The 901A Low Pressure Test Pump is a hand operated pressure pump designed to generate pressures from -6 psi to 6 psi. A high-quality screw press is designed for fine pressure adjustment, with an adjustment resolution up to 0.1 Pa. The 901A 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 901A 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 901A is an ideal comparison test pump for low pressure applications.