An absolute pressure regulator for helium cryostats

The main features of the regulator design are shown in Fig.1. The gas from the cryostat enters the chamber 10 of the regulator through tube 1. When the given pressure is reached in chamber 10, bellows 3, previously pumped down to a pressure ~ 10 -3 torr through tube 2, overcoming the force of spring 6 opens valve 4. The excess part o f the gas is discharged into space 9 connected ~.o the discharge line, bellows 3 straightens up and closes valve 4. Valve 4 in the closed state is sealed by a silicone rubber washer. Smooth control of the operating pressure in the cryostat is achieved with the help of a hollow screw 8 through the discharge connecting pipe, without dismantling the regulator. The accuracy in maintaining the operating pressure within the range from 0 to 0.3 atm is + 0.06 arm, for a change in gas temperature between 303 and 223 K and while changing the pressure in the discharge line from 0 to 1 arm. In the present design a semi-tombac bellows is used with outer diameter 32 corrugations and wall thickness 0.12 mm. The spring is made from 1.5 mm diameter spring wire and develops a force of 5.5 to 6 kg. The sealing washer is made from 1 mm thick silicone rubber. The minimum cross-