Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 10, 2025 ...

Air Line 57 Behavior

September 05, 2018, 01:21:48 pm

It appears to me that dwg B-2193 applies to a number of years.  It was dated drawn, for example, 7/20/94 and it was used in at least several 2001 coaches, maybe more.

Line 57 is fed air via the HWH 12v air compressor.

Line 57 then intersects with lines 27, 50  and seems to pick up an air flow from the Rear Brake Right Tank that I could interpret to be line 50.  But if that is so, then 50 becomes 28 and goes to the front manifold.

Does the symbol at that intersection mean the lines all interconnect or that they one passes over the other without joining?

I would think they join, otherwise line 57 would just continue on and not become line 27, to the rear manifold?

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Re: Air Line 57 Behavior

Reply #1 – September 05, 2018, 02:19:40 pm

Michael,

Not sure what is prompting your question, but here is what I think is happening at that line junction.  This is the way it works on my coach, which of course is much older.  I am also looking at drawing B-2254 (dated 03/10/97) in the Forum library.  I am assuming that it is similar to the drawing B-2193 to which you are referring.

At the point on the diagram where lines 57, 50 and 27 come together, they are also joined by a line coming out of Rear brake tank.  I think you will find that junction is actually a combo check/shuttle valve.  It has 2 input connections, and two output connections.  On our coach, it is a Haldex KN25120.

KN25120 - Check Valve - Haldex product

What this valve does is accept pressure input from two sources, and sends this input out through two lines.  The trick is, it will only pass through one of the input sources: the one that has the highest pressure.  In this case, the two inputs are the HWH compressor (line 57), and the Rear brake tank.  The two outputs are line 27 and line 50.  So what happens is lines 27 and 50 will receive their input from the higher of the two pressure sources at the shuttle valve.

Although it doesn't look like it on the schematic I'm viewing (B-2254), I think you will find the actual physical setup at the Front brake tank is very similar.  There will be a shuttle valve that accepts input from line 50, and input from the Front brake tank.  Whichever input pressure is higher will be passed through the valve to line 28 that goes to the front 6-pack manifold.

The whole point of this setup is to allow the Front and Rear tanks to supply air to the 6-pack manifolds under normal operations.  If the coach is parked, and the pressure in those tanks is insufficient to satisfy the demands of the HWH leveling system, then the HWH pump will be activated and it will supply the required pressure to the 6-packs.

Like I said, this is the way the equivalent lines on my coach work.  For what it is worth...

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Re: Air Line 57 Behavior

Reply #2 – September 05, 2018, 04:35:38 pm

Mike, you need to make sure you are looking in the upper right corner of the label block for the CN box.  Mine is for coach build numbers from 5871 on and was last modified 12/08/00.  This drawing was modified again on 8/14/2001 and is effective to coaches starting at build number 5920 and greater.  It was changed again for 2003 coaches.

My coach is 5879.  Line 50 goes from a 4 way connection through a check valve to a connection near the rear brake tank.  At that connection, line 57 connects to line 27 to supply air to the rear manifold and to line 50 which connects to line 28 to the front manifold and line 55 to the front ride height control valve.

Line 50 also connects to air from the rear service tank through the pressure protection valve (which is not the one Chuck mentions) and a check valve.  it can also get air from the auxiliary air hose connection through the check valve to raise and lower the coach.  None of the air tanks can get air from the auxiliary air hose connection.

In these drawings when two lines cross and there are four small cross lines on each at the intersection that usually means a four way connection.

When two lines cross and only three lines at the intersection have the small cross lines I am thinking that is a pair of Ts.  these drawing symbols do not correspond to the WABCO document for standard air brake symbols.

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