I just finished installing my Audiovox cruise control on my BB and I have a question about the vacuum canister I made. They say to use a check valve between it and the engine. I don't see the point because a check valve allows air only one way and not the other, so it's not holding anything in the canister when there is no vacuum because the vacuum sucks air out of the canister through the check valve and when there isn't any, air just leaks out back through the check valve in the same direction as the vacuum pulls. So what does it do??
Alain
Full Version: What does a check valve do? (cruise control)
QUOTE(arichard @ Feb 17 2006, 10:18 AM) 
I just finished installing my Audiovox cruise control on my BB and I have a question about the vacuum canister I made. They say to use a check valve between it and the engine. I don't see the point because a check valve allows air only one way and not the other, so it's not holding anything in the canister when there is no vacuum because the vacuum sucks air out of the canister through the check valve and when there isn't any, air just leaks out back through the check valve in the same direction as the vacuum pulls. So what does it do??
Alain
Alain
The same the check valve does on your brake booster (and the cruise control on older cars)... Your engine makes the most vacuum at idle, so at idle, it makes an almost perfect vacuum in the vacuum canister, so that there is more "power" to actuate the throttle when you're at cruise...
BTW, ever have a check valve go out on a brake booster? It's REALLY cool! when you go directly from the gas to the brake, you have basically manual brakes until the engine goes back down to idle, then you get full brakes again... really neat huh? :blink: This is really only an issue with automatics, BTW... you have a VERY high vacuum when you just close the throttle while you're in gear on a manual...
Mike
[/quote]
The same the check valve does on your brake booster (and the cruise control on older cars)... Your engine makes the most vacuum at idle, so at idle, it makes an almost perfect vacuum in the vacuum canister, so that there is more "power" to actuate the throttle when you're at cruise...
BTW, ever have a check valve go out on a brake booster? It's REALLY cool! when you go directly from the gas to the brake, you have basically manual brakes until the engine goes back down to idle, then you get full brakes again... really neat huh? :blink: This is really only an issue with automatics, BTW... you have a VERY high vacuum when you just close the throttle while you're in gear on a manual...
Mike
[/quote]
umm.. What would change if I didn't use the check valve then?
The same the check valve does on your brake booster (and the cruise control on older cars)... Your engine makes the most vacuum at idle, so at idle, it makes an almost perfect vacuum in the vacuum canister, so that there is more "power" to actuate the throttle when you're at cruise...
BTW, ever have a check valve go out on a brake booster? It's REALLY cool! when you go directly from the gas to the brake, you have basically manual brakes until the engine goes back down to idle, then you get full brakes again... really neat huh? :blink: This is really only an issue with automatics, BTW... you have a VERY high vacuum when you just close the throttle while you're in gear on a manual...
Mike
[/quote]
umm.. What would change if I didn't use the check valve then?
Your cruise is liable to drop out when climbing hills as that is when the vacuum drops in the manifold/ports. The check valve keeps the vacuum in the chamber at its highest level.
Stop using the word vacuum and start thinking lower pressure and this will make sense. The pressure in the chamber is maintained at a lower value as the pressure in the manifold rises.
Piping should be as follows:
Manifold o> Canister. This way if pressure is lower in the canister than in the manifold the check will close, maintaing the lower pressure. If the manifold pressure drops below the canister pressure the check will open, allowing the manifold to lower the pressure in the canister. Be careful about installing this and the material used for the check ball. Be sure it is plastic and not metal and it should be installed horizontally with the ball on the manifold side.
Stop using the word vacuum and start thinking lower pressure and this will make sense. The pressure in the chamber is maintained at a lower value as the pressure in the manifold rises.
Piping should be as follows:
Manifold o> Canister. This way if pressure is lower in the canister than in the manifold the check will close, maintaing the lower pressure. If the manifold pressure drops below the canister pressure the check will open, allowing the manifold to lower the pressure in the canister. Be careful about installing this and the material used for the check ball. Be sure it is plastic and not metal and it should be installed horizontally with the ball on the manifold side.
QUOTE(shovelstrokeed @ Feb 17 2006, 11:55 AM)
Your cruise is liable to drop out when climbing hills as that is when the vacuum drops in the manifold/ports. The check valve keeps the vacuum in the chamber at its highest level.
Stop using the word vacuum and start thinking lower pressure and this will make sense. The pressure in the chamber is maintained at a lower value as the pressure in the manifold rises.
Piping should be as follows:
Manifold o> Canister. This way if pressure is lower in the canister than in the manifold the check will close, maintaing the lower pressure. If the manifold pressure drops below the canister pressure the check will open, allowing the manifold to lower the pressure in the canister. Be careful about installing this and the material used for the check ball. Be sure it is plastic and not metal and it should be installed horizontally with the ball on the manifold side.
Stop using the word vacuum and start thinking lower pressure and this will make sense. The pressure in the chamber is maintained at a lower value as the pressure in the manifold rises.
Piping should be as follows:
Manifold o> Canister. This way if pressure is lower in the canister than in the manifold the check will close, maintaing the lower pressure. If the manifold pressure drops below the canister pressure the check will open, allowing the manifold to lower the pressure in the canister. Be careful about installing this and the material used for the check ball. Be sure it is plastic and not metal and it should be installed horizontally with the ball on the manifold side.
Yep... exactly...
Mike
QUOTE(shovelstrokeed @ Feb 17 2006, 11:55 AM)
Your cruise is liable to drop out when climbing hills as that is when the vacuum drops in the manifold/ports. The check valve keeps the vacuum in the chamber at its highest level.
Stop using the word vacuum and start thinking lower pressure and this will make sense. The pressure in the chamber is maintained at a lower value as the pressure in the manifold rises.
Piping should be as follows:
Manifold o> Canister. This way if pressure is lower in the canister than in the manifold the check will close, maintaing the lower pressure. If the manifold pressure drops below the canister pressure the check will open, allowing the manifold to lower the pressure in the canister. Be careful about installing this and the material used for the check ball. Be sure it is plastic and not metal and it should be installed horizontally with the ball on the manifold side.
Stop using the word vacuum and start thinking lower pressure and this will make sense. The pressure in the chamber is maintained at a lower value as the pressure in the manifold rises.
Piping should be as follows:
Manifold o> Canister. This way if pressure is lower in the canister than in the manifold the check will close, maintaing the lower pressure. If the manifold pressure drops below the canister pressure the check will open, allowing the manifold to lower the pressure in the canister. Be careful about installing this and the material used for the check ball. Be sure it is plastic and not metal and it should be installed horizontally with the ball on the manifold side.
That totally makes sense now. Thanks!!! I kept thinking that the canister would be pressurized and not decopressed. lol
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