scsmith
Well Known Member
Hi,
there is another thread going on about sniffle valve utility, but I would like to focus on what i think is a design problem.
The sniffle valve for horizontal induction engines acts as a drain when the engine is not running. It allows gravity to open a check valve when the manifold pressure is the same as the exterior pressure (or higher).
The valve closes only when there is some suction from the manifold pressure being LOWER than the sniffile outlet pressure.
So, here's the question: with a ram-air intake at wide-open-throttle, and the sniffle valve drain vented to the belly region with just a tube end, it is VERY LIKELY that the manifold pressure is higher than the outlet pressure, and the valve will open.
How many airplanes are flying around with the manifold pressure being vented through the sniffle valve? There is no fuel lost in this case, just a bit of manifold pressure. Maybe its insignificant?
But it seems to me the thing to do is bend the drain tube into the flow so it acts like a little pitot tube, and then will have pressure slightly higher than the ram-intake pressure to keep the sniffle valve closed.
Thoughts?
Steve
RV-8QB FWF
there is another thread going on about sniffle valve utility, but I would like to focus on what i think is a design problem.
The sniffle valve for horizontal induction engines acts as a drain when the engine is not running. It allows gravity to open a check valve when the manifold pressure is the same as the exterior pressure (or higher).
The valve closes only when there is some suction from the manifold pressure being LOWER than the sniffile outlet pressure.
So, here's the question: with a ram-air intake at wide-open-throttle, and the sniffle valve drain vented to the belly region with just a tube end, it is VERY LIKELY that the manifold pressure is higher than the outlet pressure, and the valve will open.
How many airplanes are flying around with the manifold pressure being vented through the sniffle valve? There is no fuel lost in this case, just a bit of manifold pressure. Maybe its insignificant?
But it seems to me the thing to do is bend the drain tube into the flow so it acts like a little pitot tube, and then will have pressure slightly higher than the ram-intake pressure to keep the sniffle valve closed.
Thoughts?
Steve
RV-8QB FWF