check valve vacuum level
Thread Starter
Advanced
Joined: Dec 2007
Posts: 58
Likes: 1
From: Austin TX
check valve vacuum level
Been a lurker here for years but finally took the plunge and bought my first 'vette, a 71 Coupe in need of some TLC.
been working through things sorting the various systems out. It took a bit of work to get to the point where I had one headlight popping up with either control valve (switch or override) but my check valve wasn't holding vacuum and i needed to rebuild one actuator. So i purchased from Zip. My new check valve does check in one direction (the old one didn't) BUT it only passes 9 in. to the can and 1 in. to the control side. My old one didn't check for crap but at least passed 15 in. to the can and about 6 in. to the control side. Now the actuator that used to work with the faulty check valve in place doesn't even work...
Can anyone tell me in their system what the vacuum level is before and after the check valve for both the can side and actuator side? Would like to know if this is normal before i complain to Zip.
Thanks!
Paul
been working through things sorting the various systems out. It took a bit of work to get to the point where I had one headlight popping up with either control valve (switch or override) but my check valve wasn't holding vacuum and i needed to rebuild one actuator. So i purchased from Zip. My new check valve does check in one direction (the old one didn't) BUT it only passes 9 in. to the can and 1 in. to the control side. My old one didn't check for crap but at least passed 15 in. to the can and about 6 in. to the control side. Now the actuator that used to work with the faulty check valve in place doesn't even work...
Can anyone tell me in their system what the vacuum level is before and after the check valve for both the can side and actuator side? Would like to know if this is normal before i complain to Zip.
Thanks!
Paul
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
My engine will do around 15Hg of vacuum before the check valve and it would drop to around 10 Hg from the big port and around 5 Hg from the smaller one, mine is a NOS original part, but I also tested a repro one and it did the same. 1 Hg seems like too little vacuum to be useful for just about anything, this check valve must be clogged or something.
Thread Starter
Advanced
Joined: Dec 2007
Posts: 58
Likes: 1
From: Austin TX
My engine will do around 15Hg of vacuum before the check valve and it would drop to around 10 Hg from the big port and around 5 Hg from the smaller one, mine is a NOS original part, but I also tested a repro one and it did the same. 1 Hg seems like too little vacuum to be useful for just about anything, this check valve must be clogged or something.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
When doing this check you must block either the big port or the small , you can't leave one still attached to the car.
Small port or big port the vacuum should be the same just lower volume.
Sounds like you have system leaks,I doubt very seriously the check valve is your problem.
Small port or big port the vacuum should be the same just lower volume.
Sounds like you have system leaks,I doubt very seriously the check valve is your problem.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
You said that it checks the vacuum in one direction. You mean it holds vacuum with no leaks? If it's in the correct direction, meaning no backflow towards the engine then that's all the valve does. How much vacuum your pump can suck in the other direction is not really relevant.
Unless I misread your post.
Unless I misread your post.
Thread Starter
Advanced
Joined: Dec 2007
Posts: 58
Likes: 1
From: Austin TX
When doing this check you must block either the big port or the small , you can't leave one still attached to the car.
Small port or big port the vacuum should be the same just lower volume.
Sounds like you have system leaks,I doubt very seriously the check valve is your problem.
Small port or big port the vacuum should be the same just lower volume.
Sounds like you have system leaks,I doubt very seriously the check valve is your problem.
Mike, Yes, by "check vacuum" i mean stop flow in one direction, only allow flow in the other direction--the purpose of a check valve as i learned it. Sorry if my post wasn't clear, i was never sucking with my gauge, just measuring what the engine gave me. I did suck and blow test on the check valve to make sure it performed it's primary duty of stopping flow in one direction; it does, although with more resistance in the correct flow direction than i would have thought normal...
Thanks all for comments. Anyone else can check their vacuum levels and post them up here?
Paul
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Knowing how the valve is built inside I don't see how there could be a difference in vacuum between the small and large port,they are connected. I also don't get how you can have 15" on the single port side and only 9" on the 2 port side unless there is a leak BUT I have never actually tried that test that I can remember. So I guess I have to run off to the garage (and its COLD out there )to see if the rubber tension inside can change the readings side to side in a capped off situation.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Thread Starter
Advanced
Joined: Dec 2007
Posts: 58
Likes: 1
From: Austin TX
Knowing how the valve is built inside I don't see how there could be a difference in vacuum between the small and large port,they are connected. I also don't get how you can have 15" on the single port side and only 9" on the 2 port side unless there is a leak BUT I have never actually tried that test that I can remember. So I guess I have to run off to the garage (and its COLD out there )to see if the rubber tension inside can change the readings side to side in a capped off situation.
THANKS for being insistent and for tolerating my mistake.
Paul
