This will walk through the primary reason for the shuttle valve to be exhausting air.
Your shuttle valve is leaking air, so naturally the shuttle valve is the problem. Right? Let's take another look at what is happening.
This shuttle valve has 5 ports, a main air port (port 1), 4 outlets, and 1 input port. This valve links the main port 1 to either port 2 or 4. When the main port flows to port 4, port 2 flows to port 3. When the main port flows to port 2, port 4 flows to port 5. If you have air coming out of port 3 or 5, there are two possibilities for this occurrence:
The valve is leaking.
The pneumatic device inline between port 4 and 2 is leaking.
If we have air leaking from port 3, we need to disconnect the air line on port 2. If air is flowing from the disconnected air line, the pneumatic device between port 4 and 2 is leaking. Similarly, If we have air leaking from port 5, we need to disconnect the air line on port 4. If air is flowing from the disconnected air line, the pneumatic device between port 4 and 2 is leaking. If air is not flowing from the disconnected air line, check to see if air is still leaking from the disconnected ports. If so, your shuttle valve needs to be repaired.
Note:
Maintain control of the disconnected air hose at all times. High air pressure flowing through the detached line can cause the hose to whip violently.
In most cases where air is exhausting at the shuttle valve, the cylinder being supplied is leaking through the piston cups. This is a common finding on CBW's with Flow Stop valves that are connected in parallel. Since both sides of the cylinder are powered with air, a piston leak will blow air out of the exhaust of the shuttle valve. This requires a piston cup repair, not a shuttle valve repair. Isolating the specific cylinder that is leaking requires disconnecting air lines at the cylinder itself.
If your shuttle valve needs to be repaired or replaced, read this link.
If the inline pneumatic device needs replacement, please read the article related to your device.
