There are three major types of pumps used to power vacuum-driven conveying systems. They are, in rough order of power and capability:
- Regenerative pumps
- Positive displacement pumps
- Long-distance positive displacement pumps
Regenerative pumps can serve conveying systems that are small to moderate in size, up to about 450 feet in total length, with maximum line sizes up to 2.5 inches. They are relatively simple in design, with motor power driving single or dual turbine impellers that continually draw and compress air to generate vacuum suction down the conveying line. Like all vacuum pumps, their air intake from the conveying system should be protected with a dust filter/collector to prevent particulates from entering the vacuum pump itself.
Positive displacement pumps offer considerably more power. They are designed around counter-rotating lobe-style impellers that generate higher levels of vacuum suction and airflow. Therefore, they can serve longer and larger conveying systems with lines up to 4 inches in diameter and 1000 feet long. Because they generate higher levels of vacuum and airflow over distance, they are capable of moving very large throughputs. However, the lobe-style impellers used in PD pumps can generate a high level of noise, so If PD pumps are located near personnel or work areas, they should be housed in sound-reducing enclosures.
Long-distance positive displacement (LDP) pumps are a more recent and specialized type of positive displacement pump. Instead of using lobe impellers, they use counter-rotating “claw” impellers to generate vacuum and airflow. Because claw impellers capture and compress air more efficiently, minimizing draft and vibration, LDP pumps are much quieter and up to 25% more energy-efficient than PD pumps. By increasing the level of vacuum within conveying systems, LDP pumps create an airstream that can suspend, support, and carry more material through the line. In fact, LDP pumps provide approximately twice the conveying performance (lbs/hour or distance) of PD pumps with the same horsepower.
Many typical existing conveyor systems run at vacuum levels of 10-11 inHg (absolute). However, with an LDP pump of comparable horsepower, it is possible to run at 12-16 inHg (absolute), or perhaps a bit more. This difference – a greater level of vacuum – enables the same conveying system plumbing to carry far more material over the same distance or to pull materials over much longer distances.
The additional vacuum and airflow generated by LDP pumps not only solves tough conveying problems, but also opens up new application flexibility. For instance, adding a variable-frequency drive (VFD) allows you to “tune” the pump performance (speed in rpm, airflow in cfm) to match line-size and material speed requirements, while maintaining the vacuum needed to ensure throughput over distance. In fact, with a VFD/LDP pump combination in place, you’re only a few valve and control updates away from Wave Conveying™, Conair’s automatic, variable-speed conveying technology. The LDP pump brings that much, and more, to the table.
Quick summary: Comparing vacuum pump performance
Below is a quick summary chart of vacuum pump basics. If you have other, more detailed questions, don’t hesitate to drop an e-mail or give us a call.
|Regenerative pumps||Positive displacement pumps (lobe style)||Long-distance positive displacement pumps (claw style)|
|Maximum conveying system length:||450 feet||550 feet||1000 feet|
|Maximum line sizes||2.5 inches||4 inches||5 inches|
|Impeller style||Turbine (single or dual)||Rotating lobes||Rotating claws|
|Noise||Moderate||High (may need sound abatement)||Moderate|
|Sustained vacuum level
|Wave Conveying™ capable||Yes|