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Bob uk
Unregistered guest
Posted From: 94.197.122.93
| | Posted on Monday, 30 June, 2014 - 08:03: |    |
RR call these brake distribution valves
The early type had 4 ports
The later ones 3 ports
The 3 ports are pressure in
Pressure out and return
The 4th port is for a bleed nipple which was deleted on the later ones
Return is aka dump
When the brakes are off the dump is connected to out let port and the calipers and no dot flows through the valve
When the brakes are on the inlet is connected to the outlet and the dump is shut off and dot moves through the valve
When the brake is released the inlet port is shut off and the pressure in the outlet moves the dot into the dump and back to tank
Bleeding
The line between the brake valve and the accumulator is under pressure this will squeeze any air to about 1 200th of its volume
If the brake is pumped down then as a full accumulator load of dot flows through the valve taking the air with it
Open the caliper bleeders and bleed off egg cup full and that bit of the circuit is fully bled
The valve spool is held off by a spring and hydraulic pressure which gives a modicum of feel
The valve relies on that the clearance between spool and bore is small enough to contain the molecules of dot leaking out
And a seal at the front in the bore
The out dust cover is only a dust cover
The dot is allowed to seep along the clearance to lubricate the valve
A small drip from the valve is normal
The spools are not interchangeable
As normal when overhauling don't scratch any thing
To polish the bore or spool use Worn 1200 or finer with dot as lubrication
Only polish if needed and little as possible
Clean in meths
These valves are very reliable and last well so if there is a fault look at valves last
Next the tank
(Message approved by david_gore) |
Bob uk
Unregistered guest
Posted From: 94.197.122.81
| | Posted on Wednesday, 20 August, 2014 - 11:03: | |
Randy,
Any more information needed just ask.
(Message approved by david_gore) |
Bob UK
Unregistered guest
Posted From: 94.197.122.92
| | Posted on Thursday, 21 August, 2014 - 06:16: | |
Since writing the above.
Spool valves are made by machining a body with every thing finished except the bore which would be left 2 thou undersize.
Position of ports has
tolerance of 0.001"
Then the bore is honed to 0.0001" tolerance.
Then the spool would be made to finish size complete with grooves.
the diameter has a tolerance of 0.0001
The width and position the grooves , tolerance 0.001.
Depth of grooves 0.005 tolerance.
A spool than is 0.0001 small and a bore that is 0.0001 won't fit and would stick and rip the surfaces up.
A pair that are both 0.0001" Will do the same. Interchange them and the clearance will be 0.0002 Which will leak.
To machine that tighter tolerance is a feat of engineering plus to measure it the bits have to be at 20 centigrade.
So make say a hundred pairs and hand match.
On something with O rings a 0.001 tolerance would apply. And sometimes a bit will be 0.0001 - 0.0004 say.
A good machine will hold 0.002" on the dials. Grinders Will hold a 0.001". A digital read out, will tighten the accuracy to 0.001 on a mill or lathe and 0.0002 on a grinder.
I can't get closer than 0.0005 And even then I scrap a few. Once in a while with the wind in the right direction I get to 0.0001
Not only that it has to be parallel. So that rules out 2000 grit and polish.
And a very very fine finish is required.
£600 is cheap.
(Message approved by david_gore) |