Air brake question - main reservoir and auxillary tank

[cdnmodman]

Okay guys need some techicial help here. I am starting on my build which is going to be a C Ford COE into a tandem

axle tractor. The question I have is related to the number of air tanks that would be required to support this kind

of setup.I have a lot of pics but none of a tandem so not sure what should be added to the chassis. Any help would

be appreciated.

Thanks

Rick

[Semi Trailer Mechanic]

I haven't wrenched on a 1:1 Ford C series so I can't tell you where to put them or what size air tanks to use. On average you'll find three tanks like KS Route 66 mentioned. One tank will be smaller than the other two this is what's called a wet tank. This is mounted closest to the compressor. It's nicknamed that because the compressed air from the AC condenses in that tank. The other two are the primary and secondary air system tanks. On some trucks there is a forth tank very small tank. This was an emgency reserve tank. Basically if the truck lost all air and needed to be moved the driver would have to push on the valve (yellow diamond and hold it allowing the air to release the brakes just long enough to move the truck then game over until the air system's repaired.

[Danno]

So, would there be one air line from the compressor to the wet tank, then two lines from the wet tank to the other two (one to the primary tank and the other to the secondary tank)? How many lines from the primary and secondary to the brakes? Aren't they routed through valves of some nature?

Thanks!

[SpreadAxle]

Trucking tidbit of info; When pressure drops to 60 lbs the low air warning comes to life. Not much lower then 50lbs the brakes set automatically via the tractor protection valves. Yellow "octagon" knob is the tractors brakes & Red "diamond" is your service line & trailer brakes.

Yellow is the diamond, red is the octagon.

[cdnmodman]

Thanks for the feedback, learned alot out of this one !!

Rick

[Jim B]

If the red "octagon" knob is the tractors brakes & the yellow "diamond" is your service line & trailer brakes; what's the blue "circle"?

[clayton]

If the red "octagon" knob is the tractors brakes & the yellow "diamond" is your service line & trailer brakes; what's the blue "circle"?

IF I remember rite (BLUE)is when you drop the trailer.it has been years now kinda forgetting every thing.

[dad vader]

I have been a heavy truck mechanic for 28 years and I may be able to shed just a little bit of light on the three button system.I have seen the change from most of the old systems to the new ones.I worked for several fleets and truckstop garages until getting a job at an International dealership.and worked there for 18 years until they closed.I went to work for a Cummins distributor and worked there for three years until they closed,I then went to work for a Peterbilt dealership until I was laid off in feb of 2009,when GMC stopped making medium duty trucks and Cat stopped producing truck engines,this hit this dealership hard and they laid off seven techs.I currently work for a Volvo/Mack dealership,and hope to stay there until I retire.

The three button system works like this,Yellow diamond is "System park"it should be the leftmost button,and sets all brakes,the Red octagon is"Trailer park"it should be to the far right.And sets the trailer brakes.The blue circle is "Tractor/Truck park" and should live in the middle,it sets the tractor brakes,when pulling a trailer,all three buttons must be pushed in to move,with no trailer just the yellow and blue button must be pushed in and to park you only need to pull out the blue button and it will set the tractor brakes,When parked in freezing temps it was said to pull only the blue button so the trailerbrakes wouldn't freeze to the drums with collected water.This was before advances in tractor protection valves getting them to work better.With the "Triple air brake system" the "tractor protection valve" didn't run through the foot valve and the trailer emergengy brakes where seperate from the service system.

Then our lovely federal government got involved and the system we have now was developed.Under Federal Regulation FMVSS 121(Federal Motor Vehicle Saftey Standard,It states a dual air brake system had to be used,"Primary and secondary"This is the same system used on new trucks.Though different manufacturers have gone different directions with valving styles and ways to protect the system,they all have to function in the same way.And things like electronic ABS and Traction control have been added to work with the "Dual Air Brake System".

[Jim B]

Interesting information, Richard. Thanks. So on a straight truck (dump, box van, mixer, etc.) would there only be one button (yellow diamond) on the dash? When was the switch over to the two button system from the three button system?

[dad vader]

Interesting information, Richard. Thanks. So on a straight truck (dump, box van, mixer, etc.) would there only be one button (yellow diamond) on the dash? When was the switch over to the two button system from the three button system?

Yes there would be only one button,as it is on a straight truck now,Unless the straight truck was set up to pull a pintle hitch trailer with air brakes then it would have the same system as a tractor.

FMVSS 121 was enacted in 1975 and the dual air brake system revision was added in 1979,Trucks built after 1979 had to have a dual system,as well as operating steer axle brakes.I cant remember exactly what month it was,(I want to say July But I would be guessing).So All on highway trucks had to use this system.However there are some "Vocational" applications that could still use the old system.So it may be possible to see a truck that was built after 1980 that still has the three button system,it just wouldn't be legal for on highway use.

[dad vader]

I have some really nice large laminated cards produced by Bendix that have the layout of the system.I got them way back in the 1980's when I went to an air brake school,they were a really good referance when I came accross a problem that was not normal.I know I have all my old books up in the attic and I'll try to get them down this weekend,scan and post them for you guys.They really give a good understanding of how the system works and how they are plumbed.

[Danno]

I have some really nice large laminated cards produced by Bendix that have the layout of the system.I got them way back in the 1980's when I went to an air brake school,they were a really good referance when I came accross a problem that was not normal.I know I have all my old books up in the attic and I'll try to get them down this weekend,scan and post them for you guys.They really give a good understanding of how the system works and how they are plumbed.

That would be great! Thanks for the info.

[SpreadAxle]

Ain't the first time I've been wrong & not the last!

Dont'cha hate it when it happens like that... You'd think driving the silly thing every day I would have remembered it.

Lol. It's ok.

[Aaronw]

If you want to add wierder systems, older fire trucks could have a small "booster" tank, this filled quickly before the other tanks allowing the truck to get moving in a hurry. I was told that full it was only good for 1 or 2 full stops, so we were supposed to take it easy on the brakes until the regular service tanks were full.

I haven't seen this on newer fire apparatus, only on a 1971 Van Pelt and a 1976 Mack CF we had when I started my career. I don't know if the Federal regulations mentioned above changed it or if the trucks just don't need that kind of system anymore since most new apparatus have a landline (extension cord) to an onboard electric aircompressor and battery charger which keep the air tanks full and the battery powered equipment charged while parked.

[dad vader]

Sorry Guys I never got a chance to get up in the attic this weekend to get those lamcards,My father-in-law was back in the hospital this weekend so I wasn't home that much.I'll get them as soon as I have some free time.