I can confirm that there is NO internal spring holding the shuttle valve in any particular position. Since this is described by ACS as 0 PSI for breakout, then this is expected, so Ill still rate it 5 stars. But because the operation is entirely influenced by gravity or fluid movement, it is very important to understand in which direction the shuttle operates, if you hope to plan out where to place the valve in a fuel system. The existing reviews that state simply vertical vs. horizontal dont help in this regard (vertical pointed up? or vertical pointed down?). So Ill describe as clear as I can how it operates: 1. If I put the valve to my mouth and blow in the direction of the arrow, of course air will flow no matter how I hold the valve. But thats not what were generally worried about. 2. Holding the valve vertically with the arrow pointed toward the sky, gravity causes the shuttle valve to rest in the closed position, and you get the behavior youd generally expect from a one-way valve: unable to blow air against the direction of the arrow. 3. But heres what matters... Holding the valve vertically with the arrow pointed toward the ground, you can blow air through the valve in BOTH DIRECTIONS! If you blow hard enough against the arrow, of course the shuttle valve closes. But if you blow gently, you can blow in both directions. 4. Holding the valve horizontally, the result is completely unpredictable, because the shuttle valve has no default resting position. Depending on how you shake it, sometimes you can blow air against the arrow. So be careful how you plan your design, especially if this is used in a fuel vent line for the purpose of preventing a puddle of fuel on the hangar floor. It seems to me that in all cases the best possible way to install this valve is arrow pointed to the sky.

Simple, small, with two AN mail Fittings. Just what I needed for my fuel system.

Steven M Verified Purchase

One Way Check Valve 10630

Leaks when under pressure from the gravity feed of high wing. Requested replacement

Dan K Verified Purchase

One Way Check Valve 10630

Order received within 3 days and installed on the airplane on the same day. Exact product as ordered.

Guy S Verified Purchase

One Way Check Valve 10630

I replaced my old check valve same part number that was on my aircraft for 10 years, new one works as advertised.

Installed in a gravity feed system, in parallel with a Facet boost pump. This valve is indeed free flow (zero PSI breakout pressure) and as such works well in the gravity feed system, when the pump is turned off. The pump is only turned on for extreme nose up attitudes.

The item works great at sealing as a check valve. I had to open up and clean the seats from dust and once clean it worked great. I used it for vent and gas applications.

Not as represented, will not operate in light flow conditions

Russell M Verified Purchase

One Way Check Valve 10630

It leaked, did not work

John A Verified Purchase

One Way Check Valve 10630

Tried two of these. Both leaked and I ended up with fuel all over the floor of my hanger.

Failed, wasted $75 worth of fuel on the floor. Was in the upright position.

Since it is not spring loaded, it never worked and it was in a vertical position.