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Combined Pressure/Vacuum

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Lowfields Road, Leeds LS12 6DN

Rotary vane pumps with lubrication

SA3 SB6 SC60

Technical info/full product list

The operating principle of lubricated pumps is similar to that of dry pumps, but this type of pump is equipped with oil lubrication that makes it possible to lubricate moving parts and attain significantly better pressures. However, the presence of lubricant makes it necessary to filter the exhaust air in order to recover the lubricant and emit the cleanest possible air into the atmosphere. On the contrary, when lubricant is not recovered the pump is called “open cycle”. The size of the exhaust filters determines the pressure range within which these pumps may be used continuously.

The presence of lubrication allows these pumps to take in small amounts of water vapour. To prevent the vapour from condensing inside the pump there is a device called the “Gas Ballast”. The gas ballast adds a small amount of air during the compression stage in order to adjust the saturation pressure of the vapour and prevent condensation. A pump version has been developed called the WR in which this device has been improved and enhanced.

Finally, lubricated pumps must be fitted with an anti-suck back (non-return) valve at the intake to prevent oil from returning into the user system if the pump stops with the system under vacuum. Finally, all pumps in the series starting with LB.25 are equipped with a system to recover the oil after the damping filter, to allow a wider variety of applications.

The main applications for this pumping technology include: vacuum packaging of food products, degassing, vacuum clamping on glass, marble and wood working machines, vacuum moulding machines, composites and electromedical equipment.

WR Version

The WR version of the series L pump represents an evolution of the standard lubricated pump, and includes a device capable of seperating the condensate water from the oil and draining it with the pump stopped. The distinguishing feature of this series include: gas ballast always engaged; Pyrex external pipe to keep the oil level state and viscosity under control at all times; manual oil or water drainage valve; maximum fluid (water-oil) level switch in the tank.

The principle of the Gas Ballast Valve

At a given temperature, vapour may be compressed only as far as the saturation pressure; beyond that point the vapour condenses. For example at 100 degrees centigrade vapour may be compressed to only 1013.2 mbar; the vapour will condense at higher pressures.

In a container of water (at room temperature) the pump will begin to lower the pressure to the water evaporation point ( if the water is at 25 degrees centigrade at sea level, the evaporation pressure will be 31.67 mbar abs). In phase one of the drawing opposite, the pump will be taking in a mixture of air and water vapour. During phase two the intake volume is isolated from the original vessel and exhaust pipe. In this stage, the valve on the gas ballast opens, and adds a certain of air to change the saturation pressure of the mixture. Finally, in the last stage the mixture, “enriched with fresh air”, is expelled, but since the saturation pressure was changed no condensation droplets will form, and the intake vapour may be expelled without interfering with its operation.

Two factors are thus of vital importance: the temperature of the intake vapour and the temperature of the pump. The pump must be heated before beginning to operate with condensable gases, and the temperature of the intake vapour must be as low as possible.

Pumping Concentrated Oxygen

If the pump runs with high concentrations of oxygen (>21%) it is necessary to use a special PFPE type lubricant oil, since oxygen tends to catch fire in contact with mineral oil fumes. Special versions of the oil lubricated rotary vane have been developed of these applications called PFPE.