Should the anti backfire valves used on header pan evac systems have air flow in both directions?
Installed the check valves on the header collectors and have no vacuum just exhaust pressure. Factory welded collector fittings.

I was under the impression the check valve was a one way valve yet I can blow easily through them in both directions.

Is this normal?

Bruce, they are one way only

quote:

Originally posted by nomad:
Bruce, they are one way only

I was pretty sure they should be.
Bought a evac kit and hear exhaust through each valve and little to no vacuum.
Bring up the RPM and all I feel is exhaust pressure.
Went and bought a replacement at the auto parts store and same thing. I can blow through each way.
Unfortunately everything I find appears to be import.

Yes Bruce, definitely should blow one way only, and have a block the other. Back in the good old days when I ran them on pan evac on my car, those check valves didn't last very long, made in you know where. I used to carry several spares in the trailer. Sometimes, brand new ones were junk.

I would start by looking at the fittings welded into the collector. I’ve found on my own that the direction most are welded into collectors is plain wrong. Most provide little to no vacuum some pressurized the valve covers. That’s why I will install my own.

I have an EVAC kit #52210 from Jegs (China) sitting on the shelf and just did this. I can blow air either way with my mouth. I set the air regulator on my compressor to 5 psi and with an air nozzle was able to blow air to the exhaust side but not to the engine side.

I think the best test is to install a vacuum gauge on the engine and record readings at idle and wot to see the true results of the install. This is one of the things on my list to install in the Holley DA as I have EVAC for 16 years and want to know if it is working or not.

Should only flow one direction. I use Standard brand and test them to see if they are still good. I have to pull my left one to remove my oil filter so it's when I test them both.

quote:

Originally posted by Eman:
Should only flow one direction. I use Standard brand and test them to see if they are still good. I have to pull my left one to remove my oil filter so it's when I test them both.

What’s your test method?

Like Lauren Bacall said, Just put your lips together and blow.

I know there's a reason for these things, but I've been running a header evac system without them for at least 20 years and haven't had a problem.

Did a vacuum test years ago on those setups never got more than 7 inches and that was at upper rpm way better to use vacuum pump but is pricey

quote:

Originally posted by Wooley:
I would start by looking at the fittings welded into the collector. I’ve found on my own that the direction most are welded into collectors is plain wrong. Most provide little to no vacuum some pressurized the valve covers. That’s why I will install my own.

X2 - This could be part of the issue, Bruce. Mine were welded in by a guy up in Denver who has a dyno / tuning operation and fab shop. Because they operate on the venturi principle, he said the junction between bung and collector does matter, including entry angle, and how far the bung or fitting enters into the exhaust flow. Mine definitely pull a vacuum, though nothing like a vac pump does. I can try and take a picture of the side angle and inside the collector, if you'd like.
Also, I believe what Markemark said too, it may take a certain volume of flow to get the check valve to close. Curious, are yours installed on the top side of the collector? I was just wondering if maybe gravity plays a part, never seen any instructions for them as to a specific orientation.

Here's the instructions for the Moroso crankcase evacuation system.

https://static.summitracing.co...ctions/mor-25900.pdf

Here's what mine look like. Installed at a 45* angle protruding about 1/2” into collector with tube cut opening parallel with the collector interior.

I just took both check valves off and cannot blow by mouth through them to the engine side but can to the exhaust. These are over 20 yrs old. I use cable ties for hose clamps on check valves and valve cover breather hose.

Even though I could blow through to engine side the new ones with my mouth but not with 5 psi of compressed air, I don’t believe they’re bad. One can only produce 1-2 psi at very best blowing with their mouth.

As I wrote previous, unless one has a vacuum gauge / transducer to record actual crankcase pressures it’s unsure how well their system works. To me, if it were good for 2 -5” of vacuum I’d be very pleased.

Bruce, I think these setups don't draw enough vacuum to pull open a tight-fitting disc/valve. So it kinda hangs open a little but would snap shut if there was a backfire, which is what they are intended for anyway.....When they first came out I never used the valve to get as much vacuum as possible.....If you have room to mount an electric pump I have a brand new one from GM that would pull more/some vacuum than the "in the headers" set-up. AND you can leave it running in the pits to pull vapors out in between runs. You're welcome to it if you'd like it...

quote:

Originally posted by imakehp:
Bruce, I think these setups don't draw enough vacuum to pull open a tight-fitting disc/valve. So it kinda hangs open a little but would snap shut if there was a backfire, which is what they are intended for anyway.....When they first came out I never used the valve to get as much vacuum as possible.....If you have room to mount an electric pump I have a brand new one from GM that would pull more/some vacuum than the "in the headers" set-up. AND you can leave it running in the pits to pull vapors out in between runs. You're welcome to it if you'd like it...

Dave I sent you a text message.

In OEM use! The valves prevent hot exhaust gases from flowing in reverse when the Air Injection Reaction Pump cant overcome the exhaust manifold pressure. If flow was permitted? It would wreck havoc on the rubber hoses and or plastic fittings in the AIR System. My opinion is they are not needed.

quote:

Originally posted by markemark:


As I wrote previous, unless one has a vacuum gauge / transducer to record actual crankcase pressures it’s unsure how well their system works. To me, if it were good for 2 -5” of vacuum I’d be very pleased.

I do not think you will ever even get 1 or 2 inches of vacuum with those. They may help keep it from getting positive pressure when they are working right but I would not think you could get much vacuum. And a vacuum gauge is a good idea to see what is happening even if it is just a cheap one to test with.

I've never put a vacum gauge on mine, might make an adapter and try it. I can pull the hoses off of the VC breather and feel it pull when I rev the engine My motor has never exhibited blow by and I don't get oil in the header collector. I didn't buy a kit, I bought some iron pipe and checkvalves.

quote:

Originally posted by Eman:
I've never put a vacuum gauge on mine, might make an adapter and try it. I can pull the hoses off of the VC breather and feel it pull when I rev the engine

X2, Thinking I may try that too. I can feel the vacuum, slight at idle, increases when I increase the RPM. But I am curious, and I'm especially wondering if at WOT the exhaust volume + pressure in the collector might overcome the venturi effect and actually be pressurizing the crankcase. I would imagine if that was the case, it would push some oil out somewhere, and I have no leaks.