll be listenening to all the air wooosh out at the button/valve.
  Also FWIW piggybacking springbrakes onto the original brake cans was easy, working on these old buses is kind of easier than old cars  as long as you always use impact drivers etc...

Offline TomC

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Re: Spring brakes....should I have a relay?
« Reply #1 on: August 27, 2009, 05:56:26 AM »
Usually a quick release relay valve is used at the T at the axle.  When you release the parking brakes, the air from the dash valve is what charges the brake can directly (compared to the service brakes where the pedal air is used to apply air to the relay valve at the axle that releases the air from the air tank for faster application times).  Then when it is released to increase the application time and so not to have all that air being released through the dash button, the quick release relay valve is what exhausts most of the air at the axle.  That's why when you pull out the dash button to apply the parking brakes, first you hear the hiss of air from the button then the big hiss of air from under the bus.  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline buswarrior

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Re: Spring brakes....should I have a relay?
« Reply #2 on: August 27, 2009, 06:29:26 AM »
A relay valve gets used in modern spring brake circuits in order to allow the plumbing to apply the springs via the brake pedal, invisible to the driver, and automatically, under an air failure to the rear service brakes.

Braking effort is modulated by the brake pedal, same as any other stop, until the front service tank is exhausted below spring brake set point, then they start dragging down through 60 lbs, and then apply fully when the button pops, down at whatever pressure it's old spring pops it at.

SR1 valve, and no doubt it has siblings now.

For your conversion to spring brakes, as Tom has described, unless you are going to re-plumb for a dual circuit service system and add the modern safety feature (which has been done by some busnuts) a simple quick release will do the job nicely.

Be sure that you secure and protect your airlines against rubbing on anything. Lots and lots of wrap and plastic ties at all the edges it encounters! Check under a new trailer, there's a tie every couple of inches.

happy coaching!
buswarrior
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Offline bevans6

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Re: Spring brakes....should I have a relay?
« Reply #3 on: August 27, 2009, 06:48:17 AM »
My  thought was that since the positive action of the spring brake relies on the absence of air, having a quick release valve or a relay valve in the back would release the air as quick as possible, setting the brake as quick as possible, which if you want the brake on in the first place is probably a good idea.  Plus having that air exhaust up in the cockpit, all wet and oily, probably isn't what you want as a first choice.  Plus you'll scare the chickens...   :D.  If you never had spring brakes before, would you be using a new parking brake button valve?
1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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Offline DaveG

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Re: Spring brakes....should I have a relay?
« Reply #4 on: August 27, 2009, 07:05:31 AM »
Tom & bevans are correct. You only need an QR-1 at the axle where the line for the spring brakes Ts to the left and right.

The only reason I could see for a relay valve would be if when you pushed in your dash valve (PP-1 or whatever) there was a long wait for air to travel from that valve all the way to the back of the bus to the spring brake chambers.


Offline Len Silva

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Re: Spring brakes....should I have a relay?
« Reply #5 on: August 27, 2009, 08:16:18 AM »
You also need an anti-compounding valve on the spring brakes.  This prevents actuating the main brake at the same time the spring brake is activated, thus putting excess pressure on the brake hardware.

http://zafr.com/trucktcom/brakes_compounding.htm

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Offline akbusguy2000

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Re: Spring brakes....should I have a relay?
« Reply #6 on: August 27, 2009, 08:26:05 AM »
Len is right on.

The modern component is the combination relay/quick release/anti-compounding valve - R-12 or R-14.  No spring brake conversion should be without it.

tg

Offline TomC

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Re: Spring brakes....should I have a relay?
« Reply #7 on: August 27, 2009, 08:43:59 AM »
Even on my truck with tandem axles and spring parking brakes on both axles, it does take a few seconds for the brakes to release to fill up the four parking brake chambers enough to release the brakes.  But when you pull out the button to apply the brakes, it takes only a second or two for them to grab tight-because of the quick release relay valve.  Good Luck, TomC
Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.

Offline rusty

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Re: Spring brakes....should I have a relay?
« Reply #8 on: August 27, 2009, 09:03:43 AM »
Len is correct The R14 is anti compounding relay

Good luck Wayne

Offline Dreamscape

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Re: Spring brakes....should I have a relay?
« Reply #9 on: August 27, 2009, 09:40:32 AM »
Len,

Great Link!

When I installed my spring brakes, replaced the DD-3's, I did not know that. I'll have to get one because it makes sense to not over tax the system.

Thanks,

Paul
Becky and Paul Lawry, On The Road
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Offline luvrbus

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Re: Spring brakes....should I have a relay?
« Reply #10 on: August 27, 2009, 09:46:44 AM »
Cheap insurance for 35 bucks Paul but your not  driving a 100,000 miles a year and your brakes are used less in 2 years than the average truck in 1 day.
 FWIW I have one now but I used the bus for 10 years without one with no problems.
If you install one buy the self draining type they are a pain when they freeze up, the dura drain came out  in 2000 after I installed mine some day when I think about it I'll change over

good luck
« Last Edit: August 27, 2009, 10:17:23 AM by luvrbus »
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Offline Dreamscape

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Re: Spring brakes....should I have a relay?
« Reply #11 on: August 27, 2009, 03:33:18 PM »
Good point Clifford, but if the 35 bucks will make them last longer, it's worth it. Besides, I don't mind making our brakes better, might save me buches of money sometime!

Good Insurance!

Paul
Becky and Paul Lawry, On The Road
Travel Blog - http://dreamscapetravels.wordpress.com/
Bus Blog - http://dreamscapesilvereagle.wordpress.com/
______________________________________________________

Our coach was originally owned by the Dixie Echoes.