| | Vacuum Sewers offer many advantages over gravity systems including fast installation and lower installation costs due to smaller diameter piping and shallower burial depths.
The heart of vacuum sewer systems are the vacuum pumps, which are either liquid-ring vacuum pumps or lubricated sliding vane (Rotary Vane) vacuum pumps. Liquid ring vacuum pumps can be either water sealed (requiring a continual water purge), or oil-sealed (known as Vmax).
| | | | Rotary Vane (Busch®) vacuum pumps are the most common type being installed over the last 5 to 10 years, primarily due to an emphasis on electrical efficiency, since rotary vane pumps are approximately 10-15% more efficient (CFM per HP). Per the EPA(1) :“On the negative side, there have been problems with the vulnerability of these pumps should water be carried into (or accumulated in) them. In this situation, the pumps must be taken out of service to remove the liquid; the result is a shortened service life. By contrast the liquid-ring pump can usually withstand an accident of this type with very little damage.”
|  | | | | What is usually not considered in the evaluations, however, is the life cycle costs including maintenance (labor, oil, filters, repairs) of the vacuum pumps. Rotary vane vacuum pumps, on clean service, are recommended to change oil every 500 to 750 hrs of operation (about every 3 weeks for continuous service). The Vmax only requires oil changes once every year (10,000 hrs on clean service ); for vacuum sewers- every 6 months. Water accumulation in the oil (very common problem), can damage the rotary vane pump because the vanes and bearings rely on the lubricating oil for operation, whereas the Vmax oil-sealed liquid-ring vacuum pump uses external greased bearings and the oil is used for sealing, not lubrication.(see How a Liquid Ring Pump Works)
| | | | The EPA(1) recommends “When liquid-ring pumps are used, oil is recommended as the seal liquid”, because the oil-sealed Vmax eliminates the potential for rusting, corrosion and hard water deposits when using water as the sealant.
The oil-sealed Vmax offers many advantages in vacuum sewer applications, when low maintenance and high reliability are important.
• Lower maintenance (oil change once per year)
• Quieter Operation (78 dBA vs 85 dBA)
• Higher Reliability (able in ingest liquid without damage)
• Air-cooled
• Small Footprint
(1) US-EPA Alternative Wastewater Collection Systems EPA/625/1-901/024
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Triplex VMAX #VMX0303 Oild Sealed Liquid Ring
| | | | | HP | Busch Model | Vane Capacity @24"HgV | Busch Footprint | Vmax Model | Vmax Capacity @24"HgV | Vmax Footprint | | 10 | RC250 | 160 | 40"x26"(7.2 Ft²) | VMX0153M | 145 | 37"x18"(4.6 Ft²) | | 15 | RC400 | 280 | 54"x36"(13.5 Ft²) | VMX0203K | 190 | 57"x27"(10.7 Ft²) | | 20 | | | | VMX0303K | 280 | 57"x27"(10.7 Ft²) | | 25 | RC630 | 404 | 69"x38"(18.7 Ft²) | VMX0453K | 425 | 76"x28"(14.8 Ft²) | | 40 | RC1000 | 600 | 75"x46"(24 Ft²) | VMX0553K | 550 | 76"x28"(14.8 Ft²) | | 40 | | | | VMX0653K | 650 | 73"x65"(33 Ft²) |
The above chart shows that the pumps are comparable in capacities and footprints. However there are a number of differences, which may be important:
| | Rotary Vane | Vmax | | Vacuum Pump Type | Lubricated Rotary Vane | Non-Lubricated Liquid Ring | | Recommended Oil Change Frequency
(clean service) | 500-750 hrs. | 10,000 hrs. or 1/yr | | Typical Noise Level | 81-85 dBa** | 76-78 dBa** | | Maximum ambient temperature for continuous operation | 90°F | 105°F | | Able to ingest water slugs w/o damage | No | Yes | | Standard Warranty | 12-18 months | 36 months | ** an increase of 3 dB is a doubling of perceived noise level
#- Busch manual recommends on the RC0400 and larger, a minimum of 5' of air space between the pump and any walls for cooling.
| | | | Footprint: The Vmax has a slightly different footprint than the rotary vane pumps, but in each of the above sizes the Vmax occupies about 25% less floor space than rotary vane pumps.
Oil Changes: Because of the design of the vacuum pump is non-lubricated, the Vmax does not require frequent oil changes. The recommended frequency is basically once/year on clean service versus Busch's frequency of every 500 hrs of operation. In dirty service the Vmax will operate significantly longer than the rotary vane pumps, 5-10 times longer, so in your application we would recommend Vmax oil change every 6 months or 5,000 hours.
Noise: The Vmax will run significantly quieter than the Busch rotary vane pump. Since every 3 dB is a perceived doubling of noise level, there will be a noticeable difference in the operating noise between the two pumps.
Ambient Temperature: Busch's O&M manual indicates that the maximum ambient temperature for continuous operation is 90°F (32°C). If higher temperatures are expected, then Busch recommends “optional cooling” which is an external water cooler (at significant additional cost). The Vmax ambient limit is 104°F (40°C), optional water cooling is at no additional cost.
Accidental carry-over of Liquids/soft solids: The Vmax can tolerate accidental carry-over of liquids and soft solids without mechanical damage. Rotary vane pumps have a high potential of mechanical damage from accidental carry-over.
Warranty: 3-Years for the Vmax.
Wintek is not affiliated with Busch Pumps.
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