VGD has a fine micro filter on the suction side and on the outlet side an oil and oil mist separator to return the oil to the oil circulation system. The motor fan cools the motor and pump housing. The motor and the pump have a common shaft. An integral non-return valve prevents the evacuated system from being ventilated after the pump has stopped. If the machine has been idle for more than two minutes the connected pipe should be ventilated to atmospheric pressure. A gas ballast valve prevents water vapor condensation getting inside the pump when low amounts of steam are sucked in when the pump is at operating temperature.