Ralston Instruments APOV Pneumatic Hand Pump is a high pressure pump for connection to an external calibrator. A large diameter, fine adjustment piston provides precise control at any pressure. The APOV's scissor-handle design, low internal volume, and micro-bore hose give you the advantage of higher pressure with less effort. The APOV pump has a second high pressure port for connection to an instrument to be calibrated. The second port has an internal check valve installed. This valve opens when a hose or gauge adaptor is connected to it.