G-650 Vacuum Joint Testing Gun uses air pressure to generate a vacuum around the tube-totubesheet joint to pinpoint leaking connections. Just insert the test gun into the tube end and press the air control valve to fill the cylinder with air. This expands a seal inside the tube, pulling a second seal firmly against the tubesheet surrounding the tube end. Next press the vacuum control valve to divert air through a venturi, creating a vacuum around the tube joint area. Any reduction in vacuum shown on the integral gauge indicates a faulty tube joint.