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Old 07-02-2007, 03:39 PM   #15
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OK, here is the "skinny" on the coach air tap in. Spartan "claims" that tapping into the air at the main rear relay valve will impact the brake timing. Brake timing is the interval between the front and rear brakes being applied. This is an important issue to be sure. However, AFO uses a very small amount of air. The air chamber is 3/4 by 3 inches at full extension which we all hope never happens. Given the size of the air chamber, we decided to tap into the air at the air can. No one can argue that this air reduction will effect that wheel. However, this is after the valve and cannot effect the brake timing. We want to and have tried to work with Spartan but information is not forth coming from them. We then approached Bendix with the same questions. With in two days we had an answer. The air kit that we now provide as an option is from Bendix. It is close to the Spartan Air Kit but not exactly the same. I provided Mike O'neal of Spartan a copy of the diagram for his review. SMI is the only one that offer coach protection, period. Even the Spartan kit does not protect the air output from the coach. Their kit includes a flow protection valve that is designed to close the air supply off when the air pressure reaches 65 PSI. This will allow air to jettison from the air line to the tow car if a breach occurs until the your air tanks reach 65 psi. The valve SMI provides is designed to close if a breach occurs regardless of air pressure. To us, this is the goal, total protection. Again, I have not heard back from Mike as of this post but I am sure we will talk. M & G is really the primary competitor to the AFO since they both use less air than the dead pedal counter parts and we use air from the same source after the break timing. Since last July when AFO was introduced we have had ZERO failures and ZERO complaints. It would seam logical that if the air tap was an issue, it would have surfaced by now and it has not. M & G has used this tap in for over 15 years with no reported issues.

All that aside, if a person is concerned then add the kit either the Spartan Kit or the SMI/Bendix kit for a little less money.

Now for the tag axle issue and air brakes. The bottom line is this: the tag air brake is already a separated circuit from the drive axle. While it is true that we will effect one side it is minimal at best. Since this is already a protected circuit and it can in no way effect the brake timing, I would find it impossible for a supplemental brake system to impact the drive axle braking. Spartan will argue this because they have to maintain a "hands off" liability policy to any add ons.

If I made it worse, let me and I will try again. I really just wanted to clear up some misconceptions and give you more to think about.

Pete Schuck
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Old 07-02-2007, 03:50 PM   #16
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Pete, welcome to iRV2.

Your comments are well taken, and I agree that for liability reasons, Spartan has taken a hands off position. I'm sure Spartan has to meet DOT requirements for the integrity of the brake system.

Personally, I would install the protection valve.
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Old 07-02-2007, 04:11 PM   #17
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Pete, THANK YOU for jumping in and THANK YOU for your support of iRV2 as a major sponsor.

I look forward to possibly seeing your team in Branson...
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Old 07-04-2007, 06:08 AM   #18
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Pete,

I can understand the issue that Spartan has not only with the timing but also a potential for air bleed down during braking. Additionally, a loss of control during braking, caused by a change in equality of brake application from right to left side (due to reduced coefficient of friction on the road), could create a liability issue.

Would it be possible to:

A. Add a manual valve (or wireless valve) assembly that would allow the driver to turn the air access to your unit on and off. Similiar to your safety valve but driver controlled.

B. Change the proportioning system so that less air is required from the main system to actuate your system.

C. Change the cutoff air level from 65 (which is approaching spring brake lock-up) and set it for 75 or 85 psi. Then have a metering valve that would acctuate a "spring brake" type system on the toad through your unit that would apply an emergency brake application until the default air pressure is reached. This also could have a wireless control panel off/on function in addition to a sensitivity level control.

D. Add the mechanisims needed for a "trailer" air system similiar to a tractor trailer combination. This would have the tractor protection valve and other assemblies that would safely provide air to the "trailer" (toad) and be inherently safe as it would be the same system as used on trucks. An additional air valve control (usually a red knob on the valve) could be placed in the driver cockpit to allow control of air flow depending if the toad is hooked up or not. I think this would be the safest and most dependable method of obtaining proportional air to a "trailer" which should mitigate the chassis and brake component manufacturers liability / concern.

Just some thoughts.

Ed
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Old 07-05-2007, 09:50 AM   #19
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Ed,

I do agree that those are Spartan's as well as our concerns. It is our (and Spartan's) responsibility to ensure the safety of those on both ends of the stick those driving the coach, and the others on the road. That said, there comes a point where the benefit of additional features begins to become overshadowed by more failure points and exorbitant pricing. If I were given a price cap of $500,000 per unit, I could engineer you an amazing brake you would be second to none; but our target price is $1000-$1500 max.

