A customer purchased and installed a 4-way air valve, however air leaked continuously out the exhaust port of the valve just like the old one he was replacing. He bought a second new valve, installed it, and experienced the same thing. Logical troubleshooting dictates using a holistic approach; in other words, looking at the entire circuit as an entity, then narrowing the problem to specific component(s). Looking at all the potential suspects in a simple circuit with a single 4-way valve and double-acting cylinder, possible internal leak paths include the following:
The original cylinder had not been changed, so the customer carefully disconnected the un-pressurized line between the valve and cylinder to see if air was coming from the valve or the cylinder. Air was coming from the cylinder port, which confirmed the leak was internal bypass in the cylinder, not the valve. The point where the leaking air was escaping was at the exhaust of the air valve, leading him to think the air valve was the issue. Don’t assume the symptom and the defective component are always at the same location.