FAQ

Frequently Asked Questions

Selecting the correct pump depends on :

  1. What ultimate vacuum is required?
    The ultimate vacuum required determines the type of vacuum pump to be used. Most industrial applications use a single stage pump. If the application requires pressures below 1 mbar, a two stage rotary vane vacuum pump may be needed. If there are solvents, water based solutions or condensable vapours in your process these contaminants will affect the vacuum pump reducing the efficiency of the pump and the ultimate vacuum achievable. Condensation of vapours in the vacuum pump may be minimised by the use of the vacuum pump’s gas ballast facility.
  2. What pump down time is required to reach the operating vacuum?
    On a leak tight system where the volume of the vacuum chamber is known, the pump down time can be accurately calculated for a pump of known pumping speed. A pump can be selected to provide the required pump down time.
  3. Are there contaminants in the process?
    Condensable vapours in the process will affect the vacuum level that may be achieved and the pump down time. Water based solutions will produce huge volumes of water vapour which will have to be pumped and this will significantly extend the pump down cycle. Most modern vacuum pumps have a gas ballast facility which will reduce condensation of vapours in the vacuum pump thereby maintaining the condition of the lubricating oil in the pump.
  4. Are you prepared to pay for speed of operation or would a longer cycle time with a smaller, less expensive pump be acceptable?
    The pumping speed of the vacuum pump ( the size of the pump ) will directly affect the time to achieve the required level of vacuum. Pump down time may be calculated where the chamber volume and pumping speed are known. Factors such as leakage into the vacuum chamber and contaminants in the process will significantly affect both the pump down time and the ultimate vacuum achievable.

Dry rotary vane pumps use vanes made from a carbon material. The vane material contains graphite which is self lubricating and allows the pump to operate without oil. Ultimate vacuum is usually limited to 80 % (200 mbar absolute) These vacuum pumps offer maintenance free operation and are widely used in applications such as the printing industry and in applications where access to the pump might be problematic. Dry pumps are usually noisier than oil lubricated pumps.

Good question! We sold vacuum pumps from the older manufacturers for over twenty years. We were frequently embarrassed at the prices that our customers were paying for these vacuum pumps. And that was without the accessories such as exhaust oil mist filters which should have been fitted as standard equipment! Over the past ten years a number of new vacuum pump manufacturers have become market leaders. These new comers have access to the same technology as the more traditional vacuum pump manufacturers and they are producing quality vacuum pumps with the full range of features as standard equipment. At Vacuum SA we support these modern manufacturers and strive to supply the best equipment at affordable prices.

A device known as gas ballast is fitted to most good quality vacuum pumps. When the gas ballast valve is opened, a metered amount of atmospheric air is admitted into the vacuum pump. This dry air mixes with the condensable vapours in the vacuum pump and the vapours are exhausted before they condense in the vacuum pump. Gas ballast prevents contamination of the lubricating oil in the vacuum pump and maintains superior levels of vacuum.

All vacuum pumps create an oil mist ( oil smoke ) at the exhaust when operating. The air passing through the pump combines with the pump’s lubricating oil to form this oil mist which is both unpleasant to breath and can pose a health hazard resulting in respiratory problems. The higher the pressure at which the pump is operating and therefore the more air passing through the vacuum pump, the greater the oil mist mist exhausted. Vacuum pumps from Vacuum SA are fitted as standard with an oil mist filter and oil recovery system to eliminate this health hazard. Many vacuum pump manufacturers supply this oil mist filter as an expensive accessory adding a significant hidden cost to the purchase price of the vacuum pump.

The oil mist filter contains filter elements which should be replaced every eighteen months under average conditions. Warning signs that the elements need to be replaced are when the pump runs hot, the electric motor trips the overload or the vacuum deteriorates.

Ensure that the vacuum pump has been filled with oil to the level marked on the sight glass. After operating for the first time check the level once more.

Resistance to the flow of gases through pipes can significantly affect the size of pump that you require or the pump down time that you can achieve with a given pump. Maintain the bore size of the pipe between the vacuum pump and the process chamber to the size of the pump inlet. Keep the pipes as short as possible, the longer the pipes to your process the more pumping speed you will lose.

It is advisable to install a flexible section in the pipeline between the pump and the vacuum chamber to absorb vibration and to reduce stress on the inlet flange of the vacuum pump. Always fit overload protection for the electric motor. At start up check motor direction of rotation by momentarily applying power to the motor.

Our vacuum pumps are filled with Ultragrade 19 vacuum oil. Normal 20W50 motor oil is suitable for general use but the additives in this oil may affect the readings on electronic vacuum gauges such as Pirani and thermocouple gauges.

Most manufacturers recommend service intervals of 500 to 750 hours. We say when the oil is visibly dirty it should be changed. This might be once a year or even once a week depending on the application. If you are drying transformer oil under vacuum you will draw large amounts of water through the vacuum pump. Our modern pumps are so efficient that they will exceed the ability of the pump’s gas ballast to dispose of the water. When this happens the oil will become contaminated with water and this will turn the oil white. If the water is left in the pump it will cause rust, particularly if left overnight. Drain the oil and refill with fresh oil, it is cheaper to change the oil than to repair a rusted pump.

On laboratory pumps where solvents and other nasties are drawn through the pump the contaminants can attack the seals if left for long periods, even if the pumps are fitted with ‘Viton ®’ chemical resistant seals. Contaminants in the oil will have a greater effect on the ultimate vacuum of two stage pumps than on single stage pumps. If the oil looks and smells bad, it is bad for the pump and your process.

Vacuum pumps typically operate at between 70 and 90ºC. When pumping condensable vapours the temperature of the pump should be at least 80º C to prevent condensation of the vapours in the pump.
Temperatures in excess of 90ºC will lead to deterioration of the vanes and seals and may result in premature failure of these items.

Various gauge types are available depending on the vacuum range to be measured and the accuracy required.

A ‘Bourdon’ type gauge is inexpensive. If you are not looking for great accuracy and require a gauge to read the full vacuum scale of 1000 mbar to 0 mbar (100 Kpa to 0 Kpa) this gauge is right for you. The reading on this gauge will be affected by weather conditions and the reading will not be an absolute reading ie. the reading will vary according to the altitude at which the reading is taken. Typically the reading on a bourdon gauge will be ‘reduction from ambient atmosphere’

A capsule gauge will give a true reading and will not require correction for changes in altitude. The gauge will read ‘absolute’ pressure with great accuracy. Capsule gauges are typically available in 0 to 25, 0 to 50 and 0 to 1000 mbar. Select the range that suits your application. If you need to measure 15 mbar choose a 0 to 25 mbar gauge which will provide an accuracy of 1 mbar.

Digital vacuum gauges cover the full vacuum range and are accurate to 1 mbar. Common ranges are 1000 mbar to 1 mbar and 100 mbar to 10-3 mbar (0.001 mbar)

Positioning the vacuum gauge on the vacuum chamber will give an accurate indication of the vacuum in your process. Placing the gauge closer to the vacuum pump will give a more optimistic reading (ie. better vacuum will be indicated)

If the pipes between the vacuum pump and the chamber are small, this difference can be considerable

Any other questions that you weren’t able to find answers to here?
Contact a sales representative on 028 271 3481