PBR park brake valve.

Is there a line direct to the compressor?.......that would be most unusual...........all the lines should be from the second air tank ,except the one from the maxi release tank.

I don't know the purpose of the two lines. Air comes out of both at about the same amount immediately on startup. I can't imagine why it would need two of the same feed. Valve inlets are marked "supply" and "tank".

Jarrod.

My guess is that one feed is from an air tank that builds pressure equally with the whole system, and so in normal driving the brakes will only release when the whole system is up to pressure.  I am guessing the other feed is from a single specific tank to allow for "emergency" release. 

So, in standard use the T handle is pulled out for release, in emergency the T handle is held in for release, and so i am guessing the valve admits feed from the appropriate tank depending which way the handle is operated.

Again, i'm only guessing, but that's my take on it if it makes any sense.

Brett.

It does make sense, thanks. I will have to get underneath to see if it's even possible to follow the lines. This thing has tanks everywhere.

Jarrod.

Jarrod,

What model/make of bus?

Jarrod, i guess i have concentrated on following the CA282 path with you to keep what you have original and working, but thinking further, in all honesty i reckon John.K's suggestion of a PP1 valve would be adequate, cheap, and easy, unless something/some law, or rule book, specifically states that you need the combination emergency release function. 

I can't see an issue in blocking off the feed from which ever tank is not required for the PP1, or..................., joining both feeds together before they enter the PP1, although that might? mess up the low pressure "pop" application (at around 40psi), i don't know for sure, but it think it might.

I don't recall our L9000 Ford, or the T400 KW having an "emergency" release feature, and the old G88 we still have certainly doesn't.  The Mk2 Atkinson does, but the Mk3 doesn't.  Both my A series ACCO trucks do, however both my later C series ACCO's don"t.  And our Hino GT 4x4 doesn't.

If there are no rules actually requiring the emergency release feature, the PP1 certainly looks like a good option, or perhaps a Sealco equivalent.

Just thinking out loud.

Brett.

Trucks built with a single circuit air brake system and fitted with spring brakes, (Maxis), were required to have an emergency brake release under the ARD's current at the time. Once the duaL system came into being, it was no longer required.

Had a customer with a LNT which was built at the time of the change over which had both dual circuit system and an emergency release button. Idiot inspector knocked it back because the button didn't work. He couldn't be convinced, so after consultation with RTA head office that the release was not required, I removed the knob on the button and all was good

Hi Jarrod,

I've scanned 2 brake set ups from the Bedford bus brake manual.  The use different 3 port valves, however, the concept may be the same as yours. And it explains a little about the park brake mechanism.

hope this helps. jd

 

 



 

You can ignore any pommy stuff ..its all stupid complicated .......at one time the poms had triple diaphragm brakes on every wheel.........alls needed for an old bus is a single line to the two spring chambers from the PP1 ,and a single line from an air tank to the PP1...........just so the maxis set when the button is pulled out ,release when its pushed in,and the button pops out at around 60psi falling pressure..............even with no valve ,the maxis will slowly come on as pressure in the system falls.

jon_d wrote:

Jarrod,

What model/make of bus?

1978 IBC Mk3 with 3208 and Allison.

Jarrod.