| [GMCnet] Residual pressure valves [message #270814] |
Fri, 30 January 2015 09:54  |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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Senior Member |
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I noted with interest a recent post about installing residual pressure valves to cure the low brake pedal issue when changing over to six wheel disk brakes. I was not familiar with these so started digging. Here is what one site has to say:
"Residual Pressure Valves are used in a both front and rear brake system as follows:
• 2 PSI Valves - These valves are used in a disc brake system only and are required when the master cylinder is at, or below, the height of the calipers. It's purpose is to act as an anti-siphon valve preventing the brake fluid from siphoning back into the master cylinder when the brake pedal is released. Even if the master cylinder is even or slightly above the calipers, put one in anyway. If you don't and you park on a hill, fluid will siphon! These valves are cheap insurance - put them in!
• NOTE: You will know if you need one of these valves if you had to pump the pedal twice to get a good pedal. See illustration for more.
• 10 PSI Valves - These valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. Some disc/drum master cylinders have 10 PSI residual pressure valves installed internally, some don't. If you're not sure, call us and we can tell you how to check. Also, some new style wheel cylinders have cup expanders which negate the need for the residual pressure valve. Either way, if you are not sure whether you have one or not, put one in. They are not cumulative and it won't hurt anything if you have two. Don't worry about brake drag, it takes roughly 75 PSI to overcome the return springs."
I could not find info on why they would be necessary when our master cylinder is way higher than the calipers front and rear. Can anyone shed more info on the benefits or lack there of from the use of these valves in the six wheel disk brake set up? If they would be helpful for our six wheel disk system, how many and where should these be installed?
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Jerry & Sharon Work
78 Royale
Kerby, OR
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