QUESTION:
A few months ago, I moved my pumping company from Houston to a small town near Denver. I figured since I was up in the Rocky Mountains, pumping would take less time … They always talk about the thin air up in the mountains. But when I started working, my pump nearly burned up. It seemed to take forever. I checked the oil in my pump. I double-checked my vacuum gauge to make sure it was working. I check those things in my normal operation anyway. My air-cooled pump, which ran like a champ in Houston, just got hotter and hotter. Is there something I’m doing wrong? Can you explain what I need to do to fix this situation?
Roy Vaughn
Denver
ANSWER:
You did nothing wrong. Mother Nature just took over the operation of your system. Creating a vacuum and pumping at a higher elevation doesn’t work the way you’d think it would. The assumption, like you thought, is that thinner air should make everything work easier. A strong vacuum pump should clear out the thin air in seconds, and the pumping should begin. After all, isn’t thin air easier to move?
This is where an understanding of vacuum comes into play. First, I am not a scientist — and you don’t have to be — to understand what happens at higher elevations.
When you were pumping in Houston, you arrived at the jobsite, turned on the pump, and the tank was evacuated of air, which created ample vacuum. You opened the valve on your hose and sucked up anything and everything in your path. Hopefully, it was the contents of a portable restroom. Nothing overheated. Everything worked fine.
OK, so in the Rocky Mountains, things aren’t the same. You’re right. The air is thinner. So here’s the key to explaining your situation: It’s going to take you longer to build up vacuum because vacuum is based on the differential between the lack of air in the tank and the outside air.
SEA LEVEL PUMPING
What does this mean? In Houston, which is near sea level, the air contains more molecules. Turning on your vacuum pump evacuates the air from the tank and creates a differential between the air inside the tank and the air outside. It happens relatively quickly because there are lots of molecules and the differential is the key to the creation of vacuum.
At higher elevations, where the air is thinner, it takes longer to create vacuum because there are fewer molecules in the air to start with. Your air outside the tank is already thin. So creating a vacuum inside the tank requires having to run your pump longer to create a differential between the atmosphere outside the tank and vacuum inside the tank. The longer you run the pump, the hotter it gets. Moving to a higher elevation is not a problem if you switch to a water-cooled pump. It can stand a longer pumping cycle without overheating.
One way I like to demonstrate vacuum is with an empty plastic bottle, let’s say a 20-ounce soft drink bottle. Put the bottle up to your mouth and suck the air out of it, venting the air through your nose. In a few seconds, the bottle collapses as you remove the air and create the differential between the air inside and outside of the bottle. The instant you remove your mouth from the bottle, it jumps back to its original shape as the air rushes in to “normalize” the bottle. That is the essence and the key to understanding vacuum.
The vacuum pump creates the differential inside the vacuum tank, and when the valve is opened, the air or whatever you’re pumping rushes in to balance the air pressure.
