Pnuematic Pumps

Advice on paint circulation pump motors.


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Q. What advice do you have on selecting the optimal motor for paint circulation pumps?

A. Pneumatic pumps have been the mainstay of the paint circulation world for many years, and for good reason. They are simple, reliable and with a slow-moving reciprocating motion, do not damage the paint like centripetal and other rotary pumping technologies. While all of these features are beneficial, the primary advantage of using pneumatic pumps is that they are inherently safe for hazardous locations.

Since many paints are solvent-based or have solvent components, paint kitchens are usually considered a hazardous location. As pneumatic pumps operate off of air, and not electric power, there are no sources of electrical ignition. Additionally, pneumatic pumps are a relatively inexpensive solution for pump use in hazardous locations. When electric motors are used, the cost usually increases as second party approvals (such as UL) are required, in addition to more wiring and explosion-proof conduit.

While pneumatic pumps have several advantages, they do have a few drawbacks—energy consumption being the largest. Pneumatic motors by their very nature are, at best, only about 10 percent efficient. Since pneumatic pumps operate off compressed air, they require the use of a compressor, which is not very efficient. Running at this efficiency 24/7 can really add up in energy expenses. This is even more apparent in international countries where energy can cost as much as 30 cents per kWh compared to just 6–8 cents in the United States.

In addition to inefficiency, pneumatic pumps also present the risk of icing. When moisture is in the air and it rapidly expands in the exhaust, it cools off and can freeze the water. This is especially a risk in places like Louisiana or Korea where damp, humid and cold air is present. In this type of an environment, pneumatic pumps ice up and may quit working. Further, pneumatic pumps are extremely loud when operating. Many workers require ear protection when operating near them to prevent hearing damage.

Due to the inefficiency of pneumatic pumps, the market has been moving toward other solutions such as electrically driven reciprocating pumps. While electric pumps have several advantages, the primary one is their efficiency. Electric pumps can achieve four to seven times the efficiency as pneumatic pumps. This can amount to a substantial amount of energy and cost savings, especially on larger circulation pumps running 24 hours per day. In addition to efficiency, electric pumps are quieter and offer more control over functionality, including speed and pressure. For example, if a component fails in the system, an electric motor enables operators to monitor this and shut the system down.

Electric pumps require some sort of electric motor to convert the electric power into mechanical power used to drive the pump.

There are several different types of electric motors that are used in the industry, however, AC induction motors and brushless DC motors (BLDC) are the most common.

For most general industrial applications, AC induction motors are the more popular choice. They are simple, cost-effective and, if there is not a requirement for speed control, they do not require any sort of control (a Variable Frequency Drive -VFD or an inverter). On the other hand, BLDC motors require a controller and have only become more common since the availability of low cost power electronics.

Originally published in the August 2015 issue.

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