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Tue, 12 October 2021 10:55 |
Thomas Pryor
Messages: 143
Registered: January 2011
Karma: 1
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Senior Member |
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I placed an image of a Combination Valve on the Photo site that shows the
three segments of the Combination valve.
http://www.gmcmhphotos.com/photos/combination-valves/p68350-appled-pvmh.html
THE CENTER section is a SWITCH that shuttles between front and rear brake
channels. If pressure is different in either channel the switch goes to
"on" and the Safety dash light is illuminated.
All cast iron TZE coach combination valves had this feature.
THE FRONT section is a Hold Off section (called metering) valve to delay
the engagement with the front brake channel. All cast iron TZE coach
combination valves had this feature.
THE REAR section of our cast iron TZE coach combination valve had NO
FUNCTION other than a place to thread together the rear brake line
channel. "Brake design intent" for our TZE coaches was focused on all the
rear wheels receiving all the pressure that could be produced by the
vacuum assisted master cylinder.
THE REST OF THE STORY:
AFTER THE END OF TZE PRODUCTION;
All cast iron combination valves were replaced with brass combination
valves that were designed for 4 wheel pass cars/light trucks with disc/drum
designs. Those designs added a 3rd function...........limit the pressure
to the rear brake channel. WHY? Much lighter passenger and light truck
vehicles could and did suffer from rear wheel lockup, skidding and loss of
control. Brake designs of that period required not only improved stopping
distances but also improved stop control. That is the fundamental reason
for rear pressure limiting combination valves. That also meant that no
brass valve could NOT achieve the exact and necessary requirements for our
coaches. REPLACEMENT VALVES available to the Tribe were limited to the PV2
version that limits the pressure to the rear wheels, but it plumbs right in!
In my previous life as a QC guy working at Kelsey Hayes and after the
transition from Cast iron to Brass Valves, I was able to find the technical
drawing of a brass valve that had no rear pressure limiting feature. I
found that drawing in China and also discovered it was never produced,
probably because of low demand!
If you have the OE standard TZE brake configuration on your coach use the
valve that Applied GMC offers. The PVMH is the only commercially available
brass brake combination valve that replaces the Cast Iron valve in form and
function. Jim has not yet posted the images and pricing on
his site. Patience!
Regards,
Tom Pryor
4188 Limerick Dr
Lake Wales, Fl 33859
Cell 248 470 9186
1977 23'B named "CASPER", HARDLY ORIGINAL, (455 EFI) (Pwr. Drive)
(tailgate) (rear bunk beds)
(Webasto petrol boiler) (MB Elect fan clutch) (Brake reaction arms) BUT
STILL A WORK IN PROGRESS!
ReplyForward
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