The Additel ADT901BN Low Pressure Test Pump, -6 to 6 psi (-0.4 to 0.4 bar), 1/4 NPT (F) is a hand operated pressure pump designed to generate pressures from -6 to 6 psi (-0.4 to 0.4 bar). A high-quality screw press is designed for fine pressure adjustment, with an adjustment resolution up to 0.1 Pa (0.001 mbar). The ADT901B-N is a very stable low pressure calibrator. It makes use of an isothermal bellows chamber which is designed for reducing the possible effects of environmental temperature change. Most pumps make use of a check valve (non-returning valve) and are not well insulated, which will cause large fluctuations in pressure with a change in ambient temperature or when the unit is touched. The ADT901B-N does not use a check valve and is remarkably stable. Two hand-tight connectors installed on the pump allow easy connecting and disconnecting to the test pump without the need for PTFE tape or wrenches. The ADT901B-N is an ideal comparison test pump for low pressure applications.