The key ingredient to vacuum lifters is vacuum. Selecting the right vacuum source is one of the steps Wood’s Powr-Grip® design engineers and technical sales staff take in providing the right tool for the job.

To create a vacuum, some type of vacuum pump is used. It pumps air out of the vacuum system and into the surrounding atmosphere. There are various types of vacuum pumps, including piston, wobble piston, diaphragm, rotary vane, regenerative blower, and venturi.

The venturi stands out in this list because it has no moving parts and requires compressed air to generate vacuum. The venturi itself is usually a lower cost item than the other types of vacuum pumps, but it is important to consider the cost and availability of enough pressurized airflow to run the venturi. This normally requires an air compressor and air lines that bring the air to the vacuum lifter. Even if a facility is already equipped with an air compressor, the cost of increasing the usage of the air compressor or increasing the size of the air compressor should be considered in the overall project cost. The venturi must be connected to a compressed air source, so it is usually tethered by hose. It is important to consider the routing of the hose and how that affects the use of the vacuum lifter.

Some advantages of venturis are: they are available in a wide range of performance capabilities; they are relatively inexpensive; they have no moving parts, so wear and maintenance is minimal; they are resistant to various contaminants, such as water and chemicals; and they are relatively small and light. Venturis are also known as vacuum transducers and vacuum generators. Multi-stage venturis are actually multiple venturis mounted or built together, which have some moving parts to optimize performance in certain areas.

Other types of vacuum pumps use moving parts and are generally driven by an electrical power source. Although other pumps could run on air power, the venturi is a more cost-effective way to make use of compressed air as the power source. Certain pumps also can generate vacuum manually, but that is generally limited to circumstances where the pump is close to the operator and airflow requirements are very low, such as hand cups using a type of piston pump. Usually non-venturi pumps are powered by AC or DC electricity. AC pumps are very good for high power requirements and continuous operation but are tethered by the power cord. DC power requires the weight and cost of a battery and requires regular charging and monitoring of the battery. However, DC offers the flexibility of not being tethered to a power supply, so it is a good solution for construction sites, for use with a forklift, or for use in multiple locations in a factory.

The piston pump uses a reciprocating piston inside a cylinder and move air through one-way valves. This pump draws air into the cylinder to create a vacuum, and pushes that air out another valve to prepare to repeat the cycle. The piston pump is available with medium to high vacuum ratings and moderately high airflow ratings. It is suitable in industrial applications. However it is susceptible to corrosion inside the cylinder if it is not made with more expensive non-corrosive materials. Also, the piston rings experience wear that requires maintenance, and may require lubrication or higher power requirements.

The wobble piston is similar to the piston pump. However, while a standard piston pump uses a number of joints and parts to convert rotary motion to linear motion, the wobble piston has a very thin piston that rocks inside of the cylinder. The wobble piston does not generally provide as much airflow as a piston pump, but it does generate more than diaphragm pumps. The wobble piston does have corrosion issues similar to the piston pump, but maintenance is reduced somewhat for the wobble piston.

The diaphragm pump uses a design similar to a wobble piston or piston pump, but instead of a seal around the piston, a flexible sheet of material is attached to the head of the piston and the top of the cylinder. As the piston moves up and down, the diaphragm flexes to create the volume to draw air in and to push the air out. This pump is characterized by low noise, high efficiency and gas tightness. Diaphragm pumps are able to produce relatively high vacuum levels but are limited in airflow ratings. They are particularly durable for pumping wet air with little exposure of the metal components to water. The diaphragm has very little wear, and is easily replaced when needed.

The rotary vane is a shift in technology from the piston-based pumps. In a round chamber, a rotor is positioned off center so that it almost touches the chamber wall on one point. Rotor vanes are located around the rotor in slots. Centrifugal force from the spinning rotor causes the vanes to move out against the wall of the chamber. Between adjacent vanes, the chamber wall and the rotor is a space that varies in volume as the rotor spins. At the exhaust port, the volume is small and remains at atmospheric pressure. As the rotor spins the volume increases, causing the pressure to drop. At the inlet port the volume is at maximum, with minimum pressure, so that air will rush in from the vacuum system.

Rotary vane pumps are suitable for generating relatively high airflow and reasonably high vacuum levels. However, the surfaces inside the head of a rotary vane pump can be quite susceptible to corrosion from moist air. The vanes are high wear items that need to be replaced regularly. The action of the vanes causes the head of rotary vane pumps to become quite hot during operation. In inexpensive rotary vane pumps, the vanes may not fit properly in their slots, causing them to stick and perform poorly. Some vane materials may also swell from moisture in the air and cause poor performance.

The regenerative blower is similar to the rotary vane, but it has no moving vanes or direct seal between the rotating impeller blade and the housing. This makes the regenerative blower more robust and easier to maintain than rotary vane pumps, but not able to achieve a maximum vacuum that is as high. Regenerative blowers tend to be larger, heavy pumps, often using three phase AC power. They can achieve moderate vacuum levels and produce very high airflow rates. Regenerative blowers are good vacuum pumps for porous materials where high airflow is needed.

Gary Bond is Chief Engineer managing the Wood’s Powr-Grip Product Engineering Department. He serves on the ASME B 30.20 and the BTH standards committees. He has been an engineer with Wood's Powr-Grip for 20 years.