We’ve talked a lot about crack detection in our Tech Tips – everything from Wet and Dry Magnetic Particle Inspection to Dye Penetrant Crack Detection to Vacuum Testing. Here, we’re talking about pressure testing. This method is often used along with one of those listed above as a final check that all of the cracks or pinholes have been repaired. Of course, just like life, it can’t be totally simple; there are two ways to perform pressure testing – wet or dry. The good news is the procedures are essentially the same regardless of which method you choose.
First of all, the head being tested needs to be completely clean. You will attach a special block-off plate to the head to seal off the water passages, then pump pressurized air into the head through an air line inserted into a water port. Some sources will tell you to use about 60 psi, but in my experience, 20 to 25 psi is adequate. Some heads have core plugs pressed into them and these will blow out at 60 psi. It’s not only an inconvenience, it’s a safety hazard.
Here’s where the methods differ. With the wet method, you’ll lower the head into a water tank until it’s completely submerged. If you have holes or cracks, the escaping air bubbles will show you where. The dry method is similar. Instead of taking the head to the water, you’re bringing the water to the head. Once the head is pressurized, you’ll spray it with a soapy solution (bubble fluid or a little dish soap in water). If there are cracks or holes, the solution will bubble up and you’ll know where you need to repair.
Pressure testing is one of the easiest of the crack detection methods available. But a major drawback is that pressure testing can’t identify all cracks. Surface cracks that don’t connect to a water passage won’t show any leakage so you could miss those if you just use pressure testing.