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Posted by Chriscase on Tuesday, February 03, 2009 at 09:23:31 :
In Reply to: Why not a combination valve? posted by David on Tuesday, February 03, 2009 at 01:16:02 :
I believe that what cars and light trucks have is a "combination valve", not a proportioning valve at all.
A true proportioning valve actually sends different pressures to the front and back, and is only seen in a system that has a true dual hydraulics. Each part of the master serves both front and rear, and needs to proportion different pressures. Each wheel need two wheel cylinders, one for each section of the master.
For the usual disc/drum system, there are three functions wanted:
1: hold off the pressure to the front until the rears actuate, preventing a rare fishtail if the fronts lock first.
2: In case of a leak, an internal valve shuts off the fluid to the leaky side, making a harder, higher pedal than otherwise.
3: A warning light switch to notify the driver that #2 is happening.
Do all three processes in one valve, and you have a COMBINATION VALVE.
Hot Rodders use only a small hold-off valve. Other folks use a junk yard combination valve.
Sutureself, in use and terminology. I'm running drum/drum with a dual master and power, under the floor, and no valve. But once I get my power steering hydraulic system on, I'm thinking of hydro-boost under the floor