QUESTION:
I’ve got questions concerning vacuum pumps and pump operations. I have been told — and even read in some pump literature — that these pumps can run at 28 inches of mercury. Well, I tried that. I cranked up my pump that has a 342-cfm airflow capacity, and it wasn’t 15-20 minutes and the pump was smoking like a forest fire. I read the performance sheets on the pump and then I read the data on other sheets and they said the pumps can run continuously, even at 25 inches of mercury. Why when I try to be as responsible and educated as possible, do I still end up with problems? What should these pumps really be set at to get a long life and steady performance?
Randy Shenfield
Memphis, Tenn.
ANSWER:
On first reading of your letter, we wondered if it was worthy of a response. Our first thought was that if you run anything like a vacuum pump too long, the heat will build up, the smoke will come, and the unit will end up fried. But we thought about it more and dug out our performance data sheets from the various pump manufacturers. This is where it gets interesting.
We found common points made in several manufacturer data sheets. First, they mention a lot of numbers that aren’t going to relate to real-life operation of a vacuum pump. Many, if not all of these pumps are purported to be able to run at a “continuous” vacuum of 25 to 28 inches. When a portable sanitation pumper sees this, he or she might conclude there’s no problem running these things at 25 to 28 inches and all will be well. After all, as mentioned, they say during “continuous” operation. So let’s turn it on and go to work.
We saw this information in pretty much all the performance data sheets we studied (and we pretty much have them all). There are no further instructions or disclaimers to warn you about running at these settings. They do mention that this is “maximum” vacuum but there is nothing saying that you shouldn’t run at maximum vacuum. So if these settings cause a pump to overheat and smoke, what are these numbers for?
Many pumpers and suppliers like to look at data — the hard numbers — in their selling of pumps, or in their use of pumps on their trucks. We’re not saying these numbers are wrong, but it does require a second look. So we called some of the pump manufacturers to see what they had to say about this information.
Here’s what we learned: Testing for these pumps is generally done at a factory and the data is then recorded. Sounds great. What isn’t considered in these tests, according to the pump representatives, is the elevation of where the pump is used, the temperatures and climate where it operates, and other considerations.
The plain truth is, we don’t know of anybody who runs a pump at “maximum continuous” output. And frankly, we don’t believe they run the pumps very long when conducting these tests. So it is wise to get as educated as possible and understand the strengths and powers of your pumps. But remember that most of these numbers are laboratory numbers in a controlled environment.
The basic rules of running a vacuum pump still apply. First, match the power of the pump to your tank capacity to be efficient. As we have said in the past, it doesn’t help to have a more powerful pump on a smaller tank. Second, in most places around the country, operating a vacuum pump on the job at 18 to 20 inches of mercury is plenty. This should allow you to complete a pumping job, not overheat your pump or the system, and to get the longest possible life out of your pump.
