The Comptech supercharger kit comes with a Bosch "by-pass valve." .... It is generally called a "check valve" by folks at Comptech because air can only flow in one direction. The by-pass valve vents air or liquid around a device within a system. So, the Comptech "check valve" is also a "by-pass valve".

hecash posted the above on one of the vortech sc threads.

I now have the comptech EMS which electronically prevents the ECU from seeing boost. When I installed the EMS, I TOOK OFF THE CHECK VALVE AND RETURNED THE MAP SENSOR TO ITS ORIGINAL CONFIGURATION.

Did I do a boo-boo? I haven't noticed any problems, but do I now in effect have no "blow-off" valve? I thought the SC didn't need this.

 

As far as I know the ESM replaces the check valve. I have run my car with both the check valve and "ghostbooster" and it drove the same as when I just ran the GB by itself. The check valve should not be needed if the ESM is installed.

 

I know with the EMS, the check valve is no longer needed to prevent the ECU from seeing boost. My concern now is that the check valve also served the function of venting "backpressure".

Originally, I thought the SC did not have this issue and have seen at least a couple of threads where somebody asked about a "blow-off valve" for the SC or talked about wanting a blow-off valve and was basically told that SCers didn't need this.

Recently, however, I have read some things that make me wonder if the SC doesn't need something like a blow-off valve (but not really) to relieve back pressure. If so, did the check valve serve this function also, or is there some other part that does this?

 

Hey John, there is no worry about what you are questioning.
What Harry was referring about by-pass-valve is air recirculation valve totally separate from check-valve. Kind of like the blow-off-valve version of Turboed cars when throttle is closed shut(like shifting) or partly on throttle, it will relieve building of boost and acutally going reverse to hurt the turbine.
On the Comptech kit the valve is located smack in the middle of blower and the airfilter. If you remove the airfilter housing cover, you can hear its function of pumping air like chu, chu,chu.... when cruising or shifting. And this gets very loud when you have upboost like mine. That is why I have invested in installing blow-off-valve and will be installing it shortly.
Actually there is a documented fact that on the Paxton type of blower venting of the building pressure is more of the drivability issue than safety measure like not hurting the turbine like turbo.
Without the air-venting valve you will experience what is called compressor surge(can't really describe because I never experienced) and you will hear groaning noise. The book said it will not hurt the blower this way oddly.

Anyway, I hope I put your worry aside.

Pardon my english, I admit I am horrible at explaining things.

 

randy,

thanks, that was what I was looking for - perfectly understandable

 

No problem John,
To further explain why belt driven blower like Paxton really is ok without the air-vent or blow-off valve is that unlike turbo which is driven by exaust gas, Paxton blower is driven by belt attached to crank pulley.
No matter how boosted air get to reverse its course back to the blower, turbine still turns because of constant drive from the belt unlike turbo which actually can come to a stop or reverse its course.