In a subatmospheric regeneration process, a relief valve and a roughing valve are coupled in parallel to a common roughing pump. During regeneration, the cryopump is warmed to release gases from cryopump stages. The relief valve opens at a first cryopump pressure level less than a predetermined maximum pressure. The maximum pressure is subatmospheric. The relief valve closes when the cryopump pressure drops below a second cryopump pressure level. Pressure in a line between the relief valve and the roughing pump is monitored to control the opening of the roughing valve to the roughing pump.
