Explosion proof Frequently Asked Questions
Kent Clark | Jul 30, 2019
At the beginning of the year, we introduced our first explosion proof pumps. Since then, we’ve expanded that product line, which now features several explosion proof options. In the process, we’ve received many questions about explosion proof pumps, and I hope we can answer some of the more common ones today.
If you’re a distiller working with high-proof alcohol, you want to have an explosion proof pump. Flammable materials - or worse, flammable vapors - are an explosion risk that can be ignited not only by the sparks and temperatures of pump motors but even by the arcs within standard plugs. This is why, when working with flammable substances, you need an entire assembly - from plug to switch/VFD to motor - that is spark free.
The major component of an explosion proof pump is an explosion proof motor. Explosion proof motors control and contain combustion without igniting surrounding vapors. They achieve this with narrow openings known as flame paths, which quench flames and cool escaping gasses.
Since they need to be able to control the exit heat of gasses, such motors also have limitations on how hot they can get. Division 1 Class 1 is the suggested motor class for distilleries. These motors must not develop a surface temperature hot enough to cause spontaneous ignition of gasses, which means no warmer than 230°C/446°F.
The motors we use are rated for Division 1, Class I C & D, and Class II E, F, & G
Division 1: In which ignitable concentrations of hazards exists under normal operating conditions and/or where a hazard is caused by frequent maintenance or repair work or frequent equipment failure.
Class I: locations in which flammable vapors and gases may be present.
We also ship all explosion proof pumps with explosion proof switches and plugs. Plugs can spark when connecting under load. So, within a high-risk environment (especially when working with substances like gasoline) explosion proof plugs and sockets, such as those by Meltric, are used. These have a dead front, which isolates the supply contacts and prevents fluid and gas exposure to live parts.
Not currently, but we’re working on it.
Explosion proof VFDs are rare due to the explosion risk they can pose from heating the motor through harmonic currents. Essentially, the VFD distorts the sinusoidal voltage and current waveform of the input, producing higher frequency harmonics (RW), and increasing current draw without increasing torque. The VFD can also increase heat when slowing the motor, as the lower speeds reduce airflow, reducing cooling. Because of this variability, the certification of a motor applies only when its run at a constant speed. As such, most of our explosion proof pumps are constant speed, using switches instead of VFDs.
There is, of course, one notable exception: our high-proof alcohol pump, which is attached to a is variable speed motor!
Got more questions about explosion proof pumps? Leave them in the comments below.