Let's talk a little bit more about what is going on:

Amount of air used (w/ Air Force One)

- Standard " O.D. DOT Air Hose
(ø.167 in.)
+ Coach- ~180 inches
+ Jumper- 77 inches
+ Towed Vehicle- ~84 inches

- Actuating cylinder
+ Stroke (full extension)- 2.9375 in.
+ Bore ø- 0.840 in.

With these values we, can determine that the actual volume (V=πr2h) of air used by the Air Force One braking system is approximately 9.097 in.3, or correctly rounded, 9.1 in.3. This value is more easily comprehended in unit we are more familiar with: fluid ounces. This value would be approximately 5.04 (properly rounded 5.0) fl. oz., or less than half a can of soda at full extension. Normal activation would be about stroke. This air is static, allowing the air supply to equalize. With a volume this small, equalization would be attained almost instantaneously. To actually create a perceivable difference in braking effort between wheels would be extremely difficult, nigh impossible with any short a complete failure (which would engage the spring brake).

In regard to the valve, we have found that an automatically operated valve to be far safer than a manually operated one. Our job, again, is to keep everyone safe. User error has caused more accidents than mechanical failure. A tractor-trailer application operates much differently than supplemental brakes. So much so that there are specific DOT regulations for them. We must compare apples to apples. To keep this post as concise as possible I will sum it up like this: a trailer being pulled behind a tractor uses full air brakes, while we are converting an air-brake signal to control a hydraulic braking system. Trucks have a constant air signal going to the trailer to control the spring brake as well as the control line. Hence the need for driver control of the air supply. Our valve works completely differently, and rightfully so.

Brake timing is also a tricky topic. As Pete rightly afore mentioned, "Brake timing is the interval between the front and rear brakes being applied." There are several factors involved, but the pertinent one in this case is the crack pressure of the relay valve. Crack pressure can most easily be defined as the minimum amount of air pressure required to open a valve. The standard crack pressure for these valves is four psi. When a separate valve is inserted in series with the main relay valve on the treadle line, the crack pressure is (almost) doubled. This means that neither valves will open until about eight psi. is achieved; in which case, both would simultaneously open. The only way to have two valves that still open at four psi. is to run a separate line from the treadle, hooking the valves up parallel to each other. Again, this brings me back to the $500,000 analogy.

All that said, we are currently in the works with Spartan Chassis and Bendix to engineer the safest and most effective system for our applications (air brakes operating hydraulic brakes) while maintaining the cost in the affordable range. We are definitely open to any and all suggestions and feedback, and greatly appreciate posts like yours. It makes us all think...


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Old 07-05-2007, 01:55 PM   #20
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Brent, thanks for the very clear explanation of the AFO operation with Air Brakes, and what you are trying to achieve in the final results. I have no doubt you will be successful!

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Old 07-08-2007, 10:41 AM   #21
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Brent,

Thank-you for a great post and explanation! I appreciate the time you spent and the customer service exemplified by your company in allowing this interchange of information.

I have looked seriously at the SMI products as I believe that proportional braking for a trailer or "Toad" is the only braking system that should be used (be it your product or someone else).

My personal opinion is that you currently have the best product on the market. I will be watching this issue and should warranty issues brought up by Spartan or Freightliner be resolved I certainly would purchase an SMI system.

For most users the SMI proportional braking system is / would be a great product and I am in no way trying to dissuade anyone from purchasing your product.

Thanks again,
Ed
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Old 07-09-2007, 07:00 PM   #22
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">With these values we, can determine that the actual volume (V=πr2h) of air used by the Air Force One braking system is approximately 9.097 in.3, or correctly rounded, 9.1 in.3. </div></BLOCKQUOTE>
Hi! I wish you were around to help with my math homework. Your system sounds great. How does the actuator on the brake get hooked up, and work? Thanks, Paul
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Old 07-11-2007, 01:43 PM   #23
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Paul,

The actuator mounts on the brake arm (even with or above the dash). There is a short cable that hard-mounts to the firewall. This is merely an anchor point that the cylinder uses to pull against. When air pressure is applied to the cylinder, it causes the cable length to shorten. Since it is anchored to the firewall, this shortening motion causes the brake arm to move downward. Here are a couple of pictures. Bear in mind that these pictures were taken from the floorboard up. The cylinder is not normally visible.



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