1. Initial vacuum is good, but vacuum varies on process
2. Condensed vapor and moisture emulsify with vacuum oil & cause process unstable
3. Vane or piston's abrasion is hig Maintenance is difficult
4. Frequent vacuum oil change
5. Limit on capacity. Only for small size
6. Too much power consumption compare with capacity
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1. Dry type vacuum pump (constant vacuum)
2. Suitable for compressed vapor or moisture
3. No need for oil changed (but, oil in bearing should be changed every 3-6 months)
4. No contact between rotor & casing-No water
5. Suitable for any capacity from low capacity to high one
6. Save 1/2∼1/5 of power consumption than oil rotary vacuum pump of same size
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